sediment dispersal and quantitative stratigraphic architecture across an ancient shelf two large 200 to 300 km near continuous outcrop transects and extensive well log data ca 2800 wells allow analysis of sedimentological characteristics and stratigraphic architecture across a large area ca 60 000 km2 of the latest santonian to middle campanian shelf along the western margin of the western interior seaway in eastern utah and western colorado usa genetically linked depositional systems are mapped at high chronostratigraphic resolution ca 0 1 to 0 5 ma within their sequence stratigraphic context in the lower part of the studied interval sediment was dispersed via wave dominated deltaic systems with a compound clinoform geomorphology in which an inner wave dominated shoreface clinoform was separated by a muddy subaqueous topset from an outer clinoform containing sand poor gravity flow deposits these strata are characterized by relatively steep net regressive shoreline trajectories 0 1 with concave landward geometries narrow nearshore belts of storm reworked sandstones 2 to 22 km wide offshore mudstone belts 250 km and relatively high sediment accumulation rates ca 0 27 mm year 1 the middle and upper parts of the studied interval also contain wave dominated shorefaces but coeval offshore mudstones enclose abundant isolated tide influenced sandstones that were transported sub parallel to the regional palaeoshoreline by basinal hydrodynamic tidal circulation these strata are characterized by relatively shallow net regressive shoreline trajectories 190 km and relatively low sediment accumulation rates ca 0 11 mm year 1 the change in shelfal sediment dispersal and stratigraphic architecture from i compound clinoform deltas characterized by across shelf sediment transport to ii wave dominated shorelines with isolated tide influenced sandbodies characterized by along shelf sediment transport is interpreted as reflecting increased interaction with the hydrodynamic regime in the seaway as successive shelfal depositional systems advanced out of a sheltered embayment utah bight this advance was driven by a decreasing tectonic subsidence rate which also suppressed autogenic controls on stratigraphic architecture

discontinuity surfaces clinoforms and facies architecture in a wave dominated shoreface shelf parasequence abstract detailed outcrop analysis of a wave dominated shoreface shelf parasequence exposed in the book cliffs utah reveals minor stratigraphic discontinuities which define clinoforms two types of discontinuity are recognized each with a distinctive lithologic character and geometry nondepositional discontinuities are marked by an abrupt decrease in the thickness and amalgamation of storm generated event beds and are interpreted to record hiatuses in sedimentation these discontinuities define clinoforms with a concave upward geometry that dip gently 0 02 0 58 over distances of 800 6000 m down depositional dip erosional discontinuities are marked by an abrupt increase in event bed amalgamation grain size and sand content and are interpreted as enhanced storm wave scours these discontinuities define more steeply dipping 0 22 0 95 concave upward clinoforms that extend over 100 1600 m down depositional dip and 500 1500 m along depositional strike the distribution and amalgamation of minor stratigraphic discontinuities defines linear zones of distinctive facies architecture that are oriented parallel to the paleoshoreline trend using the simple assumption that the shoreface shelf equilibrium profile remained approximately constant for each type of discontinuity throughout shoreface migration the bruun rule intra parasequence facies architecture can be speculatively interpreted in terms of shoreline trajectory which reflects the balance between sediment supply and accommodation the resulting interpretations support the notion that shoreline trajectory exerts a strong control on intra parasequence facies architecture and preservation of the shoreface shelf profile

from quantitative 3d seismic stratigraphy to sequence stratigraphy insights into the vertical and lateral variability of shelf margin depositional systems at different stratigraphic orders abstract a major challenge in sequence stratigraphy is objectively identifying stratigraphic surfaces and sequences across multiple scales of observation identification is commonly dependent on the resolution of the data used i e seismic vs well data its dimension i e 1d vs 2d vs 3d or the criteria chosen to select sequence boundaries through shelf edge trajectory analysis the clinothem i e highest order seismic sequence identified on seismic data can constitute the elementary building block of an observation based and data driven quantitative workflow to develop sequence stratigraphic frameworks across different orders and ranks of hierarchy here we use high quality 3d seismic data to interpret a late tithonian early cretaceous shelf margin the lower barrow group lbg developed in the northern carnarvon basin on the north west shelf of australia based on full volume seismic interpretation techniques that integrate the 3d variability of the data when identifying seismic unconformities a high resolution seismic stratigraphic framework was built 73 interpreted clinothems with an average time duration of 63 000 yrs the computation of high frequency shelf edge trajectory angle tse curves on selected seismic cross sections is used to objectively pick sequence stratigraphic surfaces based on the accommodation succession method thereby highlighting small changes in trajectory and proposing a method reproducible by interpreters based on the same quantitative data within the d lobispinosum interval 142 3 140 9 ma the definition of stratigraphic sequences and composite stratigraphic sequences through this workflow is used to discriminate the controls at high and low temporal frequency on the vertical and lateral variability which is here quantified of this shelf slope basin system the results show that the high frequency interplay between short term glacio eustasy i e milankovitch eccentricity cycles of 100 000 yrs and sediment supply locus of fluvial input along the margin impacted the three dimensional stratigraphic architecture of the lbg in contrast tectonic subsidence had a significant impact on the stratigraphic architecture of the lbg within the main depocentre at lower temporal frequency by overprinting the eustatic signal and accelerating decelerating the rates of accommodation creation however identification of long term glacio eustatic milankovitch cycles 400 000 yrs outside the main depocentre where the rates of accommodation creation due to rift related subsidence are moderate also suggests low frequency eustatic control therefore the vertical and lateral variability of the lbg results from variations in sediment supply and subsidence regime under local i e process regime currents regional i e tectonics and global i e eustasy climate forcing parameters interplaying across timescales in contrast to standard sequence stratigraphic workflows that are based on model dependent choices to select sequence boundaries quantitative 3d seismic stratigraphy constitutes an improved method to interpret 3d seismic data in shelf margin depositional systems within a sequence stratigraphic framework which provides an observation based and model independent tool allowing the definition of stratigraphic sequences with results that are reproducible across multiple stratigraphers this work highlights the need for developing new sequence stratigraphic tools and methods that integrate the 4d variability of depositional systems and moves beyond the two dimensionality inherent to current sequence stratigraphic methods quantitative 3d seismic stratigraphy represents a first step towards the creation of 3d sequence stratigraphic workflows that could improve the prediction of stratigraphic patterns and facies relationships source reservoir seal distribution across shelf margins

accommodation and sediment supply controls on clastic parasequences a meta analysis this study combines data from many published case studies to undertake a quantitative characterization of clastic parasequences with the aim to determine how accommodation sediment supply and autogenic sediment storage dynamics are recorded in their sedimentary architecture and stacking patterns results of this study are used to critically evaluate the validity of paradigms and models that are routinely used to explain and predict trends in the anatomy and arrangement of parasequences data on 957 parasequences from 62 case studies of clastic shallow water successions were coded in a relational database which includes outcrop and subsurface datasets of ancient and quaternary examples these units cover the preserved records of both river dominated deltas and wave dominated coasts representing shoreline transits over a breadth of timescales likely of both local and regional extent the role of extant accommodation rates of creation of accommodation and rates of sediment supply in determining parasequence architecture is assessed through analysis of relationships between i proxies of these variables at different scales rates of aggradation and progradation facies belt shoreline trajectories systems tract type parasequence set stacking patterns parasequence progradation angle and stratigraphic rise size of feeder rivers and ii parameters that describe the geometry and stacking style of parasequences and associated shallow water sand bodies statistical analyses of database outputs indicate which proxies of accommodation sediment supply and accommodation sediment supply ratio are significant as predictors of parasequence architecture and allow for interpretations of the importance of allogenic and autogenic factors the principal results of this study reveal the following i parasequence thickness varies as a function of water depth accommodation generation and erosional truncation and these variations are also reflected across types of systems tracts and parasequence sets ii the dip length of parasequence sand bodies demonstrates scaling with measures of accommodation sediment supply ratio at multiple scales partly in relation to the possible effect of sediment supply on progradation rates iii in systems tracts stratigraphic trends in parasequence stacking due to autogenic mechanisms or to acceleration or deceleration in relative sea level fluctuations are not revealed quantitatively iv some association is seen between the abundance of deltaic or river dominated parasequences and progradational stacking v positive but modest correlation is observed between measures of river system size and the dip length of shallow marine parasequence sand bodies the resulting insights can be applied to guide sequence stratigraphic interpretations of the rock record and the characterization of sub seismic stratigraphic architectures of subsurface successions

geometry spatial arrangement and origin of carbonate grain dominated scour fill and event bed deposits late jurassic jubaila formation and arab d member saudi arabia

patterns of early post depositional and burial cementation in distal shallow marine sandstones upper cretaceous kenilworth member book cliffs utah usa there is a limited understanding of the spatial linkage between cementation processes in shoreface coastal plain successions and those operating in distal offshore successions to address this an integrated sedimentological sequence stratigraphic and diagenetic study was undertaken on a distal shallow marine succession the upper cretaceous kenilworth member book cliffs utah usa laterally extensive carbonate cement is the most volumetrically significant diagenetic feature it constitutes up to 55 vol of the distal lower shoreface sandstone and sandy siltstone units beneath major flooding surfaces during rising relative sea level major flooding events resulted in low sedimentation which extended residence time of sediments in early diagenetic zones and promoted enhanced cementation beneath these boundaries carbonate for early calcite cements was probably derived from sulphate reduction marine water and oxidation of organic matter stable isotopic composition of later ankerite 18o 11 9 to 6 0 vdpb 13c 4 5 to 0 3 vdpb suggests precipitation during progressive burial c 1 7 to 3 4 km 72 to 122 c from evolved marine fluids the carbonate and other mineralizing solutes were derived increasingly with burial from decarboxylation of organic matter and clay mineral transformations in adjacent siltstones and shales these interbedded overlying and underlying facies provided an important source of mineralizing solutes that influenced the extent of pervasive cementation during burial the combination of stratigraphic and lithofacies control resulted in laterally extensive cements that differ to shoreface successions although are similar in form to those described for many offshore mudstone dominated successions limited early concretionary ferroan dolomite beneath the expression of the sequence boundary and some flooding surfaces however suggests cementation by meteoric fluids at times of relative sea level lowstand similar processes have been demonstrated in more proximal successions in the book cliffs

the depositional architecture and facies variability of shelf deltas in the eocene battfjellet formation nathorst land spitsbergen deltas are commonly classified according to their plan view morphology as either river dominated tide dominated or wave dominated however most deltas form under the mixed influence of these processes commonly with laterally varying process regimes it has also become clear that there is a mismatch between the plan view morphology and internal facies composition in some deltas combined outcrop and subsurface data from the eocene battfjellet formation spitsbergen provide an example of ancient shelf deltas that formed under mixed influence internally these shelf deltas are characterized by wave dominated facies that are normally associated with strike extensive nearly linear shoreline sandstones however the formation comprises partially overlapping sandstone bodies of limited lateral extent 20 km in any direction this stacking pattern is attributed to frequent autogenic lobe switching that caused localized and rapid transgressions such processes typify fluvial dominated deltas and occur less commonly in wave dominated ones thus there is an apparent mismatch between inferred plan view morphology and internal facies composition it is argued that the battfjellet deltas were flood dominated and prograded mainly during periods of high fluvial discharge however reworking of the fluvial flood facies by fair weather and storm waves as well as longshore currents resulted in a wave dominated facies character delta lobes undergoing auto retreat were particularly prone to reworking by basinal processes including tidal currents it is suggested that repeated delta progradation from inner shelf settings towards the outer shelf and shelf edge was aided by high sediment supply rather than relative falls in sea level as previously suggested this interpretation is supported by i the lack of major facies dislocations and extensive sub aerial unconformities and ii an overall relative rise in sea level as evidenced by an overall low angle 0 8 to 1 2 ascending shoreline trajectory the latter results from the combined effect of basin subsidence eustatic highstand and sediment compaction

new insights into deformation and fluid flow processes in the nankai trough accretionary prism results of ocean drilling program leg 190 moore g f taira a klaus a becker l boeckel b cragg b a dean a fergusson c l henry p hirano s hisamitsu t et al 2001 new insights into deformation and fluid flow processes in the nankai trough accretionary prism results of ocean drilling program leg 190 geochemistry geophysics geosystems 2 article no 2001gc000166

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

beach ridges and prograded beach deposits as palaeoenvironment records abstract beach ridges are landforms commonly developed on prograded coasts with beach shorelines a sequence of beach ridges coupled with their subsurface deposits can be regarded as a time series of coastal evolution methodological advances in field surveying and chronology applicable to beach ridges have led to detailed palaeoenvironmental reconstructions to be derived from such sequences this paper reconsiders the basic aspects of beach ridges and deposits which need to be properly understood for their comprehensive interpretation in a palaeo environmental context it also reviews case studies in which beach ridge sequences have been used to unveil past sea level history catastrophic events and climate changes proposed formative processes of beach ridges include 1 progradation of sandy beach and berm formations in relation to fairweather waves coupled with aeolian foredune accumulation 2 building of gravel ridges by storm waves 3 welding of longshore bars beach ridge formation through sea level oscillation is thought to be questionable and caution is suggested for this process when undertaking palaeoenvironmental reconstruction beach deposit stratification is known to dip either landwards or seawards but landward dips are uncommon seaward dipping stratification is formed in relation to beachface progradation and is usually dissected in places by erosion surfaces resulting from episodic beach retreat the boundary between the foreshore and the underlying shoreface is well defined only in the case that longshore bars lead to complex bedding structure relative to that of the foreshore reliable chronology of beach ridges can be determined by radiocarbon and optically stimulated luminescence osl dating radiocarbon dating of articulated shells which are considered not to be extensively reworked provides robust results but osl dating is more useful as it enables direct dating of sediment grains it is noted that there are restrictions in chronological resolution and continuity inherent to beach ridge and beach deposits the plan view geomorphic expression of beach ridges typically consists of ridge sets with multi decadal intervals whereas their internal sedimentary structures define shorter time scales records of beach sedimentation and erosion are likely to be reworked by episodic high magnitude beach retreat and the resultant record of the net progradation is likely to be sporadic and discontinuous the height of sandy beach ridges is often variable due to differing degrees of aeolian sand accumulation and they are thus not used as sea level indicators unless purely wave built gravel ridge height is a relatively reliable indicator of sea level but can vary in response to storminess fluctuations subsurface sediment facies boundaries are preferred as sea level indicators and those proposed include boundaries of aeolian beach foreshore shoreface and upper lower shorefaces catastrophic events are expressed in both erosional and depositional records erosion surfaces or scarp imprints revealed in a cross section of beach deposits indicate storm or tsunami events however erosional events are likely to rework previous records of sedimentation and even other erosional events and thus the apparent history decoded from the resultant deposits tends to be biased several attempts for estimating the frequency and intensity of prehistoric cyclones rely on assumed relationships between the level of coarse sand beach ridges and cyclone inundation the formative process of coarse sand ridges remains uncertain and needs to be clarified as it constitutes the fundamental basis of these attempts the growth rates of beach ridge systems are expected to reflect fluctuations in river sediment discharge to the coast and in aeolian sand flux due to onshore winds both of which are affected by climate change assessment of the growth rate is potentially improved by ground penetrating radar survey of subsurface structure and by detailed chronology orientation of beach ridges reflects long term trends in wave direction inferred relationships between beach ridges and cyclic fluctuations of sea level and climate rely on weak assumptions and are not substantiated by rigid chronological evidence and thus remain highly questionable correlation between the inherently decadal signal of beach ridge intervals and possible climate cycles such as sunspot activity is probably coincidental as it lacks causal explanations

intra shoreface erosion in response to rapid sea level fall depositional record of a tectonically uplifted strand plain pacific coast of japan this study documents lowering of the surf zone i e the upper shoreface leading to intra shoreface erosion following two rapid relative sea level falls along a tectonically uplifted coast during the holocene and the characteristics of the resultant prograding shoreface deposits these findings are based on high resolution analysis and radiocarbon dating of three new drill cores obtained from the kujukuri strand plain pacific coast of eastern japan combined with previously published borehole data and information on modern shoreline profile adjustments a shallowing upward sandy succession composed of lower and upper shoreface facies foreshore and backshore facies was recognized in the drill cores two rapid falls in relative sea level at 2ae 3t o 2ae6 and 1ae 8t o 2ae0 ka are recorded by downstepping of the base of the foreshore facies and farther seawards by the lowering of an erosional boundary between the upper and lower shoreface facies superimposed bed profiles of an adjacent modern beach define an envelope the base of which reflects shore normal migration of longshore bars and troughs the base of the envelope represents an erosional surface that divides the surface mobile layer above from preserved deposits beneath the surface is concave upwards and steeper than the mean beach profile and exhibits a flat platform approximately at the lower limit of the upper shoreface equating to the storm surf zone the seaward transition of this surface rather than the mean equilibrium profile controls the metre scale to decimetre scale internal structure of the kujukuri shoreface deposits depositional models for sea level fall based on an exponential equilibrium profile do not adequately account for the presence and migration of longshore bars and troughs

pinch out style and position of tidally influenced strata in a regressive transgressive wave dominated deltaic sandbody twentymile sandstone mesaverde group nw colorado the upper cretaceous twentymile sandstone of the mesaverde group in nw colorado usa has been analysed with respect to its pinch out style and the stratigraphic position of tidally influenced facies within the sandstone tongue detailed sedimentological analysis has revealed that the twentymile sandstone as a whole is a deltaic shoreface sandstone tongue up to 50 m thick proximally facies change character vertically from very fine grained storm wave dominated shelf sandstones and mudstones to fine grained wave dominated sandstones and finally to fine to coarse grained tidally dominated sandstones the pinch out style is characterized by a basinward splitting of the massive proximal sandbody into seven coarsening upward fourth order sequences consisting of a lower shaly part and an upper sandy part sandstone tongue these are stacked overall to reflect the regressive to transgressive development of the tongue each of the lower sandstone tongues 1 3 are gradationally based very fine grained and dominated by hummocky cross stratification and were deposited on the lower to upper shoreface sandstone tongues 4 and 5 prograded further basinwards than the underlying tongues are erosively based fine to coarse grained and mainly hummocky herringbone and trough cross stratified especially in tongue 5 tidal indicators such as bipolar foresets and double mud drapes are common these tongues were deposited as upper shoreface and tidal channel sandstones respectively sandstone tongues 6 and 7 retrograded in relation to tongue 5 are very fine to fine grained and hummocky cross stratified these tongues were deposited in lower shoreface to offshore transition environments the two lower fourth order sequences were deposited during normal regressions during slowly rising or stable relative sea level and represent the highstand systems tract the three succeeding fourth order sequences which show succeedingly increasing evidence of tidal influence were deposited during falling and lowstand of relative sea level and represent the falling stage forced regressive and lowstand systems tracts the uppermost two fourth order sequences were deposited during rapidly rising sea level in the transgressive systems tract the maximum tidal influence occurred during lowstand progradation in contrast to most other published examples reporting maximum tidal influence during transgression

pressure solution in sedimentary basins effect of temperature gradient abstract pressure solution is an important process in sedimentary basins and its behaviour depends mainly on the sediment rheology and temperature distribution the compaction relation of pressure solution is typically assumed to be a viscous one and is often written as a relationship between effective stress and strain rate a new derivation of viscous compaction relation is formulated based on more realistic boundary conditions at grain contacts a non linear diffusion problem with a moving boundary is solved numerically and a simple asymptotic solution is given to compare with numerical simulations pressure solution is significantly influenced by the temperature gradient porosity reduction due to pressure solution is enhanced in an environment with a higher thermal gradient while porosity decreases much slowly in the region where the thermal gradient is small pressure solution tends to complete more quickly at shallower depths and earlier time in higher temperature environment than that in a low one these features of pressure solution in porous sediments are analysed using a perturbation method to get a solution for the steady state comparison with real data shows a reasonably very good agreement

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

hrtem and saed investigations of polytypism stacking disorder crystal growth and vacancies in chlorites from subgreenschist facies outcrops selected area electron diffraction saed combined with experimental and computed high resolution transmission electron microscopy hrtem images were used to investigate polytypism stacking disorder mixed layering and vacancies in chlorites from subgreenschist facies outcrops of the taveyanne sandstone from the helvetic nappes switzerland saed patterns reveal increased ordering of the stacking sequences in chlorite with increasing metamorphic grade however semi randomness and rotational faults occur even if the saed photographs imply a regular ordered stacking sequence in diagenetic t 210 250 degrees c p 2 1 2 2 kbar and anchizonal grade outcrops t 270 300 degrees c p

open system constant volume development of slaty cleavage and strain induced replacement reactions in the martinsburg formation lehigh gap pennsylvania no important changes in the volume of mudrocks occur across the mudstone to slate transition in the martinsburg formation at lehigh gap pennsylvania mass balance calculations based on chemical analyses and specific gravity measurements of 48 mudstones and 26 graywackes from the martinsburg formation across this 130 m strain gradient show constant ratios of al2o3 tio2 feot mgo mno y v and zr this reflects the relatively low differential mobility of these components during diagenesis and slaty cleavage development as well as the uniformity of compositions of the mudstones and graywackes at deposition using minimum strain samples and al2o3 as references the calculations show no loss in sio2 but large losses of cao na2o ba and sr from the outcrop that are directly proportional to strain and reflect an open system on the scale of kilometers analyses of graywacke mudstone metagraywacke slate pairs show that losses in sio2 na2o and volume and gains in k2o and ba in the graywacke metagraywacke are balanced by opposite changes in the adjacent mudstone slate this documents a local mobility of sio2 on the scale of centimeters the inertness of most major components over the 100 m outcrop especially sio2 however requires 1 that the composition of the fluid passing through the rocks was closely buffered by the quartz albite muscovite chlorite assemblage 2 that the volume of the fluid was small and 3 that the p t gradient down which it traveled was gentle the changes in chemical composition identified can be explained by the inferred replacement reaction plag 1m musc k 2m musc qz ca 2 na sr 2 ba 2 the strong correlation of minor element chemistry and strain indicates that this reaction was strain induced and that changes in bulk chemical composition are defined by the progress of this reaction

spatial and temporal evolution of coastal depositional systems and regional depositional process regimes campanian western interior seaway u s a abstract this paper provides a critical review and regional synthesis of late cretaceous shallow marine deposits along part of the western margin of the western interior seaway of north america which contains the most extensively documented outcrop based studies of siliciclastic coastal depositional systems in the world the results of this synthesis are presented in the form of paleogeographic maps covering present day new mexico utah colorado and wyoming usa for five timeslices in the campanian these maps are used to evaluate the spatial and temporal evolution of regional depositional process regimes along a large 1000 m stretch of coastline the evolution of regional depositional process regimes is linked to tectonic and paleoceanographic controls on the western interior seaway which enables the results of this synthesis to be applied to prediction of depositional process regimes in other less intensively studied basins six gross depositional environments have been mapped for each timeslice 1 alluvial to coastal plain sandstones 2 coastal plain coals mudstones and sandstones 3 shoreline sandstones 4 marine mudstones 5 gravity flow siltstones and sandstones and 6 marine marls and chalk shoreline sandstones in each timeslice are interpreted in further detail using documented evidence for the three principal classes of depositional process wave tidal and fluvial and published reconstructions of coastal morphology which is widely considered to reflect depositional process regime based on these interpretations shoreline sandstones are assigned to five categories of depositional process regime 1 regressive wave dominated shorefaces and delta fronts 2 regressive river dominated delta fronts 3 regressive mixed tide and wave influenced delta fronts 4 regressive tide dominated delta fronts and 5 transgressive barrier islands back barrier lagoons and estuaries the accuracy of and uncertainty in classification of depositional process regime are critically evaluated additionally stratal thickness and sediment routing pathways have been interpreted in order to assess the impact of tectonic and paleoceanographic controls on spatial and temporal changes in all of the evaluated shallow marine successions thin tide influenced intervals were deposited in back barrier and lagoon systems associated with net transgressive shorefaces and estuaries however it is notable that all preserved tide dominated and tide influenced regressive deltaic systems are located along the northern margin of the utah bight a tectonically related embayment that had a pronounced expression during the middle campanian the southern margin of the embayment and coastlines to the north are conspicuously more wave dominated which supports their exposure to a larger wave fetch in contrast the northern margin of the embayment was relatively wave protected it is concluded that tidal range was amplified due to resonance of the principal semidiurnal tide in the strongly embayed geometry of the middle campanian utah bight

deformation and fluid flow of a major out of sequence thrust located at seismogenic depth in an accretionary complex nobeoka thrust in the shimanto belt kyushu japan 1 nobeoka thrust in kyushu southwest japan was investigated to understand the relationship between the seismogenic out of sequence thrust ost and fluid flow in accretionary prisms the nobeoka thrust is a fossilized ost being active at seismogenic depth the hanging wall exhibits a penetrative plastic deformation while a brittle cataclastic melange like occurrence characterizes the footwall although both of them have same shale and sandstone dominant protolith vitrinite reflectance analyses indicate that the maximum temperatures of the hanging wall and footwall are approximately 320 and 250 c respectively this thermal gap across the thrust corresponds to 8 6 14 4 km of displacement assuming a 28 47 c km geothermal gradient the brittle damage zone of the thrust is asymmetric only 2 m for hanging wall side and 100 m for footwall three types of mineral veins quartz and carbonate are well developed especially in the damaged footwall the tension crack filling vein the fault filling vein and postmelange one the first is harmonious with fabric perpendicular to the p surface fluid inclusion geothermobarometry indicates the p t of fluid in the intensively damaged zone of the footwall is 300 c 230 250 mpa higher than that from vitrinite reflectance which suggests that hydrothermal fluid flow is associated with deformation the same type vein in the lowest portion of the footwall damaged zone includes a much lower p t fluid this difference suggests that continuous underplating caused the damaged zone to propagate downward with cooling and shallowing which differs from faults characterized by shear localization and might be unique to aquiferous ost in accretionary complexes

large volume loss during cleavage formation hamburg sequence pennsylvania green reduction spots in red slate of the hamburg sequence exposed near shartlesville pennsylvania have axial ratios of 1 42 1 0 0 28 on the limbs of near isoclinal folds and 1 0 0 79 0 41 in fold hinge zones conodont cusps and denticles within the reduction spots have been brittlely pulled apart and give independent measures of extension in various directions comparison of conodont extensions with reduction spot shapes on limbs and hinges indicates that sedimentary compaction of 44 preceded the tectonic strain associated with cleavage formation this strain having identical maximum extensions but greater shortening in fold hinges as compared to limbs was characterized by 41 extension in x no change in y 50 to 59 shortening in z and 29 to 42 tectonic volume loss the general lack of directed overgrowths on grains reflects the large volume loss and contrasts with other slates where deformation was an almost constant volume process and extension in x compensated for shortening in z

early holocene coastal environment change inferred from deposits at okinoshima archeological site boso peninsula central japan abstract a series of deposits recording the early holocene drastic changes in coastal environment was investigated in terms of sedimentology and paleontology at the okinoshima archeological site on the southwest coast of boso peninsula central japan the deposits ca 3 m thick exposed in trenches consist of structureless mud and overlying stratified sand divided into three units i ii and iii in ascending order unit i is poorly sorted sandy mud with abundant opal phytoliths unit ii gradually overlying unit i is poorly sorted sandy mud containing more organic material and pieces of wood and archeological remains unit iii overlies unit ii with a sharp erosional contact and is composed of well sorted medium grained sand intercalated by mud layers with abundant plant fossils unit i suggests a dry surface on a coastal plain near uplands unit ii was transported from the upland onto the coastal plain by a debris flow unit iii deposits resulted from high energy river and storm surge flows onto the coastal plain the succession records that the sedimentary environments of the study site changed successively from a slope near the uplands to a fluvial plain to a coastal plain in response to a sea level rise in the early holocene ams ages of the units are approximately 10 000 cal bp and deposition occurred within 1000 years

characterization of controls on high resolution stratigraphic architecture in wave dominated shoreface shelf parasequences using inverse numerical modeling abstract a new inverse numerical modeling method is used to constrain the environmental parameters e g relative sea level sediment supply and wave climate histories that control stratigraphic architecture in wave dominated shallow marine deposits the method links a process response forward stratigraphic model that simulates wave and storm processes barsim to a combination of inverse methods formulated in a bayesian framework that allows full characterization of uncertainties this method is applied for the first time to a real geologic dataset collected at outcrop from two shoreface shelf parasequences in the aberdeen member blackhawk formation of the book cliffs east central utah usa the environmental parameters that controlled the observed stratigraphic architecture are quantified and key aspects of stratigraphic architecture are successfully predicted from limited data stratigraphic architecture at parasequence stacking and intra parasequence scales was driven principally by relative sea level varying by up to about 55 m and sediment supply varying by up to 70 m2 yr whose interplay determines the shoreline trajectory within zones of distinctive shoreline trajectory variations in wave climate of up to about 3 m in fairweather wave height controlled superimposed variations in sandstone and shale content e g the development of upward coarsening and upward fining bedsets the modeling results closely match the observed stratigraphic architecture but their quality is limited by 1 the formulation and assumptions of the forward modeling algorithms and 2 the observed data distribution and quality which provide poor age constraint

evidence for syntectonic crystallization for the mudstone to slate transition at lehigh gap pennsylvania u s a data primarily for phyllosilicates have been obtained for the continuous transitional sequence from mudstone to slate with well developed slaty cleavage at lehigh gap pennsylvania and for slates from quarries in the same area samples were studied by optical microscopy powder x ray diffraction and electron microprobe analysis with emphasis on transmission and analytical electron microscopy mineral grains are virtually free of deformation induced strain concomitant with the gradual development of cleavage normal to bedding the following changes are observed or confirmed 1 the orientation of phyllosilicate grains changes discontinuously from being preferentially parallel to bedding to being parallel to cleavage 2 crystal imperfections as expressed in layer terminations low angle grain boundary like features and other defects decrease in density 3 complex mixed layering is replaced by homogeneous packets of layers of single phases and 4 illite transforms to muscovite with increase in k a1 and change from a lmd to 2m polytype slaty cleavage apparently develops due in part to pressure solution of phyllosilicates oriented parallel to bedding mass transport of components and crystallization to form new grains parallel to cleavage it reflects transitions from imperfect metastable phases toward ordered stable phases in a low temperature 225 c metamorphic environment

interstratification and other reaction microstructures in the chlorite berthierine series transmission electron microscopy tem results show there is a series of periodically and nonperiodically interstratified structures composed of berthierine and chlorite layers in low temperature chlorite that is one of the alteration products of granulite facies archean ironstone from the eastern border of the beartooth mountains montana an antiphase domain structure suggests that the interstratified structures are intermediate transformation products formed by reaction from berthierine serpentine structure to chlorite periodically interstratified structures consisting of chlorite c and serpentine like s or berthierine layers include cs ccs cccs ccccs and ccccccs the layer sequences in interstratified chlorite berthierine are indicative of the reaction mechanisms that produce the interstratified structures e g crystallization from solution or solid state transformation the reaction from berthierine to chlorite is crystallographically much like a cell preserved phase transformation even though it is highly reconstructive berthierine can be considered a polymorph of the fe rich chlorite mineral chamosite with berthierine as the los temperature phase interstratification and integrowths in the chlorite berthierine series may be common phenomena in low temperature layer silicates resembling chlorite although such relations are difficult to recognize from chemical analyses or powder x ray diffraction patterns they can be observed readily with tem method

a sequence stratigraphic model for an intensely bioturbated shallow marine sandstone the bridport sand formation wessex basin uk the bridport sand formation is an intensely bioturbated sandstone that represents part of a mixed siliciclastic carbonate shallow marine depositional system at outcrop and in subsurface cores conventional facies analysis was combined with ichnofabric analysis to identify facies successions bounded by a hierarchy of key stratigraphic surfaces the geometry of these surfaces and the lateral relationships between the facies successions that they bound have been constrained locally using 3d seismic data facies analysis suggests that the bridport sand formation represents progradation of a low energy siliciclastic shoreface dominated by storm event beds reworked by bioturbation the shoreface sandstones form the upper part of a thick up to 200 m steep 2 3 mud dominated slope that extends into the underlying down cliff clay clinoform surfaces representing the shoreface slope system are grouped into progradational sets each set contains clinoform surfaces arranged in a downstepping offlapping manner that indicates forced regressive progradation which was punctuated by flooding surfaces that are expressed in core and well log data in proximal locations progradational shoreface sandstones corresponding to a clinoform set are truncated by conglomerate lags containing clasts of bored reworked shoreface sandstones which are interpreted as marking sequence boundaries in medial locations progradational clinoform sets are overlain across an erosion surface by thin 10 m and overlie conglomerate lags at sequence boundaries sequence boundaries are thus interpreted as being amalgamated with overlying transgressive surfaces to form composite erosion surfaces in distal locations oolitic ironstones that formed under conditions of extended physical reworking overlie composite sequence boundaries and transgressive surfaces over most of the wessex basin clinoform sets corresponding to high frequency sequences are laterally offset thus defining a low frequency sequence architecture characterized by high net siliciclastic sediment input and low net accommodation aggradational stacking of high frequency sequences occurs in fault bounded depocentres which had higher rates of localized tectonic subsidence

modern sedimentation in the japan trench implications of the mineralogy and chemistry of clays sampled from sediment traps abstract to determine the mineralogical and chemical characteristics of clay minerals the composition of the clay sized fraction and the sedimentological processes which affect these clay particles two sediment traps were moored at depths of 8700 and 4000 m at the triple junction of the japan trench six types of clay minerals and nine types of non clay minerals were identified by transmission electron microscopy smectite and illite were the most important clay minerals whereas quartz and plagioclase were the major non clay minerals chemical analyses of the clay minerals showed that the smectite was an fe al beidellite illite a di octahedral type rich in potassium and chlorite an fe mg type two major mechanisms govern the transportation of the lithogenic mineral particles in the japan trench 1 transportation by the turbidity currents in the neighbouring trough and canyon and 2 wind borne transport of loess from mainland china the settling time of clay sized minerals to the bottom of the japan trench was roughly estimated to be 1 year

paleothermal structure of the shimanto accretionary prism shikoku japan role of an out of sequence thrust vitrinite reflectance study on the cretaceous shimanto accretionary prism of southwest japan shows that the vitrinite reflectance varies from 0 6 to 3 0 corresponding to the estimated maximum paleotemperature variation of 90 210 c the thermal structure shows a sharp discontinuity across an out of sequence thrust separating it into two thermal blocks in each block vitrinite reflectance values increase systematically toward the prism younging direction and the thermal structure is clearly overprinted on the tectonic imbrication of turbidite and melange units this provided us with a set of data to calculate the geometry and displacement of the out of sequence thrust the fission track zircon partial annealing ages indicate that this thrust was active about 43 ma probably in response to the accretion of eocene rocks this study shows that initial thickening of the accretionary prism in an order of several kilometres was mainly controlled by out of sequence thrust

along strike variations in stratigraphic architecture of shallow marine reservoir analogues upper cretaceous panther tongue delta and coeval shoreface star point sandstone wasatch plateau central utah u s a abstract along strike variations in sediment supply and process regime may result in different facies distributions preservational biases and stratigraphic architectures in shallow marine strata data from a large c 100 km nearly continuous outcrop belt aligned oblique to depositional strike was integrated with nearby subsurface well data and petrological analysis of distal fine grained deposits to analyze along strike variations in stratigraphic architecture in a single parasequence in the upper cretaceous star point sandstone wasatch plateau central utah usa the parasequence comprises wave dominated shoreface deposits in the southern part of the study area and represents a single episode of shoreline regression and transgression four progradationally stacked bedsets bs1 bs4 in the distal deposits of the parasequence are the expression of minor variations in relative sea level sediment supply and or wave climate the four bedsets can be traced to river dominated deltaic deposits panther tongue in the northern part of the study area we interpret the parasequence on the scale of the wasatch plateau outcrop belt as the record of deposition in a regressive river and wave influenced delta deflected asymmetrically towards the ssw subparallel to the regional paleo shoreline trend and a coeval wave dominated strandplain the lateral transition from river to wave dominated facies is attributed to the localization of a major river acting as a sediment point source in the north with wave induced longshore transport to the south our results imply that characterizing lateral facies distributions and the expression of bedsets is vital for interpreting along strike variability in controlling mechanisms of stratigraphic architecture and that external forcing may be recorded differently along depositional strike

sequence stratigraphic significance of sharp based lowstand shoreface deposits kenilworth member book cliffs utah the kenilworth member of the blackhawk formation upper cretaceous campanian is nearly continuously exposed from price to hatch mesa in the book cliffs utah five main depositional environments are recognized coastal plain foreshore and upper shoreface lower shoreface inner shelf and incised valley fill deposits the shelf to shoreface deposits combine to form nine coarsening upward wave to storm dominated parasequences that are 7 32 m thick and that split basinward into smaller coarsening upward successions or bedsets that are 2 18 m thick a maximum of four bedsets occurs within an individual parasequence bedset bounding surfaces are occasionally marked by thoroughly bioturbated iron rich carbonate cemented sandstones within the parasequences in the subsu face similar bedset bounding surfaces may act as permeability barriers or baffles leading to reservoir compartmentalization parasequences 1 6 form an aggradational to progradational parasequence set of the highstand systems tract parasequences 7 and 8 occur as sharp based lowstand shoreface deposits at price river and battleship butte forming the attached lowstand systems tract and parasequence 9 forms the transgressive systems tract the base of each lowstand shoreface is marked by an organic rich lag deposit that consists of granules coarse grained sandstone wood fragments coal intraclasts and shell debris the sharp base basal lag deposit and basinward shift in facies delineate a sequence boundary at the base of each lowstand shoreface deposit the presence of two sharp based lowstand shorefaces suggests that the kenilworth lowstand was punctuated by a stillstand the sharp based lowstand shoref ce sandstones form the bulk of the attached lowstand systems tract and represent one end member in a continuum of lowstand deposits the other end member is the detached lowstand systems tract revising existing sequence stratigraphic models to include both types of lowstand systems tracts is a first step toward improving the accuracy of these models which are often used as prospecting tools in lowstand deltaic environments

mass transfer and pressure solution in deformed shale of accretionary complex examples from the shimanto belt southwestern japan abstract this study investigates volume changes in the accretionary complex in southeastern shikoku japan using mesoscopic and microscopic observations and chemical analyses of shale three types of deformation in shale were recognized 1 coherent type compacted 2 type i melange less deformed and 3 type ii melange sheared pressure solution seams pss are common and reflect large volume reductions for coherent type 13 50 and type ii melange 17 54 positive correlations exist between pss density and concentration of the immobile chemical component tio2 and between pss density and paleotemperature for type ii melange and coherent type under constant temperature conditions the pss density is higher for type ii melange than for coherent type indicating more efficient generation of pss for type ii melange based on the analysis of rheological equations we conclude that generation of pss may be controlled by differences in differential stress and or the duration of deformation the positive correlation between pss density and tio2 concentration indicates that volume change in accretionary complexes can be described by a simple equation using pss density

chlorite illite muscovite interlayered and interstratified crystals a tem stem study phyllosilicates in rocks which are transitional from mudstone to slate from lehigh gap pa have been studied by a variety of techniques including high resolution transmission electron microscopy and analytical electron microscopy the principal minerals are white mica which is transitional from illite in mudstone to ordered twolayer mica in slate and chlorite 7a berthierine occurs more rarely dioctahedral and trioctahedral layers are shown to be interleaved in individual crystals at all scales between the following two end members 1 both random and regular 1 1 interlayering at the scale of individual layers as shown in part by lattice fringe images 2 packets of trioctahedral and dioctahedral layers up to a few thousand angstroms or microns in thickness detectable with ordinary optical techniques the complete range of intermediate structures is represented in samples which are in transition to slate bulk analytical empa x ray diffraction or other measurements are shown to result in averages over both kinds of layers when tem techniques are not used

sea level variation during the holocene deduced from the morphologic and stratigraphic evolution of morgan peninsula alabama u s a abstract recent gulf of mexico shoreline studies interpret middle to late holocene sea level as falling from a level above present elevation or stable at present elevation however the architecture of morgan peninsula alabama does not support this morgan peninsula is a beach ridge strandplain composed of two obliquely aligned holocene beach ridge sets ground penetrating radar profiles discriminate between parallel even to wavy reflectors of the eolian dune environment and the underlying seaward dipping complex sigmoidal oblique reflectors of the foreshore and upper shoreface environment the contact between foreshore and eolian facies in beach ridges can be used as a sea level indicator the average elevation of this contact in morgan peninsula rises throughout shoreline accretion which occurred throughout the last 5 4 ka suggesting that there was continual sea level rise during this time morgan peninsula is a useful modern analog to ancient shoreface shelf parasequences and demonstrates the significant internal complexities that can exist in these deposits erosional discontinuities imaged in the holocene foreshore upper shoreface environment are laterally continuous extend to elevations above mean sea level and correlate to beach ridges and the transition between beach ridge sets an increase in the wave regime or fluctuations in sediment supply appear to be likely mechanisms for forming erosional discontinuities below beach ridges the erosional surface separating beach ridge sets may have formed by increased storm activity and associated barrier breaching or a reconfiguration of the mobile bay tidal delta complex superimposed on a gradual rate of sea level rise this boundary is recognized by a change in beach ridge orientation at the surface and an increase in the aggradational component of shoreline accretion

variations in shoreface progradation and ravinement along the texas coast gulf of mexico shoreface architecture evolution mid holocene to present and depths of transgressive ravinement were examined from sabine pass at the texas louisiana border to south padre island near the texas mexico border using 30 shoreface transects shoreface transects extend out to 16 m water depth each created from an echo sounding profile and on average seven sediment cores the shoreface is composed of three broad sedimentological facies the upper shoreface composed almost entirely of sand the proximal lower shoreface composed of sand with thickly to medium bedded 50 10 cm mud and the distal lower shoreface composed dominantly of mud with medium to thinly bedded 20 3 cm sand shoreface architecture and evolution is extremely variable along the texas coast shoreface gradients increase from 2 25 m km 1 in east texas to 3 50 m km 1 in south texas shoreface sands coarsen towards south texas east and south texas shoreface deposits are thin and retrograding whereas central texas shoreface deposits are thicker and prograding central texas is characterized by stacked shoreface successions whereas in east texas lower shoreface sands are preserved only in offshore banks preservation of shoreface deposits is low in south texas although eustatic fluctuations and accommodation space have a strong impact on overall mid holocene to present shoreface evolution and preservation potential along strike variations in sediment supply and wave energy are the main factors controlling shoreface architecture the transgressive ravinement surface varies from 6 to 15 m along the texas coast

forced regressions in a sequence stratigraphic framework concepts examples and exploration significance sequence stratigraphic concepts suggest that stratal geometries develop and are largely controlled by changes in relative sea level on the shelf lowstand deposits which form during falls and subsequent stillstands of relative sea level can be recognized by the presence of an unconformity at the base the isolated and basinward position relative to the previous shoreline and the abrupt seaward translation of shallow water and shoreline facies into the basin across an unconformity surface this seaward translation of facies and shoreline regression in response to relative sea level lowering is termed a forced regression a forced regression is independent of variations of sediment flux and is in contrast with normal regressions that occur in response to excess sediment flux relative to space available on the shelf i e accommodation forced regressions commonly are associated with a zone of sedimentary bypass subaerial exposure and possible fluvial erosion between the newly formed and preceding shorelines certain shelf sands previously interpreted as offshore or mid shelf sand bodies thus can be reinterpreted as stranded lowstand shorelines associated with forced regressions this alternative interpretation has economic significance insofar as it suggests different subsurface correlations and reservoir geometries with the potential for development of new play types and enhanced recovery in o der fields examples of forced regression can be observed at a variety of scales and ages several such examples include the modern east coulee fan delta and the lower cretaceous viking formation in alberta canada the quaternary rhone delta and the quaternary hudson valley system

detrital illite crystals identified from crystallite thickness measurements in siliciclastic sediments illite crystals in siliciclastic sediments are heterogeneous assemblages of detrital material coming from various source rocks and at paleotemperatures 70 c of superimposed diagenetic modification in the parent sediment we distinguished the relative proportions of 2m1 detrital illite and possible diagenetic 1md 1m illite by a combined analysis of crystal size distribution and illite polytype quantification we found that the proportions of 1md 1m and 2m1 illite could be determined from crystallite thickness measurements bwa method using the mudmaster program by unmixing measured crystallite thickness distributions using theoretical and calculated log normal and or asymptotic distributions the end member components that we used to unmix the measured distributions were three asymptotic shaped distributions assumed to be the diagenetic component of the mixture the 1md 1m polytypes calculated using the galoper program phase a was simulated using 500 crystals per cycle of nucleation and growth phase b 333 cycle and phase c 250 cycle and one theoretical log normal distribution phase d assumed to approximate the detrital 2m1 component of the mixture in addition quantitative polytype analysis was carried out using the rockjock software for comparison the two techniques gave comparable results r 2 0 93 which indicates that the unmixing method permits one to calculate the proportion of illite polytypes and therefore the proportion of 2m1 detrital illite from crystallite thickness measurements the overall illite crystallite thicknesses in the samples were found to be a function of the relative proportions of thick 2m1 and thin 1md 1m illite the percentage of illite layers in i s mixed layers correlates with the mean crystallite thickness of the 1md 1m polytypes indicating that these polytypes rather than the 2m1 polytype participate in i s mixed layering

accretionary prisms in subduction earthquake cycles the theory of dynamic coulomb wedge 1 we expand the theory of critically tapered coulomb wedge for accretionary prisms by considering stress changes in subduction earthquake cycles building on the coulomb plasticity of the classical theory we assume an elastic perfectly coulomb plastic rheology and derive exact stress solutions for stable and critical wedges the new theory postulates that the actively deforming most seaward part of an accretionary prism the outer wedge overlies the updip velocity strengthening part of the subduction fault and the less deformed inner wedge overlies the velocity weakening part the seismogenic zone during great earthquakes the outer wedge is pushed into a compressively critical state with an increase in basal and internal stresses and pore fluid pressure after the earthquake the outer wedge returns to a stable state the outer wedge geometry is controlled by the peak stress of the updip velocity strengthening part of the subduction fault achieved in largest earthquakes the inner wedge generally stays in the stable regime throughout earthquake cycles acting as an apparent backstop and providing a stable environment for the formation of forearc basins the new theory has important implications for the studies of the updip limit of the seismogenic zone the evolution of accretionary prisms and forearc basins activation of splay faults and tsunami generation evolution of the fluid regime and mechanics of frontal prisms at margins dominated by tectonic erosion

rollover drowning and discontinuous retreat distinct modes of barrier response to sea level rise arising from a simple morphodynamic model we construct a simple morphodynamic model to investigate the long term dynamic evolution of a coastal barrier system experiencing sea level rise using a simplified barrier geometry the model includes a dynamic shoreface profile that can be out of equilibrium and explicitly treats barrier sediment overwash as a flux with barrier behavior primarily controlled by the maximum potential overwash flux and the rate of shoreface response the modeled barrier system demonstrates four primary behaviors height drowning width drowning constant landward retreat and a periodic retreat height drowning occurs when overwash fluxes are insufficient to maintain the landward migration rate required to keep pace with sea level rise on the other hand width drowning occurs when the shoreface response rate is insufficient to maintain the barrier geometry during overwash driven landward migration during periodic barrier retreat the barrier experiences oscillating periods of rapid overwash followed by periods of relative stability as the shoreface resteepens this periodic retreat which occurs even with a constant sea level rise rate arises when overwash rates and shoreface response rates are large and of similar magnitude we explore the occurrence of these behaviors across a wide range of parameter values and find that in addition to the maximum overwash flux and the shoreface response rate barrier response can be particularly sensitive to the sea level rise rate and back barrier lagoon slope overall our findings contrast with previous research which has primarily associated complex barrier behavior with changes in external forcing such as sea level rise rate sediment supply or back barrier geometry

low grade metamorphism around the down dip limit of seismogenic subduction zones example from an ancient accretionary complex in the shimanto belt japan abstract reactions involving clay minerals during low grade metamorphism at the depth of an ancient accretionary complex in the shimanto belt kyushu japan were studied by integrated transmission electron microscopy energy dispersive x ray spectroscopy and x ray diffraction analyses of the bulk rock and clay fraction the analyzed metasediment the kitagawa unit contain an incipient sub horizontal slaty cleavage illite crystallinity data and mica b dimensions indicate that the conditions of metamorphic deformation were anchizone epizone grade and intermediate pressure cleavage formation was linked to two reactions involving clay minerals 1 the recrystallization of 1m dominant matrix mica inherited from the original sedimentary fabric into thick defect free 2m1 packets along cleavage planes and 2 the formation of chlorite from 7 a berthierine balanced equations among the clay phases based on compositional data and their relative abundance suggest that the decomposition of matrix mica resulted in the formation of paragenetic mica and chlorite along the cleavage planes without significant elemental outflux although a modal increase in phyllosilicates is not indicated by the data the growth of chlorite and mica along cleavage planes may have a large influence on the rheological properties of a decollement and may be related to the occurrence of the seismic aseismic transition at 350 c

storm generated sedimentary structures in subtidal marine facies with examples from the middle and upper ordovician of southwestern virginia abstract the role of storms is of major importance in forming stratification in open shelf facies though storm processes on modern shelves are not fully understood enough is known to see how sediments are influenced storms transport sand away from coastal areas and suspend and transport sand and mud on the open shelf when wave base is lowered storms generate winnowed lag deposits of shells or gravel but coarser sediment and shells of megafauna are little transported except in very near shore environments the martinsburg formation middle and upper ordovician of southwestern virginia was deposited on a storm influenced open marine platform in contrast to the classic turbidite flysch basin of the martinsburg in the great valley of virginia to the northeast deposition of most martinsburg sediments was due to storms sediments deposited during single storm events occur in characteristic fining upward sequences 1 to 80 cm thick in both carbonate and terrigenous clastic dominated areas of the platform individual storm deposits consist of a sharp erosional base overlain by a couplet of whole fossil packstone and laminated calcarenite siltite or quartzose siltstone to very fine sandstone which is gradational to shale packstones are typically intraclastic have shells aligned parallel o bedding and convex up often with adhering or contained mud and have abundant infiltration textures such as cement filled shelter voids packstones grade abruptly to a laminated bed with horizontal plane lamination large and small scale in phase undulatory lamination and wave ripple cross lamination commonly occurring in ordered vertical sequences laminated beds contain escape burrows are weekly graded and have irregularly mounded upper bed surfaces laminated beds grade upward to shale containing horizontal branching burrows and marine fossils the faunal content of the fining upward sequences matches that of the interbedded shale storm generated beds vary greatly in thickness laterally and frequently pinch out completely fining upward sequences formed by scouring winnowing and suspension of the sand and mud during the height of the storm to form the erosional base and autochthonous lag of whole fossils storms preferentially preserve whole fossils rather than fragmenting them infiltration of finer sediment into the lag deposit and deposition of the laminated bed occurred as the storm waned laminated beds are molded into a distinctive suite of sedimentary structures by wave generated currents the shale represents deposition of finest storm suspended material and continued hemipelagic sedimentation similar sequences are widely distributed in the geologic record variability of storm generated sequences can be related to changing water depth thus storm deposits may be useful in basin analysis to estimate relative water depths and trace transgressive and regressive events

frictional slip of granite at hydrothermal conditions sliding on faults in much of the continental crust likely occurs at hydrothermal conditions i e at elevated temperature and elevated pressure of aqueous pore fluids yet there have been few relevant laboratory studies to measure the strength sliding behavior and friction constitutive properties of faults at hydrothermal conditions we slid laboratory granite faults containing a layer of granite powder simulated gouge velocity stepping experiments were performed at temperatures of 23 to 600 c pore fluid pressures ph2o of 0 dry and 100 mpa wet effective normal stress of 400 mpa and sliding velocities v of 0 01 to 1 m s 0 32 to 32 m yr conditions were similar to those in earlier tests on dry granite to 845 c by lockner et al 1986 the mechanical results define two regimes the first regime includes dry granite up to at least 845 and wet granite below 250 c in this regime the coefficient of friction is high 0 7 to 0 8 and depends only modestly on temperature slip rate and ph2o the second regime includes wet granite above 350 c in this regime friction decreases considerably with increasing temperature temperature weakening and with decreasing slip rate velocity strengthening these regimes correspond well to those identified in sliding tests on ultrafine quartz we infer that one or more fluid assisted deformation mechanisms are activated in the second hydrothermal regime and operate concurrently with cataclastic flow slip in the first cool and or dry regime is characterized by pervasive shearing and particle size reduction slip in the second hot and wet regime is localized primarily onto narrow shear bands adjacent to the gouge rock interfaces weakness of these boundary shears may result either from an abundance of phyllosilicates preferentially aligned for easy dislocation glide or from a dependence of strength on gouge particle size major features of the granite data set can be fit reasonably well by a rate and temperature dependent three regime friction constitutive model chester this issue we extrapolate the experimental data and model fit in order to estimate steady state shear strength versus depth along natural slipping faults for sliding rates as low as 31 mm yr we do this for two end member cases in the first case pore pressure is assumed hydrostatic at all depths shallow crustal strength in this case is similar to that calculated in previous work from room temperature friction data while at depths below about 9 13 km depending on slip rate strength becomes less sensitive to depth but sensitive to slip rate in the second case pore pressure is assumed to be near lithostatic at depths below 5 km strength is low at all depths in this case 20 mpa in agreement with observations of weak faults such as the san andreas the predicted depth of transition from velocity weakening to velocity strengthening lies at about 13 km depth for a slip rate of 31 mm yr in rough agreement with the seismic aseismic transition depth observed on mature continental faults these results highlight the importance of fluid assisted deformation processes active in faults at depth and the need for laboratory studies on the roles of additional factors such as fluid chemistry large displacements higher concentrations of phyllosilicates and time dependent fault healing

evidence for major mass transfer and volume strain during regional metamorphism of pelites systematic examination of published sedimentary and metamorphosed pelite analyses has revealed evidence of significant mass transfer and volume strain during regional metamorphism statistical analysis of the data shows that barrovian zone metamorphism of pelitic schist generally causes increases in the whole rock concentrations of the low solubility elements ti and all the observed increases in ti and al contents as functions of metamorphic grade are almost certainly due to residual enrichment caused by the removal of other more soluble species application of mass balance principles to the petite compositional trends indicates that the average pelite may lose as much as 30 of its mass and volume during progressive metamorphism from subgreenschist to amphibolite facies conditions the bulk of the lost mass is silica not volatiles in addition other elements particularly ca na and k appear to be highly mobile in deep crustal metamorphism contrary to conventional interpretations it is concluded that the regional metamorphism of pelites is not an isochemical process

limited localized nonvolatile element flux and volume change in appalachian slates geometric evidence for major nonvolatile volume losses at several appalachian slate localities contradicts geochemical evidence for minimal compositional changes during low grade metamorphism of shales relative to adjoining microlithons spaced cleavage zones are depleted in si quartz na albite and for carbonate rich slates ca mn and mg calcite and dolomite zr ti al p and fe are enriched in cleavage zones the greatest enrichments are in zr proportional k gains and na and si losses suggest that cleavage fractionation combines stoichiometric reactions e g k albite chlorite muscovite sio 2 na with pressure solution of quartz and carbonate minerals cleavage and sorting pelite to psammite fractionation patterns are similar but can be distinguished by higher zr in al rich cleavage zones relative to zr in al rich pelitic rocks the compositional similarities of homogeneous shales and slates do not indicate large volume losses during slate metamorphism for paleozoic slates from localities where large volume losses have been hypothesized on geometric grounds martinsburg slate belt of pennsylvania and new jersey meguma group of nova scotia and taconic slate belt of vermont and new york slate compositions show no evidence of large nonvolatile volume losses relative to likely shale protoliths detailed sampling of slates folded at hand specimen to quarry scales indicate that substantial element and volume fluxes are limited to the submeter scale in small scale folds volume losses in tight inner arcs appear to be balanced by volume gains in adjoining areas the complications of metamorphic recrystallization and heterogeneous strain are probably responsible for erroneous interpretations of large nonvolatile volume losses in these appalachian slate localities

geomorphological and sequence stratigraphic variability in wave dominated shoreface shelf parasequences physical stratigraphy within shoreface shelf parasequences contains a detailed but virtually unstudied record of shallow marine processes over a range of historical and geological timescales using high quality outcrop data sets it is possible to reconstruct ancient shoreface shelf morphology from clinoform surfaces and to track the evolving morphology of the ancient shoreface shelf our results suggest that shoreface shelf morphology varied considerably in response to processes that operate over a range of timescales 1 individual clinoform surfaces form as a result of enhanced wave scour and or sediment starvation which may be driven by minor fluctuations in relative sea level sediment supply and or wave climate over short timescales 10 1 10 3 years these external controls cannot be distinguished in vertical facies successions but may potentially be differentiated by the resulting clinoform geometries 2 clinoform geometry and distribution changes systematically within a single parasequence reflecting the cycle in sea level and or sediment supply that produced the parasequence 10 2 10 5 years these changes record steepening of the shoreface shelf profile during early progradation and maintenance of a relatively uniform profile during late progradation modern shorefaces are not representative of this stratigraphic variability 3 clinoform geometries vary greatly between different parasequences as a result of variations in parasequence stacking pattern and relict shelf morphology during shore face progradation 10 5 10 8 years these controls determine the external dimensions of the parasequence

mechanisms for forming discontinuity surfaces within shoreface shelf parasequences sea level sediment supply or wave regime abstract a 2d process response model was used to evaluate potential mechanisms involved in the formation of small scale stratigraphic variability that is observed within progradational wave dominated shoreface shelf parasequences model experiments which are based on scenarios that consist of a 25 ky progradational phase suggest that discontinuity surfaces form when either sediment supply or sea level fall rapidly or when wave height regime increases over relatively short time periods 102 104 y during coastal progradation in these cases mean deposition rate near the lower shoreface drops which combined with coastal progradation results in a discontinuity surface both observed and simulated discontinuity surfaces form predominantly in lower shoreface deposits and bound meter scale stratigraphic cycles simulations show that wave regime variability affects the shoreface shelf to a much greater depth than minor sea level change therefore facies shifts along wave climate induced bounding surfaces occur over wider reaches of the shoreface shelf system than sea level induced facies shifts high frequency variability in sediment supply rate results in the formation of discontinuity surfaces across which there are no distinct facies shifts

deformation of chlorite in naturally deformed low grade rocks the intracrystalline deformation of chlorite in naturally deformed low grade rocks was investigated with transmission electron microscopy tem as in other phyllosilicates the deformation of chlorite is dominated by the 001 slip plane slip along this plane is very easy through the generation and movement of partial dislocations with burgers vector b 1 n uv0 after initial bending of the 001 planes through a flexural slip mechanism accommodated by slip along 001 the misorientation is concentrated in tiltwalls subnormal to 001 which are formed by partial dislocations with b 1 n uv0 tiltwalls subparallel to 001 are formed by arrays of dislocations with a total burgers vector 001 these boundaries are either initiated at the grain boundary and move inwards by dislocation climb or form by movement of free dislocations towards the tip of propagating boundaries by glide along planes inclined to 001 once a boundary is formed the increasing misfit is accommodated by climb of these dislocations along 001 due to the combination of very easy slip along 001 and the ability to form subgrain boundaries subparallel to 001 by dislocation climb and activation of hard slip systems chlorite deforms plastically even at temperatures below 300 c

updip limit of the seismogenic zone beneath the accretionary prism of southwest japan an effect of diagenetic to low grade metamorphic processes and increasing effective stress off southwest japan the seaward limit of coseismic displacement or updip limit of the seismogenic zone of the 1946 mw 8 3 thrust earthquake reaches to 4 km depth and 40 km landward of the trench this limit coincides with the estimated location of the 150 c isotherm and has been linked to changes in physical properties associated with the smectite to illite clay mineral transition here we show that this limit correlates with a suite of diagenetic to low grade metamorphic processes characterized by 1 declining fluid production and decreasing fluid pressure ratio and 2 active clay carbonate and zeolite cementation and the transition to pressure solution and quartz cementation these diagenetic to low grade metamorphic changes cause the onset of velocity weakening during thrust faulting an increase in effective stress and strengthening of the hanging wall which together combine to produce recordable earthquakes

interlaboratory standardization and calibration of day mineral crystallinity and crystallite size data clay mineral crystallinity and crystallite domain size data determined by x ray diffraction xrd are methods extensively used in the characterization of very low grade metamorphic conditions however the lack of sufficient interlaboratory standardization has made comparisons between different research groups unreliable due to significant variations in numerical results obtained a consequence of the different machine conditions measurement methods and sample preparations used during analysis a calibration approach to the standardization of data using rock chip standards is presented which allows data sets produced by different research groups to be directly and quantitatively compared a standardized scale the crystallinity index standard cis is proposed with illite crystallinity anchizonal boundary limits of 0 25d 2 and 0 42d 2 and equivalent illite crystallite sizes of 52 and 23 nm respectively determined by the warren averbach method calibrating both old and new data will enable more reliable comparisons between similar and contrasting geological environments and should improve the accuracy and reliability of correlations made between xrd data and other indicators of very low grade metamorphism hence increasing the value of such clay mineral studies

fault stability inferred from granite sliding experiments at hydrothermal conditions seismicity on crustal faults is concentrated in the depth interval 1 3 to 12 15km tse and rice 1986 suggested that the lower bound on seismicity is due to a switch with increasing temperature from velocity weakening destabilizing to velocity strengthening stabilizing friction they inferred this transition from friction data for dry granite however pore fluids exist at elevated temperatures throughout the crust and may strongly influence strength and sliding behavior we present new data from sliding experiments on granite at elevated t 23 to 600 plus elevated ph2o 100 mpa our results show velocity strengthening at room temperature but velocity weakening from 100 to 350 c except at 250 from 350 to 600 there are systematic trends from velocity weakening to strong velocity strengthening and from high to low friction neither trend was seen in tests on dry granite the velocity dependence data imply the potential for unstable slip in the interval 100 to 350 using a geotherm to map temperature to depth this interval closely matches the observed earthquake distribution

transition of accretionary wedge structures around the up dip limit of the seismogenic subduction zone the nankai accretionary prism is divided into three segments outer and inner wedges and their transition zone these wedges reflect different aspects of wedge taper internal deformation and basal plate boundary fault the outer wedge is characterized by narrow critical taper internal deformation by in sequence fold and thrust and aseismic decollement the inner wedge represents a stable narrow taper weakly deformed internal structure and seismogenic plate boundary fault along its base the transition zone between the two wedges shows large critical taper with steep surface slope internal structure of out of sequence thrust and step down of decollement onto the sediment oceanic basement interface the trench slope break and oceanward margin of forearc basin is located around the landward edge of this transition zone these common aspects might be related to the lithification of both accreted and underthrust sediments and the resultant switch of the plate boundary fault deformation and lithification process recorded in exhumed on land melange of accretionary complexes suggest that the step down of the plate boundary decollement occurs around the up dip limit of seismogenic subduction zone

reflection signature of seismic and aseismic slip on the northern cascadia subduction interface at the northern cascadia margin the juan de fuca plate is underthrusting north america at about 45 mm yr 1 ref 1 resulting in the potential for destructive great earthquakes2 3 the downdip extent of coupling between the two plates is difficult to determine because the most recent such earthquake thought to have been in 1700 4 occurred before instrumental recording thermal and deformation studies5 indicate that off southern vancouver island the interplate interface is presently fully locked for a distance of 60 km downdip from the deformation front great thrust earthquakes on this section of the interface with magnitudes of up to 9 4 5 have been estimated to occur at an average interval of about 590 yr ref 3 further downdip there is a transition from fully locked behaviour to aseismic sliding where high temperatures allow ductile deformation with the deep aseismic zone exhibiting slow slip thrust events6 here we show that there is a change in the reflection character on seismic images from a thin sharp reflection where the subduction thrust is inferred to be locked to a broad reflection band at greater depth where aseismic slip is thought to be occurring this change in reflection character may provide a new technique to map the landward extent of rupture in great earthquakes and improve the characterization of seismic hazards in subduction zones

hanging wall deformation of a seismogenic megasplay fault in an accretionary prism the nobeoka thrust in southwestern japan the structure and occurrence of deformation within the hanging wall of the nobeoka thrust in kyushu japan was investigated to understand the dynamic aspects of splay faulting in relation to seismic events from field observations hanging wall is suggested to have undergone four phases of deformation the first phase involved horizontal shortening as documented by folding and thrusting followed by a phase of vertical loading shown by the development of horizontal slaty cleavages pressure solution and cleavage parallel mineral vein precipitation a third phase involved shearing and deformation along cleavage restricted to near the nobeoka thrust while the fourth phase produced widespread brittle fracturing associated with the development of pseudotachylyte bearing faults and tension crack filling veins high angle to cleavage these four phases can be explained as follows during the inter seismic period an extensionally stable taper was maintained in the inner wedge of the accretionary prism by dominant vertical loading 1 in combination with a lesser amount of horizontal compression 2 related to the locking of the mega thrust elastic strain energy in the hanging wall of the inner wedge was co seismically released by slip on the mega thrust and horizontal shortening in the outer wedge associated with dynamic ductile weakening of the fault plane this sudden release of elastic strain caused brittle fracturing with 1 at a high angle to the shear surface of the nobeoka thrust most of the displacement resulting from deformation of the footwall

an integrated model for transitional pressure solution in sandstones abstract a key aspect of the deformation of sedimentary rocks during diagenesis is pressure solution however it is often not clear why some rocks of a given mineralogy depth and pressure exhibit a great deal of pressure solution while very similar rocks under similar conditions do not to address such difficulties which we believe arise from the natural non linear physico chemical processes a quantitative model for pressure solution applied to sandstones has been developed this model subsumes various factors 1 pressure temperature and burial rate 2 grain size shape and packing of the mineral grains 3 the variability of water film thickness and coefficient of diffusion between any two grains in contact as a function of stress across the contact pore fluid pressure salinity ph and temperature in this study we distinguish several types of surface sites over quartz grains in a sandstone with corresponding differences in chemical potential thus allowing the diffusive transfer of matter from one site to another the contact between two grains is divided into two parts the actual true contact between two grains is a site of water film diffusion and the inclusions inside the contact the free face inclusion contacts are sites of free face pressure solution on the pore surface site precipitation occurs it is shown that a kinetics transition from a reaction limited deformation to a diffusion limited deformation occurs in the upper crust a geometric transition occurs too due to the textural evolution of the rock with deformation the main goal of this paper is to show the dynamics of the shifting importance of actual and free face inclusion contacts using a unified model including both features the result is a predictive model for porosity variations with depth due to pressure solution in sandstones

along strike variations in underthrust sediment dewatering on the nicoya margin costa rica related to the updip limit of seismicity 1 along the costa rican subduction zone offshore the nicoya peninsula an offset in the updip limit of seismicity coincides with a transition between subduction of warm crust generated at the cocos nazca spreading center and cool crust formed at the east pacific rise we evaluate whether the observed difference in thermal state of incoming crust would result in significant differences in sediment dehydration reaction progress along strike thought to be a control on the updip limit of seismicity we combine thermal models with models of dehydration reaction kinetics for opal and smectite to estimate the distribution of diagenetic fluid sources the modeled distribution of diagenetic fluid sources mimics the pattern of the updip limit of seismicity seismicity begins 15 20 km landward of most of the smectite to illite transition this suggests that the location of the updip limit of seismicity may be influenced by the dissipation of fluid overpressures landward of smectite to illite dehydration

contrasts in physical properties between the hanging wall and footwall of an exhumed seismogenic megasplay fault in a subduction zone an example from the nobeoka thrust drilling project 1 we examined the physical properties of an exhumed and fossilized subduction zone megasplay fault by analyzing geophysical logging data obtained by the nobeoka thrust drilling project which provide a high resolution transect of properties across the main fault zone the footwall cataclasite exhibits higher averages of neutron porosity 7 6 and lower values of electric resistivity 232 m compared to the hanging wall phyllite 4 8 453 m this clear contrast between the hanging wall and footwall may account for the difference in maximum burial and structural variation despite the contrast observed between the hanging wall and footwall in macroscopic scale the resistivity and porosity data from both the hanging wall and footwall can be fit with a single curve using archie s law suggesting the similarities in microstructures and mineralogy in this low porosity range above the main fault core of the nobeoka thrust a brittle damage zone in the hanging wall contains pseudotachylyte as evidence of the seismogenic slip and does not follow archie s law damage zones in the hanging wall are also observed in the modern splay fault at shallow depth in the nankai trough but with much thicker width whereas the footwall damage zone is more extensive in the nobeoka thrust splay faults may exhibit strong deformation in the hanging wall in the early stage and as fault rocks get buried deeper and as displacement and physical property contrast increase across the fault the damage effect may eventually be enlarged in the footwall

fluid circulation in the depths of accretionary prisms an example of the shimanto belt kyushu japan accretionary prisms constitute ideal targets to study fluid circulation and fluid rock interactions at depths beyond the reach of active margin deep drilling the highest grade rocks from the shimanto belt on kyushu were buried under 3 5 kbars at 300 c toriumi and teruya 1988 they contain abundant quartz veins formed throughout burial and exhumation and variably affected by brittle and ductile deformation cathodoluminescence cl reveals the existence of two distinct types of quartz characterized by a blue and brown color respectively cl blue quartz fills macro veins width 10 m while cl brown quartz is present in micro veins width 1 10 m and ductilely recrystallized domains on the basis of microstructures the fluids associated with the cl blue and cl brown quartz are interpreted as external and local respectively quartz growth rims of alternating cl colors as well as mutually cross cutting veins show that the two fluids cyclically wetted the host rock from fluid inclusions analysis the fluid associated with cl blue quartz has a salinity similar to seawater while the fluid associated with cl brown quartz is less saline in addition cl blue quartz is richer in aluminum than the cl brown one in contrast to the salinity aluminum signature the 18o isotopic signature of both quartz types is similar and buffered by host rock the difference between the preservation of the salinity signature of the fluid and the loss of its 18o signature is explained by quicker exchange kinetics and larger host rock buffering capacity for isotopic reequilibration the local fluid associated with cl brown quartz reflects the dilution of pore water by the pure water produced by prograde dehydration reactions of clay minerals the external fluid associated with cl blue quartz is interpreted as seawater or pore water from shallow depth 1 2 km below seafloor sediments we propose that downward percolation of shallow water to depths 10km is a transient process associated with mega earthquakes

shoreface tongue geometry constrains history of relative sea level fall examples from late cretaceous strata in the book cliffs area utah progradational shoreface tongues preserve a near complete depositional record of relative sea level highstands falls and lowstands two distinct styles of progradational shoreface tongue are examined in an extensive outcrop and subsurface dataset from late cretaceous strata of the book cliffs area utah representing i highstand through attached lowstand progradation and ii highstand through detached lowstand progradation using this dataset key geometrical attributes of the shoreface tongues and their internal facies architecture are identified and quantified that enable the reconstruction of relative sea level fall history for example attached wave dominated lowstand shoreface deposits record a slow 0 2 0 3 mm yr 1 low magnitude 14 m relative sea level fall punctuated by minor rises detached weakly wave influenced lowstand shoreface deposits record a more rapid 0 4 0 5 mm yr 1 high magnitude 45 m relative sea level fall synchronous with a marked change in sediment delivery and depositional process regime at the shoreline

smectite to chlorite conversion by frictional heating along a subduction thrust abstract an ancient subduction thrust developed at the top of oceanic basaltic crust is exposed in the shimanto accretionary complex of eastern shikoku southwest japan the fault zone structure indicates that slip was localized along a few centimeters thick layer in which fluidization of comminuted material is recorded to identify possible clay mineral reactions during frictional heating along subduction thrusts we examined the clay mineralogy of the basalt derived fault zone rocks including ultracataclasite altered basalt foliated cataclasite and massive basalt all samples include chlorite mixed layer chlorite smectite c s and corrensite among the samples the highest chlorite content in the c s is found in the ultracataclasite the significant chloritization in the ultracataclasite is unlikely to reflect hydrothermal alteration and regional very low grade metamorphism during subduction down to seismogenic depths instead it is interpreted to have resulted from frictional heating associated with localized slip based on chlorite geothermometry and the presence of small quantities of corrensite we estimate the temperatures during this frictional heating to have been in the range of 185 260 c which is 35 130 c higher than the ambient temperature this difference of 35 130 c is consistent with a temperature rise of 50 150 c indicated by the stretching of fluid inclusions in calcite therefore the crystallographic and chemical properties of c s are potentially useful in detecting small temperature rises associated with frictional heating and the method could be widely applicable to c s bearing faults

tem and aem constraints on the origin and significance of chlorite mica stacks in slates an example from central wales u k chlorite mica stacks grains of intergrown chlorite and white mica in a matrix of fine grained white mica and chlorite have been studied using xrd sem empa tem and aem methods the stacks occur in a weakly cleaved llandoverian mudstone central wales which has a white mica illite crystallinity index of 0 35 a20 corresponding to the lower anchizone white mica occurs as packets 100 to 8 m thick interleaved with dominant chlorite packets in stacks with both apparent coherent interfaces or cross cutting small angle boundaries with chlorite layers it is well crystallized 2m polytype with phengitic composition and low paragonite component na na k 0 0 07 chlorite in stacks is fe rich and relatively homogeneous tio2 crystals surround stacks and occur within chlorite and white mica is ti rich compared to matrix white mica fine grained white mica and chlorite in the matrix have two different orientations one parallel to bedding and one parallel to cleavage which is approximately 30 50 to bedding matrix white mica is predominantly a 2m1 polytype but some cleavage parallel white mica is 3 t and some bedding parallel white mica is 1md it is na rich na na k 0 14 0 42 and relatively heterogeneous some discrete paragonite and phengitic muscovite are observed to coexist in the cleavage orientation matrix white mica and chlorite each contain less fe than corresponding white mica and chlorite in stacks both matrix and stack chlorite are one layer polytypes the data imply that chlorite in the stacks is largely derived from the replacement of volcanogenic biotite and other ferromagnesian minerals probably via intermediate expandable trioctahedral phyllosilicates most intergrowths of chlorite and mica in stacks formed by mica replacement of chlorite and altered biotite along cleavage fissures subsequent deformation caused further modification of pre existing chlorite mica stacks whereas partial dissolution of stacks and bedding parallel matrix phyllosilicates resulted in the formation of cleavage parallel phyllosilicates

compositional and fluid pressure controls on the state of stress on the nankai subduction thrust a weak plate boundary abstract we show that both fault mineralogy and regional excess fluid pressure contribute to low resolved shear stresses on the nankai subduction plate boundary off southwest japan ring and direct shear tests indicate that saturated clay minerals in the fault possess intrinsically low residual friction coefficients r at stress levels between 1 0 and 40 mpa the direct shear r values for purified smectite are 0 14 0 02 for illite 0 25 0 01 and for chlorite 0 26 0 02 for point load velocities of 0 0001 mm s these clay minerals dominate the nankai subduction decollement zone illite plus quartz is mechanically important in the altered incoming muroto section and the predicted decollement r should lie between 0 2 and 0 32 this low residual strength together with elevated fluid pressure limits shear stresses to below 4 mpa within the frontal 50 km of the subduction system consistent with the low wedge taper in this region a higher wedge taper off the ashizuri peninsula indicates basal shear stresses rise slightly along strike towards this region our analysis indicates lower fluid pressures must predominantly be responsible because only small second order along strike variations in r are predicted to occur as a result of variations in smectite and total clay content these variations should be further reduced at depth under the wedge as smectite is diagenetically altered to illite however our data suggest the low r values of the clay rich decollement still limit shear stresses to between 17 and 29 mpa within the frontal 50 km of the wedge consistent with other estimates of plate boundary weakness indeed we propose that it should be expected that subduction plate boundaries like nankai will be weak because of the intrinsic presence of clay rich faults and moderate fluid overpressures our data do not support the hypothesis that the smectite to illite reaction directly controls the onset of seismogenic behavior deep in the nankai system because there is already a mechanical dominance of illite rather than smectite in the shallow decollement zone and we find all the clay phases tend to velocity strengthen however temperature activated clay diagenesis and dehydration may cause secondary changes in the fault properties and state of stress across the up dip limit of the seismogenic zone

the structure and the phyllosilicates chemistry crystallinity and texture of talas ala tau tien shan kyrgyz republic comparison with more recent subduction complexes abstract geological mapping and structural analysis of the talas ala tau tien shan kyrgyz republic have revealed a complex structure composed of folds with axial plane cleavage and thrust faults verging towards the ne the main structures of the range correspond to minor tertiary and carboniferous permian deformation superimposed on the main deformation event that took place during the baikalian orogeny the pervasive axial plane cleavage diminishes in penetrativity from the hinterland to the foreland in both the uzunakhmat and karagoin sheets the main thrusts developed phyllonitic shear related rocks on the hangingwall immediately above the thrust planes a crystal chemical study of the phyllosilicates growth during the baikalian deformation event along a cross section revealed changes in the crystallinity composition and lattice parameters of them the phyllosilicates present in the talas ala tau rocks were crystallized in very low grade metamorphic conditions that is below 300 c as indicated by their kubler index ki which decreases from sw towards the ne detailed tem study of the phyllosilicates reveals a clear textural difference at the lattice level between samples with higher or lower ki parameters there is also a clear difference in crystal chemical parameters ki and b and composition between the phyllosilicates growth in relation to the axial plane cleavage and the ones belonging to the thrust related phyllonites the first ones are more affected by the ferrimuscovitic vector than the phyllosilicates of phyllonites closer to the theoretical phengitic component huge ranges of values of phengitic content of micas at sample level are interpreted as the result of a decompression path from at least 8 kbar we propose a subduction geodynamic environment for the regional deformation and the origin of the phyllosilicates as they are similar to those obtained in more recent accretionary complexes

facies architecture and geometry of landward stepping shoreface tongues the upper cretaceous cliff house sandstone mancos canyon south west colorado the campanian cliff house formation represents a series of individually progradational shoreface tongues preserved in an overall landward stepping system in the mancos canyon area the formation consists of four 50 to 55 m thick and 10 to 20 km wide sandstone tongues which pinch out landwards into lower coastal plain and lagoonal deposits of the upper menefee formation and seawards into offshore shales of the lewis shale formation photogrammetric mapping of lithofacies along the steep and well exposed canyon walls was combined with sedimentary facies analysis and mapping of the detailed facies architecture two major facies associations have been identified one comprising the mostly muddy and organic rich facies of lagoonal and lower coastal plain origin and one comprising the sandstone dominated facies of shoreface origin key stratigraphic surfaces were identified by combining the mapped geometry of the lithofacies units with the interpretation of depositional processes the stratigraphic surfaces master ravinement surface shoreface coastal plain contact transgressive surface maximum flooding surface and the sequence boundary allow each major sandstone tongue to be divided into a simple sequence consisting of a basal transgressive system tract tst overlain by a highstand system tract hst within each sandstone tongue a higher frequency cyclicity is evident the high frequency cycles show a complex stacking pattern development and are commonly truncated in the downdip direction by surfaces of regressive marine erosion the complexities of the cliff house sandstone tongues are believed to reflect changes in the rate of sea level rise combined with the responses of the depositional system to these changes synsedimentary compaction causing a thickness increase in the sandstone tongues above intervals of previously uncompacted lagoonal coastal plain sediments also played a role this study of the facies architecture geometry and sequence stratigraphy of the cliff house formation highlights the fact that there may be some problems in applying conventional sequence stratigraphical methods to landward stepping systems in general these difficulties stem from the fact that no single stratigraphic surface can easily be identified and followed from the non marine to the fully marine realm i e from the landward to the basinward pinch out of the sandstone tongues in addition the effects of synsedimentary compaction and changes in the shoreface dynamics are not easily recognized in limited data sets such as from the subsurface

high resolution sequence stratigraphy of clastic shelves v criteria to discriminate between stratigraphic sequences and sedimentological cycles abstract in contrast to high frequency sequences driven by high magnitude relative sea level changes those controlled by short term minor relative sea level and or sediment supply changes may be difficult to discriminate from sedimentological cycles i e bedsets unrelated to shoreline shifts especially in case of limited outcrop exposures in fact meter scale fully shallow marine high frequency sequences and typical meter scale bedsets may share a similar simple facies succession documenting either an upward increase or decrease of event beds it is therefore necessary to define a set of criteria that allows to discriminate between thin high frequency sequences and bedsets based on sedimentological stratigraphic micropaleontological mineralogical and diagenetic data in particular the sedimentological and stratigraphic criteria that aid discriminating between high frequency sequences and bedsets include 1 occurrence of environmental changes across bounding surfaces 2 occurrence of water depth changes across bounding surfaces 3 physical appearance of bounding surfaces and associated substrate controlled ichnofacies 4 lateral extent of bounding surfaces 5 presence of condensed deposits 6 cycle thickness 7 recognition of a set of clinoforms in a regressive shoreface shelf succession moreover the formation of wave ravinement surfaces in the shoreface is usually associated with an increase in the percentage of benthic micro foraminifera specimens documenting energetic conditions and in the abundance of heavy minerals extensive cementation may also be found just below and or above transgressive surfaces however the integration of more than one of the above criteria is necessary to reliably discriminate between sequence stratigraphic surfaces and therefore high frequency sequences and bedset boundaries the latter being only related to changes of energy level and or local sediment supply without shoreline shifts this work is essential to correctly reconstruct the sequence stratigraphic framework of a given succession and to interpret the factors that controlled the cyclicity

local thickening of the cascadia forearc crust and the origin of seismic reflectors in the uppermost mantle seismic reflection profiles from three different surveys of the cascadia forearc are interpreted using p wave velocities and relocated hypocentres which were both derived from the first arrival travel time inversion of wide angle seismic data and local earthquakes the subduction decollement which is characterized beneath the continental shelf by a reflection of 0 5 s duration can be traced landward into a large duplex structure in the lower forearc crust near southern vancouver island beneath vancouver island the roof thrust of the duplex is revealed by a 5 12 km thick zone identified previously as the e reflectors and the floor thrust is defined by a short duration reflection from a b2 km thick interface at the top of the subducting plate we show that another zone of reflectors exists east of vancouver island that is approximately 8 km thick and identified as the d reflectors these overlie the e reflectors together the two zones define the landward part of the duplex the combined zones reach depths as great as 50 km the duplex structure extends for more than 120 km perpendicular to the margin has an along strike extent of 80 km and at depths between 30 km and 50 km the duplex structure correlates with a region of anomalously deep seismicity where velocities are less than 7000 m s 1 we suggest that these relatively low velocities indicate the presence of either crustal rocks from the oceanic plate that have been underplated to the continent or crustal rocks from the forearc that have been transported downward by subduction erosion the absence of seismicity from within the e reflectors implies that they are significantly weaker than the overlying crust and the reflectors may be a zone of active ductile shear in contrast seismicity in parts of the d reflectors can be interpreted to mean that ductile shearing no longer occurs in the landward part of the duplex merging of the d and e reflectors at 42 46 km depth creates reflectivity in the uppermost mantle with a vertical thickness of at least 15 km we suggest that pervasive reflectivity in the upper mantle elsewhere beneath puget sound and the strait of georgia arises from similar shear zones

event based stratigraphic simulation of wave dominated shallow marine environments abstract the presence of event beds in the shallow marine stratigraphic record indicates formation is governed by high magnitude low frequency processes rather than low magnitude high frequency processes in this paper a 2 d multiple grain size process response model barsim is presented which uses event deposition to simulate stratigraphic response to changes in sea level and sediment supply barsim uses variable time steps to simulate individual storm event and fair weather periods deposition during storm conditions solely consists of reworked shoreface sediment while fair weather deposits consist of reworked shoreface sediment combined with sediment supplied by littoral drift and suspension simulations using variations in sea level sediment supply both amount and grain size and wave height regime result in distinct depositional patterns stratal geometry and bed characteristics model results indicate that both wave height regime and grain size of supplied sediment have considerable effect on shoreface morphology and stratal characteristics unraveling coastal evolution from the shallow marine stratigraphic record may therefore be more difficult than previously assumed as both variables are expected to vary over geologic time scales

anatomy and sequence architecture of the early post rift in the neuquen basin argentina a response to physiography and relative sea level changes abstract a detailed architectural and sequence stratigraphic analysis was carried out in the early post rift succession of central neuquen basin middle jurassic cuyo group integrating outcrop and subsurface information from a 3 000 km2 area sedimentary facies analysis allowed the definition of six marine facies associations which are grouped in two main depositional systems during the late toarcian to early bathonian a storm and wave dominated shoreface to offshore system was developed this is overlain by a late bathonian early callovian fluvio deltaic depositional system the sequence stratigraphic analysis of this succession identified parasequences limited by marine flooding surfaces with little evidence of erosion parasequences could be grouped into four parasequence sets that show the evolution of the depositional systems and can be interpreted in terms of shoreline trajectories in this sense a log term transgressive event defined by a complicated retrogradational stacking pattern and spanning for almost 10 my is identified for the older deposits this succession is eventually replaced by a progradational unit that represents highstand conditions the cuyo succession identified in this part of the basin is completed by the development of a regressive surface and the onset of a deltaic depositional system with no parasequence development but indicating an abrupt basinward facies shift the long term transgression that dominates the early post rift succession in this part of the basin is interpreted to represent a period of sustained accommodation creation produced by the combination of thermal subsidence differential compaction of syn rift deposits and eustatic rise under a relatively low sediment supply changes in the stacking pattern of retrogradational parasequence sets are thought to be produced by changes in the bathymetry of the topography being flooded which is a relic of a complex array of footwalls and shoulders generated during the syn rift stage regional changes in thickness and timing for the early post rift succession could be therefore the result of the relatively passive infill of an inherited topography of the syn rift suggesting that most of the accommodation was already created before the onset of the long term transgressive trend that characterizes the post rift succession in this part of the basin the cuyo group succession reported here reflects the complexity in terms of depositional styles sequence stratigraphic patterns and controls that can be expected during the early post rift infill of syn rift structural depressions therefore the results of this study can provide useful lessons for post rift systems having prolific hydrocarbon production worldwide e g in the northern north sea norwegian sea thailand and argentina and chile