tidal modeling of an ancient tide dominated seaway part 1 model validation and application to global early cretaceous aptian tides abstract the utility of deep time global paleotidal modeling is evaluated with a series of modeling experiments focused on the early cretaceous aptian the results from a series of paleobathymetry sensitivity experiments indicate that despite paleogeographic and paleobathymetric uncertainty appropriate use of global paleotidal models complements and enhances stratigraphic and sedimentological methods before being applied to global paleotidal modeling the imperial college ocean model icom is validated for the computation of modern global tides the icom results only deviate slightly from a state of the art published model and were achieved with considerably less computational expense and without data assimilation the results from global paleotidal modeling of the early cretaceous aptian were assessed by comparison with the published geological record icom predicts high mesotidal to macrotidal ranges on the arabian platform around india especially to the north and west along the pacific coast between north and south america northeast of australia and around southeast asia the model predicts low microtidal ranges in the proto south atlantic ocean and weddell sea a further validation test assessed the ability of the model to predict the dominant tidal constituents diurnal or semidiurnal in the aptian lower greensand seaway of southeastern england and northern france during the aptian this region was connected to the boreal proto atlantic and neotethys oceans and now preserves superbly documented tidal deposits the model predicts low microtidal ranges in the proto central atlantic ocean and boreal ocean suggesting that they had little impact on tides in the lower greensand seaway higher tidal amplitudes especially of diurnal once daily tides are predicted in the northwestern neotethys ocean suggesting that this ocean was an important source of tidal energy to the lower greensand seaway sensitivity tests to paleogeographic and paleobathymetric uncertainty indicate that the model predictions are robust the prediction of predominantly diurnal tides is supported by published analyses of large dune scale deposits in the lower greensand of southeast england

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

reconstruction of northeast asian deformation integrated with western pacific plate subduction since 200 ma abstract the configuration and kinematics of continental deformation and its marginal plate tectonics on the earth s surface are intrinsic manifestations of plate mantle coupling the complex interactions of plate boundary forces result in plate motions that are dominated by slab pull and ridge push forces and the effects of mantle drag these interactions also result in continental deformation with a complex basin mountain architecture and evolution the kinematics and evolution of the western pacific subduction and northeast asian continental margin deformation represent a first order tectonic process whose nature and chronology remains controversial this paper implements a deep time reconstruction of the western pacific subduction continental accretion or collision and basin mountain deformation in northeast asia since 200 ma based on a newly revised global plate model we use gplates software to examine strain recovery geological and seismic tomography constraints for the western pacific plate subduction and sequentially backward rotations of deforming features the results indicate a nw se oriented shortening from 200 to 137 ma a nww see oriented extension from 136 to 101 ma a nearly n s oriented extension and uplift with a short term nww see oriented compressional inversion in northeast china from 100 to 67 ma and a nw se and nearly n s oriented extension from 66 ma to the present day the western pacific oceanic plate subducted forward under east asia along mudanjiang honshu island during the jurassic and the trenches retreated to the sikhote alin north shimanto and south shimanto zones from ca 137 128 ma ca 130 90 ma and in ca 60 ma respectively our time dependent analysis of plate motion and continental deformation coupling suggests that the multi plate convergent motion and ocean continent convergent orogeny were induced by advance subduction during the jurassic and earliest cretaceous our analysis also indicates that intra continent rifting and back arc extension were triggered by trench retreat during the cretaceous and that the subduction of the oceanic ridge and arc were triggered by trench retreat during the cenozoic therefore reconstructing the history of plate motion and subduction and tracing the geological and deformation records in continents play a significant role in revealing the effects of complex plate motions and the interactions of plate boundary forces on plate mantle coupling and plate motion intracontinental deformation coupling

early mesozoic basin development in north china indications of cratonic deformation we integrated a systematic sedimentary data into a regional early mesozoic stratigraphic framework which demonstrated a detailed picture of spatiotemporal variations in basin deposition and formation in the north china craton the early mesozoic basin sedimentary evolution is utilized to interpret polyphase tectonism and to unravel the craton deformation the late triassic nearly wnw trending giant intracratonic ordos basin was widely distributed across most of north china craton with a southern wedge top depozone along the northern east qilian qinling orogenic belt and a northwestern rift depozone along the helanshan the continuous subsidence and deposition within the basin were dominantly related to the thrust load of the east qilian qinling belt and inferred mantle flow effects associated with paleotethys plate subduction and the rift in the northwestern ordos was driven by nearly north vergent compression of the eastern north qilian north qinling active margins with the stable north china craton this intracratonic ordos basin formation initiated the deformation of the north china craton formation of the jurassic nne trending walled intracratonic ordos basin and the broken flexural basins indicates the north china craton underwent the second even more abroad nearly nne trending crustal deformation with lithosphere thickening in the eastern part of the north china craton and dynamic subsidence in the west which may have been driven by nearly northwestward subduction of the izanagi plate and the eastward extrusion and underthrusting of the western north china craton crustal basement

provenance of synorogenic foreland basin strata in southwestern montana requires revision of existing models for laramide tectonism north american cordillera

the 2010 maule chile earthquake downdip rupture limit revealed by space geodesy radar interferometry from the alos satellite captured the coseismic ground deformation associated with the 2010 mw 8 8 maule chile earthquake the alos interferograms reveal a sharp transition in fringe pattern at 150 km from the trench axis that is diagnostic of the downdip rupture limit of the maule earthquake an elastic dislocation model based on ascending and descending alos interferograms and 13 near field 3 component gps measurements reveals that the coseismic slip decreases more or less linearly from a maximum of 17 m along strike average of 6 5 m at 18 km depth to near zero at 43 48 km depth quantitatively indicating the downdip limit of the seismogenic zone the depth at which slip drops to near zero appears to be at the intersection of the subducting plate with the continental moho our model also suggests that the depth where coseismic slip vanishes is nearly uniform along the strike direction for a rupture length of 600 km the average coseismic slip vector and the interseismic velocity vector are not parallel which can be interpreted as a deficit in strike slip moment release

the case for dynamic subsidence of the u s east coast since the eocene the dynamic subsidence of the united states east coast is addressed using the discrepancy between regional and global estimates of sea level elevation of paleoshorelines and adjoint models of mantle convection that assimilate plate motions and seismic tomography the positions of eocene and miocene paleoshorelines are lower than predicted by global sea levels suggesting at least 50 m and possibly as much as 200 m of subsidence since the end of the eocene dynamic models predict subsidence of the east coast since the end of eocene although the exact magnitude is uncertain this subsidence has been occurring during an overall global sea level fall with the eustatic change being larger than the dynamic subsidence this results in a regional sea level fall in the absence of land subsidence dynamic subsidence is consistent with the difference between eustasy and regional sea level at the new jersey coastal plain

migration of dynamic subsidence across the late cretaceous united states western interior basin in response to farallon plate subduction backstripped cross sections of the late cretaceous succession across central utah colorado and southern wyoming in the western interior basin united states reveal a component of continuously evolving long wavelength residual subsidence in addition to subsidence driven by the sevier thrust belt and associated sediment loads the loci of maximum rates of this residual subsidence moved eastward from ca 98 to 74 ma in phase with the west to east passage of the farallon slab as reconstructed from tomography based on quantitative inverse models these new subsidence data allow testing of existing subduction models and confi rm the dynamic subsidence origin of the western interior basin furthermore regional variations in subsidence rates suggest a possible defi cit of negative buoyancy mantle loading inside the slab beneath colorado supporting the hypothesis that the thickened slab represents a subducted oceanic plateau this paper documents how the cretaceous stratigraphy records the timing patterns and position of underlying mantle processes during farallon slab subduction the new data also reveal patterns indicative of the commencement of the laramide orogeny in the western united states

the ups and downs of north america evaluating the role of mantle dynamic topography since the mesozoic the driving force for transient vertical motions of earth s surface remains an outstanding question a main difficulty lies in the uncertain role of the underlying mantle especially during the geological past here i review previous studies on both observational constraints and physical mechanisms of north american topographic evolution since the mesozoic i first summarize the north american vertical motion history using proxies from structural geology geochronology sedimentary stratigraphy and geomorphology based on which i then discuss the published physical models overall there is a progressive consensus on the contribution of mantle dynamic topography due to buoyancy structures associated with the past subduction at the continental scale a largely west to east migrating deformation pattern suggests an eastward translation of mantle dynamic effects consistent with models involving an eastward subduction and sinking of former farallon slabs since the cretaceous among the existing models the inverse model based on an adjoint algorithm and time dependent data constraints provides the most extensive explanations for the temporal changes of north american topography since the mesozoic at regional scales debates still exist on the predicted surface subsidence and uplift within both the western and eastern united states where discrepancies are likely due to differences in model setup e g mantle dynamic properties and boundary conditions and the amount of time dependent observational constraints toward the development of the next generation predictive geodynamic models new research directions may include 1 development of enhanced data assimilation capabilities 2 exploration of multiscale and multiphysics processes and 3 cross disciplinary code coupling

late cretaceous paleocene synorogenic sedimentation and kinematic history of the sevier thrust belt northeast utah and southwest wyoming integration of cross cutting structural relationships overlapping sedimentary units new conglomerate provenance data and radiometric and palynological dates provides a basis for reinterpretation of the distribution and timing of late cretaceous through paleocene thrust faulting in the northeast utah southwest wyoming part of the sevier thrust belt these data indicate a general eastward progression of deformation that was punctuated by local out of sequence and hinterlandward verging events provenance data delimit a sequential restoration of a regional cross section the principal thrust systems in northeast utah and southwest wyoming are the willard ogden crawford absaroka and hogsback thrusts the willard is the westernmost structurally highest and oldest of the thrusts it carries a unique section of thick proterozoic sedimentary rocks as well as paleozoic rocks and was folded during displacement on younger thrust systems the next youngest thrust system is the ogden which comprises several basement rooted imbricate thrusts that together form a large antiformal stack with a structural culmination in the wasatch range growth of the wasatch culmination took place during coniacian through paleocene time contemporaneous with sequential displacement on the frontal crawford absaroka and hogsback thrusts total shortening in this part of the thrust belt was 100 km and structural relief of 25 km developed in the area of the wasatch culmination during coniacian through paleocene time thrusting followed an overall eastward progression that was interrupted by local out of sequence and hinterlandward verging events several episodes of synchronous displacement on two or more thrusts can be demonstrated shortening occurred in three main episodes the first episode 89 84 ma involved 33 km of shortening on the crawford thrust and its footwall imbricates approximately 19 km of structural relief on the basement cover contact developed in the area of the wasatch culmination the second episode 84 62 ma with a break between 75 69 ma involved 30 km of shortening mainly on the absaroka thrust and development of an additional 6 km of structural relief in the culmination the third episode of shortening 56 50 ma took place on the hogsback thrust involved 21 km of horizontal shortening and produced no significant increase in structural relief in the culmination long term rates of shortening ranged between 3 0 mm yr and 6 6 mm yr these three episodes of shortening produced three large accumulations of synorogenic conglomerate totaling 3 km in thickness the henefer formation and echo canyon and weber canyon conglomerates were deposited during crawford thrusting the evanston formation was deposited during and after absaroka thrusting and the lower conglomeratic part of the wasatch formation was deposited during and after hogsback thrusting most of the sediment in these synorogenic units however was derived from repeated uplift of the willard thrust sheet and from the eastern flank of the wasatch culmination in the rear part of the thrust belt only local minor accumulations were derived from the frontal ramp anticlines sediment accumulation and structural deformation were generally out of phase periods of regional shortening and uplift were marked by development of unconformities and sediment bypassing to distal parts of the foreland basin periods of structural inactivity were marked by accumulation of aerially widespread braided river conglomerate on top of the thrust belt one exception to this pattern is the henefer echo canyon weber canyon conglomerate deposit which contains evidence of progressive deformation in close proximity to the tip of the crawford thrust comparison of the sequential restoration with the late cretaceous subsidence history and isopach patterns in the distal foreland basin of western wyoming demonstrates that the principal controls on regional subsidence and sediment supply were the growth and erosion of the wasatch culmination growth of the duplex beneath the culmination may have been a means of maintaining critical taper in the thrust wedge

cenozoic subsidence and uplift of continents from time varying dynamic topography time varying global dynamic topography has been computed for the entire cenozoic the spherical viscous flow model is driven by a distribution of density heterogeneity based on mesozoic and cenozoic subduction by using the calculated topography the uplift and subsidence histories of five regions fixed to the north american indian australian indonesian and south american continents are computed predicted vertical motions are in qualitative agreement with observed values except for india and south america for australia and north america the predicted periods of uplift and subsidence are out of phase with respect to observations but display the correct overall trend the latest phase of uplift for north america is directly related to the cessation of kula plate subduction after 48 ma dynamic topography depends on the viscosity structure of the mantle a lower mantle that is 50 times more viscous than the upper mantle yields the best agreement between modeled and predicted vertical motions the presence of a low viscosity channel beneath the lithosphere has only a small influence on our results compared to dynamic topography the time varying geoid is insignificant in controlling relative sea level

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

flexural subsidence and basement tectonics of the cretaceous western interior basin united states the flexural subsidence history recorded in cenomanian to early campanian 97 to 80 ma strata in the cretaceous u s western interior basin was studied with two dimensional flexural backstripping techniques results indicate that the flexural subsidence resulting from thrust loading was superimposed on epeirogenic subsidence in the foreland basin the flexural component exhibits significant spatial and temporal variations along both the strike and dip relative to the sevier thrust belt the greatest cumulative subsidence occurred in southwestern wyoming and northern utah concurrent subsidence in northwestern montana and southern utah was insignificant temporal trends in subsidence also show a distinct regional pattern from the cenomanian to late turonian 97 to 90 ma subsidence rates were high in utah and much lower in wyoming and montana in contrast during the coniacian and santonian 90 to 85 ma subsidence accelerated rapidly in wyoming increased slightly in montana and decreased in utah we suggest that these spatially and temporally varying subsidence patterns reflect the interplay of several geodynamic factors including 1 temporal and spatial variation in emplacement of the thrust loads 2 segmentation of the basement into adjacent blocks with different rheological properties 3 reactivation of basement fault trends and 4 regional dynamic topographic effects

a new seismogeodetic approach applied to gps and accelerometer observations of the 2012 brawley seismic swarm implications for earthquake early warning 1 the 26 august 2012 brawley seismic swarm of hundreds of events ranging from m1 4 to m5 5 in the salton trough california provides a unique data set to investigate a new seismogeodetic approach that combines global positioning system gps and accelerometer observations to estimate displacement and velocity waveforms first in simulated real time mode we analyzed 1 5 hz gps data collected by 17 stations fully encircling the swarm zone at near source distances up to about 40 km using precise point positioning with ambiguity resolution ppp ar we used a reference network of north american gps stations well outside the region of deformation to estimate fractional cycle biases and satellite clock parameters which were then combined with ultrarapid orbits from the international gnss service to estimate positions during the brawley seismic swarm next we estimated seismogeodetic displacements and velocities from gps phase and pseudorange observations and 100 200 hz accelerations collected at three pairs of gps and seismic stations in close proximity using a new tightly coupled kalman filter approach as an extension of the ppp ar process we can clearly discern body waves in the velocity waveforms including p wave arrivals not detectable with the gps only approach for earthquake magnitudes as low as mw 4 6 and significant static offsets for magnitudes as low as mw 5 4 our study shows that gps networks upgraded with strong motion accelerometers can provide new information for improved understanding of the earthquake rupture process and be of critical value in creating a robust early warning system for any earthquake of societal significance

the late cretaceous western interior seaway as a model for oxygenation change in epicontinental restricted basins abstract deoxygenation is a critical problem facing the ocean as the world warms and has the potential to effect coastal upwelling zones shelf areas influenced by high runoff and nutrification and restricted and semi restricted basins the mechanisms that drive deoxygenation in these diverse environments are still not fully understood in part because the modern record of redox change is short and anoxia is still relatively rare in the modern ocean here we address this problem of scale by studying deoxygenation in the geologic past we summarize decades of individual studies of benthic foraminifera to generate a record of bottom water oxygen change in the cretaceous western interior sea wis of north america over 13 myr cenomanian campanian spanning two major sea level cycles the wis was prone to major changes in dissolved oxygen content throughout its long history sometimes directly antiphase to trends in the global ocean presented as maps our data show that bottom water oxygen within the wis was controlled by a combination of water mass source and mixing moderated by sea level and basin restriction areas flooded by cool boreal northern sourced waters in the northern and western parts of the seaway were better oxygenated than the eastern and southern portions of the seaway which were flooded by warmer tethyan southern sourced waters beyond east west differences explained by water mass the entire seaway was better oxygenated during periods of transgression and more poorly oxygenated to anoxic during periods of peak transgression highstand and regression we suggest that this pattern was due to the formation and downwelling of western interior intermediate water by the mixing of tethyan and boreal waters during transgressions an increasing volume of these watermasses entered the seaway mixed and downwelled well oxygenated surface water to the seafloor during late transgression highstand partial stratification and the encroachment of low oxygen waters from the open ocean caused dissolved oxygen levels to drop at the seafloor but continued downwelling prevented anoxia during the subsequent regression a decline in the volume of outside watermasses entering the seaway caused a reduction in mixing and weakened downwelling which led to stratification and seafloor anoxia as a model for other semi restricted basins the trends observed in the wis show that local changes in relative sea level mixing and circulation are critical in controlling oceanic deoxygenation in these environments in clear contrast to continental margins impinged by oxygen minimum zones like the contemporaneous demerara rise in the southern caribbean although the wis is larger than most semi restricted basins it is characterized by quasi estuarine circulation driving the interaction of normal marine and brackish watermasses and thus serves a model for similar shallow epicontinental basins of any size understanding how these processes vary in different environments is key to predicting susceptibility of regional water bodies to deoxygenation in the future with a warming world

localized fault slip to the trench in the 2010 maule chile mw 8 8 earthquake from joint inversion of high rate gps teleseismic body waves insar campaign gps and tsunami observations the 27 february 2010 mw 8 8 maule earthquake ruptured 500 km along the plate boundary offshore central chile between 34 s and 38 5 s establishing whether coseismic fault offset extended to the trench is important for interpreting both shallow frictional behavior and potential for tsunami earthquakes in the region joint inversion of high rate gps teleseismic body waves interferometric synthetic aperture radar insar campaign gps and tsunami observations yields a kinematic rupture model with improved resolution of slip near the trench bilateral rupture expansion is resolved in our model with relatively uniform slip of 5 10 m downdip beneath the coast and two near trench high slip patches with 12 m displacements the peak slip is 17 m at a depth of 15 km on the central megathrust located 200 km north from the hypocenter and overlapping the rupture zone of the 1928 m 8 event the updip slip is 16 m near the trench another shallow near trench patch is located 150 km southwest of the hypocenter with a peak slip of 12 m checkerboard resolution tests demonstrate that correctly modeled tsunami data are critical to resolution of slip near the trench with other data sets allowing but not requiring slip far offshore large interplate aftershocks have a complementary distribution to the coseismic slip pattern filling in gaps or outlining edges of large slip zones two clusters of normal faulting events locate seaward along the plate motion direction from the localized regions of large near trench slip suggesting that proximity of slip to the trench enhanced extensional faulting in the underthrusting plate

facies and architectural analysis to interpret avulsion style and variability upper cretaceous blackhawk formation wasatch plateau central utah u s a abstract sequence stratigraphic models emphasize the role of external allogenic controls such as relative sea level tectonic subsidence and climate on alluvial to coastal plain stratigraphic architecture at the expense of internal autogenic behaviors such as avulsion these models are tested via sedimentologic analysis of fine grained floodplain deposits and their relationship to channelized fluvial sandbodies in a well exposed alluvial to coastal plain succession developed under progressively increasing distance from the coeval shoreline and an accompanying decrease in the rate of accommodation creation late cretaceous blackhawk formation wasatch plateau central utah u s a the studied alluvial to coastal plain succession contains fourteen lithofacies which are grouped into four associations and eight architectural elements facies associations consist of 1 channelized fluvial sandstone bodies 2 nonchannelized fluvial sandstone and siltstone bodies 3 fine grained floodplain deposits and 4 brackish floodplain deposits paleosols are immature and are classified as entisols inceptisols and histosols integrated analysis of paleosol character facies analysis and architectural element analysis indicates deposition on a rapidly aggrading floodplain that was subject to frequent crevassing and channel belt switching the character relative abundance and vertical stacking of the paleosol types architectural elements and the first three facies associations exhibit little variation stratigraphically from base to top of the blackhawk formation c 250 m or paleogeographically between the northern and southern limits of the outcrop belt c 100 km local stratigraphic architectures record three styles of avulsion representing avulsion by reoccupation avulsion by progradation and avulsion by incision avulsion style displays no consistent pattern with stratigraphic position or paleogeographic location in combination these results suggest that floodplain sedimentation and local stratigraphic architecture are dominated by autogenic avulsion the three observed avulsion mechanisms operated in apparent uniformity over a range of tectonic subsidence rates c 80 700 m ma and distances from the coeval shoreline c 0 100 km

cretaceous anomalous subsidence and its response to dynamic topography in the songliao basin northeast china to understand the formation mechanisms and evolution of the songliao basin we applied backstripping and strain rate inversion methods to 20 wells and reinterpret two seismic sections in the songliao basin the obtained data were used to reconstruct the tectonic subsidence history and further assess the potential subsidence mechanisms of this area the predicted post rift subsidence based on the uniform stretching model that followed earlier lithospheric thinning events was much lower than the subsidence provided by backstripping the anomalous subsidence during the post rift stage was between 200 m and 800 m in the songliao basin and the depocenter of anomalous subsidence moved eastward between ca 110 and 80 ma before returning to the west between ca 80 and 65 ma regional variations in the subsidence rates suggest a possible deficit in the negative buoyancy mantle loading that is induced by the sinking slab beneath the songliao basin in addition the anomalous post rift subsidence was primarily driven by downward drag pressure from the subducting western izanagi slab and asthenospheric mantle flow beneath the songliao basin the basement rifting in the songliao basin during the early cretaceous and the normal faulting that occurred during the post rift stage resulted in a secondary contribution to the anomalous post rift subsidence unlike the songliao basin several early cretaceous rift basins south of the yanshan belt were only filled during the syn rift subsidence and the anomalous post rift uplift of the yanshan belt was driven by deep mantle flow

sea level and vertical motion of continents from dynamic earth models since the late cretaceous dynamic earth models are used to better understand the impact of mantle dynamics on the vertical motion of continents and regional and global sea level change since the late cretaceous a hybrid approach combines inverse and forward models of mantle convection and accounts for the principal contributors to long term sea level change the evolving distribution of ocean floor age dynamic topography in oceanic and continental regions and the geoid we infer the relative importance of dynamic versus other factors of sea level change determine time dependent patterns of dynamic subsidence and uplift of continents and derive a sea level curve we find that both dynamic factors and the evolving distribution of sea floor age are important in controlling sea level we track the movement of continents over large scale dynamic topography by consistently mapping between mantle and plate frames of reference and we find that this movement results in dynamic subsidence and uplift of continents the amplitude of dynamic topography in continental regions is larger than global sea level in several regions and periods so that it has controlled regional sea level in north and south america and australia since the late cretaceous northern africa and arabia since the late eocene and southeast asia in the oligocene miocene eastern and southern africa have experienced dynamic uplift over the last 20 to 30 m y whereas siberia and australia have experienced cenozoic tilting the dominant factor controlling global sea level is a changing oceanic lithosphere production that has resulted in a large amplitude sea level fall since the late cretaceous with dynamic topography offsetting this fall

dynamic versus flexural controls of late cretaceous western interior basin usa the united states cretaceous western interior basin has long been considered a foreland basin driven by the sevier thrust and associated basin sediment loads however flexural studies demonstrate that this effect exists only within a narrow band in front of the thrust belt most of the basin appears to be due to mantle flow induced dynamic subsidence associated with farallon plate subduction here we show how the components of evolving long wavelength dynamic subsidence and flexural subsidence created the accommodation space and controlled the stratigraphy across the western united states based on a correlated stratigraphic section across central utah and colorado these backstripped subsidence data reveal the dynamic topography driven nature of the western interior basin the results seem to support that the depocenters track the trough of dynamic subsidence with ca 18 myr cycles through time and space and the stratigraphic patterns of large scale progradation eastward migration of depocenter and regional clinoform like downlap are related with the dynamic subsidence interpretation of these data also provides more insights into the repeated ca 2 to 6 myr cycles of thrust induced subsidence in front of the thrust belt which control the local eastward progradation of the sand bodies from the thrust belt the dynamic flexural subsidence and eustatic sea level changes interacted and controlled the timing and distribution of unconformities our work shows how the stratigraphy precisely records the timing patterns and position of dynamic versus flexural subsidences and that combination of such data leads to important geophysical discoveries and supplies strict constraints for geodynamic modeling

new timing constraints for the onset of laramide deformation in southwest montana challenge our understanding of the development of a thick skinned structural style during flat slab subduction

subduction evolution and mantle dynamics at a continental margin central north island new zealand 1 central north island new zealand provides an unusually complete geological and geophysical record of the onset and evolution of subduction at a continental margin whereas most subduction zones are innately two dimensional north island of new zealand displays a distinct three dimensional character in the back arc regions specifically we observe mariana type subduction in the back arc areas of central north island in the sense of back arc extension high heat flow prolific volcanism geothermal activity and active doming and exhumation of the solid surface evidence for emplacement of a significant percent of new lithosphere beneath the central north island comes from heat flux of 25 mw km of strike of volcanic zone and thinned crust underlain by rocks with a seismic wave speed consistent with underplated new crust seismic attenuation qp 1 is high 240 and rhyolitic and andesitic volcanism are widespread almost complete removal of mantle lithosphere is inferred here in pliocene times on the basis of the rock uplift history and upper mantle seismic velocities as low as 7 4 0 1 km s in contrast southwestern north island exhibits chilean type back arc activity in the sense of compressive tectonics reverse faulting low heat flow thickened lithosphere and strong coupling between the subducted and overriding plates this rapid switch from mariana type to chilean type subduction occurs despite the age of the subducted plate being constant under north island moreover stratigraphic evidence shows that processes that define the extensional back arc area the central volcanic region are advancing southward into the compressional system wanganui basin at about 10 mm yr we link the progression from one system to another to a gradual and viscous removal of thickened mantle lithosphere in the back arc regions thickening occurred during the miocene within the taranaki fault zone the process of thickening and convective removal is time and temperature dependent and has left an imprint in both the geological record and geophysical properties of central north island which we document and describe

miocene forebulge development previous to broken foreland partitioning in the southern central andes west central argentina 1 in the distal region of the modern flat slab segment in the southern central andes an unusual stack of middle miocene paleosols together with regional upwarping and normal faulting indicate episodic aggradation and condensed sedimentation contemporaneous with the principal stage of foreland basin development associated with foreland flexure farther to the west these features are consistent with development of a forebulge zone during the early stages of a proposed asymmetric foreland basin system sedimentary thickness farther east and far from the cordilleran tectonic loads suggests accommodation and preservation driven by nonisostatic dynamic subsidence regional overlapping relationships and basin modeling suggest that the modern broken foreland present sierras pampeanas can be interpreted as a reactivation of a formerly partitioned broad forebulge

heterogeneous plate locking in the south central chile subduction zone building up the next great earthquake abstract we use global positioning system gps velocities and kinematic finite element models fe models to infer the state of locking between the converging nazca and south america plates in south central chile 36 s 46 s and to evaluate its spatial and temporal variability gps velocities provide information on earthquake cycle deformation over the last decade in areas affected by the megathrust events of 1960 m w 9 5 and 2010 m w 8 8 our data confirm that a change in surface velocity patterns of these two seismotectonic segments can be related to their different stages in the seismic cycle accordingly the northern 2010 segment was in a final stage of interseismic loading whereas the southern 1960 segment is still in a postseismic stage and undergoes a prolonged viscoelastic mantle relaxation after correcting the signals for mantle relaxation the residual gps velocity pattern suggests that the plate interface accumulates slip deficit in a spatially and presumably temporally variable way towards the next great event though some similarity exist between locking and 1960 coseismic slip extrapolating the current decadal scale slip deficit accumulation towards the 300 yr recurrence times of giant events here does neither yield the slip distribution nor the moment magnitude of the 1960 earthquake this suggests that either the locking pattern is evolving in time to reconcile a slip deficit distribution similar to the 1960 earthquake or that some asperities are not persistent over multiple events the accumulated moment deficit since 1960 suggests that highly locked patches in the 1960 segment are already capable of producing a m 8 event if triggered to fail by stress transfer from the 2010 event

tectonic and dynamic controls on the topography and subsidence of the argentine pampas the role of the flat slab abstract we analyze the pampean foreland the pampas along the modern flat slab segment of the south central andes between 31 and 33 south latitude and to the east of the argentine flat slab province using flexural and gravity studies and computations of dynamic topography bouguer anomalies and flexural analysis predict a foredeep of 250 km width and a peripheral bulge amplitude of 25 m which match the regional morphologies of the modern argentine pampean plain however these studies do not account for the subsurface miocene quaternary basin preservation represented by sedimentary thicknesses 400 m and with depocenters 400 km eastward with respect to flexural models the discrepancy suggests that two mechanisms acting at different wavelengths influence the argentine pampas the basin preservation is likely the result of a large scale geodynamic forcing models of mantle flow driven by realistic flat slab subduction geometry and density contrasts reproduce the depocenter location and the wavelength of subsidence as well as most of the remaining amplitude nonetheless more sophisticated studies e g considering lateral viscosity variations in the mantle wedge might help reduce the dynamic amplitudes and better reproduce the observed geological record

late cretaceous subsidence in wyoming quantifying the dynamic component the late cretaceous western interior basin of north america is generally considered to have been a retroarc foreland basin flexural backstripping of the stratigraphic record from 97 2 ma to 73 4 ma along a section perpendicular to the wyoming idaho salient of the sevier belt clearly demonstrates that there were components of subsidence in addition to those driven by the thrust and associated sediment loads the simulation demonstrates that the flexural foredeep is only 180 120 km wide and shows a forebulge located near the subsequent laramide rock springs uplift foredeep strata between the rock springs uplift on the east and the thrust front to the west were mostly involved in the eastward overlapping thrust belt or deeply truncated by inferred rebound after 78 5 ma the difference between the observed decompacted cumulative subsidence and the amount of subsidence that can be explained by simple flexural loading the residual subsidence increases from 800 m in eastern wyoming to 1 8 km near the thrust belt the westward thickening upper cretaceous sediment wedge filled the accommodation space generated by downward tilting to the west of the north american cratonic margin by underplating and mantle flow associated with the shallowly subducted farallon plate

dynamic topography and vertical motion of the u s rocky mountain region prior to and during the laramide orogeny dynamic topography of earth s surface occurs in response to hydrodynamic stresses due to mantle flow beneath a flexible lithosphere here we compare the predicted dynamic topography from an inverse convection model that includes flat slab subduction with the known geologic history of the western united states from late cretaceous through paleocene time to evaluate the validity of the model results downwarping behind the evolving cordilleran volcanic arc took place after its inception in late triassic time culminating in the formation of the western interior seaway in late cretaceous time subsidence behind arcs is a consistent prediction of most models of dynamic topography a more detailed convection model is evaluated here by comparing it to the geologic history of the central rocky mountain region from 100 to 50 ma the match of predicted and observed tectonic subsidence is good up until the time that local deformation by the laramide orogeny begins this is most likely due to local flexural effects of mountain building overwhelming regional dynamic effects maps for successive time intervals show that the model matches the geologic history quite well through time and space in particular the subduction of the previously postulated oceanic plateau the conjugate shatsky rise has a significant impact on surface movements 1 from 95 to 88 ma the locations of most significant regional unconformities match the eastward migration of a zone of high topography 2 from 90 to 85 ma the zone of maximum subsidence coincides with the motion of the leading edge of the conjugate shatsky rise 3 from 78 to 60 ma the site of initiation of laramide deformation migrates coincidently with the position of the center of the conjugate shatsky rise 4 from 70 to 60 ma the time transgressive deposition of thin fluvial conglomerate units in the southern part of the study area is generally coincident with surface uplift caused by the trailing part of the conjugate shatsky rise these results suggest that the inverse model approximates the vertical motion history quite well synchroneity of the position of the center of the passing conjugate shatsky rise the landward limit of the evolving cordilleran volcanic arc and the initiation of laramide deformation suggests that the farallon plate became coupled with the overlying north american plate as the subducted oceanic plateau passed beneath progressively enhanced mechanical coupling between the plates was likely the impetus for laramide shortening this comparison of model results with surface geologic history provides a means to validate but not verify predictions of dynamic mantle flow models

reservoir quality modeling of tight gas sands in wamsutter field integration of diagenesis petroleum systems and production data the late cretaceous almond formation is a lithic rich tight gas sandstone reservoir in wamsutter field wyoming the almond has measured porosities of less than 12 and permeabilities that are generally less than 0 1 md this is the result of significant mechanical and chemical compaction precipitation of carbonate cements and authigenic clays and deep burial cementation by quartz despite the advanced diagenesis and poor reservoir quality of this tight gas sandstone touchstone diagenetic modeling was used successfully to simulate rock properties during burial basin modeling and fluid inclusion data were integrated with touchstone simulations to constrain the timing of petroleum charge into the reservoir model results indicate that the almond was initially charged by liquid petroleum when the reservoir retained high porosity and permeability subsequent gas charging flushed most of the liquids from the system as the reservoir continued to experience porosity and permeability reduction from continued quartz cementation the almond touchstone model was applied to 15 well locations throughout the field ranging from areas of low thermal stress to high thermal stress a comparison of touchstone predicted permeability and standard thermal stress yielded a correlation that was used to build a pseudopermeability reservoir quality risk map across the wamsutter area a comparison of this map with historical production data demonstrates that the map successfully predicts areas of enhanced well performance the method used to build this risk map may be applied elsewhere as a quick means of high grading areas of risk during field development

stratigraphic architecture of a net transgressive marginal to shallow marine succession upper almond formation rock springs uplift wyoming u s a abstract the upper part of the almond formation records the overall retreat of a wave dominated shoreline and associated lagoons or bays exposures of these strata on the eastern flank of the rock springs uplift wyoming u s a enable analysis of their stratigraphic architectures along sections oriented oblique to depositional strike the upper almond formation comprises at least nine vertically stacked regressive transgressive cycles the regressive component of each cycle consists of thick up to 22 m laterally continuous wave dominated shoreface and overlying coastal plain deposits that occur in paleoseaward locations and have abrupt 400 m paleolandward pinchouts the transgressive component of each cycle consists of one or more bay fill successions that occur in paleolandward locations and gradually thin in a paleoseaward direction transgressive bay fill deposits in each cycle are thick up to 18 m and associated with preservation of surfaces that record in progressively paleoseaward locations initiation of a lagoon or bay transgressive surface erosional retreat of tidal inlet channels tidal ravinement surface and the shoreface wave ravinement surface and marine flooding marine flooding surface this architecture records regression of a strandplain or wave dominated delta and subsequent transgression of a barrier island and spit with associated lagoon or bay the occurrence of such thick and fully preserved bay fill successions indicates that accretionary transgressive shoreline trajectories were developed strongly aggradational to weakly retrogradational stacking of successive regressive transgressive cycles results in a layered stratigraphic architecture with laterally continuous shoreface sandstone layers interbedded with bay fill shale layers shoreface sandstones layers pinch out up dip abruptly 400 m into bay fill shales and have limited vertical connectivity sandstones within bay fill and coastal plain deposits occur as small laterally discontinuous bodies of variable geometry and connectivity however these sandstones may provide additional connectivity where they erode through bay fill shales between two shoreface sandstone layers

are diamond bearing cretaceous kimberlites related to low angle subduction beneath western north america abstract diamond bearing cretaceous kimberlites of western north america were emplaced 1000 1500 km inboard of the farallon plate subduction margin and overlap with the development of the western interior seaway shut down of the sierra nevada arc and the laramide orogeny these events are consistent with a decrease in subduction angle along much of the margin which placed the subducted farallon plate in close proximity to the continental interior at the time of kimberlite magmatism our numerical models demonstrate that low angle subduction can result from high plate convergence velocities and enhanced westward motion of north america further rapid subduction allows hydrous minerals to remain stable within the cool interior of the subducting plate to more than 1200 km from the trench destabilization of these minerals provides a fluid source that can infiltrate the overlying material potentially triggering partial melting and kimberlite lamproite magmatism

constraining uncertainty in interpretation of seismically imaged clinoforms in deltaic reservoirs troll field norwegian north sea insights from forward seismic models of outcrop analogs forward seismic modeling of outcrop analogs has been used to characterize the seismic expression of clinoforms in different deltaic depositional environments and thus constrain uncertainty in interpretation of intra reservoir clinoforms imaged in seismic data from the troll field norwegian north sea three outcrop analogs from the cretaceous western interior seaway united states were studied to quantify the geometry distribution and lithologic character of clinoforms in fluvial dominated and mixed influence deltaic deposits outcrop derived geometric data were calibrated to sedimentological and petrophysical data from the krossfjord and fensfjord formations in the troll field and then used to create a suite of forward seismic models for comparison with real seismic reflection data from the troll field clinoforms were imaged in the forward seismic models in which they were 1 spaced wider than the tuning thickness 10 m 33 ft 2 marked by pronounced interfingering of facies associations with different acoustic properties and or 3 lined by relatively thick 50 cm 20 in carbonate cemented layers however where clinothems are thinner than the vertical resolution limit of seismic data destructive interference occurred creating misleading geometrical relationships furthermore our ability to image clinoforms is dependent on 1 the frequency of the seismic wavelet 2 the overburden velocity and or 3 the acoustic impedance contrast at the boundary between the overburden and the clinoform bearing target the established methodology has allowed characterization of deltaic clinoformal architectures in reservoir seismic data from the troll field and has facilitated a more robust interpretation by bridging the critical gap in resolution between well and seismic data

continental scale landscape evolution a history of north american topography the generation and evolution of continental topography are fundamental geologic and geomorphic concerns in particular the history of landscape development might contain useful information about the spatiotemporal evolution of deep earth processes such as mantle convection a significant challenge is to generate observations and theoretical predictions of sufficient fidelity to enable landscape evolution to be constrained at scales of interest here we combine substantial inventories of stratigraphic and geomorphic observations with inverse and forward modeling approaches to determine how the north american landscape evolved first stratigraphic markers are used to estimate postdepositional regional uplift present day elevations of these deposits demonstrate that 2 km of long wavelength surface uplift centered on the colorado rocky mountain plateaus occurred in cenozoic times second to bridge the gaps between these measurements an inverse modeling scheme is used to calculate the smoothest spatiotemporal pattern of rock uplift rate that yields the smallest misfit between 4 161 observed and calculated longitudinal river profiles our results suggest that cenozoic regional uplift occurred in a series of stages in agreement with independent stratigraphic observations finally a landscape evolution model driven by this calculated rock uplift history is used to determine drainage patterns denudation and sedimentary flux from late cretaceous times until the present day these patterns are broadly consistent with stratigraphic and thermochronologic observations we conclude that a calibrated inverse modeling strategy can be used to reliably extract the temporal and spatial evolution of the north american landscape at geodynamically useful scales

some thoughts on the use of insar data to constrain models of surface deformation noise structure and data downsampling repeat pass interferometric synthetic aperture radar insar provides spatially dense maps of surface deformation with potentially tens of millions of data points here we estimate the actual covariance structure of noise in insar data we compare the results for several independent interferograms with a large ensemble of gps observations of tropospheric delay and discuss how the common approaches used during processing of insar data affects the inferred covariance structure motivated by computational concerns associated with numerical modeling of deformation sources we then combine the data covariance information with the inherent resolution of an assumed source model to develop an efficient algorithm for spatially variable data resampling or averaging we illustrate these technical developments with two earthquake scenarios at different ends of the earthquake magnitude spectrum for the larger events our goal is to invert for the coseismic fault slip distribution for smaller events we infer the hypocenter location and moment we compare the results of inversions using several different resampling algorithms and we assess the importance of using the full noise covariance matrix

evolution of the cenozoic tarim basin by flexural subsidence and sediment ponding insights from quantitative basin modelling abstract the tarim basin became a closed continental sedimentary basin in the cenozoic due to uplift of the western kunlun tian shan and the altyn tagh ranges in the context of the indian asia collision a north northeast trending seismic profile across the basin reveals that cenozoic strata comprise a wedge of sediments in the southern and northern regions generated by flexural subsidence overlain by a more uniform regional sediment drape we obtain the subsidence profiles across the basin at 26 ma 13 ma 5 ma and the present day using backstripping based on the sedimentary architecture shown in the seismic profile we use a numerical finite elastic plate to model these subsidence profiles our modelling indicates that the southern and northern flexural depressions started to interfere to form a single flexural bulge within the basin since late paleogene times the flexural bulge migrated 52 km toward the western kunlun range since 26 ma reflecting a decrease in the ratio of loads of the western kunlun range versus the tian shan we separate the sediment drape from the flexural subsidence according to the preceding modelling results our separating demonstrates that the thickness of the drape increased from 230 30 m at 26 ma to 1910 200 m at present occupying 30 of cenozoic strata in the profile the rise in the base level since the paleogene is estimated as 356 80 m by correcting for sediment loading of the drape we adopt a decreasing basin width to model the evolution of the flexural subsidence suggesting significant uplifting of the western kunlun range and the tian shan from 26 ma to 13 ma relative stable elevations in these ranges from 13 ma to 5 ma and their rapid uplifts since 5 ma

stratigraphic modeling of foreland basins interpreting thrust deformation and lithosphere rheology the authors incorporate the processes of erosion and deposition in a numerical model to predict the stratal geometries and facies patterns produced during episodic thrusting in a nonmarine foreland basin the resultant stratigraphic record is characterized by a stairstepped facies package in which each retrogradation of facies toward the thrust marks the onset of a thrusting event the retrogradation of facies coincides with the migration of the forebulge toward the thrust and the generation of an erosional unconformity in the past changes in basin wavelength during basin evolution have been interpreted to record viscoelastic relaxation of the lithosphere this model suggests that changes in basin wavelength are a natural consequence of the interplay between thrust and sediment loading on an elastic lithosphere

architecture and formation of transgressive regressive cycles in marginal marine strata of the john henry member straight cliffs formation upper cretaceous of southern utah usa marginal marine deposits of the john henry member upper cretaceous straight cliffs formation were deposited within a moderately high accommodation and high sediment supply setting that facilitated preservation of both transgressive and regressive marginal marine deposits complete transgressive regressive cycles comprising barrier island lagoonal transgressive deposits interfingered with regressive shoreface facies are distinguished based on their internal facies architecture and bounding surfaces two main types of boundaries occur between the transgressive and regressive portions of each cycle i surfaces that record the maximum regression and onset of transgression bounding surface a and ii surfaces that place deeper facies on top of shallower facies bounding surface b the base of a transgressive facies bounding surface a is defined by a process change from wave dominated to tide dominated facies or a coaly shelly interval indicating a shift from a regressive to a transgressive regime the surface recording such a process change can be erosional or non erosive and conformable a shift to deeper facies occurs at the base of regressive shoreface deposits along both flooding surfaces and wave ravinement surfaces bounding surface b these two main bounding surfaces and their subtypes generate three distinct transgressive regressive cycle architectures i tabular shoaling upward marine parasequences that are bounded by flooding surfaces ii transgressive and regressive unit wedges that thin basinward and landward respectively and iii tabular transgressive lagoonal shales with intervening regressive coaly intervals the preservation of transgressive facies under moderately high accommodation and sediment supply conditions greatly affects stratigraphic architecture of transgressive regressive cycles acknowledging variation in transgressive regressive cycles and recognizing transgressive successions that correlate to flooding surfaces basinward are both critical to achieving an accurate sequence stratigraphic interpretation of high frequency cycles

sequence stacking patterns in the western canada foredeep influence of tectonics sediment loading and eustasy on deposition of the upper cretaceous kaskapau and cardium formations the kaskapau and cardium formations span late cenomanian to early coniacian time and were deposited on a low gradient foredeep ramp the studied portion of the kaskapau formation spans ca 3 5 myr and forms a mudstone dominated wedge thinning from 700 to 50 m from sw to ne over ca 300 km in contrast the cardium formation spans about 2 1 myr is about 100 m thick sandstone rich and broadly tabular the kaskapau and cardium formations are divided respectively into 28 and nine allomembers each bounded by marine flooding surfaces kaskapau allomembers 1 to 7 show about 200 km of offlap from the forebulge accompanied by progradation of thin sandstones from the eroded forebulge crest in contrast kaskapau allomembers 8 to 28 and cardium allomembers c1 to c9 show overall onlap onto the forebulge of about 350 km and contain no forebulge derived sandstones this broad pattern is interpreted as recording a latest cenomanian pulse of tectonic loading which led to shoreline back step in the proximal foredeep and coeval uplift of the forebulge leading to erosion the advance of the sediment wedge after kaskapau allomember 7 is attributed primarily to the isostatic effect of a distributed sediment load the advance of the orogenic wedge had a subordinate effect on subsidence of the forebulge for kaskapau allomembers 1 to 6 isopachs trend north to south suggesting a load directly to the west allomembers 7 to 28 show an abrupt rotation of isopachs to nw se suggesting that the load shifted several hundred kilometres to the south this re orientation might be related to a change from an approximately orthogonal to a dextral transpressive stress regime within the longer term offlap onlap cycle recorded by the kaskapau and cardium formations individual allomembers are grouped into packages reflecting higher frequency onlap offlap cycles each spanning ca 0 5 to 0 7 myr offlap from the forebulge tends to be accompanied by more pronounced transgression in the foredeep whereas onlap onto the forebulge is accompanied by progradation of tongues of shoreface sandstone this relationship suggests that changes in deformation rate in the orogenic wedge modulated proximal subsidence rate enhancing or suppressing shoreline progradation and also causing subtle uplift or subsidence of the forebulge region wedge shaped allomembers in the kaskapau formation contain shoreface sandstone and conglomerate that prograded respectively 40 and 25 km from the preserved basin margin progradation of coarse clastics was limited by rapid flexural subsidence tabular allomembers of the cardium formation imply a low flexural subsidence rate and contain sandy and conglomeratic shoreface deposits that prograded up to ca 180 km from the preserved basin margin this relationship suggests that low rates of flexural subsidence promoted steeper alluvial gradients more vigorous gravel transport and more extensive shoreface progradation overall observed stratal geometry and facies distribution is explained readily in terms of current elastic flexural models most shoreface sandstones in the proximal foredeep show evidence of forced regression eustasy provides the most plausible explanation for relative sea level rise fall cycles on the 125 kyr allomember timescale geometric relationships suggest eustatic oscillations of about 10 m forced regressive shoreface development was suppressed during kaskapau allomembers 1 to 10 when the rate of flexural subsidence was at its highest

flexural isostasy constraints from gravity and topography power spectra we have used spherical harmonic coefficients that describe earth s gravity anomaly and topography fields to quantify the role of isostasy in contributing to crustal and upper mantle structure power spectra reveal that the gravity effect of topography and its flexural compensation contributes significantly to the observed free air gravity anomaly spectra for spherical harmonic degree 33 400 and lower n 33 degrees but topography appears either uncompensated or fully compensated at these degrees irrespective of the actual te all isostatic models underpredict the spectra at 2 n 12 and so we interpret the low order earth s gravity field as caused at least in part by non isostatic processes due to dynamic motions such as those associated with convective upwellings and downwellings in earth s mantle

thrust loads and foreland basin evolution cretaceous western united states two dimensional modeling of loading during the formation of the idaho wyoming thrust belt shows that regional isostatic compensation by flexure of an elastic lithosphere is sufficient to control the formation of a foreland basin the flexural rigidity of the lithosphere is inferred to have been approximately 1023 nm 1030 dyne cm on the basis of palinspastic comparison of predicted downwarping due to the thrust plate loads to the shape of the sedimentary wedge on the west side of the cretaceous western interior seaway erosion of part of the uplifted thrust plates redistributed the load depositing it farther to the east thereby causing subsidence over a much wider area than could have been accomplished only by the loading by thrust plates paleotopography after major cretaceous thrust events was calculated the resulting mountainous terrain gentle alluvial plain and flat sea floor correspond well with the topography of the modern foreland thrust belt and basin system in the andes of south america and to paleogeographic reconstructions in the western united states thrust belt topography is controlled by the subsurface geometry of the thrust faults particularly the positions of ramp zones and by isostatic subsidence

sequence stratigraphy of the mancos shale lower tres hermanos formation and coeval middle cenomanian to middle turonian strata southern new mexico usa sequence stratigraphic analysis of four widely spaced outcrops of middle cenomanian to middle turonian strata deposited in the western interior foreland basin in southern new mexico usa defines ten sequence boundaries in a marine shale rich interval ca 200 m thick the majority of sequence boundaries are based on basinward shifts in lithofacies characterized by either a non waltherian contact between distal bar or lower shoreface sandstone and underlying lower offshore shale or an erosional contact between distal bar or lower shoreface sandstone and underlying upper offshore shale the sequence boundaries commonly correlate basinward to packages of storm deposited sandstone and to beds of sandy grainstone composed of winnowed inoceramid shell fragments in several cases however the sequence boundaries pass basinward into presumably conformable successions of lower offshore shale maximum flooding surfaces within the sequences are represented by one or more beds of locally phosphatized globiginerid wackestone and packstone or exist within a conformable succession of lower offshore shale following initial south south westward transgression into the study area the regional trend of palaeoeshorelines was north west to south east although isopach data indicate that lobes of sandstone periodically spread south eastward across the study area the ten sequences in the study area are arranged into a third order composite megasequence that is characterized by overall upward deepening followed by upward shallowing of sequences the composite megasequence is similar but not identical to the previously established t 1 transgression and r 1 regression in new mexico based on radioisotopic dates of bentonites the average frequency of the sequences within the study area was ca 327 kyr which is consistent with fourth order cycles of ca 400 kyr interpreted in coeval marine strata elsewhere in the world

neogene residual subsidence and its response to a sinking slab in the deep mantle of eastern china abstract mantle convection could have a significant effect on basin evolution however research quantifying this relationship is controversial to understand the formation mechanism and evolution of the cenozoic rift basins in eastern china we applied the back stripping technique and strain rate inversion modeling to 119 wells from sangjiang basin bohai bay basin north yellow sea basin south yellow sea basin east china sea shelf basin and four basins within the northern south china sea margin the modeled results can be used to reconstruct the tectonic subsidence history and further assess the potential subsidence mechanisms of eastern china residual subsidence is defined as the difference between the theoretical and observed tectonic subsidences our results show that the residual subsidence since 20 ma in eastern china generally increases from 100 to 300 m in terrestrial areas to 1 2 1 8 km on the continental shelf our observed residual subsidence is generally consistent with the present day dynamic topography that is predicted from mantle flow models and it is associated with a stagnant slab within the mantle that has been observed by seismic tomography the migration pathway of the residual subsidence since 20 ma is consistent with the movement direction of the pacific and philippine plates therefore we suggest that the residual subsidence might be a dynamic subsidence induced by a negative buoyancy of the sinking slab in the deep mantle beneath eastern china

slab1 0 a three dimensional model of global subduction zone geometries 1 we describe and present a new model of global subduction zone geometries called slab1 0 an extension of previous efforts to constrain the two dimensional non planar geometry of subduction zones around the focus of large earthquakes slab1 0 describes the detailed non planar three dimensional geometry of approximately 85 of subduction zones worldwide while the model focuses on the detailed form of each slab from their trenches through the seismogenic zone where it combines data sets from active source and passive seismology it also continues to the limits of their seismic extent in the upper mid mantle providing a uniform approach to the definition of the entire seismically active slab geometry examples are shown for two well constrained global locations models for many other regions are available and can be freely downloaded in several formats from our new slab1 0 website http on doi gov d9arbs we describe improvements in our two dimensional geometry constraint inversion including the use of average active source seismic data profiles in the shallow trench regions where data are otherwise lacking derived from the interpolation between other active source seismic data along strike in the same subduction zone we include several analyses of the uncertainty and robustness of our three dimensional interpolation methods in addition we use the filtered subduction related earthquake data sets compiled to build slab1 0 in a reassessment of previous analyses of the deep limit of the thrust interface seismogenic zone for all subduction zones included in our global model thus far concluding that the width of these seismogenic zones is on average 30 larger than previous studies have suggested

deformation cycles of subduction earthquakes in a viscoelastic earth subduction zones produce the largest earthquakes over the past two decades space geodesy has revolutionized our view of crustal deformation between consecutive earthquakes the short time span of modern measurements necessitates comparative studies of subduction zones that are at different stages of the deformation cycle piecing together geodetic snapshots from different subduction zones leads to a unifying picture in which the deformation is controlled by both the short term years and long term decades and centuries viscous behaviour of the mantle traditional views based on elastic models such as coseismic deformation being a mirror image of interseismic deformation are being thoroughly revised snapshots of subduction zones using space geodesy reveal that the viscous behaviour of the mantle controls crustal deformation requiring the revision of traditional elastic models for earthquake risk assessment space geodesy the use of satellites to monitor earth has revolutionized our view of crustal deformation between consecutive earthquakes however the brevity of such measurements means that studies must be done by comparing multiple subduction zones at different stages of the earthquake cycle by piecing together geodetic snapshots from the sumatra chile and cascadia subduction zones this review presents a unifying picture in which deformation is controlled by the viscous behaviour of the mantle in both the short term years and the long term decades to centuries

intra parasequence architecture of an interpreted asymmetrical wave dominated delta although modern wave dominated shorelines exhibit complex geomorphologies their ancient counterparts are typically described in terms of shoreface shelf parasequences with a simple internal architecture this discrepancy can lead to poor discrimination between and incorrect identification of different types of wave dominated shoreline in the stratigraphic record documented in this paper are the variability in facies characteristics high resolution stratigraphic architecture and interpreted palaeo geomorphology within a single parasequence that is interpreted to record the advance of an ancient asymmetrical wave dominated delta the standardville ab1 parasequence of the aberdeen member blackhawk formation is exposed in the book cliffs of central utah usa this parasequence and four others in the aberdeen member record the eastward progradation of north south trending wave dominated shorelines within the standardville ab1 parasequence distal wave dominated shoreface shelf deposits in the eastern part of the study area are overlain across a downlap surface by southward prograding fluvial dominated delta front deposits which have previously been assigned to a separate stranded lowstand parasequence formed by a significant allogenic change in relative sea level high resolution stratigraphic analysis of these deposits reveals that they are instead more likely to record a single episode of shoreline progradation characterized by alternating periods of normal regressive and forced regressive shoreline trajectory because of minor cyclical fluctuations in relative sea level interpreted normal regressive shoreline trajectories within the wave dominated shoreface shelf deposits are marked by aggradational stacking of bedsets bounded by non depositional discontinuity surfaces interpreted forced regressive shoreline trajectories in the same deposits are characterized by shallow incision of fluvial distributary channels and strongly progradational stacking of bedsets bounded by erosional discontinuity surfaces that record enhanced wave base scour fluvial dominated delta front deposits most probably record the regression of a lobate delta parallel to the regional shoreline into an embayment that was sheltered from wave influence wave dominated shoreface shelf and fluvial dominated delta front deposits occur within the same parasequence and their interpretation as the respective updrift and downdrift flanks of a single asymmetrical wave dominated delta that periodically shifted its position provides the most straightforward explanation of the distribution and relative orientation of these two deposit types

influence of peruvian flat subduction dynamics on the evolution of western amazonia convection in the earth s mantle is mainly driven by cold dense subducting slabs but relatively little is known about how 3d variations in slab morphology and buoyancy affect mantle flow or how the surface above deforms in response i e dynamic topography we investigate this problem by studying the dynamics of an active region of flat slab subduction located in peru in south america here the slab geometry is well known based on the regional seismicity and we have observations from the local geological record to validate our models of particular interest is the widespread subsidence and deposition of the solimoes formation across western amazonia that coincided with the development of the peruvian flat slab during the mid late miocene this formation covers an extensive area from the foredeep to the purus arch located view the mathml source 2000km away from the trench close to the andes the preservation of several kilometers of sedimentary thicknesses can be easily accounted for by flexure based on an estimate of the andean loading we predict 2 8 to 3 6 km of accommodation space that spans 100 km the spatial and temporal history of the solimoes formation however particularly the thick distal foreland accumulations up to 1 2 km deep can only be matched with the addition of a longer wavelength dynamic source of topography following the transition from normal to flat subduction we predict over 1 km of dynamic subsidence view the mathml source 1500km wide that propagates over 1000 km away from the trench tracking the subduction leading edge this is followed by a pulse of dynamic uplift over the flat segment behind it we therefore propose that a combination of uplift flexure and dynamic topography during slab flattening in peru is responsible for the sedimentation history and landscape evolution of western amazonia that eventually led to the configuration of the amazon drainage basin we know today

crustal motion in the zone of the 1960 chile earthquake detangling earthquake cycle deformation and forearc sliver translation temporary deformation in great earthquake cycles and permanent shear deformation associated with oblique plate convergence both provide critical clues for understanding geodynamics and earthquake hazard at subduction zones in the region affected by the mw 9 5 great chile earthquake of 1960 we have obtained gps observations that provide information on both types of deformation our velocity solutions for the first time span the entire latitudinal range of the 1960 earthquake the new observations revealed a pattern of opposing roughly arc normal motion of coastal and inland sites consistent with what was reported earlier for the northern part of this region this finding supports the model of prolonged postseismic deformation as a result of viscoelastic stress relaxation in the mantle the new observations also provide the first geodetic evidence for the dextral motion of an intravolcanic arc fault system and the consequent northward translation of a forearc sliver the sliver motion can be modeled using a rate of 6 5 mm a accommodating about 75 of the margin parallel component of nazca south america relative plate motion with the rate diminishing to the north furthermore the new gps observations show a southward decrease in margin normal velocities of the coastal area we prefer explaining the southward decrease in terms of changes in the width or frictional properties of the megathrust seismogenic zone because of the much younger age of the subducting plate and warmer thermal regime in the south the currently locked portion of the plate interface may be narrower using a three dimensional viscoelastic finite element model of postseismic and interseismic deformation following the 1960 earthquake we demonstrate that this explanation although not unique is consistent with the gps observations to the first order

three dimensional density model of the nazca plate and the andean continental margin 1 we forward modeled the bouguer anomaly in a region encompassing the pacific ocean 85 w and the andean margin 60 w between northern peru 5 s and patagonia 45 s the three dimensional density model that reproduces the gravity field is a continental scale representation of density structure to 410 km depth that characterizes the mantle and crust of the oceanic nazca plate subducted slab and continental margin with a minimum number of bodies we predefined the density of each body after studying the dependency of density on composition of crustal and mantle materials and pressure temperature conditions appropriate for the andean setting a database of independent geophysical information constrains the geometry of the top of the subducted slab locally the moho of the oceanic and continental crusts and indirectly the lithosphere asthenosphere boundary underneath the continental plate other boundaries notably the intracrustal density discontinuity separating upper from lower crust below the continent were not constrained and their geometry is the result of fitting the observed and calculated bouguer anomaly during forward modeling this contribution presents the model to the andean geoscientific community and contains some tools like a sensitivity analysis that helps potential users of the model to interpret its results we describe and discuss some of these results in order to illustrate the application of the model to the study of a wide range of phenomena e g modification of oceanic plate structure by hot spots shape of the subducted slab thermal structure of the continental lithosphere compensation mechanism and formation of orogenic relieve causes of andean segmentation

depositional environment sediment provenance and oxygen isotope paleoaltimetry of the early paleogene greater green river basin southwestern wyoming u s a depositional process sediment provenance and paleotopography are critical to paleogeographic reconstruction during the coeval laramide and sevier orogenies in the cordillera orogenic system here we conduct lithofacies analysis sediment provenance and paleoelevation studies in the fluvial lower paleogene fort union and the main body of the wasatch formations in the center of the greater green river basin in order to reconstruct paleogeography the depositional environment changed from low energy floodplains and associated meandering river during the paleocene to braided rivers during the earliest eocene the lowermost eocene strata have more precambrian basement derived feldspar grains compared to the paleocene strata this change in sediment provenance was associated with the change to dominant northwestward paleoflow direction suggesting major uplift of the laramide uinta mountains during the earliest eocene the 18o values of authigenic carbonates were stable during the early paleocene but decreased gradually from 10 permil during the late paleocene to 18 permil during the earliest eocene suggesting the lack of highland precipitation in the basin catchment during the early paleocene and significant surface uplift and arrival of highland precipitation from the uinta mountains during the earliest eocene the reconstructed paleoelevation of the uinta mountains was at least 3 km possibly greater than 3 5 km and the paleoelevation of the greater green river basin floor was at most 1 km and the paleorelief between the greater green river basin and uinta mountains was 2 km during the earliest eocene our record of the earliest eocene establishment of high topography of the uinta mountains through renewed uplift is 4 to 6 myr older than previously thought if the carbonate cements in the fort union formation record the isotope compositions of surface water from the sevier orogen their high 18o values likely suggest that the sevier orogen had rugged topography during the paleocene

rapid cenozoic subsidence in the gulf of mexico resulting from hess rise conjugate subduction enigmatic surface deflections occurred in north america starting from the cretaceous including the continental scale drainage reorganization and the long wavelength subsidence in the western interior seaway these surface undulations cannot be simply explained by sea level change or flexure loading coinciding with the large scale surface deflection the gulf of mexico gom has an immense paleocene sediment deposition probably caused by tectonic subsidence increasing evidence indicates a distinct seismic anomaly localized in the mantle below the gom with geodynamic models we show that the hess rise conjugate coincides with the position of the seismic anomaly the basalt eclogite transition in the hess conjugate can lead to a localized dynamic subsidence in the gom which is superimposed on the broad surface deflection caused by the farallon slab the hess conjugate transformed to eclogite could tilt the surface southward in the u s and help frame the gom as a main depocenter in the cenozoic

climate induced formation of a closed basin great divide basin wyoming large closed basins are often associated with regions of active tectonics in contrast we provide the example of the great divide basin in southern wyoming where climate change through its impact on erosion and fl exure provides the primary mechanism of basin closure two and three dimensional fl exural models that incorporate the effects of local basin abandonment due to aridity as well as minor extrabasinal extension demon strate that basin closure with 40 m of base ment relief tilt could have been achieved in the great divide basin under reasonable assumptions of sediment rock density and fl exural rigidity the primary drive for ba sin abandonment was insuffi cient discharge that retarded river downcutting continued erosion in the surrounding drainage led to fl exural rebound against which erosion by the outlet from the great divide basin was unable to compete eventually the basin became detached and isolated from the sur rounding drainage and a few tens of meters of differential tilt developed between the ba sin fl oor and spillover point an extra amount of tilt up to a few meters could have been at tained by rift shoulder effects associated with minor nearby extension outside of the basin to the north hence closure of the great di vide basin took place with no internal fault ing nor did it require any extrabasinal tec tonic activity to force basin closure hence basin closure and or drainage reorganization need not record tectonic activity in all cases differential erosion provides an alternative hypothesis that does not refl ect local tectonic timing our model of the evolution of the great divide basin illustrates a mechanism by which basins can become closed by cli matic effects alone

the first since 1960 a large event in the valdivia segment of the chilean subduction zone the 2016 m7 6 melinka earthquake abstract we present results for joint kinematic inversion of high rate gps strong motion and insar data for the 2016 m7 6 melinka earthquake we show that the source is a compact 35 s long rupture with 5 0 0 15 m of peak slip we find the melinka earthquake occurs inside the slip region for the 1960 m9 5 valdivia earthquake and within the highly locked portion of the megathrust inferred from inter seismic velocity analysis we show that there is very modest post seismic deformation at a nearby gps site qlln and argue that this indicates the melinka earthquake ruptures within the intermediate portion of the megathrust and is an isolated asperity surrounded by locked velocity weakening material further we find that the peak slip observed during this earthquake is larger than what has been accumulated in the intervening 57 years since the 1960 rupture and conclude that at least in the area of the melinka earthquake this is indicates that the 1960 valdivia event might not have used all the slip deficit available on the megathrust

high resolution sequence stratigraphy and implications for cretaceous glacioeustasy of the late cretaceous gallup system new mexico u s a

imaging short period seismic radiation from the 27 february 2010 chile mw 8 8 earthquake by back projection of p pp and pkikp waves 1 teleseismic short period 0 5 5 s p waves from the 27 february 2010 chile earthquake mw 8 8 are back projected to the source region to image locations of coherent short period seismic wave radiation several receiver array configurations are analyzed using different p wave arrivals including networks of stations in north america p japan pkikp and europe pp as well as a global configuration of stations with a broad azimuthal distribution and longer period p waves 5 20 s coherent bursts of short period radiation from the source are concentrated below the chilean coastline along the downdip portion of the megathrust the short period source region expands bilaterally with significant irregularity in the radiation comparison with finite fault slip models inverted from longer period seismic waves indicates that the regions of large slip on the megathrust are located updip of the regions of short period radiation a manifestation of frequency dependent seismic radiation similar to observations for the great 2011 tohoku earthquake mw 9 0 back projection of synthetic p waves generated from the finite fault models demonstrates that if the short period energy had radiated with the same space time distribution as the long period energy back projection analysis would image it in the correct location updip we conclude that back projection imaging of short period signals provides a distinct view of the seismic source that is missed by studies based only on long period seismic waves geodetic data and or tsunami observations

onshore offshore correlations of cretaceous fluvial deltaic sequences southern baltimore canyon trough we evaluate cretaceous depositional sequences on approximately 4400 km 2700 mi of newly released multichannel seismic profiles and five wells on the continental shelf in the southern baltimore canyon trough and tie the data to three wells drilled onshore in the maryland coastal plain seismic geometries coupled with facies and biostratigraphy from the wells are used to delineate mid cretaceous aptian turonian depositional sequences and paleogeography beneath these sequences 400 1000 m 1300 3300 ft of lower cretaceous sedimentary rocks underlie the modern shelf they thicken along strike to the southwest implying a southern sediment source aptian to cenomanian sediments were deposited in shelf to nearshore settings a landward movement of the depocenter and a shift toward facies indicative of deeper paleodepths marks a 107 yr mid cretaceous transgression within which we identify five sequences a composite maximum flooding surface mfs within the uppermost of these retrogradational units is associated with the cenomanian turonian boundary and ocean anoxic event 2 shingled lower turonian seismic reflections prograde across the outer shelf downlapping onto the composite mfs and are truncated by a mid turonian sequence boundary the upper cretaceous section thickens seaward and along strike to the northeast implying a northern source and little late cretaceous accommodation beneath the modern shelf mid cretaceous strata offshore maryland are likely sand prone considering their proximity to the correlative fluvial facies of the onshore potomac group these potential reservoir sands are capped by regional confining units generated by 107 yr global mean sea level flooding events and are excellent targets for supercritical carbon storage

flexural versus dynamic processes of subsidence in the north american cordillera foreland basin 1 dynamic subsidence related to subduction is an important process in retroarc foreland basin systems dynamic subsidence in the north american retroarc foreland has been proposed as dominant in the late cretaceous however questions remain about the nature of the subcrustal load and the basin response to such processes we present new isopach data using 130 data points covering a large portion of the u s and a revised flexural analysis of the sevier foreland higher rigidity associated with the wyoming craton can best model flexural subsidence directly prior to 81 ma we constrain the transition from flexural to nonflexural subsidence to 81 ma and correlate this with large late cretaceous progradation the locus of subsidence and the location of the subducted shatsky oceanic plateau suggest that dynamic loading from viscous flow above the subducting plate is the mechanism driving dynamic subsidence in the retroarc foreland basin of the north american cordillera

high resolution correlation of the upper cretaceous stratigraphy between the book cliffs and the western henry mountains syncline utah u s a abstract exposures of upper cretaceous strata in the book cliffs have played a key role in the formulation of modern sequence stratigraphic concepts and yet correlations with time equivalent strata in nearby regions remain uncertain resulting in an incomplete understanding of regional paleogeography this study presents detailed high resolution correlations of the upper cretaceous stratigraphy between the book cliffs the wasatch plateau and the western henry mountains syncline in utah with emphasis on the campanian interval two newly acquired measured vertical sections at coal canyon near green river in the book cliffs and blind trail in the henry mountains inform the correlations which also incorporate the substantial body of previous research correlations are further constrained by vertical and lateral facies stacking patterns and changes in sediment dispersal directions at discrete stratigraphic horizons derived from paleocurrent measurements much of the campanian succession can be characterized as a single low frequency third order depositional sequence within which are nested numerous high frequency sequences while it is not possible to correlate every high frequency sequence recognized in individual outcrop areas we define four intervals numbered 1 4 in ascending stratigraphic order that we correlate across the entire region interval 1 basal campanian is represented by initially deltaic and later wave dominated shoreface strata of the star point sandstone and equivalent basal muley canyon sandstone interval 2 lower campanian comprises coastal plain facies passing eastward into shallow marine strata of the lower blackhawk formation and equivalent muley canyon sandstone interval 3 lower to mid middle campanian comprises a thick aggradational stack of coastal plain fluvial strata that pass eastward into coastal and shallow marine facies blackhawk formation and equivalent masuk formation interval 4 overlying a major facies dislocation third order sequence boundary comprises amalgamated sheet fluvial deposits of the lower castlegate sandstone and equivalent tarantula mesa sandstone during the early to middle campanian the northern wasatch plateau and western henry mountains regions were along depositional strike with respect to one another the book cliffs near green river were located obliquely down depositional dip from the western henry mountains region during the campanian these new correlations and the improved understanding of paleogeography that derive from them have the potential to inform basin scale stratigraphic interpretations to a greater extent than has been hitherto possible

layer parallel shortening across the sevier fold thrust belt and laramide foreland of wyoming spatial and temporal evolution of a complex geodynamic system abstract varying patterns of layer parallel shortening lps and vertical axis rotations from the thin skin sevier fold thrust belt to the thick skin laramide foreland of wyoming are quantified from integrated structural anisotropy of magnetic susceptibility ams and paleomagnetic analyses within the sevier belt widespread early lps was accommodated by spaced cleavage fracture sets minor folds and minor faults lps directions are subperpendicular to structural trends of systematically curved thrust sheets of the wyoming salient reflecting a combination of primary dispersion and secondary rotation during thrusting within the laramide foreland limited lps was accommodated mostly by minor faults with conjugate wedge and strike slip geometries lps directions in gentler fold limbs vary from perpendicular to acute with structural trends of variably oriented anastomosing basement cored arches steep forelimbs display more complex relations including younger fault sets that developed during evolving stress states and localized vertical axis rotations although internal strain is limited weak ams lineations defined by kinked and rotated phyllosilicates are widely developed and consistently oriented perpendicular to measured lps directions palinspastically restored lps directions corrected for paleomagnetically determined vertical axis rotations vary on average from w e in the sevier belt to wsw ene in the laramide foreland in detail lps directions display deflections related to primary sedimentary wedge geometry and basement fabrics lps in the sevier belt is interpreted to partly reflect stress transmitted from the hinterland through the growing orogenic wedge and topographic stress along the front of the wedge lps in the laramide foreland is interpreted to partly reflect basal traction during flat slab subduction beneath thick cratonic lithosphere with spatial temporal variations in stress trajectories related to basement heterogeneities and evolving fault systems evidence for significant late n s laramide shortening as proposed by multi stage shortening models is not observed

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

dynamic uplift during slab flattening subduction exerts a strong control on surface topography and is the main cause of large vertical motions in continents including past events of large scale marine flooding and tilting the mechanism is dynamic deflection the sinking of dense subducted lithosphere gives rise to stresses that directly pull down the surface here we show that subduction does not always lead to downward deflections of the earth s surface subduction of young lithosphere at shallow angles flat subduction leaves it neutrally or even positively buoyant with respect to underlying mantle because the lithosphere is relatively warm compared with older lithosphere and because the thickened and hence drier oceanic crust does not undergo the transformation of basalt to denser eclogite accounting for neutrally buoyant flat segments along with large variations in slab morphology in the south american subduction zone explains along strike and temporal changes in dynamic topography observed in the geologic record since the beginning of the cenozoic our results show that the transition from normal subduction to slab flattening generates dynamic uplift preventing back arc marine flooding