tectonic denudation of the shuswap metamorphic terrane of southeastern british columbia large scale over thrusting and regional extension are both known to have been operative within the shuswap metamorphic terrane of the southern omineca belt the monashee core complex of the northern shuswap terrane is interpreted to be a crustal scale duplex that was developed during late mesozoic shortening and thickening of the crust uplift of the monashee complex caused by basement duplexing is estimated to have been in excess of 25 km late cretaceous overthrusting of high grade metamorphic and related plutonic rocks during later stages of uplift and basement duplexing led to weakening of the crust and to gravitationally driven extension of a regional crustal welt shuswap culmination denudation and spreading of this uplifted metamorphic terrane are attributed to displacements across listric normal shear zones and faults localized along the outward dipping flanks of the shuswap culmination total extension across the shuswap culmination at the northern end of the monashee complex is estimated to be no greater than 30 this model of denudation and gravity induced spreading is extrapolated southward into the valhalla and okanagan regions where extension may be far more significant

crustal paleorheology of the southeastern canadian cordillera and its influence on the kinematics of jurassic convergence the kinematic evolution of the southeastern canadian cordillera 52 n 54 n during the jurassic is characterized by an eastward migration of the active boundary of convergence between north america and allochthonous terranes and by two reversals in regional structural vergence to investigate possible mechanical controls on the kinematics of convergence the thermal and geological structure of the jurassic continental margin at three stages in its history of shortening were palinspastically reconstructed and analyzed with the use of strength versus depth profiles the resulting models reproduce to a first order the observed distribution of brittle and ductile deformation and provide a mechanical basis for the localization and orientation of displacement zones during shortening of the continental margin the initial eastward migration of the active boundary of convergence between north america and allochthonous terranes from outboard of the continental margin sediment prism into the thick central part of the continental margin prism is attributed to thermal weakening of the continental margin lithosphere during obduction of the oceanic terrane the subsequent eastward migration of the convergence boundary into the inner part of the continental margin lithosphere is attributed to thermal weakening of the lithosphere during prograde regional metamorphism reversals in regional structural vergence accompanying each migration apparently occur because the push necessary to continue displacement on one displacement trajectory exceeds the failure strength of another displacement trajectory that dips in the opposite direction

rheological stratification of the lithosphere abstract the rheology of the lithosphere is estimated on the basis of pore pressure dependent frictional failure in the brittle regime and power law steady state creep in the ductile regime different petrological models of the continental and oceanic lithosphere combined with different geotherms and thicknesses are used to generate models covering a variety of geodynamic situations results show that the depth dependence of lithospheric rheology varies with the tectonic province and that in many instances the continental lithosphere has one at the bottom of the crust or two the previous one plus another at mid crustal levels soft ductile layers sandwiched between brittle layers the depth distribution of geophysical parameters seismicity seismic wave velocity and electrical conductivity matches the theological predictions well the lithospheric rheological profiles are used to analyze observed variations in the structural style of deformed continental margin and oceanic terranes in the southeastern canadian cordillera the large scale characteristics of the system show a satisfactory agreement with the inferred rheological structure sub horizontal decollements should be the rule rather than the exception where the lithospheric rheology is strongly stratified

ploughing the deep sea floor bottom trawling is a fishing technique whereby heavy nets and gear scrape along the sea bed and is shown here to disturb sediment fluxes and modify the sea floor morphology over large spatial scales the direct impact of bottom trawling on local fish populations has received much attention but trawling also affects other aspects of the ocean environment this paper shows that bottom trawling a commercial practice in which heavy nets and gear are dragged along the ocean floor induces sediment reworking and erosion causing the gradient of the sea floor to become smoother over time this reduces the morphological complexity of deep sea environments the authors draw parallels between the effects of bottom trawling at sea and intensive agriculture on land with the important difference that on land ploughing takes place once or twice a year whereas at sea bottom trawling can be a frequent occurrence bottom trawling is a non selective commercial fishing technique whereby heavy nets and gear are pulled along the sea floor the direct impact of this technique on fish populations1 2 and benthic communities3 4 has received much attention but trawling can also modify the physical properties of seafloor sediments water sediment chemical exchanges and sediment fluxes5 6 most of the studies addressing the physical disturbances of trawl gear on the seabed have been undertaken in coastal and shelf environments7 8 however where the capacity of trawling to modify the seafloor morphology coexists with high energy natural processes driving sediment erosion transport and deposition9 here we show that on upper continental slopes the reworking of the deep sea floor by trawling gradually modifies the shape of the submarine landscape over large spatial scales we found that trawling induced sediment displacement and removal from fishing grounds causes the morphology of the deep sea floor to become smoother over time reducing its original complexity as shown by high resolution seafloor relief maps our results suggest that in recent decades following the industrialization of fishing fleets bottom trawling has become an important driver of deep seascape evolution given the global dimension of this type of fishery we anticipate that the morphology of the upper continental slope in many parts of the world s oceans could be altered by intensive bottom trawling producing comparable effects on the deep sea floor to those generated by agricultural ploughing on land

middle jurassic exhumation along the western flank of the selkirk fan structure thermobarometric and thermochronometric constraints from the illecillewaet synclinorium southeastern british columbia new thermobarometric and thermochronometric data from the illecillewaet synclinorium a broad regional southwest verging structure in the western flank of the selkirk fan structure indicate that accretion of the intermontane superterrane resulted in deep burial 20 25 km of the outer margin of ancestral north america and that subsequent southwest verging folding and thrusting were accompanied by rapid exhumation southwest verging folding of lower paleozoic rocks in the illecillewaet synclinorium was initiated during regional peak metamorphic conditions at 6 7 kbar crystallization of late synkinematic granitoid plutons that intrude the illecillewaet synclinorium also occurred at pressures of 6 7 kbar however equilibration of the contact aureoles of the plutons occurred at 3 3 5 kbar during the latter stages of the southwest verging deformation evidently a decompression on the order of 3 kbar occurred concurrently with southwest verging folding and thrusting in the illecillewaet synclinorium thermochronometric analyses further indicate that plutonic rocks from the illecillewaet synclinorium cooled rapidly between times of crystallization and times of ar closure in biotite regional relationships indicate that the accretion of the intermontane superterrane to the edge of the north american margin in southeastern british columbia occurred between 187 and 173 ma toarcian bajocian subsequent southwest verging deformation occurred approximately between 173 and 168 ma bajocian bathonian thus the removal of at least 10 km of rocks from above the illecillewaet synclinorium inferred from thermobarometric data occurred approximately between 173 and 168 ma rapid denudation of the selkirk fan structure was probably the result of synorogenic extension or extensional collapse contemporaneous with the development of southwest verging structures at deeper levels of the orogen the data presented here indicate that all significant deformation and most of the exhumation along the western flank of the selkirk fan structure were complete by late middle jurassic time after the middle jurassic the selkirk fan structure must have been transported passively northeastward along the basal decollement of the cordilleran foreland thrust and fold belt together with the intermontane superterrane as the fold and thrust belt tectonically overrode the margin of the north american craton

hyperconcentrated sand water mixture flows over erodible bed field surveys and experiments in a tilting flume on hyperconcentrated sand water mixture swm flows were conducted at slopes slightly smaller than the equilibrium slope a rapid development of sand bars propagating upstream was observed these bars consist of an almost horizontal terrace with subcritical flow a steep lee side slope with supercritical flow and a hydraulic jump between subsequent bars the erosion processes on the bar are limited by the high sand concentrations and flow velocities on the steep slopes as a result the erosion rate is more moderate than predicted by the pickup functions used in classical sediment transport theory a simple one dimensional model is presented to study the behavior of triangular schematized bars from an analysis of the equations it is concluded that an increase in erosion rate requires an increase in bed slope to maintain equilibrium flow conditions finally simulations with the model are compared with observations in the field and in the tilting flume t

architectural analysis of a volcaniclastic jokulhlaup deposit southern iceland sedimentary evidence for supercritical flow the 1918 eruption of the glacially capped katla volcano southern iceland generated a violent jokulhlaup or glacial outburst flood inundating a large area of m rdalssandur the proglacial outwash plain where it deposited ca 1 km3 of volcaniclastic sediment the character of the 1918 jokulhlaup is contentious having been variously categorized as a turbulent water flow a hyperconcentrated flow or as a debris flow based on localized outcrop analysis in this study outcrop based architectural analyses of the 1918 deposits reveal the presence of lenticular and tabular bedsets associated with deposition from quasi stationary antidunes and down current migrating antidunes and from regular based bedsets associated with transient chute and pool bedforms all of which are associated with turbulent transcritical to supercritical water flow conditions antidune wavelengths range from 24 to 96 m corresponding to flow velocities of 6 to 12 m sec 1 and average flow depths of 5 to 19 m this range of calculated flow velocities is in good agreement with estimates made from eyewitness accounts architectural analysis of the 1918 jokulhlaup deposits has led to an improved estimation of flow parameters and flow hydraulics associated with the 1918 jokulhlaup that could not have been achieved through localized outcrop analysis the observations presented here provide additional sedimentological and architectural criteria for the recognition of deposits associated with transcritical and supercritical water flow conditions the physical scale of sedimentary architectures associated with the migration of bedforms is largely dependent on the magnitude of the formative flow events or processes sedimentary analyses must therefore be undertaken at the appropriate physical scale if reliable interpretations regarding modes of deposition and formative flow hydraulics are to be made

shipwrecks and man made coastal structures as indicators of historical shoreline position an interdisciplinary study in the sancti petri sand spit bay of cadiz sw spain abstract shoreline evolution studies are mostly performed by comparison of vertical images e g aerial photographs and satellite imagery being limited to the last decades however phenomena such as longer term climatic fluctuations may cause important secular coastal changes which are mostly unknown the use of archaeological remains as shoreline proxies could overcome this limitation by allowing to expand back in time the historical shoreline record the present study endorses the effectiveness of the use of shipwrecks and man made structures as proxy data for analyzing historical shoreline evolution this was confirmed by the evaluation of nearshore evolution historical shorelines from 1787 to 1823 and recent changes from 1956 to 2013 and the reconstruction of the palaeobathymetry along sancti petri sand spit sw spain by means of the analysis of historical documents historical maps modern aerial photographs and a recent bathymetry 2011 along with the archaeological prospection supported by the numerical modelling of the dispersion of archaeological remains the analysis of historical maps has revealed a significant shoreline retreat over the medium term scale in sancti petri sand spit averaging 1 2 m year 1 results from historical maps and archaeological remains show slight differences with respect to the most recent retreat rates 0 9 m year 1 obtained from aerial photographs for the period 1956 2013 spatial variations in coastal retreat along the sandspit are closely linked to local patterns of wave height and wave induced currents significant temporal variation in rates of shoreline change was observed probably related to storminess variability in the study area as indicated by the relation between the rates of coastal change for each analyzed period and the corresponding rate of change of winter nao index

a re examination of the type area of the devono mississippian cariboo orogeny central british columbia three tectonostratigraphic successions are established from remapping of the area near barkerville and cariboo river the first of late proterozoic to cambrian sediments was deposited on the shallow to moderately deep platformal shelf west of and derived from the exposed north american craton the second is an unconformably overlying ordovician to permian sequence of sedimentary and volcanic rocks representing a basinal environment with periodic highs these packages of sediments were deposited on the north american craton and its western transitional extensions the third succession composed of oceanic chert and basalt of the permo pennsylvanian antler formation was thrust eastward over the other two during the early mesozoic the three successions were folded faulted and metamorphosed during the mid mesozoic columbian orogeny the devono mississippian cariboo orogeny which was thought to have affected all of the first sequence and part of the second could not be documented in its type locality

u th pb geochronologic constraints on the structural evolution of the selkirk fan northern selkirk mountains southern canadian cordillera abstract in the southern canadian cordillera a zone of structural divergence marks the eastward transition from penetrative ductile deformation and metamorphism in the omineca belt to the more brittle thin skinned style of deformation typical of the foreland belt in the selkirk mountains of southern british columbia this zone includes a regional scale structure termed the selkirk fan the fan trends northwest consists primarily of medium to high grade metamorphic rocks and comprises at least three generations of superposed structures idtims and shrimp analyses provide new u th pb age constraints for the structural evolution of the selkirk fan the data demonstrate that the thermo structural development of the fan s west flank occurred principally in the middle jurassic ca 172 167 ma whereas in the east flank significant cretaceous ca 104 84 ma deformation was superimposed on an early transposition fabric these data require revision of previous models that concluded fan formation occurred primarily during middle jurassic time rather the selkirk fan is a composite structure comprising middle jurassic and cretaceous deformation development of the fan during the early middle jurassic accretion of the intermontane superterrane was followed by extensive reworking and tightening of structures in the fan s east flank during the cretaceous accretion of the insular superterrane

channel fill and sheet flood facies sequences in the ephemeral terminal river gash kassala sudan abstract detailed facies analysis of the river gash fluvial sediments on two dimensional profiles across and along the main channel has revealed a number of facies and two distinct types of sequences channel fill and sheet flood sequences it seems that each sequence type is produced by specific depositional event and both sequences represent two end members for suite of mixed sequences the facies and sequences show rapid lateral variability and they merge and interfinger with each other they also show partial to complete modification due to subsequent floods and stage variation it seems that the thick sediments of the river gash in the kassala area were produced in two phases first by braided channel aggradation and lateral migration second by both channelized and unchannelized sheet flood deposition deposits of these two phases contribute to the sediments of the present day gash fluvial basin in the kassala area the gash sediments show some similarities and differences to those of ephemeral and low sinuosity braided streams the predominance of sheet flood deposits is consistent with the ephemeral flashy high flow regime in the river gash the non conformity of the river gash depositional style with the braided model of fluvial deposition may be due to this semi arid terminal flashy character which has control on the depositional processes and patterns

a geodynamic model for extension in the shuswap core complex southeastern canadian cordillera the shuswap core complex records mesozoic and paleocene crustal shortening with superimposed eocene extension during the shortening phase the crust was thickened and slowly uplifted within at most 20 ma of the climax of compression the crustal welt was rapidly uplifted and tectonically denuded shortening of the continental crust may be balanced in the underlying lithosphere by thickening or underplating forming in either case a lithospheric root beneath the crustal welt we consider a model whereby tertiary crustal extension in the shuswap core complex and possibly also in other segments of the north american cordillera is accounted for by the detachment of this root both the time frame and the stress field resulting from the detachment are compatible with geological and geophysical observations far field stresses played an accommodating role but the potential energy required for extension of the shuswap complex was induced by lithospheric thickening

age and geological setting of gold creek gneiss crystalline basement of the windermere supergroup cariboo mountains british columbia gold creek gneiss the most recently discovered body of crystalline basement in the canadian cordillera is a northwest trending granitic to dioritic orthogneiss straddling the eastern end of the canoe river valley near the southeastern end of the cariboo mountains u pb geochronometry of zircons from two samples of quartz diorite orthogneiss from two separate localities yielded similar nearly linear discordant arrays with upper intercepts of 2 08 ga the patterns of discordance in both samples preclude assigning a precise age although a date between 2 0 and 2 1 ga is geologically reasonable north of canoe river gold creek gneiss is inferred to be nonconformably overlain by quartzite and marble which in turn are inferred to be unconformably overlain by a conglomerate and diamictite bearing unit at the base of the lower kaza group of the windermere supergroup in contrast with other exposures of basement and cover in the area neither contact is marked by anomalously high strain or mylonitic rocks

tectonic links between the clachnacudainn terrane and selkirk allochthon southern omineca belt canadian cordillera the clachnacudainn terrane in the southern omineca belt is interpreted as an integral part of the overlying selkirk allochthon based on stratigraphic igneous metamorphic and deformational links across the boundary between them the standfast creek fault an inverted homocline correlated with lower paleozoic lardeau group metasedimentary and metavolcanic rocks is continuous across the fault the fault is transected by post ductile strain granitoids of inferred and known mid cretaceous age such as the 104 1 ma albert stock as well as by peak regional metamorphic m2 isograds and contact metamorphic m3 isograds associated with the albert stock three phases of regional ductile deformation including major west verging second phase f2 folds are correlated across the fault these tectonic links strongly suggest that the clachnacudainn terrane and selkirk allochthon share a similar tectonic history and thereby require that the standfast creek fault has minor tectonic significance compared with other faults in the southern omineca belt m2 and coeval f2 folds are interpreted as resulting from middle jurassic tectonism documented elsewhere in the selkirk allochthon the main aspect that differentiates the clachnacudainn terrane from the rest of the selkirk allochthon east of the monashee complex is the clachnacudainn igneous complex which dominates the northern part of the terrane and is the product of prolonged igneous activity

seismic reflection geometry of the columbia river fault zone and east margin of the shuswap metamorphic complex in the canadian cordillera vibroseis conoco incorporated seismic reflection data recorded near the transition between the cordilleran fold and thrust belt and the east margin of the shuswap metamorphic complex of the southern canadian cordillera outline an east tapering wedge geometry in the upper crust the wedge comprises part of the shuswap metamorphic complex and may be the result of either a foreland dipping duplex or tectonic wedging the geometric wedge separates the overlying miogeoclinal rocks of the selkirk fan structure from the crystalline basement rocks below and delineates the eastern limit of the monashee complex brittle motion on the columbia river fault zone produced an east dipping listric normal fault which may have offset the upper portion of the monashee complex the columbia river fault zone is imaged over the entire 15 km of the profile and can be traced to a depth of at least 10 km reflections from the lower crust are generally subhorizontal and discontinuous and they may be a manifestation of crustal extension the crust mantle transition is probably represented as reflections with travel times of 11 0 12 0 s

plagioclase clinopyroxene garnet quartz equilibria and the geobarometry and geothermometry of garnet amphibolites from mica creek british columbia metabasites form a small but significant volume of the upper precambrian horsethief creek group near mica creek british columbia sillimanite zone assemblages in metabasites are hornblende plagioclase ilmenite quartz garnet clinopyroxene sphene calcite the incoming of garnet clinopyroxene in metabasites very nearly coincides with the kyanite sillimanite isograd fe mg distributions between coexisting garnet and clinopyroxene suggest a temperature range of 650 705 c ellis and green calibration the higher temperature estimates disagree with the upper thermal stability limits of muscovite plagioclase quartz sillimanite from adjacent pelitic rocks pressure estimates based upon clinopyroxene garnet plagioclase quartz equilibria are 5 6 0 3 and 7 2 0 3 kbar 560 30 and 720 30 mpa respectively using two different calibrations of this geobarometer these estimates bracket the pressure estimated from garnet plagioclase al2sio5 equilibria in pelitic rocks

p t history and kinematics of the monashee decollement near revelstoke british columbia microstructural and petrofabric analyses of mylonites from the monashee decollement demonstrate that the hanging wall was displaced eastward over the footwall microstructural kinematic indicators include shear band foliation asymmetric strain shadows and s c fabrics quartz c axes locally exhibit asymmetric fabrics that are consistent with the microstructural evidence for sense of shear the kinematic evidence is reliable because multiple criteria coexist within individual specimens metamorphic assemblages from footwall monashee complex pelites at the revelstoke damsite indicate that the peak metamorphic assemblage was sillimanite k feldspar biotite almandine quartz plagioclase biotite garnet geothermometry and garnet plagioclase sillimanite quartz geobarometry set broad constraints on metamorphic temperatures but closer constraints on pressures near 650 c and 630 mpa comparison of these data with late cretaceous hornblende cooling ages from the same locality indicates that the metamorphism is at

biocalcarenite and mixed cool water prograding bodies of the mediterranean pliocene and pleistocene architecture depositional setting and forcing factors

shuswap terrane of british columbia a mesozoic core complex the shuswap terrane of the northwest cordillera owes its distinctive characteristics to deformation and high grade regional metamorphism that occurred primarily during the mesozoic within the terrane the monashee complex the overlying selkirk allochthon and the intervening monashee decollement record strain and metamorphism that occurred in middle to late jurassic time during and subsequent to the accretion of a western allochthonous terrane the selkirk allochthon moved eastward across the monashee complex after emplacement of the western allochthonous terrane but before late mesozoic to early cenozoic telescoping of the rocky mountain belt in this latter event the monashee complex and overlying allochthonous slices were transported eastward relative to the north american craton on a sole fault that developed during listric thrusting of the rocky mountain foreland synmetamorphic to late metamorphic elongation lineations and associated fabrics of the mylonitic rocks of the monashee decollement zone were generated by shear strain during the middle jurassic emplacement of the selkirk allochthon and are not related to any upper crustal extension that occurred in the tertiary uplift normal faulting brittle reactivation of the mylonitic decollement zone widespread resetting of k ar and rb sr mineral dates and arching of the terrane are events that culminated in the eocene

stratigraphy and deformational history of the scrip nappe monashee mountains british columbia the scrip nappe a large recumbent anticline that occupies the northern selkirk and northern monashee mountains has an inverted lower limb some 50 km in length across strike and comprises stratigraphic divisions of the hadrynian horsethief creek group which can be traced southward with decreasing metamorphic grade through the selkirk mountains to the northern purcell mountains the scrip nappe has a southwesterly vergence and it formed that way during the first folding phase of the mesozoic columbian orogeny metamorphism no greater than biotite zone accompanied that first deformation the nappe was subsequently refolded into tight northeast verging folds metamorphism rose to upper amphibolite facies late in the second deformation phase after the metamorphic climax northeast verging buckle folds and associated crenulation cleavage formed locally during a third folding episode the entire nappe complex was then carried northeastward on the purcell thrust over the folds and thrusts of the western r

traction carpet stratification in turbidites fact or fiction abstract the spaced stratification that characterizes some thick deep water sandstones consists of a stack of layers 5 10 cm thick that are inversely graded at their base and structureless at their top these layers have been attributed to deposition from a succession of collapsed inertia layers traction carpets prior to collapse each layer was believed to have been maintained by shear from the overriding turbidity current this depositional model is based on the mistaken assumption that the distribution of shear stress in such a traction carpet is indistinguishable from the distribution of shear stress in a grain flow on a steep slope instead shear stress in an externally sheared traction carpet should be approximately constant from the top to the base of the layer and deposition sho ld be a gradual process leaving no record of sequentially active inertia layers inertia layers that do form under large turbidity currents are probably never as thick as 5 10 cm based on available data from shear cell experiments instead inertia layers are probably about 1 cm thick similar to the thickness of the inversely graded basal part of each layer in field examples of spaced stratification the rest of each inversely graded stratum probably forms due to rapid fallout from suspension the basal inversely graded 1 cm is believed to record strong shear that may accompany impingement on the bed of large turbulent eddies hence spaced stratification may not be a structure produced beneath steady flows but may record strong y fluctuating hydrodynamic conditions and vigorous burst sweep cycles in large turbidity currents

comparison of the bedform distribution and dynamics of modern and ancient sandy ephemeral flood deposits in the southwestern karoo region south africa abstract during january 1981 unusually high rainfall patterns in the semi arid southwestern karoo region of south africa gave rise to catastrophic floods in the area the most devastating of which was the ephemeral flash flood that partially destroyed the town of laingsburg flood waters at laingsburg spread from a dry river bed rising to a depth of 12 m within 7 h washing away houses and burying the town with up to 3 5 m of sand and silt facies sequences and bedforms in the laingsburg flood deposits are related to specific subenvironments and flow conditions during the flood event two large scale sedimentary units in erosive contact with each other were deposited by two major discharge pulses within the same flood event vertical and lateral variations in the bedform distributions reflect fluctuations in flow velocity and turbulence comparison is drawn between the laingsburg flood deposits and fluvial sandstones of the permian lower beaufort in the southwestern karoo the multistoried sandstone bodies composed mainly of a horizontally laminated lithofacies are interpreted as the products of a complex series of ephemeral flooding events individual storey units in the palaeochannel sequences are generally envisaged as the deposits of different floods however evidence from the modern flood shows that separate pulses of a single flooding episode can also produce a sequence of storey units bounded by erosive scours spectacular palaeosurfaces in the lower beaufort also have modern analogues in the laingsburg overbank deposits discussion on the preservation potential of delicate sedimentary structures and biogenic traces on these surfaces emphasizes the necessity for pulsatory deposition of bedload and suspended load material over short intervals of time by comparing facies profiles and surface bedforms the ephemeral fluvial facies model for the lower beaufort is critically appraised

kinematic interpretation of mylonitic rocks in part of the columbia river fault zone shuswap terrane british columbia mylonitic rocks of the columbia river fault zone have been examined in a 600 m thick section 20 km north of revelstoke british columbia at this locality coarse grained granite with well preserved igneous texture lies in the hanging wall of the fault zone adjacent to the boundary of the mylonite zone the granite is foliated and mineral segregation gives rise to well defined compositional layering the foliation sf is defined by oriented mineral grains and flattened porphyroclasts in areas of intense strain compositional layering sc is parallel to sf at the boundary of the mylonite zone and in weakly deformed areas within the mylonite zone sc and sf are inclined at angles up to 30 sf is taken to be a plane of flattening and sc appears to parallel a plane of shear after correction for effects of late stage flexural slip folding the angular relationship of sc to sf may be used to determine sense of shear in the mylonitc zone the hanging wall rocks have been displaced toward the east relative to

structureless coarse tail graded bouma ta formed by internal hydraulic jump of the turbidity current abstract turbidity currents are commonly super critical if they travel on slopes steeper than 0 001 hence upon deceleration such flows must pass a hydraulic jump it is therefore surprising that sedimentary features related to the hydraulic jump are so poorly known and not clearly related to the bouma sequence to study this missing link a stability diagram of bed forms generated by decelerating initially super critical turbidity currents is presented here to sketch the position of hydraulic jump deposits relative to super and sub critical bed forms observed in turbidites the axes of the diagram are formed by the densiometric froude number the grain size and the particle fall out rate experimental evidence shows that the hydraulic jump is hardly manifested in the deposit if turbidity currents pass the jump as a low concentration single phase suspension flow only those turbidity currents that develop two phase suspension flow with a super critical flowing traction carpet cause vigorous erosion and liquefaction of the substrate at the jump locality to produce rip up of the substrate rip up clasts and flame structures which are trapped in structureless coarse tail graded deposits characteristic of the classic bouma ta unit the location of the jump is sensitive to density velocity variations of the traction carpet and can shift rapidly up and down the slope this would explain why structureless coarse tail graded deposits such as bouma ta develop sheet like

quantification of bottom trawl fishing damage to ancient shipwreck sites abstract bottom trawl fishing presents a severe yet largely unquantified threat to shipwreck sites here we present a quantification of damage to sites from the aegean and black seas through high resolution imaging of 45 shipwrecks discovered by the e v nautilus expeditions 2009 2012 these shipwrecks are part of a modern submarine landscape that is heavily damaged by trawls which also remove sediment and smooth out natural features of the seabed we quantify the severity of this threat to archaeological sites through repeat visits to one ancient shipwreck and quantify the change to the seabed over a period of eleven months the results illustrate the benefits of enforced areas of restricted bottom trawling marine protected areas to the in situ preservation of shipwreck sites and to natural seabed features and benthic habitats careful marine spatial planning and coordinated management of fishing activity can mitigate this destructive activity in addition we counter the claim made by some commercial salvors who use trawl damage as an excuse to salvage artifacts from wrecks further destroying historically significant sites for profit

tectonic interpretation of west verging folds in the selkirk allochthon of the southern canadian cordillera the selkirk allochthon a composite tectonic slice composed of north american paleocontinental margin deposits and more distal possibly marginal basin suspect terrane was displaced eastward toward the craton in the late jurassic and late cretaceous the carnes nappe a major west verging recumbent anticline within the selkirk allochthon is considered the southern continuation of scrip nappe which in the monashee mountains has an inverted limb length of 50 km the west verging nappe and associated structures are interpreted as having originated in the early to middle jurassic during accretion of western allochthonous terranes and prior to eastward displacement of the selkirk allochthon the reversal from westward vergence away from the north american craton to eastward vergence is considered as marking a fundamental change in the evolution of the orogenic belt and may reflect a transition from underthrusting of western allochthonous terranes on blind shear zones to east directed breakthrough thrusts

structural and metamorphic constraints on ca 70 ma deformation of the northern valhalla complex british columbia implications for the tectonic evolution of the southern omineca belt abstract penetrative deformation occurred ca 70 ma ago throughout the northern valhalla complex in valhalla and passmore domes and in the gwillim creek shear zone exposed at the deepest structural levels in both domes intense strain s t in the gwillim creek shear zone domain ii was synchronous with and outlasted deformation d 2 throughout the northern complex domain i upper amphibolite facies peak mineral assemblages define the predominant foliation temperature and pressure results determined from microdomains with established relationships to reaction textures and microstructures provide constraints on conditions under which deformation occurred deformation was synchronous with and outlasted peak metamorphic conditions at all structural levels peak conditions of 825 c and 730 mpa and 850 c and 840 mpa were determined for domains i and ii respectively this was followed by cooling and retrograde garnet breakdown at conditions of 715 c and 490 mpa and 765 c and 730 mpa in domains i and ii respectively the faster cooling rate per kilometer of exhumation for domain ii relative to domain i is consistent with a model of conductive cooling via thrusting of domain ii on to a cold footwall metamorphism is interpreted to have resulted from crustal thickening and burial to depths of ca 25 km based on an inferred clockwise p t path and the paucity of late cretaceous intrusions lack of retrograde metamorphism throughout the complex and the high degree of annealing of microstructures indicates that the rocks remained above greenschist facies conditions until they were exhumed in the early tertiary on the valkyr slocan lake extensional shear zone system previous workers have determined that the peak of metamorphism occurred at 72 67 ma in a restricted locality in the core of passmore dome near vallican our study links this dated metamorphism with the structural evolution and metamorphic history throughout the area and shows that supracrustal rocks at all structural levels in valhalla and passmore domes underwent the same metamorphic and deformation event as those near vallican therefore we assign a ca 70 ma age to the penetrative high temperature deformation in northern valhalla complex and the gwillim creek shear zone this coincides with a major period of shortening in the rocky mountains of the foreland belt strain in northern valhalla complex may represent a local transient shear zone that accommodated crustal thickening in the hinterland during orogen scale compression or it may be an exhumed part of the basal detachment of the rocky mountains

froude supercritical flow processes and sedimentary structures new insights from experiments with a wide range of grain sizes recognition of froude supercritical flow deposits in environments that range from rivers to the ocean floor has triggered a surge of interest in their flow processes bedforms and sedimentary structures interpreting these supercritical flow deposits is especially important because they often represent the most powerful flows in the geological record insights from experiments are key to reconstruct palaeo flow processes from the sedimentary record so far all experimentally produced supercritical flow deposits are of a narrow grain size range fine to medium sand while deposits in the rock record often consist of a much wider grain size distribution this paper presents results of supercritical flow experiments with a grain size distribution from clay to gravel these experiments show that cyclic step instabilities can produce more complex and a larger variety of sedimentary structures than the previously suggested backsets and scour and fill structures the sedimentary structures are composed of irregular lenses mounds and wedges with backsets and foresets as well as undulating planar to low angle upstream and downstream dipping laminae the experiments also demonstrate that the froude number is not the only control on the sedimentary structures formed by supercritical flow processes additional controls include the size and migration rate of the hydraulic jump and the substrate cohesion this study further demonstrates that froude supercritical flow promotes suspension transport of all grain sizes including gravels surprisingly it was observed that all grain sizes were rapidly deposited just downstream of hydraulic jumps including silt and clay these results expand the range of dynamic mud deposition into supercritical flow conditions where local transient shear stress reduction rather than overall flow waning conditions allow for deposition of fines comparison of the experimental deposits with outcrop datasets composed of conglomerates to mudstones shows significant similarities and highlights the role of hydraulic jumps rather than overall flow condition changes in producing lithologically and geometrically complex stratigraphy

an examination of froude supercritical flows and cyclic steps on a subaqueous lacustrine delta lake chelan washington u s a density driven submarine flows including turbidity currents play an important role in the transfer of sediment into deep water these bottom hugging flows often produce flow transverse bedforms along their path a sedimentological and geophysical survey of the stehekin river delta in lake chelan washington reveals a downslope elongate field of bedforms on the delta foreset associated with hyperpycnal discharges of the stehekin river an analysis of the bedform morphologies delta geometry and density contrast between lake and river water suggests that these hyperpycnal flows are froude supercritical the bedforms are likely cyclic steps flow transverse bedforms that are bounded by stable hydraulic jumps between alternating subcritical and supercritical flow regimes the ability to examine the three dimensional bed configuration produced by natural density driven flows adds valuable information to the body of experimental work focused on the behavior of cyclic steps in flumes

selkirk fan structure southeastern canadian cordillera tectonic wedging against an inherited basement ramp a revised cross section through the selkirk fan structure provides the basis for a new model for the middle jurassic tectonic evolution of the southern omineca belt canadian cordillera palinspastic restoration of this cross section shows that the southwest verging structures along the west flank of the selkirk fan structure formed as a result of tectonic wedging of distal north american strata clachnacudainn complex beneath more proximal north american strata and that the selkirk fan structure developed outboard from a crustal ramp dogtooth high inherited from late proterozoic early paleozoic rifting along the western margin of north america the first episode of mesozoic deformation in southeastern british columbia occurred between 187 and 173 ma and involved the northeastward juxtaposition of the intermontane superterrane over the outer part of the north american continental terrace wedge it resulted in deep burial 20 25 km of the outer margin of north america a crustal ramp localized along the western edge of the late proterozoic early paleozoic dogtooth high impeded the northeastward propagation of the orogenic wedge comprising the intermontane superterrane and the imbricate underlying northeast verging thrust sheets of north american supracrustal rocks tectonic wedging involving southwest verging deformation occurred within the orogenic wedge and the resulting crustal thickening established sufficient topography and gravitational potential to drive the propagation of the deformation eastward into the dogtooth range and the rocky mountains the southwest verging structures along the west flank of the selkirk fan developed between approximately 173 and 168 ma concurrent with synorogenic extension and 10 km of exhumation the initial subsidence of the foreland basin during kimmeridgian time ca 154 ma provides the first indication of tectonic loading and lithospheric flexure of the north american plate it is interpreted to mark the time at which the orogenic wedge overrode the crustal ramp of the dogtooth high and advanced onto relatively thick and rigid continental lithosphere the tectonic model proposed for the selkirk fan structure illustrates how the configuration of the rifted margin influenced the style of crustal thickening during subsequent compressional deformation