the cowichan fold and thrust system vancouver island southwestern british columbia the cowichan fold and thrust system is a southwest verging linked thrust system formed by northeast southwest large scale crustal contraction involving the upper cretaceous nanaimo group and its wrangellian basement the geometry of the thrust system from plan and profile perspectives illustrates its thick skinned structural style the thrust system is interpreted to be a leading imbricate fan thrusting was most likely in sequence creating an estimated minimum 20 30 shortening at the basement cover interface both fault propagation and fault bend folding are evident the former being more common kinematic indicators and the geometry of the thrust system show no evidence of significant transpressional or transtensional displacement fields contraction postdates deposition of the nanaimo group and is indirectly dated as late eocene the sole fault of the thrust system is interpreted to rise from northwest to southeast on a series of deep lateral to oblique ramps and merge with the san juan fault system this explains the rapidly westward thickening wedge of thrusted wrangellian basement in the study area in the east the sole fault is interpreted to have locally permitted the nanaimo group to overthrust the san juan terrane investigation of the cowichan fold and thrust system reveals how shortening during westward progressing terrane accretion is accommodated in a forearc region dominated by a large slab of rigid semicontinental crust

paleomagnetism of the upper cretaceous nanaimo group southwestern canadian cordillera the baja b c model has the insular superterrane and related entities of the canadian cordillera subject to 3000 km of northward displacement with respect to cratonic north america from 90 to 50 ma the upper cretaceous nanaimo group on and about vancouver island british columbia is a prime target to test the model paleomagnetically because of its locality and age we have widely sampled the basin 67 sites from seven islands spread over 150 km santonian to maastrichtian age most samples have low unblocking temperatures 450 c and coercivities 10 mt and strong present field contamination forcing us to reject three quarters of the collection beds are insufficiently tilted to provide a conclusive fold test and we see evidence of relative vertical axis rotations however inclination only analysis indicates pretilting remanence is preserved for many samples both polarities are observed and reversals correlate well to paleontological data proving that primary remanence is observed the mea

obducted nappe sequence in the san juan islands northwest cascades thrust system washington and british columbia the san juan islands northwest cascades thrust system in washington and british columbia is composed of previously accreted terranes now assembled as four broadly defined composite nappes stacked on a continental footwall of wrangellia and the coast plutonic complex emplacement ages of the nappe sequence are interpreted from zircon ages field relations and lithlogies to young upward the basal nappe was emplaced prior to early turonian time 93 ma indicated by the occurrence of age distinctive zircons from this nappe in the sidney island formation of the nanaimo group the emplacement age of the highest nappe in the thrust system postdates 87 ma detrital zircons within the nappe the nappes bear high pressure low temperature hp lt mineral assemblages indicative of deep burial in a thrust wedge however several features indicate that metamorphism occurred prior to nappe assembly metamorphic discontinuities at nappe boundaries absence of hp lt assemblages in the footwall to the nappe pile and absence of significant unroofing detritus in the nanaimo group a synorogenic relationship of the thrust system to the nanaimo group is evident from mutually overlapping ages and by conglomerates of nanaimo affinity that lie within the nappe pile from the foregoing relations and broader cordilleran geology the tectonic history of the nappe terranes is interpreted to involve initial accretion and subduction zone metamorphism south of the present locality uplift and exhumation orogen parallel northward transport of the nappes as part of a forearc sliver and finally obduction at the present site over the truncated south end of wrangellia and the coast plutonic complex

some late eocene depositional environments of the coal bearing puget group of western washington state u s a abstract plant bearing sediments of the puget group in the area of detailed study accumulated in large flood basins cutoff meanders and along channel margins in point bars and crevasse splay settings in addition to the plant bearing deposits peat swamp deposits and coarse grained channel deposits are represented by stacked sandstone bodies and thick coal sequences the depositional environments of the fluvial deltaic deposits are distinguished by the presence and distribution of sedimentary structures grain size grain size variability and the densityand layering of organic remains both plant and invertebrate the importance of organic matter distribution in the sediments to differentiation of subenvironments was unexpected and may prove to be a valuable sedimentary characteristics in depositional interpretations within a single basin the sedimentary characterization of environments was made exclusive of the taxonomic composition of the plants preserved and is presented here without paleobotanical interpretation the separation of depositional interpretation from taxonomic identity of the fossil plants allows an independent assessment of the paleoecology of the plants preserved two prominent coal depositional models are discussed and evaluated in light of these data from the puget group it is concluded that peat accumulation in this system can be attributed most easily to a domed peat swamp model

comment on depositional history of the eocene chumstick formation implications of tectonic partitioning for the history of the leavenworth and entiat eagle creek fault systems washington by james e evans

upper crustal structure beneath the strait of georgia southwest british columbia summary we present a new three dimensional 3 d p wave velocity model for the upper crustal structure beneath the strait of georgia southwestern british columbia based on non linear tomographic inversion of wide angle seismic refraction data our study part of the georgia basin geohazards initiative gbgi is primarily aimed at mapping the depth of the cenozoic sedimentary basin and delineating the near surface crustal faults associated with recent seismic activities e g m 4 6 in 1997 and m 5 0 in 1975 in the region joint inversion of firstarrival traveltimes from the 1998 seismic hazards investigation in puget sound ships and the 2002 georgia basin experiment provides a high resolution velocity model of the subsurface to a depth of 7 km in the southcentral georgia basin sedimentary rocks of the cretaceous nanaimo group and early tertiary rocks have seismic velocities between 3 0 and 5 5 km s 1 the basin thickness increases from north to south with a maximum thickness of 7 1 km depth to velocities of 5 5 km s 1 at the southeast end of the strait the underlying basement rocks probably representing the wrangellia terrane have velocities of 5 5 6 5 km s 1 with considerable lateral variation our tomographic model reveals that the strait of georgia is underlain by a fault bounded block within the central georgia basin it also shows a correlation between microearthquakes and areas of rapid change in basin thickness the 1997 1975 earthquakes are located near a northeast trending hinge line where the thicknesses of sedimentary rocks increase rapidly to the southeast given its association with instrumentally recorded moderate sized earthquakes we infer that the hinge region is cored by an active fault that we informally name the gabriola island fault a northwest trending southwest dipping velocity discontinuity along the eastern side of vancouver island correlates spatially with the surface expression of the outer island fault the outer island fault as mapped in our seismic tomography model is a thrust fault that projects directly into the lummi island fault suggesting that they are related structures forming a fault system that is continuous for nearly 90 km together these inferred thrust faults may account for at least a portion of the basement uplift at the san juan islands

new paleogene paleoclimate analysis of western washington using physiognomic characteristics from fossil leaves abstract the chuckanut and manastash formations were deposited in a lowland fluvial environment in western washington during the paleocene eocene we provide a thorough paleotemperature analysis using the physiognomic characteristics from the fossil dicotyledonous leaves from these formations using two techniques leaf margin analysis lma and climate leaf analysis multivariate program clamp this work differs from previous analyses by 1 analyzing more localities and including the assessment of the never before described taneum ridge body and manastash main body within the manastash formation and the maple falls member of the chuckanut formation and 2 using two different techniques to decipher mean annual temperatures through time in this study mean annual temperatures mat were determined from 125 distinct morphotypes and are several degrees higher at each locality than previously reported mat values derived from lma ranged from 17 0 to 28 8 c for the lowermost and 13 4 to 19 5 c for the uppermost chuckanut formation the manastash formation had mats ranging from 17 1 c to 29 1 c using clamp paleotemperatures ranged from 15 3 to 19 4 c for the lowermost and 12 3 to 15 6 c for the uppermost chuckanut formation and 15 8 to 21 3 c for the manastash formation these data are compared to other eocene paleocene formations in the western us the chuckanut and manastash formations record some of the warmest paleotemperatures in the paleogene in the western us because of their low elevation locations these paleotemperatures may reflect the terrestrial signal of paleoclimate optima defined in marine rocks during the paleocene eocene

linked thrust and strike slip faulting during late cretaceous terrane accretion in the san juan thrust system northwest cascades orogen washington the san juan thrust system makes up the western elements of the late cretaceous northwest cascades orogen of washington a stack of metamorphic nappes with terranes ranging in age from early paleozoic to middle cretaceous the tectonic development of the nappes is an unresolved issue important to understanding plate convergent processes operating in the north american cordillera in the creta ceous as well as at other times two terrane bounding fault zones were studied in this project the lopez and the rosario fault zones the fault zone rocks were affected by two cataclastic plastic late cretaceous deformational events d1 and d2 that included accretion and lateral motion during blueschist facies metamorphic conditions d1 produced upright folds and a subvertical axial planar s1 foliation fabric in the lopez fault zone and southwest vergent folds and gently northeast dipping axial planar s1 foliation in the rosario fault zone in the lopez fault zone d2 produced northwest striking and subvertical strike slip shear zones s2 with dominant sinistral displacements whereas in the rosario fault zone d2 generated low angle s2 shear zones and various slip crenulation fabrics formed by northwest directed thrust motion the d1 fabrics are inferred to be related to initiation of subduction related accretion of the nappes by orogen normal southwest northeast shortening and accretionary tectonics the subsequent d2 fabrics developed as temporally overlapping subduction related low angle thrusts in the rosario fault zone and high angle sinistral strike slip faults in the lopez fault zone in an overall transpressive setting due to oblique convergence this model suggests that the high angle lopez fault zone d2 was located above a gently northeast dipping thrust detachment s2 expressed by the rosario fault zone that allowed the accreted nappes to move parallel to the orogen the kinematic model cannot validate regional scale dextral terrane translation of the san juan thrust system as inferred by paleomagnetic data elsewhere in the western united states but addresses important tectonic processes caused by oblique subduction and changing plate conditions

stratigraphy age and paleogeography of the eocene chuckanut formation northwest washington the eocene chuckanut formation of washington s north cascades comprises as much as 6000 m of alluvial strata and is one of the thickest nonmarine sequences in north america it is exposed in several disconnected outcrop belts that are remnants of what was probably an extensive fluvial system in western washington in this study seven stratigraphic members are defined in the main outcrop belt of the chuckanut formation near the town of bellingham their ages based on fission track zircon dates palynologic studies and correlation by mapping extend from the early to the late eocene three types of fluvial systems contributed to the chuckanut formation and are distinguished on the basis of their lithology sedimentology and petrology the first comprises fine load meandering river deposits of the lower eocene bellingham bay member and the middle eocene slide member sandstones are arkosic and had their main source in rapidly uplifted high grade metamorphic terranes in eastern washington the second type

tectonic history of northern alaska canadian arctic and spitsbergen regions since early cretaceous the correlation of interregional unconformities structures and magmatic activity suggests tectonic events in the arctic were controlled by the early cretaceous collision and combined interaction of the eurasian and north american plates in northeastern ussr the late mesozoic cenozoic accretion of exotic terranes in the north pacific and north atlantic arctic sea floor spreading contemporaneous with the accretion of exotic terranes in northeastern ussr and interior alaska the brooks range developed as a cordilleran mountain belt at the same time during the cretaceous between 125 and 85 ma the canada basin spread north of alaska about a pole of rotation located southeast of the mackenzie delta the alaskan plate was first a part of the northwestern nose of the north american plate when the canada basin spreading ceased the basin was severed by movement along the kaltag and associated strike slip faults and became a part of the northeasterly moving eurasian plate the kaltag fault system is inferred to extend from the western bering sea at the northern end of the kuril arc through alaska and along the outer margin of the arctic islands to the north of greenland it is postulated to have formed the transform boundary between the north american and eurasian plates with the alaskan plate bonded to the latter since the late cretaceous the late eocene change in the direction of pacific spreading terminated the subduction related laramide orogeny as well as the right lateral displacements of major cordilleran faults such as the tintina and denali faults changing eurasian plate movement may have caused most of the strong middle eocene right lateral displacement along the kaltag fault zone continuing displacement from the southwest caused the development of a late cenozoic foldbelt in coastal northeastern alaska herein named the romanzof disturbance coeval with balancing right lateral movement along the kaltag fault zone the huge undrilled marsh creek anticline is a part of this foldbelt seismic data show evidence of middle eocene compression followed by weak extension east of the kaltag fault zone in the beaufort sea the same activity is evident at the northeastern end of the north american plate at nares strait located between the arctic islands and greenland eocene fault movement along the kaltag nares strait and de geer separating greenland and spitsbergen transforms is regarded as complementary the presence of eocene thrust zones located on the western side of nares strait and in western spitsbergen suggests that northward movement of the greenland plate formed both the transforms and the thrust belts

geochemical and isotopic composition of groundwater in the complex terminal aquifer in southwestern tunisia with emphasis on the mixing by vertical leakage the complex terminal ct confined aquifer of the djerid basin southwestern tunisia was studied using major ion concentrations and stable isotope contents in order to 1 investigate the changes on its hydrodynamic functioning due to the long term over pumping and the large scale flood irrigation practices 2 determine the principal mineralization processes of its fossil groundwater and 3 examine the mode of recharge of this aquifer and whether it contains part of modern hydrological regime the observed geochemical patterns indicated that the main mineralization processes affecting the ct groundwater water rock interactions and mixing the native na cl and cl so4 ca na waters resulting from the dissolution of halite and gypsum and from pyrite oxidation interacted with those of the underlying and the overlying aquifers without changing their chemical facies stable isotope data provided evidences about upward and downward leakage into the ct aquifer and their relationships with anthropogenic activities they demonstrated that the long term over pumping of the ct aquifer which contributed to the loss of its potentiometric pressure favored the upward leakage of the artesian deep groundwater along parts of the major faults moreover the large scale flood irrigation practices in the oases domain which ensured the recharge of the shallow water table by return flow enhanced the downward leakage toward the ct aquifer

water geochemistry controlled by carbonate dissolution a study of the river waters draining karst dominated terrain guizhou province china concentrations of major ions and sr and sr isotopic compositions of two major river systems wujiang river and yuanjiang river in karst dominated regions and during winter were measured the rivers and their tributaries have high total dissolved solid concentrations with tz ranging from 2 1 to 6 3 meq l which are significantly higher than that of the global river average calcium and hco3 followed by mg2 and so42 dominate the chemical composition of major ions in the river waters both na k and cl si account for 5 10 of the cations and anions respectively the waters of the wujiang river have high sr2 concentrations and lower 87sr 86sr ratios 0 7077 0 7110 while those of the qingshuijiang river one of two major tributaries of the yuanjiang river system show higher sr isotopic ratios 0 7090 0 7145 and low sr concentrations the lithology and geography of the river basins largely control the chemical and isotopic compositions of these rivers analyses of the stoichiometry of the river waters show that the water chemistry is controlled by carbonate dissolution by both carbonic and sulfuric acid especially of the wujiang river and suggest an origin of sulfate mainly from atmospheric input because of coal combustion and or oxidation of sulfide minerals in the catchments we identify three main weathering sources limestone dolomite and silicates chemical and sr isotopic composition of wujiang river waters are characterized mainly by limestone weathering while those of the qingshuijiang river waters mainly by dolomite and silicate weathering chemical weathering rates of carbonate and silicate are estimated and the results indicate that the chemical weathering rates of carbonate in the catchments are remarkably high significantly higher than most large rivers it is considered that presence of sulfuric acid in the rock weathering overuse of land and deterioration of vegetation are most likely the key factors responsible for the high weathering rates of carbonate in the catchments

polygenetic topography of the cascade range washington state usa we evaluate models for the cenozoic topographic evolution of the cascade range of washington state by analyzing the topography geology and exhumation patterns across the range the models for topographic evolution include 1 post miocene surface uplift of the range from initially low relief topography 2 post miocene surface uplift of the range superimposed on pre existing high relief topography and 3 post miocene surface uplift of high relief cascades in northern washington and low relief cascades in southern washington the third model a polygenetic topographic history is most consistent with our analysis of topographic data and the previously contradictory geologic paleontologic and isotopic lines of evidence regarding the cascades physiographic history between snoqualmie pass and the columbia river the east derived 15 my old columbia river basalt crb reaches nearly as far west as the modern drainage divide and is warped upward to the crest of the range these observations require subdued relief on the east flank of the southern cascades during the late miocene in the northern cascades the crb does not extend into the range and crb deformation only reflects 30 to 60 percent of the total relief thus the northern cascades were likely already a topographic barrier to the west flowing flood basalts moreover a polygenetic topographic history appears most consistent with the geologic data and the paleontologic and isotopic evidence for rainshadow formation during the middle miocene despite differences in topographic history and rock type the maximum and mean altitudes of the cascade range decrease smoothly from northern to southern washington we suggest that post uplift erosion particularly glacial erosion has reduced the topographic distinctions between the northern and southern cascades resulting in a single mountain range with a polygenetic topographic history

lithostratigraphy and deep water setting of the upper nanaimo group upper cretaceous outer gulf islands of southwestern british columbia the upper cretaceous nanaimo group consists of extensive shaly units and lenticular bodies of sandstone and conglomerate deposited in neritic to bathyal marine paleoenvironments single sandstone and conglomerate lenses cannot be traced throughout the basin but instead tend to concentrate at particular stratigraphic levels defining crudely sheet like composite units of coarse grained rocks many of the lenticular coarse grained units rest in major channels as deep as about 550 m sand and gravel were generally transported to the west and northwest by sediment gravity flows through these channels into the basin centre recognition of widespread channeling is critical to the definition of formal lithostratigraphic units four formations and two informal members are defined here for the upper nanaimo group the top of the nanaimo group is probably truncated by a major unconformity with local relief of at least 2 km the effect of the unconformity can only be seen by mapping the orientation of offshore rid

cenozoic thermal evolution and tectonics of the coast mountains of british columbia 1 fission track dating apparent uplift rates and patterns of uplift the high relief of the coast mountains of british columbia has been produced in part by rapid late neogene uplift the relationship of this uplift to the presently diverse and complex plate tectonic regime off the west coast of british columbia however is not clear cut to study this problem the areal patterns rates and total amounts of cenozoic uplift from 50 to 55 n have been determined by using fission track dating of zircon and apatite separated from rocks collected at high and low altitudes along several traverses through the mountains accepting closure temperatures of 105 c 10 c and 175 c 20 c for apatite and zircon respectively and a likely closure temperature difference between zircon and apatite of 70 15 c paleogeothermal gradients have been measured at kemano c km 35 ma ago and near ocean falls king island c km 20 ma ago subcrustal heat flow is suggested to have significantly increased in the late neogene near king island uplift rates in the axial part of the northern 52 55 n coast mountains were 0 1 0 2 km ma from 25 to 15 ma ago this uplift was temporally and tectonically related to part of the subsidence in the adjacent queen charlotte basin uplift rates increased somewhat in the late miocene to about 0 4 km ma probably due to passage of the anahim hot spot beneath the area late miocene recent erosion in the north 52 55 n has reduced summit altitudes and been more extensive than farther south despite this relicts of miocene river valleys and topography are still locally preserved partly beneath 7 10 ma basalts the area of the present southern 50 to 52 n coast mountains was near sea level and experienced very low uplift rates 0 5 km ma of the southern coast mountains the profile of this uplift was broadly plateaulike and this uplift led to the inversion of the miocene coastal topography middle cenozoic uplift from 52 to 55 n was probably the result of denudation and diminishing uplift after the terminal paleocene eocene orogenic episode which grossly thickened the crust this middle cenozoic erosion resulted in the restoration of a normal crustal thickness late neogene uplift in the coast mountains was the result of thermal expansion in the mantle caused by a mantle hot spot near 53 n and changes in the geometry of the subducted slab farther south

integration of macrofossil biostratigraphy and magnetostratigraphy for the pacific coast upper cretaceous campanian maastrichtian of north america and implications for correlation with the western interior and tethys new biostratigraphic data obtained from measured stratigraphic sections of santonian through maastrichtian age located along the west coast of north america necessitate changes to the currently accepted chronostratigraphic framework for this region of the north pacific biotic province we recognize and or define 12 molluscan zones over this interval of the upper cretaceous and propose revisions to the currently accepted integration of ammonite zones with global upper cretaceous magnetochrons our findings demonstrate that there was significantly more faunal interchange between the north american pacific coast and both the western interior and gulf coast regions of north america during the late cretaceous than has previously been recognized and because of this novel and direct biostratigraphic correlations can be made these new faunal correlations are augmented with the magnetostratigraphic record from pacific coast localities to arrive at better interregional correlation for the upper cretaceous globally the new integration of the global polarity time scale with the local west coast ammonite zonation now allows better correlation between sections both within the north pacific province but geographically far from our study areas as well as to sections outside of the province itself however we note here that previous correlations between biostratigraphy and the top and bottom of magnetochron 33r in west coast north american sections appear to have been in error due to unrecognized modern day normal field overprint of originally reversed polarity in upper cretaceous sections we reinterpret the position of this chron based on this new information

apatite fission track dating of the cowichan fold and thrust system southern vancouver island british columbia the cowichan fold and thrust system on southern vancouver island comprises a linked system of folds and thrust faults in crystalline and sedimentary rocks of the wrangellia terrane and its sedimentary cover the upper cretaceous nanaimo group and upper paleocene to lower eocene sandstones of the chuckanut formation apatite fission track analysis indicates that cooling below the closure temperature of fission track retention in apatite 100 20 c for both the island plutonic suite from the wrangellian basement and the nanaimo group occurred at 50 40 ma middle eocene thrusting is interpreted to have occurred immediately prior to this time in the middle eocene but after post cretaceous regional burial of the turonian to maastrichtian nanaimo group and deposition of upper paleocene and lower eocene sandstones which are involved in the deformation these timing constraints support the hypothesized temporal linkage between contraction and uplift of wrangellia during the middle eocene and continued margin normal contraction of the pacific rim terrane the crescent terrane at 45 ma

mesozoic evolution of exotic terranes and marginal seas western north america abstract regional terrane analysis has been combined with a global evaluation of plate kinematics to produce a new tectonic model for the mesozoic evolution of western north america and its associated marginal seas the model employs a two tiered data reliability ranking system to resolve conflicts within data sets the lower tier of the ranking system involves the assignment of a numerical rank to paleomagnetic and or paleobiogeographic data based on each data set s reliability the upper tier of the ranking system places the paleomagnetic and paleobiogeographic data in perspective by assigning a relative order of importance to different types of data the most reliable data are considered to be departure rift and arrival collision times that are tightly constrained by independent data sets evidence of subduction and or strike slip motion also ranks high in the master ranking system paleomagnetic and vertebrate paleobiogeographic data come next in the hierarchy followed by invertebrate and floral paleobiogeographic data application of this approach to a case study the baja british columbia controversy has resulted in a coherent model for the entire region results derived from the application of this modelling approach to the problem of the mesozoic assembly of western north america suggest that its evolution may be modeled using a minimum of 57 large terranes oblique convergence may have been the dominant tectonic process along the western north american margin during the mesozoic causing large scale latitudinal transport of many exotic terranes the motions of the terranes produced a number of marginal seas yukonia etc that were short lived but important components of western margin tectonics a combination of collision events side swiping episodes and changes in plate kinematics led to the initiation of several regional tectonic upheavals including the nevadan and sevier orogenies

ages and stratigraphy of lower and middle tertiary sedimentary and volcanic rocks of the central cascades washington application to the tectonic history of the straight creek fault in the central cascade range of washington three structural blocks of early tertiary sedimentary and volcanic rocks help to define the position and history of the southern segment of the straight creek fault east of the fault in the teanaway river block the early eocene fluviatile feld spathic sandstone of the swauk formation is interbedded with largely dacitic volcanic rocks of the silver pass volcanic member zircon fission track ages on the silver pass are about 52 m y overlying the tightly folded swauk and silver pass is the teanaway formation a gently dipping accumulation of basalt andesite rare dacite and rhyolite that yields middle eocene about 47 m y whole rock k ar ages conformably overlying the teanaway is the roslyn formation a coal bearing fluviatile feld spathic sandstone of probable middle to late eocene age the late eocene and oligocene naches formation exposed west of the straight creek fault in the cabin creek block is rich in fluviatile feldspathic sandstone and rhyolite flows and tuffs in its lower part but grades upward into a sequence dominated by basalt but with some andesite the basal guye sedimentary member of the naches formation underlies and is interbedded with the mount catherine rhyolite member in the snoqualmie pass area on the basis of zircon fission track ages on silicic tuffs and whole rock k ar ages on basalt the basal part of the naches is about 40 to 44 m y old the formation is tightly folded and complexly faulted along the straight creek fault the straight creek fault intersects the olympic wallowa lineament in the strongly deformed manastash river block in this block fluviatile coal bearing feldspathic sandstone of the manastash formation is overlain by principally dacitic volcanic rocks of the taneum formation overlying the taneum is the basalt of frost mountain we correlate this threefold sequence feldspathic sandstone dacite basalt with the sequence in the teanaway river block small patches of rhyolitic ash flow tuff dated at 33 m y late oligocene and interbedded feldspathic sandstone overlie the roslyn and teanaway formations in the teanaway river block and are probably correlative with the late oligocene wenatchee formation exposed in the chiwaukum graben east of the teanaway river block as well as with the late oligocene volcanic rocks 30 m y along the cascade crest to the southwest these latter rocks are little deformed and unconformably overlie the naches formation the ages and depositional record in the three blocks indicate a tertiary history of dominantly vertical movement along the straight creek fault and its southeasterly splays that merge with the olympic wallowa lineament the horst and graben structure of the blocks as well as enechelon fold axes in the swauk formation suggests some post early eocene right lateral shear along the fault although there is no direct evidence of lateral offset vertical movement significant since early eocene swauk deposition followed late eocene naches deposition but tapered off by late oligocene time and ceased by miocene time when the fault was intruded by the 25 m y old snoqualmie batholith and other plutons however structures with olympic wallowa lineament trends appear to have influenced folding of the miocene yakima basalt subgroup

extension in south central british columbia mechanical and thermal controls abstract geological data indicate that the omineca belt in the canadian cordillera experienced a rapid episode of extension between 58 and 48 ma following a compressional event and crustal thickening in the early tertiary restored crustal sections have been constructed using listric fault geometries to infer that the amount of eocene extension affecting the southern omineca belt exceeded 50 at the end of compression in the early tertiary the omineca and intermontane belts of southern british columbia reached a crustal thickness of 60 km isostatic compensation implies that these belts formed elevated ranges this is consistent with sediment deposition west of these ranges and the absence of in situ sedimentary basins the stress induced by topography and crustal thickening is calculated the calculations show that the stress in homogeneously thickened lithosphere is small and that tensile stress in the crust is compensated by compression in the mantle removal of the mantle lithosphere induces a stress field that is tensile throughout the lithosphere this local stress field combined with stress induced at the plate boundary by the oblique impingement of the kula farallon ridge controlled the position and direction of crustal extension in south central british columbia the present high heat flow on the west flank of the omineca belt 80 mw m 2 is interpreted as the relict of eocene extension following removal of the lithospheric mantle

chemical characteristics of groundwater in parts of mountainous region alvand hamadan iran eighty seven groundwater samples have been collected from a mountainous region alvand iran for hydrochemical investigations to understand the sources of dissolved ions and assess the chemical quality of the groundwater most water quality parameters are within world health organization acceptable limits set for drinking water the least mineralized water is found closest to the main recharge zones and the salinity of water increased towards the north of the basin the most prevalent water type is ca hco3 followed by water types ca no3 ca cl ca so4 and mg hco3 the ca no3 water type is associated with high nitrate pollution agricultural and industrial activities were associated with elevated level of no3 mineral dissolution weathering of evaporites dominates the major element hydrochemistry of the area chemical properties of groundwater in alvand region are controlled both by natural geochemical processes and anthropogenic activities

geochemical evolution of groundwater on saturna island british columbia a detailed geochemical study of surface waters spring waters and groundwaters was undertaken to examine the geochemical evolution of groundwater on saturna island british columbia the purpose of the study was to characterize the nature and occurrence of saline waters and to provide insight on chemical processes that lead to salinization in the fractured sedimentary bedrock aquifers of this small island major ion chemistry shows that groundwater is recharged locally but mixes with saline waters that occur at depth or near the coast simple mixing is complicated by cation exchange between calcium rich waters and sodium rich exchange sites offered by mudstone beds and results in a spatially variable hydrochemical composition that is dependent on the island topography and geological framework structural sedimentological and glacial in combination with groundwater use patterns sodium present at exchange sites is speculated to be a remnant of ocean water intrusion during the pleistocene when the

the skipjack island fault zone an active transcurrent structure within the upper plate of the cascadia subduction complex abstract the skipjack island fault zone has been mapped in the san juan islands between vancouver island canada and the washington state mainland usa a decade ago interpretation of multibeam sonar seafloor imagery revealed that skipjack island an east west striking sedimentary bedrock outcrop was a fault controlled structural feature a major fault separates skipjack island from a deformed sedimentary bedrock outcrop on the seafloor to the north recently the skipjack island fault zone s morphology and extent have been explored both to the west and east of the island using multibeam echosounder bathymetry seismic reflection profiles and sediment cores the character of the skipjack island fault zone is well defined locally by the interpreted seismic reflection profiles which show active faults that displace sediments deposited since the last glacial maximum the central part of the fault zone near skipjack island appears as a near vertical structure in the shallow subsurface that has been subjected to left lateral motion as evidenced by a bedrock exposure on the seabed north of the island where folded strata bend eastward against the fault the result of drag from fault motion interpretations of recent geophysical data suggest an extension of the skipjack island fault zone farther to the west where it trends towards and possibly connects with the fulford fault on vancouver island and to the east where it either terminates north of lummi island or continues eastward onto the mainland the skipjack island fault zone is interpreted to be the northern boundary of the san juan archipelago with the devils mountain fault zone being the southern boundary both fault zones represent the longest continuous faults of the san juan archipelago this newly mapped fault zone and its zone of deformation to the north may represent the northern boundary of the cascadia forearc potential sesimicity of the skipjack island fault zone and its proximity to the steep unstable northeastern side of orcas island and the southern front of the fraser river delta poses a geohazads problem in the form of earthquakes landslides submarine slides and tsunamis

petrologic evolution and paleogeography of the late cretaceous nanaimo basin washington and british columbia implications for cretaceous tectonics systematic variations in sandstone petrofacies of the upper cretaceous nanaimo group are related to basin evolution and uplift of surrounding tectonic provinces a subaerially exposed horst partially separated southern and northeastern portions of the nanaimo basin volcaniclastic and arkosic sediment was derived from this horst the horst subsided below wave base during very early evolution of the nanaimo basin but it controlled sediment dispersal throughout basin development lower units of the nanaimo group in the southern nanaimo basin are chert rich and were derived largely from terranes of the san juan islands and north cascades basaltic and plutonic debris from the insular belt was deposited into the northwestern nanaimo basin during early basin development minor deposition of arkosic debris from the coastal plutonic belt also occurred upper units of the nanaimo group contain abundant plagioclase rich sediment derived from the coastal plutonic belt rocks along the southeastern margin of the basin however reflect continued sedimentation from terranes of the san juan islands and north cascades arkosic and dacitic debris from insular belt sources is recognized in the northwestern nanaimo basin the nanaimo basin may have developed as a pull apart basin within a broad zone of normal and transcurrent faulting in response to oblique convergence or transform faulting between the kula plate and the pacific margin of washington and british columbia

evaluation of paleoclimatic conditions east and west of the southern canadian cordillera in the mid late paleocene using bulk organic δ13c records abstract carbon isotope records from organic matter provide a key data set for constraining past fluctuations in the isotopic composition of atmospheric carbon dioxide 13catm hydrologic conditions and plant community composition here we evaluate spatiotemporal shifts in these three conditions using 13c values of bulk organic carbon 13cbulk from paleocene strata in northwest washington u s a and west central alberta canada our data set contains 352 analyses from the chuckanut and paskapoo formations mean 13cbulk values in the two areas are statistically indistinguishable 24 5 and 24 4 vpdb respectively and exhibit a wide range of values 5 7 in both areas sequential vertical samples show large fluctuations in 13cbulk values on average of 1 0 1 0 1 there are no distinct up section trends or structured excursions in the 850 meter stratigraphic section in the chuckanut formation nor the 125 meter section in the paskapoo formation furthermore 13cbulk values are independent of the weight percent organic carbon c and lithology of the sample the lack of a systematic relationship and correlation between 13cbulk and c values indicates isotopic fractionation during post mortem processes such as microbial respiration exerted minimal influence on the isotopic patterns the independence of 13cbulk values from lithology suggests variability is unrelated to local spatial gradients in vegetation community and water availability across the paleo landscape however the wide range and large fluctuations in 13cbulk values is similar to stochastic intra site variability of plant 13c values within modern settings the absence of structured up section trends indicates minimal secular variation in the carbon isotopic composition of atmospheric co2 rainfall and plant community composition moreover we show that a previous carbon isotope excursion ascribed to the paleocene eocene thermal maximum in the paskapoo formation is actually a result of aliasing related to sampling density finally the statistically indistinguishable mean 13cbulk values in the two regions imply similarly wet and humid climatic conditions when combined with sedimentologic and paleobotanical data the records support early paleogene circulation models that show strong orographic precipitation patterns in the pacific northwest associated with incipient extensional tectonics in the region and enhanced transport of moisture laden polar air masses southward into the canadian continental interior

geomorphology of a cordilleran ice sheet drainage network through breached divides in the north cascades mountains of washington and british columbia the skagit river valley in northern washington and southern british columbia contains long interconnected valleys barbed tributaries underfit streams and low elevation mid valley divides quantitative measures of connectivity between valleys draining through breached mountain divides aerial photographs and a field verified process form model were used to assess the impact of continental glaciation on the drainage pattern and geomorphology of the watershed structural control on drainage patterns and intense repeated continental glaciation rendered the skagit an extremely interconnected valley with meltwater routes opening it to the fraser and okanagan watersheds divide elimination by drainage of large proglacial lakes led to several hundred meters of erosion at 10 breached divides other geomorphic effects of recurrent continental glaciation include the bisection of a major mountain valley divide migration of as much as 50 km erosion of canyons 15 30 km downstream of breached divides and deposition of exceptionally large alluvial fans at canyon mouths drainage patterns established in the tertiary were reorganized to accommodate southern drainage of glacial meltwater trapped in mountain valleys at the southern margin of the cordilleran ice sheet the skagit basin is now a regional focus for drainage to puget sound from the northernmost north cascades and parts of southern interior british columbia the key to establishing this system was the elimination of a regional divide in what is now skagit gorge which resulted in the capture of the upper skagit valley by the lower skagit river patterns of drainage modification caused by continental glaciation in the skagit basin are similar to those in other mountain areas the skagit s interconnected valleys are similar to the great through valleys of scotland transmountain valleys of british columbia and ice portals of scandinavia

a conceptual model for the preservation of thick transgressive shoreline successions examples from the forearc nanaimo basin british columbia canada abstract sequence stratigraphic models derived from passive margins and foreland basins characterize transgressive shorelines excluding incised valleys as recording periods of sediment starvation and are commonly represented as thin 10 m are more likely to be developed in active tectonic settings e g forearc and rift basins which generally experience high sedimentation rates and relatively rapid changes in base level settings with high sedimentation rates and moderate base level rise lead to progradational trends despite overall transgression of the shoreline in settings where changes in eustatic sea level mainly control the resulting stratigraphic architecture e g passive margins thin transgressive successions 1 10 m are more likely to be produced finally in settings defined by relatively slow base level change e g foreland basins the resultant transgressive succession typically comprises a lag 1 m overlain by offshore mudstones this conceptual model highlights the importance of the interplay between sedimentation rates and base level rise and is intended as a guide for the predictive modeling of sedimentary basins

thermal history of rocks in southern san joaquin valley california evidence from fission track analysis the theory of the fission track method and its application to sedimentary basin analysis is illustrated by a case study in the southern san joaquin valley california fission tracks provide a powerful tool for studying the thermal history of sedimentary basins because the two minerals most commonly used in fission track studies apatite and zircon occur as detrital constituents in many sedimentary rocks and their annealing temperatures span the main temperature range for oil generation fission tracks also provide information on the sedimentation record and provenance of rocks in a basin we have used fission track analysis to study the thermal and depositional history of the subsurface tertiary sedimentary rocks on both sides of the active white wolf reverse fault in the southern san joaquin valley the distinctly different thermal histories of the rocks in the two structural blocks are clearly reflected in the apatite fission track data which suggest that rocks in the rapidly subsiding basin northwest of the fault have been near their present temperature for only about 1 m y compared with about 10 m y for rocks southeast of the fault these estimates of heating time agree with previous estimates for these rocks zircon fission track data indicate that the tertiary sediments were derived from parent rocks of more than one age however from at least the eocene to late miocene or pliocene the major sediment source was rocks related to the youngest sierra nevada mesozoic intrusive complexes which are presently exposed east and south of the southern san joaquin valley

high resolution temporal and stratigraphic record of siletzia s accretion and triple junction migration from nonmarine sedimentary basins in central and western washington the presence of early eocene near trench magmatism in western washington and southern british columbia has led to speculation that this area experienced ridge trench interaction during that time however the effects of this process as they are preserved in other parts of the geologic record are poorly known we present high precision u pb zircon geochronology from paleogene nonmarine sedimentary and volcanic sequences in central and western washington that preserve a record of tectonic events between ca 60 and 45 ma the data reveal that the swauk chuckanut and manastash formations formed a nonmarine sedimentary basin along the north american margin between 59 9 and 51 3 ma this basin experienced significant disruption that culminated in basinwide deformation uplift and partial erosion during accretion of the siletzia terrane between 51 3 and 49 9 ma immediately following accretion dextral strike slip faulting began or accelerated on the darrington devil s mountain entiat leavenworth eagle creek and straight creek fraser fault zones between 50 and 46 ma during this time the chumstick formation was deposited in a strike slip basin coeval with near trench magmatism faulting continued on the entiat eagle creek and leavenworth faults until a regional sedimentary basin was reestablished 45 9 ma and may have continued on the straight creek fraser fault until 35 30 ma this record of basin disruption volcanism and strike slip faulting is consistent with ridge trench interaction and supports the presence of an oceanic spreading ridge at this latitude along the north american margin during the early eocene

remagnetization during cretaceous normal superchron in eastern san juan islands wa implications for tectonic history abstract the eastern san juan islands expose an island arc ophiolite sequence and one or more ocean floor terranes cover rocks of the former including red radiolarian tuff and arc derived sandstone have no penetrative fabric and lack high pressure minerals in contrast pillow basalts and ribbon cherts of the latter are strongly deformed and the overlying metagraywacke is folded with a penetrative axial plane cleavage all ocean floor rocks have aragonite in veins indicative of higher pressure conditions than experienced by the island arc rocks a downward magnetization is common to the ocean floor rocks consistent with widespread remagnetization during the cretaceous normal superchron this magnetization is carried by magnetite and in red rocks by hematite fluid flow during or after deformation and high p metamorphism likely facilitated remagnetization at low temperature the magnetic directions are somewhat scattered but most are moderately to steeply down to the southeast they are far from directions expected with or without northward transport of baja bc rotation of observed directions into agreement with those expected for either present or more southerly locations also rotate structural elements in the host rocks three alternative rotation histories explored here all produce structural reconstructions that differ considerably from the present structure a tectonic history of the eastern san juan islands based on any of these reconstructions would be superior to one based on present attitudes of structures this is because at least a constraint that the restored paleomagnetic directions match a paleomagnetic field direction is satisfied choices among alternative reconstructions would become clearer with better understanding of relative ages of specific structures and their magnetizations improved geologic understanding of the regional setting where the rocks could have been deformed and remagnetized would also help

north american nonmarine climates and vegetation during the late cretaceous abstract analyses of physiognomy of late cretaceous leaf assemblages and of structural adaptations of late cretaceous dicotyledonous woods indicate that megathermal vegetation was an open canopy broad leaved evergreen woodland that existed under low to moderate amounts of rainfall evenly distributed through the year with a moderate increase at about 40 45 n many dicotyledons were probably large massive trees but the tallest trees were evergreen conifers megathermal climate extended up to paleolatitude 45 50 n mesothermal vegetation was at least partially an open broad leaved evergreen woodland perhaps a mosaic of woodland and forest but the evapotranspirational stress was less than in megathermal climate some dicotyledons were large trees but most were shrubs or small trees evergreen conifers were the major tree element some mild seasonality is evidenced in mesothermal woods precipitational levels probably varied markedly from year to year northward of approximately paleolatitude 65 n evergreen vegetation was replaced by predominantly deciduous vegetation this replacement is presumably related primarily to seasonality of light the southern part of the deciduous vegetation probably existed under mesothermal climate comparisons to leaf and wood assemblages from other continents are generally consistent with the vegetational climatic patterns suggested from north american data limited data from equatorial regions suggest low rainfall late cretaceous climates except probably those of the cenomanian had only moderate change through time temperatures generally appear to have warmed into the santonian cooled slightly into the campanian and more markedly into the maastrichtian and then returned to santonian values by the late maastrichtian the early eocene was probably warmer than any period of the late cretaceous latitudinal temperature gradients were lower than at present for the campanian and maastrichtian a gradient of about 0 3 c 1 latitude is inferred equability was high a mean annual range of temperature of about 8 c is inferred for paleolatitude 51 56 n during the campanian most late cretaceous plants evolved in a climate characterized by absence of freezing and low to moderate amounts of precipitation a brief low temperature excursion and a major long lasting increase in precipitation occurred at the cretaceous tertiary boundary in megathermal climates these events selected for plants that could exist in rainforest environments in mesothermal climates deciduousness and contamitant structural adaptations were selected the events at the cretaceous tertiary boundary had a major and long lasting impact on the evolution of land plants and their ecosystems low precipitation at low to middle late cretaceous latitudes is suggested to be the result of high levels of atmospheric co2 which in turn are probably related to inability of warm saline oceans to store large amounts of carbon conditions appear to have rapidly changed at the cretaceous tertiary boundary when oceanic circulation and stratification may have been fundamentally altered after the boundary the oceans were apparently able to store much greater amounts of carbon and the oceans withdrew large amounts of co2 from the atmosphere in turn more precipitation fell at low to middle latitudes the resulting high biomass vegetation formed a second major carbon reservoir to keep atmospheric co2 low relative to the late cretaceous changes in oceanic and atmospheric circulation probably resulted from some factor external to the ocean atmosphere system

geochemical and quality assessment of groundwater of marand basin east azarbaijan province northwestern iran the chemical analysis of 83 water wells in the marand area azarbaijan province nw of iran was evaluated to determine the hydrogeochemical processes and ion concentration background in the region over the entire area the dominated hydrochemical types are ca mg so4 cl ca so4 na cl and ca mg hco3 based on the total hardness the softness of the groundwater is determined according to electrical conductivity ec and sodium adsorption ratio sar the most dominant classes are c3 s1 c3 s2 c4 s2 and c2 s1 the major ion concentrations are below the acceptable level for drinking water the groundwater salinity hazard is medium to high but the na hazard is low to medium with regard to irrigation water the quality is low to medium so a drainage system is necessary to avoid the increase of toxic salt concentrations

aspects of vertical drain design darcian or non darcian flow the classical consolidation equations developed by barron in 1944 and 1948 are well known among engineers working on soil improvement by preloading in combination with installation of vertical drains these equations have been gradually refined and are generally utilized in conventional design the design may seem simple in theory but is connected with a great number of uncertainties from a practical point of view the problems connected with the choice of consolidation parameters will be commented on and practical advice for the design will be given in this paper a number of case records will be presented and compared with on one hand the conventional method of design and on the other hand the so called method developed by the author in 1960 to take into account the effect of smear the method is based on an exponential correlation between hydraulic gradient and flow velocity we find that the correlation between the conventional theory and practice based on back analysis of field data is les

geochemistry characterization of groundwater in an agricultural area of razan hamadan iran this study was conducted to evaluate factors regulating groundwater quality in an area with agriculture as main use thirty groundwater samples have been collected from razan area hamadan iran for hydrochemical investigations to understand the sources of dissolved ions and assess the chemical quality of the groundwater the chemical compositions of the groundwater are dominated by na ca2 hco3 cl and so42 which have been derived largely from natural chemical weathering of carbonate gypsum and anthropogenic activities of fertilizer s source the production of so42 has multiple origins mainly from dissolution of sulphate minerals oxidation of sulphide minerals and anthropogenic sources the major anthropogenic components in the groundwater include na cl so42 and no3 with cl and no3 being the main contributors to groundwater pollution in razan area

reply to comment on depositional history of the eocene chumstick formation implications of tectonic partitioning for the history of the leavenworth and entiat eagle creek fault systems washington

identification and evolution of hydrogeochemical processes in the groundwater environment in an area of the palar and cheyyar river basins southern india the palar and cheyyar river basins in tamil nadu state of southern india are characterised by different geological formations and groundwater is the major source for domestic agricultural and other water related activities hydrogeochemical studies were carried out in this area with the objective of identifying the geochemical processes and their relation to groundwater quality groundwater samples were collected once a month from 43 groundwater wells in this area from january 1998 to july 1999 sampling procedures and chemical analysis were carried out as per the standard methods chemical data are used for mathematical calculations and graphical plots to understand the chemical process and its relation to the groundwater quality the chemical composition of groundwater in the central part of the study area mainly depends on the recharge from lakes and the river which is explained by a mixing mechanism in addition weathering of silicate minerals controls the concentration of major ions such as sodium calcium magnesium and potassium in the groundwater of this area further the activity ratios indicate that the groundwater is in equilibrium with kaolinite smectite and montmorrillonite the reverse ion exchange process controls the concentration of calcium magnesium and sodium in hard rock formations and dissolution of carbonate minerals and accessory minerals is the source of ca and mg in addition to cation exchange in the sedimentary formations in general the chemical composition of the groundwater in this area is influenced by rock water interaction dissolution and deposition of carbonate and silicate minerals ion exchange and surface water interactions

back calculation of consolidation parameters from field measurements at a reclamation site a pilot test was carried out at a land reclamation project site to study the effect of vertical drains on the rate of consolidation of a marine clay deposit in singapore theoretical and numerical analyses were conducted to interpret the field measurements of pore pressure and settlement and consolidation parameters were back calculated the back calculated preconsolidation pressure is similar to that obtained from the laboratory consolidation test on undisturbed samples but the field deduced compression index is generally larger than that measured in the laboratory the coefficient of consolidation back calculated from the settlement measurement is larger than that from the pore pressure measurement the coefficient of consolidation for horizontal flow obtained from the rowe cell test which is comparable to that back calculated from the field settlement measurement is recommended for the preliminary design of vertical drains without the need of considering the smear effect key words clays consolida

basin architecture and density structure beneath the strait of georgia british columbia georgia basin is located within one of the most seismically active and populated areas on canada s west coast over the last decade geological investigations have resolved important details concerning the basin s shallow structure and composition yet until recently relatively little was known about deeper portions of the basin in this study new seismic velocity information is employed to develop a 3 dimensional density model of the basin comparison of the calculated gravity response of this model with the observed gravity field validates the velocity model at large scales at smaller scales several differences between model and observed gravity fields are recognized analysis of these differences and correlation with independent geoscience data provide new insights into the structure and composition of the basin fill and underlying basement specifically four regions with thick accumulations of unconsolidated pleistocene and younger sediments which were not resolved in the velocity model are id

contribution of ductile flow to exhumation of low temperature high pressure metamorphic rocks san juan cascade nappes nw washington state the san juan cascade sjc nappes were subducted to a depth of 18 km metamorphosed under low temperature high pressure conditions and then exhumed all within 16 m y during exhumation penetrative deformation by solution mass transfer smt resulted in a widespread spaced cleavage strain directions were determined for 27 sandstone samples and absolute strain measurements for a subset of 19 samples z directions generally plunge moderately to the ne and x and y directions are scattered in the plane perpendicular to z smt deformation is constrictional at the local scale but the tensor average indicates plane strain uniaxial shortening at the regional scale with sx sy and sz equaling 1 01 0 91 and 0 58 respectively the average flattening plane xy dips 30 to the ne and the average x direction plunges 20 to the north the large shortening in z was compensated by a mass loss volume strain of 47 we present a simple one dimensional model that illustrates the relationship between finite strain and ductile exhumation for a steady state convergent wedge assuming depth dependent ductile flow and no reversal of principal strain rates with depth this model indicates that ductile thinning of the sjc nappes accomplished only 13 of the total exhumation despite a vertical shortening strain of 36 there is no evidence that normal faulting contributed significantly to exhumation we conclude that erosion operating at an average rate of 1 1 km m y 1 was the dominant exhumation process

revised ages of blueschist metamorphism and the youngest pre thrusting rocks in the san juan islands washington new ages of rocks in the san juan islands northwest washington significantly change our understanding of the evolution of the san juan islands thrust system re examination of foraminifera bearing mudstones at richardson on lopez island indicates a late aptian 112 115 ma not late albian 100 ma age as currently presented in the literature the age brackets of thrusting marked by these pre thrusting mudstones and 84 ma post thrusting sedimentary rocks span a much longer period than previously thought diminishing controls on rates of displacement in the thrust system and the timing of regional deformation in western washington new 40 ar 39 ar plateau ages of phengite in blueschist facies meta volcanic rock also at richardson are 124 0 7 ma 2 late barremian these blueschist facies volcanic rocks are in fault contact with the fossiliferous mudstones therefore the blueschist facies metamorphism at richardson previously inferred to be associated with the thrusting now appears to have occurred prior to thrusting further the ar ages demonstrate that blueschist facies fabric formed earlier than the thrust event and is therefore not directly useful in analyzing the thrusting kinematics the richardson 40 ar 39 ar age is similar to isotopic ages found in the eastern san juan islands and in the shuksan blueschist terrane in the northwest cascades and thus fits into an emerging regional age pattern of blueschist facies metamorphism during late jurassic early cretaceous up to barremian but not late albian cenomanian if this pattern is more broadly confirmed for the san juan islands all the blueschist facies metamorphism can be regarded as having formed in subduction zones elsewhere along the continental margin rather than in the anomalous setting of an on land thrust system as in the san juan islands resume de nouveaux ges pour les roches des iles san juan dans le nord ouest de l etat de washington changent profondement notre comprehension de l evolution du systeme de chevauchement san juan un reexamen des mudstones foraminiferes a richardson sur l ile lopez indique un ge aptien tardif 112 115 ma et non albien tardif 100 ma tel qu indique actuellement dans la litterature les plages d ges pour le chevauchement marquees par ces mudstones precedant le chevauchement et des roches sedimentaires 84 ma posterieures au chevauchement couvrent une periode beaucoup plus grande que stipulee anterieurement diminuant les controles sur les taux de deplacement dans le systeme de chevauchement et le moment de la deformation regionale dans l ouest de l etat de washington de nouveaux ges plateaux 40 ar 39 ar de la phengite dans des roches volcaniques au facies des schistes bleus aussi a richardson datent

assessment of groundwater quality for irrigation purposes and identification of hydrogeochemical evolution mechanisms in pengyang county china groundwater is an important water source for agricultural irrigation in penyang county some traditional methods such as irrigation coefficient sodium adsorption ratio total alkalinity total salinity and total dissolved solids were employed to assess groundwater quality in this area in addition an improved technique for order preference by similarity to ideal solution model was applied for comprehensive assessment the origin of major ions and groundwater hydrogeochemical evolution was also discussed groundwater in penyang county contains relative concentrations of dominant constituents in the following order na ca2 mg2 k for cations and hco3 so42 cl co32 for anions groundwater quality is largely excellent and or good suggesting general suitability for agricultural use calcite and dolomite are found saturated in groundwater and thus tend to precipitate out while halite fluorite and gypsum are unsaturated and will dissolve into groundwater during flow groundwater in the study area is weathering dominated and mineral weathering carbonate and silicate minerals and ion exchange are the most important factors controlling groundwater chemistry

factors controlling shelf sediment dispersal along the southeast african continental margin abstract four major factors control sediment dispersal along the southeast african continental margin 1 morphology of the upper continental margin 2 wave regime and wind driven circulation 3 influence of the agulhas current and 4 sediment supply these factors interact on various scales to produce a unique regional sediment dispersal pattern the continental shelf is very narrow and the adjacent slope extremely steep the shelf platform is interrupted by a number of structural offsets and locally the shelf break is dissected by numerous submarine canyons the nearshore zone down to about 60 m waterdepth is dominated by a high energy swell regime and in most places is underlain by a thin wedge of sandy sediment this wedge appears to have achieved dynamic equilibrium with the prevailing energy regime and additional sediment is rapidly dispersed and fed into a sandstream situated on the central shelf where the agulhas current dominates sediment transport along some parts of the coast the sediment wedge is dammed behind a drowned coastal dune ridge within the sandstream sediment is transported alongshelf until a structural offset is reached where sediment spills over the shelf break four major localities for off shelf transport are recognized between maputo and port elizabeth most of the suspended load appears to be expelled from the system without being deposited on the shelf in the lee of each offset a clockwise gyre is developed which produces return flow currents capable of moving sediment northward thereby creating bedload partings in the vicinity of these partings depositional features are observed that are similar to those normally associated with tidal regimes e g bedforms migrating in opposite directions most of the bedload sediment entering the system is eventually deposited in well defined sinks situated in the lee of structural offsets this model applies only to inter glacial high sea level situations accompanied by strong western boundary flow of the agulhas current

paleoecology of the marine endobenthos endobenthic animals which reside within the sea bottom include stationary suspension feeders mobile deposit feeders and both stationary and mobile carnivores their activities especially with regard to dwelling feeding walking crawling and resting nesting are recorded as trace fossils abundance diversity and density of some kinds of trace fossils allow interpretation of the population strategies of the trace makers in terms of opportunistic r selected and equilibrium k selected strategies opportunistic ichnotaxa tend to be faciesbreaking traces which are highly localized in low diversity high density trace fossil associations in rocks representing environmental extremes e g variable salinities harsh temperatures low oxygen levels or shifting substrates equilibrium ichnotaxa usually are restricted to particular sedimentary facies and are characteristic of high diversity low dominance trace fossil associations in sediments reflecting stable predictable environmental conditions the most important environmental factors influencing the composition of trace fossil assemblages in marine settings are bathymetry substrate oxygen and hydrodynamic energy the four factors are closely interrelated because as water depth increases there is a general decrease in sediment grain size and hydrodynamic energy of the depositional environment as depth below the water sediment interface increases the firmness of the sediment due to compaction and dewatering increases and the oxygen content of interstitial waters drops drastically marine ichnofacies are largely substrate controlled soupgrounds are water saturated incompetent substrates typified by highly compressed and usually unidentifiable burrows softgrounds commonly contain numerous distinctive burrows and are zoned bathymetrically by the skolithos cruziana zoophycos and nereites ichnofacies firmgrounds are characterized by stiff compacted sediments in which traces of the glossifungites ichnofacies are excavated hardgrounds are cemented substrates in which bioerosion traces of the trypanites ichnofacies are bored woodgrounds are woody materials that have been exposed to the sea and bored by bivalves which produce characteristic traces of the teredolites ichnofacies tiering of endobenthic communities is common and is related to substrate preference of the burrowers and oxygen stratification of interstitial waters

arc parallel extension and fluid flow in an ancient accretionary wedge the san juan islands washington structural analysis of the lopez structural complex a major late cretaceous terrane bounding fault zone in the san juan thrust system reveals a sequence of events that provides insight into accretionary wedge mechanics and regional tectonics after formation of regional ductile flattening and shear related fabrics the area was crosscut by brittle structures including 1 southwest vergent thrusts 2 extension veins and normal faults related to northwest southeast extension and 3 conjugate strike slip structures that record northwest southeast extension and northeast southwest shortening aragonite bearing veins are associated with thrust and normal faults but only rarely with strike slip faults high pressure low temperature hp lt minerals constrain the conditions for brittle deformation to 20 km and

identification of hydrogeochemical processes and pollution sources of groundwater resources in the marand plain northwest of iran the main aims of the present study are to identify the major factors affecting hydrogeochemistry of groundwater resources in the marand plain nw iran and to evaluate the potential sources of major and trace elements using multivariate statistical analysis such as hierarchical clustering analysis hca and factor analysis fa to achieve these goals groundwater samples were collected in three sampling periods in september 2013 may 2014 and september 2014 and analyzed with regard to ions e g ca2 mg2 na and k hco3 so4 2 cl f and no3 and trace metals e g cr pb cd mn fe al and as the piper diagrams show that the majority of samples belong to na cl water type and are followed by ca hco3 and mixed ca na hco3 cross plots show that weathering and dissolution of different rocks and minerals ion exchange reverse ion exchange and anthropogenic activities especially agricultural activities influence the hydrogeochemistry of the study area the results of the fa demonstrate that 6 factors with 81 7 of total variance are effective in the overall hydrogeochemistry which are attributed to geogenic and anthropogenic impacts the hca categorizes the samples into two clusters samples of cluster c1 which appear to have higher values of some trace metals like pb and as are spatially located at the eastern and central parts of the plain while samples of cluster c2 which express the salinization of the groundwater are situated mainly westward with few local exceptions

fission track dating of the tectonic development of the san juan islands washington the san juan islands of washington state form a geologically complex province located between the north cascades vancouver island and the olympic peninsula we have obtained 53 fission track dates from the san juan islands province that help constrain its late paleozoic to early cenozoic tectonic and sedimentary history and its relationship to neighboring geologic terranes the san juan islands can be divided into two main blocks separated by the haro fault south of the haro fault complexly deformed metamorphosed and probably exotic early paleozoic to early late cretaceous rocks form four imbricate thrust plates separated by south and east dipping late early to late cretaceous thrust faults reset zircon fission track dates indicate that thrusting may have produced an upside down geothermal gradient in the uppermost plate the decatur terrane if present this gradient was probably produced by conductive or frictional heating associated with a now eroded overlying thrust fault and hot thrust plate

a case study on geochemical anomaly identification through principal components analysis supplementary projection abstract based on a case study in which a single geochemical anomaly was located in the vicinity of an abandoned mine in central portugal a recursive methodology for anomaly background separation was developed this methodology relies on the supplementary projection of each of the samples taken from a subset of anomaly candidates onto the axes provided by principal components analysis of the background subset the concept of anomaly intensity defined by the average of the distances from the original to the supplementary projections is the basis for final anomaly identification

geology of denman and hornby islands british columbia implications for nanaimo basin evolution and formal definition of the geoffrey and spray formations upper cretaceous nanaimo group the upper cretaceous nanaimo group of southwest british columbia is a 4 km thick succession consisting mostly of deep marine siliciclastics deposited directly on the insular superterrane as such this succession has been the focus of several paleomagnetic isotope geochemistry paleontology and sedimentology studies in attempts to elucidate the tectonic history and paleolatitude of the insular superterrane and associated entities during the critical time of nanaimo group deposition ca 90 65 ma however disagreement as to whether deposition occurred into a single or multiple basins has led to confusion concerning the formal stratigraphy and formation names for the succession and has resulted in problems with both local and regional correlations the upper two thirds of the succession is continuously and well exposed on denman and hornby islands and represents the best example of this part of the succession in the northern half of what we consider the single nanaimo basin this area includes the pre

polyphase brittle and ductile deformation of late jurassic ophiolitic basalt argillite matrix melange and stratigraphic overlap sequence northwestern washington state abstract a belt of jurassic to cretaceous ophiolitic rocks borders the western margin of the u s cordillera and stretches from central california to northwestern washington state the northern end of this belt lies between the san juan islands and the northwest cascades within this region ophiolitic rocks consist of a succession of oceanic and arc affinity igneous and sedimentary rocks which form a sedimentary melange and sedimentary overlap sequence which is imbricated during the mid cretaceous the melange contains blocks and olistoliths of peridotite plagiogranite chert basalt and volcanoclastic conglomerate which range in size from a meter to over 1 km and are contained within a matrix of argillite and volcanoclastic breccia and conglomerate peridotites were exposed to the sub aqueous surface along serpentinized shear zones prior to their incorporation into the melange and the sedimentary matrix of the melange underwent brittle deformation during the earliest stages of its structural history melange rocks are overlain in angular unconformity by a jura cretaceous arc sourced sedimentary succession which is at least 500 meters thick and passes upward from a basal breccia containing clasts of plagiogranite gabbro tonalite chert and basalt into argillite containing late jurassic radiolarians the argillite is overlain by poorly sorted greywacke and conglomerate with clast populations similar to those of the basal breccia the conglomerate fines upward into a massive to bedded feldspathic lithic arenite and greywacke that yields mid cretaceous detrital zircons the overlap succession and the melange are deformed by two generations of highly penetrative structures d1a and d1b which produced north to east vergent tight to isoclinal folds and axial planar pressure solution cleavages all units are further deformed by three generations of penetrative structures the successively younger nne to nw ne and e w to wnw trending folds have foliations that cross cut the earlier structural fabrics and faults formation of the melange required differential elevations during the time of deposition and the presence of rocks which are sourced from both arc and oceanic crust extension within the forearc provides a mechanism to exhume peridotites and generate differential topography for arc and oceanic affinity rocks to erode and be incorporated into the melange as part of olistostromal deposits

paleogeographic evolution of the united states pacific northwest during paleogene time paleogeographic reconstructions for oregon and washington during paleogene time illustrate a major transition from a dominantly compressional prior to middle eocene time to an extensional tectonic regime this transition resulted in the development of three phases of paleogene basin evolution in the united states pacific northwest during the initial phase basins formed along the continental margin during collision of oceanic islands sediments in these basins were derived from nearby orogenic highlands the second phase of basin development began in middle eocene time and consisted of rapid subsidence of individual basins that formed within a broad forearc region nonmarine basins that formed during this phase were caused by extension possibly associated with transcurrent faulting rapid sedimentation in both marine and nonmarine basins during this time consisted dominantly of sandstone derived from cretaceous plutonic sources far to the east the final stage of basin development was the modification

depositional history of the southeastern outcrop belt of the chuckanut formation implications for the darrington devil s mountain and straight creek fault zones washington u s a the southeastern outcrop belt of the eocene chuckanut formation contains the erosional remnants of a larger depositional system in the study area the chuckanut formation can be split into four units based upon differences in age lithology sedimentology paleocurrents and provenance relationships the coal mountain unit early eocene represents a southwest flowing fluvial system that shows no evidence for fault control of drainage the overlying higgins mountain unit early middle eocene represents a northeast flowing fluvial system east of the devil s mountain fault zone dmfz with lithologies derived from western source areas the sperry peak unit early middle eocene represents a fluvial system with a wide dispersion of paleocurrent azimuths and a possible mixture of sediment source areas we believe the sperry peak unit was deposited in a fault wedge graben at the junction of the dmfz and straight creek fault zone scfz with sediment sources from both east and west the grade creek unit ag

identification of probable groundwater paths in the amargosa desert vicinity in this study the hydrogeochemical program phreeqc was used to determine the chemical speciation and mineral saturation indices sis of groundwater in the vicinity of the proposed high level nuclear waste repository at yucca mountain nevada usa in turn these data were used to interpret the origin and recharge mode of groundwater to elucidate the mechanisms of flow and transport and to determine potential sources of groundwater contamination phreeqc was run to determine aqueous dissolved species and minerals that would be in equilibrium with the study area s groundwater selected major ions associated si f and ca na ion exchange were then examined using the multivariate statistical methods of principal component factor analysis and k means cluster analysis analysis of dissolved ion concentrations sis and ca na ion exchange allows simultaneous consideration of arithmetic raw concentrations and logarithmic si ion exchange variables that describe the hydrochemical system and therefore can provide further insight into the system s behavior the analysis indicates that the dominant processes and reactions responsible for the hydrochemical evolution in the system are 1 evaporative concentration prior to infiltration 2 carbonate equilibrium 3 silicate weathering reactions 4 limited mixing with saline water 5 dissolution precipitation of calcite dolomite and fluorite and 6 ion exchange principal component factor analysis and k means cluster analysis of factor scores allow the reduction of dimensions describing the system and the identification of hydrogeochemical facies and the processes that defined and govern their evolution statistical analysis results indicate that the northern west face and southern yucca mountain groundwater is fresh water with low concentrations of ca2 mg2 cl ca2 na 2 and caf2 the fortymile wash groundwater is dilute the carbonate signature is shown in the ash meadows and death valley waters with high fluorite si finally the crater flat stripped hills and skeleton hills are dominated by ca na ion exchange mg and ca the hydrochemical and statistical analyses showed three main groundwater signatures or hydrochemical processes indicating groundwater evolution potential flowpaths and recharge areas the flowpaths are the trace of the amargosa river the trace of fortymile wash and its convergence with the amargosa river this appears to represent not just a groundwater flow path but traces of surface runoff infiltration as well

plate tectonics and basin subsidence history tectonic setting exerts fi rst order control on basin formation as refl ected in basin subsidence history while our approach ignores the effects of fl exural loading and eustatic sea level change consistency of backstripped subsidence histories i e with local loading effects of sediment removed suggests consistent tectonic driving mechanisms in each tectonic setting with the possible exception of forearc basins based on published subsidence curves and open fi le stratigraphic data we show the subsidence characteristics of passive margins strike slip basins intracontinental basins foreland basins and forearc basins passive margin subsidence is characterized by two stages rapid initial synrift subsidence and slow post rift thermal subsidence with increasing subsidence rates toward the adjacent ocean basin subsidence of intracontinental basins is similar in magnitude to that seen in passive margin settings but the former is generally slower longer lived and lacks initial subsidence long lived subsidence for many intracontinental basins is consistent with cooling following thermal perturbation of thick lithosphere found beneath old parts of continents basins associated with strike slip faults are usually short lived with very rapid subsidence changes in local stress regimes as strike slip faults evolve and migrate over time coupled with three dimensional heat loss in these small basins likely explain this subsidence pattern foreland basin subsidence rates refl ect the fl exural response to episodic thrust loading resultant subsidence curves are punctuated by convex up accelerating segments forearc basins have the least consistent subsidence patterns subsidence histories of these basins are complex and may refl ect multiple driving mechanisms of subsidence in forearc settings second order deviations in subsidence suggest reactivation or superimposed tectonic events in many basin settings the effects of eustatic sea level change may also explain some deviations in curves for many of these settings subsidence histories are suffi ciently distinctive to be used to help determine tectonic setting of ancient basin deposits

stratigraphy and age of the chumstick and wenatchee formations tertiary fluvial and lacustrine rocks chiwaukum graben washington summary the chiwaukum graben in central washington contains two unconformity bounded fluvial and lacustrine units here named the chumstick and wenatchee formations the chumstick is dated at 45 m y middle eocene and the wenatchee is dated at 34 m y early oligocene by the fission track method on zircons from tuffs previously both formations were thought to be part of the swauk formation which is older the chumstick formation rests on weathered crystalline basement and is several thousands of metres thick fanglomerate occurs at the base and along the margins most of the formation consists of feldspathic sandstone and pebbly sandstone of fluvial origin but within the upper part there is a lacustrine unit herein designated the nahahum canyon member tuff is common in the lower part of the formation both of the bounding faults the leavenworth and the entiat were active during deposition of the chumstick formation but relief was greatest on the northeast entiat side the wenatchee formation occurs in the vicinity of wenatchee washington and is 300 m thick it unconformably overlies the chumstick formation within the graben but overlaps the northeast side of the graben where it lies directly on weathered metamorphic basement the wenatchee formation like the chumstick was deposited primarily in fluvial and lacustrine environments unlike the chumstick much of the sediment is mature quartz sandstone relief in the source area probably was very subdued during its deposition

holocene sedimentation in the shallow nearshore zone off nauset inlet cape cod massachusetts abstract present conditions and sedimentary evolution of the shallow offshore region near nauset inlet on cape cod massachusetts were clarified using high resolution seismic reflection profiles sidescan sonar records surface grab samples and current meter measurements the study area contains three provinces 1 a nearshore province shallower than 18 m with a relatively steep slope 0 6 and a cover of medium sand 2 a northern offshore province covered with coarse sand gravel and boulders interpreted to be glacial drift and 3 a southern offshore province with a gentle seaward dipping slope 0 3 and a surface sediment of coarse sand the glacial drift exposed in the northern offshore province can be traced southward under the coarse sand province the overlying fill is comprised of either outwash sediment derived from the pleistocene south channel ice lobe to the east or holocene aged marine sediments eroded from seacliffs to the north latest holocene sediment appears to be limited to the zone shoreward of 18 m where the medium sand occurs near bottom mean flows measured over two winter months in 10 m water depth average 6 cm sec 1 to the south mean flows exceeded 20 cm sec 1 approx 23 of the time ninety percent of the flows exceeding 20 cm sec 1 were directed to the south reflecting the dominant atmospheric forcing during these winter months waves had an average variance of 650 cm 2 with variance exceeding 5000 cm 2 3 of the time indicating moderate wave activity present processes are actively reshaping the nearshore province which is characterized by many east to northeast trending shore oblique channels that do not extend seaward of the 18 m contour coarse sand in the floors of these channels suggests they may be erosional features and the presence of megaripples oriented perpendicular to the channel axes indicates active transport in these channels megaripple orientation and the current and wave regime of the study area support a rip current origin for these channels

in situ and laboratory stress strain relationships the question of whether or not the end of primary consolidation curve from laboratory oedometer tests is representative of in situ behaviour has been the subject of much discussion the behaviour of the berthierville test embankment is described and in situ effective stress strain curves are defined for two well defined clay sublayers these compressibility curves are then compared with laboratory end of primary consolidation curves similar comparisons are also made for sublayers under three other well instrumented embankments all the results show that the laboratory end of primary consolidation curve strongly underestimates in situ settlements and thus that theory a is not valid on s est souvent demande si la courbe de la fin de consolidation primaire obtenue a partir d essais oedometriques en laboratoire represente effec tivement le comportement en place l article decrit le comportement du remblai experimental de berthierville et definit les courbes contrainte deformation effectives en place pour de

seismic investigation of the coast plutonic complex insular belt boundary beneath the strait of georgia the strait of georgia a topographic depression between vancouver island and the mainland of british columbia is considered to be the boundary between two tectonic provinces the coast plutonic complex on the east and the insular belt to the west the allochthonous nature of the insular belt has been established mainly on the basis of paleomagnetic measurements various tectonic models to explain the geological differences between the two provinces have been proposed one of these suggests that the boundary is an old transform fault zone and is represented currently by a thrust fault along the eastern side of the strait of georgia other models propose that the coast plutonic complex is a feature superimposed by tectonic and metamorphic events after the accretion of the insular belt such models do not require a major crustal discontinuity along the strait of georgia in may 1982 a seismic refraction survey using a 32 l air gun and a radio telemetering sonobuoy system was carried out in the strait of ge

geological evidence for post 40 m y b p large scale northwestward displacement of part of southeastern alaska the leech river complex on southern vancouver island and schistose rocks on southern baranof island have very similar geologic histories both were derived from probable upper jurassic cretaceous terrigenous clastic rocks and minor associated volcanogenic rocks and chert each underwent 1 at least two penetrative deformations locally involving folding disruption and transposition of thinly layered sequences and 2 synkinematic low pressure buchan type metamorphism progressive metamorphic zones ranging from greenschist to amphibolite facies are related to granitic intrusive bodies deformation metamorphism and intrusion culminated about 40 to 42 m y ago apparently these units now separated by more than 1 100 km were once contiguous and lay at least as far south as the latitude of southern vancouver island shortly after 40 m y b p the allochthonous leech river complex was emplaced at the southern edge of vancouver island and the schists of baranof island and perhaps the entire chugach terrane began their long northwestward journey along a system of dextral transcurrent faults

fission track evidence for late triassic oceanic crust in the french occidental alps five zircons and one apatite from plutonic rocks of the ophiolitic sequence from the piemontese zone western alps southeast france have been dated by the fission track method the ages obtained indicate that the minimum age of the alpine oceanic crust in this zone is between 192 6 and 212 8 m y late triassic liassic consideration of the available data on fission track retention conditions in zircons and pressure temperature conditions allowed by the high pressure mineralogic assemblages of the rocks leads to the conclusion that in the external part of the piemontese zone the temperature duration conditions of the high pressure alpine metamorphism were inadequate to significantly reset the zircons9 fission track clock suggesting a short lived metamorphic event

stratigraphy depositional setting and tectonic significance of the clastic cover to the fidalgo ophiolite san juan islands washington the san juan islands of northwest washington state comprise a diverse assemblage of paleozoic and mesozoic terranes amalgamated during a regional cretaceous orogenic event detailed tectono stratigraphy of the sedimentary cover to the fidalgo complex indicates the presence of several stratigraphically distinct units which are described and formalized in this paper the fidalgo complex and its sedimentary cover are the structurally highest rocks in the san juan thrust system the fidalgo complex is a highly disrupted middle to upper jurassic ophiolite with arc related intrusives volcanics and sediments the trump unit is an informally named sequence of siliceous sediments volcanic graywacke and minor volcanics that occurs at the stratigraphically highest portion of the fidalgo complex complex facies lithologies and provenance indicate that deposition of this oxfordian to upper tithonian unit occurred in an arc proximal setting the upper tithonian and younger lummi group elevated here lies depos

the kanaka creek fossil flora huntingdon formation british columbia canada paleoenvironment and evidence for paleocene age using palynology and macroflora paleogene sediments of the huntingdon formation a correlative to the chuckanut formation of neighbouring washington state usa are exposed in the greater vancouver area british columbia canada

time scales of metamorphism deformation and crustal melting in a continental arc north cascades usa the record of metamorphism deformation and melting in the north cascades continental arc provides insights into the timing and mechanisms of extensional unroofing that followed crustal thickening the skagit gneiss north cascades is composed of variably deformed 90 45 ma tonalitic to granitic intrusive rocks these lithologies and metasedimentary rocks are migmatitic zircon and monazite from different textural varieties of migmatite from three outcrops along an east west transect were analyzed using the isotope dilution thermal ionization mass spectrometry id tims technique the data reveal two main migmatization pulses 1 68 63 ma and 2 53 47 ma in the westernmost locality leucosome zircon yields group 1 dates and mesosome sillimanite garnet biotite gneiss zircon is as young as 61 ma leucosome zircon in the easternmost outcrop yields only group 2 dates and biotite gneiss contains 47 ma zircon the third outcrop has leucosome dates from both groups 65 ma and 53 ma monazite from leucosomes and mesosomes likely records the timing of prograde metamorphism ca 69 ma and later synkinematic fluid mediated growth 49 46 ma these results indicate that partial melting occurred during 71 61 ma metamorphism and lasted through 46 ma deformation associated with exhumation the results and field observations suggest the presence of ductilely deforming crust from 68 to 46 ma the similarity between the youngest u pb dates in the migmatites and cooling and basin filling ages suggests a link between ductile and brittle processes over a range of structural levels in the arc from a zone of crustal melting flow and migmatite crystallization to earth9s surface

high chromium contents in tertiary coal deposits of northwestern washington a key to their depositional history abstract chromium contents obtained from 20 coal and 5 associated rock samples collected from the basal part of the eocene chuckanut formation in skagit and whatcom counties northwest washington range between 30 and 300 ppm mean 120 ppm whole coal basis the lenticular coals ranging in rank from subbituminous to anthracite and with an ash content of 12 46 crop out along the western flank of the cascade range results of x ray diffraction analysis of low temperature ash show that the mineral matter in the coal samples consists predominantly of quartz and clay kaolinite illite and chlorite group however accessory minerals isolated from the coal samples and analyzed by x ray diffraction scanning electron microscope and optical methods contain angular fragments and euhedral crystals of the spinel group chromite magnetite and trevorite kaolinite serpentine group antigorite and chrysotile chlorite group amphibole group and pyroxene group minerals augite diopside and enstatite all of which are commonly enriched in chromium although associated primarily with the inorganic fraction of the coal concentrations of chromium in the samples show no statistically significant correlation with ash content localized concentrations of chromium in the coal are the result of natural contamination from the alteration of detrital chromium bearing mineral grains introduced into the peat forming mires from nearby jurassic ophiolite bodies the coals formed in the early eocene in rapidly subsiding small basins that developed during the uplift and erosion of the pre tertiary ophiolite terrain scattered bodies of source rock random distribution of chromium bearing minerals within the coal and sample heterogeneity account for the variation in cr contents of the samples

the eocene southern vancouver island orocline a response to seamount accretion and the cause of fold and thrust belt and extensional basin formation abstract a deflection of the fault controlled southwestern coastline of vancouver island suggests the presence of a minor orocline with a southern crustal block south of barkley sound alberni inlet rotated 20 counterclockwise relative to a northern fixed crustal block about a pole of rotation located northeast of port alberni in this paper two models of orocline development one of pure block rotation and one of pure bending are proposed the predictions of these models are tested against available geological maps structural orientation data identified regions of extension and contraction and paleomagnetic data structural orientation and paleomagnetic data are consistent with 18 of post late cretaceous counter clockwise rotation of the southern crustal block relative to the northern fixed crustal block a southward increase in the magnitude of rotation evident in the structural orientation data argues for a model of bending both bending and block rotation models predict the development of a zone of contraction along the northeast margin of the southern crustal block coincident with the location of the eocene cowichan fold and thrust belt that diminishes northward toward the pole of rotation as predicted the fold and thrust belt is characterized by a northerly decrease in the amount of shortening from 30 at the south end of the thrust belt to 0 shortening north of port alberni the northerly decrease in shortening is complemented by a north to south change in structural style from cylindrical to conical folds and finally to planar undeformed strata the model of block rotation predicts the presence of a zone of extension extending southwest from the zone of rotation coincident with the location of eocene extensional structures within barkley sound and with horst and graben structures in the offshore eocene to miocene tofino basin extension is less than predicted by a model of pure block rotation and suggests that much of the oroclinal rotation was accommodated by bending timing constraints indicate that orocline development was coeval with and resulted from the eocene accretion of seamounts of the crescent terrane these findings demonstrate that oroclinal orogeny the buckling of a linear crustal beam about vertical axes of rotation can significantly impact the geometry structure and character of an orogenic belt even where the buckles are minor

new paleomagnetic data from the aleutian islands implications for terrane migration and deposition of the zodiac fan sedimentary rocks of late eocene to early oligocene age from the aleutian islands have been paleomagnetically studied to determine the paleolatitude of this island arc samples were collected from gently dipping thin bedded laminated siltstone mudstone and very fine grained sandstone of marine origin after demagnetization samples from each locality showed both polarities of a remanent magnetization that thermal isothermal remanent magnetization and js t experiments suggest is carried by magnetite after tectonic correction the 95 decreases in both localities suggesting magnetization was acquired before folding of the beds the characteristic magnetization shows that no significant poleward motion of the aleutian arc has occurred with respect to the north american plate since the early oligocene amlia f 4 f 5 umnak f 0 8 f 3 5 but the declinations are rotated significantly clockwise amlia r 70 r 23 umnak r 36 7 r 11 2 using these paleomagnetic data relevant euler poles and hotspot locations we propose a new model for the formation of the zodiac fan in this model the start of zodiac fan deposition corresponds to accretionary igneous and erosional events in the pacific northwest and fragmentation of the farallon plate along the margin of the north american plate into small plates fan deposition on the pacific plate was controlled by the geometry of the bowie and cobb seamount chains which prevented sediment from being dispersed over the bathymetrically lower oceanic crust to the west and by the bathymetry of the pacific plate which focused sedimentation in the magnetic bight region of the plate our model suggests that the present day zodiac fan is only a remnant of a much larger fan system

orogen parallel extension in the north cascades crystalline core washington metamorphic stretching lineations throughout the crystalline core of the north cascades washington show a strong preferred orientation in a horizontal nw se direction foliations strike nw and dip steeply preliminary observations of shear sense features indicate noncoaxial right lateral motion we interpret these observations to indicate that the crystalline core was a broad right lateral shear zone the ages of the fabrics as recorded by metamorphic minerals and syntectonic plutons range from pre 85 ma in the south to post 45 ma in the north thus the shear regime was active during an extended interval of metamorphism and plutonism in the orogen a similar kinematic pattern is suspected for at least part of the coast plutonic complex british columbia which lies on strike with the crystalline core to the northwest

the haslam formation a late santonian early campanian forearc basin deposit in the insular belt of southwestern british columbia and adjacent washington abstract the upper cretaceous santonian lower campanian haslam formation nanaimo group of southern vancouver island and the gulf islands of british columbia and the san juan islands of washington includes 1 inner submarine fan facies consisting of channel axis conglomerate and sandstone intercalated with channel margin and interchannel turbidites and 2 outer submarine fan and basin plain facies consisting of fan lobe and lobe fringe turbidites thin bedded turbidites and shales outer submarine fan facies are more common in the lower part of the formation and in the westernmost exposures on vancouver island whereas inner submarine fan facies characterize the upper part of the haslam in the san juan islands and are more common throughout the formation to the east and southeast these ubmarine fan facies were deposited in a forearc basin on rocks of the wrangellia exotic terrane seaward of the cretaceous magmatic arc in the coastal plutonic belt the haslam submarine fan complex prograded to the northwest or west into the forearc basin the sediment supplied to the fan was derived from terrane to the east and south where metasedimentary sedimentary metavolcanic and volcanic rocks were the dominant source areas during the late santonian and early campanian haslam sandstone and conglomerate records the first appearance of sediment from the east in the nanaimo basin older upper cretaceous santonian rocks of the nanaimo group the comox formation were derived in large part from upper paleozoic to lower mesozoic volcanic and metavolcanic rocks and jurassic plutonic rocks of the insular belt later nanaimo formations campanian maestrichtian that overlie the haslam were derived from low grade metamorphic and plutonic sources with only minor input of volcanic and sedimentary material thus three petrologic intervals can be recognized in the nanaimo group on southern vancouver island the gulf islands and the san juan islands the santonian interval comox formation characterized by sediment derived from the insular belt the late santonian early campanian interval haslam formation characterized by sediment derived from a sedimentary and subordinate volcanic source to the east and the campanian maestrichtian interval extension to gabriola formations derived from a low grade metamorphic and crystalline source to the east paleocurrent dispersal atterns are similar for the haslam and extension gabriola intervals which suggests that sediment supplied to the forearc basin was derived from uplifted subduction magmatic arc complexes that were probably related to the sourthern margin of the insular belt and were deformed when the magmatic arc shifted westward in the mid cretaceous the petrologic intervals are interpreted to reflect unroofing of this source terrane although other interpretations are possible if transcurrent faulting was active in this region in the late cretaceous

turonian upper cretaceous lithostratigraphy and biochronology southern gulf islands british columbia and northern san juan islands washington state clastic strata preserved on sidney island barnes island and adjacent islands of the southernmost gulf islands of british columbia and the northern san juan islands of washington state are assigned to new stratigraphic units the sidney island formation and the barnes island formation the sidney island formation consists of basal conglomerate and sandstone that grades upward through planar stratified sandstone into hummocky cross stratified sand stone and siltstone all of which are deposited in relatively shallow marine environments the barnes island formation in contrast consists of deep marine conglomerate sandstone and mudstone that was deposited in a submarine fan setting mollusk fossils from the sidney island formation are of early to middle turonian age whereas ammonites and foraminifers from the barnes island formation indicate a late turonian age the sidney island formation thus records initial marine transgression and inundation of basement rocks followed by basin deepening that is transitional to the deep marine submarine fan deposits of the barnes island formation sidney island formation strata have been considered previously as derived from uplift along the nearby san juan thrust system in mid cretaceous time however the shallow marine strata are internally well organized and the facies succession is persistent across the formation s out crop area in addition the formation lacks the distinctive detrital metamorphic mineral assemblages that are characteristic of older rocks of the san juan islands these observations suggest that strata of the sidney island formation did not accumulate immediately adjacent to active thrusting but rather in a more distal setting relative to the thrust system

tenth canadian geotechnical colloquium recent developments in consolidation of natural clays a global analysis of the consolidation of natural clays is realized considering the consolidation process to be a combination of the effects of compressibility and of permeability the compressibil

consolidation by vertical drains a theory is described which can be used in designing a vertical drainage system this theory incorporates important parameters such as vertical discharge capacity remoulding effects during installation and filter resistance the importance of these parameters is widely recognized but very seldom taken into account in the design by engineers six well documented case records related to different drain types are briefly presented experience gained from these case records shows that in many cases even if the overall performance appears successful there are aspects of soil drain behaviour that cannot be explained on the basis of existing theories l article decrit une theorie que l on peut appliquer a la conception d un systeme de drainage vertical cette theorie renferme d importants parametres tels que la capacite de decharge verticale les effets du remaniement pendant l installation et la resistance de filtration l importance de ces parametres est reconnue par bien des ingenieurs mais ils en tien

reliability of settlement prediction case history a geotextile reinforced embankment was built over soft ground staged construction and vertical prefabricated drains were used to obtain strength gain via consolidation of the foundation material settlement and pore pressure were measured as a part of construction control settlement differential settlement and rate of consolidation were predicted by simple models uncertainties in the predictions were evaluated to assess the reliability of the predictions the estimated errors were compared with the measured values and major contributors to prediction errors were identified

eocene bird tracks from the chuckanut formation northwest washington early tertiary nonmarine sediments occur as a discontinuous series of outcrops that extends throughout large areas of northwest washington and southwestern british columbia these fluvial and deltaic deposits contain abundant plant fossils but faunal remains are rare the recent discovery of an outcrop of chuckanut formation arkose containing nine fossil bird tracks provides the first clear evidence of terrestrial vertebrate life in the extensive coastal wetland zone that existed prior to the uplift of the cascade range

the southern washington cascades conductor a previously unrecognized thick sedimentary sequence geophysical studies in the southern washington cascades have outlined a possible previously unrecognized sequence of sedimentary rocks these postulated sedimentary units are interpreted to correspond to at least the upper section of a low resistivity high conductivity assemblage of rocks at depths of 1 10 km and with thicknesses up to 15 km that we call the southern washington cascades conductor swcc structure on the upper surface of this conductive assemblage correlates in some places with anticlines that bring tertiary marine rocks near the surface these anticlines have recently been imaged in detail with seismic reflection surveys the conductive rocks have also been traced to the surface west of morton washington where they correlate with eocene marine sands ones and shales the geometry of the conductive rocks consists of a east dipping low angle wedge that thickens to the north and with an undulating upper surface corresponding to the anticlines we suspect that marine sedimentary rocks are the primary constituent of the swcc but recognize that parts of the conductive section may be composed of nonmarine and marginal marine sedimentary rocks like those in the upper part of the puget group geothermal fluids may be a contributing factor to low resistivities in the deeper parts of the conductive section greater than 6 7 km other possible candidates for the conductive units are thick sections of highly altered volcanic flows and or graphitic conductive pre tertiary metamorphic rocks

sand waves echinocardium traces and their bathyal depositional setting monte torre palaeostrait plio pleistocene southern italy stacked cross sets up to 2 5 m thick produced by sand wave migration and meniscate trace fossils produced by echinocardium cordatum both considered in the literature as typical of shallow water marine depositional settings commonly occur in the bathyal plio pleistocene deposits of monte torre calabria southern italy the plio pleistocene sediments form two coarsening upward depositional sequences separated by an unconformity and by a palaeobathymetric gap of at least 300 m the lower sequence passes upwards from hemipelagic marls and thin bedded turbidites to thick bedded sandy turbidites then to sand wave deposits alternated with sandy turbidites and finally to base of slope megabreccias facies characteristics and relationships and the occurrence of deep sea faunal associations indicate deposition in the bathyal zone the facies of the upper sequence reflect a fan delta environment no deeper than a few tens of metres the depositional setting of the lower sequence where the sand wave deposits and meniscate trace fossils occur appears to have been a tectonically controlled seaway connecting the tyrrhenian and ionian seas this seaway became progressively narrower with time evolving into a strait the overall coarsening upward trend reflects the upward transition from a low to a high energy environment possibly caused by the tectonic narrowing of the seaway deposition and erosion from high concentration turbidity currents and from tidal bottom currents were important processes periods of tectonic activity producing first the uplift of the seaway margins and culminating with the uplift of the strait sequence itself are marked by scattered rockfall deposits the strait setting causing the development of powerful oxygenated bottom currents produced optimal conditions in the bathyal zone for the colonization of sandy bottoms by a single infaunal r selected species echinocardium sp

determining the factors controlling the chemical composition of groundwater using multivariate statistics and geochemical methods in the xiqu coal mine north china studying the hydrogeochemical processes that control groundwater quality in different aquifers helps to identify the sources of inrush water into coal mines in this paper 65 mine water samples were collected from xiqu coal mine during 2016 and 2017 to determine the hydrogeochemical processes and controlling factors of mine water using hydrochemical methods and multivariate statistical analysis the mine water is acidic to alkaline in nature the dominant anions in the mine water are so42 and hco3 and cations were dominated by ca2 na and mg2 the dominant hydrochemical facies of groundwater were so4 na ca and so4 ca mg water types based on multivariate statistical analysis four principal components and two clusters were obtained concentrations of so42 showed significant positive correlations with ca2 mg2 fe2 and fe3 and strong negative correlations with hco3 and ph the mine water chemistry was dominated by the oxidation of iron bearing sulfide minerals cation exchange and the dissolution of silicate carbonate and sulfate minerals in addition human activities such as agriculture are also likely to have influences groundwater chemistry at the mine site

depositional history of the eocene chumstick formation implications of tectonic partitioning for the history of the leavenworth and entiat eagle creek fault systems washington the chumstick basin opened as an extensional half graben prior to 51 ma and was subsequently modified by two episodes of tectonic partitioning of drainage prior to basin deformation initially westward flowing fluvial systems formed a unified depositional system with the swauk basin tectonic partitioning of drainage at 51 49 ma and at 44 42 ma was controlled by localized uplift on the leavenworth lfz eagle creek ecfz and entiat efz fault zones and led in each instance to the truncation of regional depositional systems modification and reversal of paleoflow and internal drainage relief on the lfz at 51 49 ma may be the result of isostatic uplift of the extensional footwall producing the swauk and chumstick basins as a pair of west facing half grabens the earliest convincing evidence for the onset of oblique slip in the region is at about 48 ma folding in the swauk basin or about 44 42 ma probable transpressive uplift at left stepping bends of the lfz development of a transtensional step over basin between the ecfz and efz horsetail splays in the ecfz and possible flower structures in the lfz and ecfz in the chumstick basin each episode of tectonic partitioning was followed by proximal onlap and overtopping of fault zones to reestablish regional flow systems the chumstick formation was deformed by dextral transpression between 37 34 ma and is unconformably overlain by the oligocene wenatchee formation the chumstick basin is an example of an extensional basin modified by subsequent strike slip tectonics thus caution should be used in applying idealized basin models