diagenesis and hydrocarbon accumulation brent sandstone jurassic bergen high area north sea diagenesis of brent group sandstones in the bergen high area was studied and related to the history of hydrocarbon maturation and pore fluid environment calcite and kaolinite are low temperature diagenetic precipitates that formed as meteoric pore water entered the brent at the end of brent deposition and later during late cimmerian erosion a major period of feldspar dissolution associated with quartz and illite cementation occurred at huldra field precipitation of diagenetic illite in brent sandstones was closely linked with hydrocarbon maturation in the adjacent viking graben and accumulation of generated fluids in traps at structural highs at huldra field illite k ar ages suggest onset of illite diagenesis in the latest cretaceous initial reservoiring of hydroca bons during the latest paleocene to early eocene 58 ma and filling of the reservoir by early oligocene 38 ma pore water character during illite diagenesis interpreted from oxygen isotope and quartz overgrowth fluid inclusion data was warmer than predicted by burial history analysis and one and a half to two times seawater salinity the incursion of saline isotopically evolved fluids at huldra suggests replacement of paleometeoric water by basin compaction fluid illite k ar ages from veslefrikk field indicate a minimum age of hydrocarbon accumulation at about 30 ma modern pore water chemistry in the brent at veslefrikk is unlike the suggested water chemistry at huldra and indicates that migrating compaction water did not completely displace older fresh connate water this sugge ts that hydrocarbons migrated into veslefrikk as a discrete phase without great volumes of associated compaction water

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

lithospheric processes and products in the southern canadian cordillera a lithoprobe perspective analyses of lithoprobe and other data from southwestern canada provide new insights on how this portion of the cordillera formed during plate convergence along the western margin of north america crustal rocks are detached from their mantle lithosphere which must have been consumed during subduction detachment occurred at or near the base of the crust beneath the intermontane and or omineca belts probably along the tips of tectonic wedges while the rocks were still outboard of the relatively cool mechanically rigid north american craton during the late cretaceous and early tertiary rotation of detached rocks caught between the north american craton and the oceanic plates accounts for some apparently conflicting results between paleomagnetic data that indicate large northward translation of rocks in the western cordillera and regional geological features that appear to preclude comparable amounts of translation of rocks in the eastern cordillera during the same time interval transpression assoc

middle jurassic terrane accretion along the western edge of the intermontane superterrane southwestern british columbia two small lower mesozoic terranes the bridge river and cadwallader lie along the southwestern margin of the intermontane superterrane and represent fragments of a volcanic arc and marginal basin that bordered north america in the early mesozoic during middle jurassic time these terranes were juxtaposed and deformed this event was synchronous with deformation in northern and central british columbia and it probably records accretion of the cadwallader and stikine volcanic arcs against quesnellia during closure of the bridge river cache creek ocean basin

structural geometry and kinematic evolution of the eastern cascades foldbelt washington and british columbia the eastern cascades foldbelt is one of three structural domains lying within the complex collision zone between the insular and intermontane composite terranes in northern washington and southern british columbia the foldbelt resides between the high grade metamorphic backbone of the cascade orogen on the west and rocks of the composite intermontane terrane to the east it encompasses the stratigraphically coherent basalt floored jura cretaceous methow basin as well as more chaotically disposed permian jurassic oceanic rocks of the hozameen terrane methow basin rocks are thought to have been sutured above the oceanic rocks prior to the middle cretaceous contractional episode described in this report based on the analysis presented herein between ca 100 and 88 ma the rocks in the foldbelt underwent shortening in an east northeast west southwest direction by 50 km or more largely by displacement on the east vergent jack mountain chuwanten thrust system the early stages of contraction occurred by

atmospheric boundary layer structure and turbulence during sea fog on the southern china coast abstractsmall scale turbulence has an essential role in sea fog formation and evolution but is not completely understood this study analyzes measurements of the small scale turbulence together with the boundary layer structure and the synoptic and mesoscale conditions over the life cycle of a cold advection fog event and a warm advection fog event both off the coast of southern china the measurement data come from two sites one on the coast and one at sea these findings include the following 1 for cold advection fog the top can extend above the inversion base but formation of an overlaying cloud causes the fog to dissipate 2 for warm advection fog two layers of low cloud can merge to form deep fog with the depth exceeding 1000 m when strong advection of warm moist air produces active thermal turbulence mixing above the thermal turbulence interface 3 turbulence near the sea surface is mainly thermally driven for cold advection fog but mechanically driven for warm advection fog 4 the mo

proterozoic and cenozoic subduction complexes a comparison of geometric features mantle reflections along the lithoprobe slave northern cordillera lithospheric evolution snorcle deep seismic reflection transect in northwestern canada are interpreted as a relict subduction zone geometric features of the data in the vicinity of the interpreted subduction zone are compared with those of the vancouver island profile which images a modern convergent margin comparisons are made at both a regional scale as in the case of the location of the magmatic arc with respect to the subduction zone as well as a local scale such as the geometry of structures within the accretionary wedge the comparison provides a test for the paleosubduction hypothesis and aids the interpretation of the deep reflection profile where it is difficult to trace individual features to outcrop the similarity of geometry and scales of the structures gives support to the interpretation that the lithospheric structures in the wopmay orogen are the products of accretionary processes at 1 88 1 84 ga and that these accretionary processes are similar to those observed today

lithoprobe seismic reflection structure of the southeastern canadian cordillera initial results nearly 270 km of crustal seismic reflection data obtained by lithoprobe in the southern canadian cordillera provide a geometric link between the rocky mountain foreland thrust and fold belt the purcell anticlinorium and the extensional regime superimposed on the crystalline core zone autochthonous north american basement and its overlying deformed and transported cover can be traced from the thrust and fold belt beneath the rocky mountain trench to 20 km depth beneath the central part of the purcell anticlinorium the purcell anticlinorium is cored by foreshortened proterozoic supracrustal rocks that were carried northeastward on a series of west dipping imbricate thrust faults these faults crop out within and east of the anticlinorium and converge downward with subhorizontal detachments above the autochthonous north american basement beneath the western purcell anticlinorium and kootenay arc reflections associated with the purcell stratigraphy and its underlying crystalline basement terminate at about 20 km depth and may be truncated against the east dipping eocene slocan lake fault zone the slocan lake fault zone is clearly imaged from the surface to about 12 km depth and can probably be followed discontinuously to about 25 km depth a west dipping high amplitude reflection from beneath the valhalla gneiss complex outlines the domal geometry of the complex and is probably related to an east verging compressional shear zone

seismic structure across the active subduction zone of western canada the vancouver island seismic project was conducted in 1980 to study the structure of the subducting oceanic juan de fuca plate and the overriding continental america plate the principal seismic refraction line line i was a 350 km onshore offshore profile perpendicular to the continental margin an array of 32 receivers was located on the america plate on the mainland and across vancouver island and extended offshore with three ocean bottom seismometers obs s two shots were fired at the eastern end of the line and 17 shots were located along the westernmost 100 km of the profile control for the interpretation of the onshore offshore profile was provided by a reversed refraction profile along the length of vancouver island and by a marine refraction profile recorded on the obs s modeling of the seismic structure of this complex region utilized an iterative inversion method for travel times from explosions in which shots at several locations are recorded on the same set of receivers and utilized an algorithim based on asymptotic ray theory for the calculation of synthetic seismograms through two dimensional media the major features of the refraction structural model are that 1 the oceanic lithosphere dips at 3 or less beneath the continental slope so the bend in the subducting slab occurs landward of the foot of the slope 2 the oceanic lithosphere dips at 14 16 beneath the continental shelf until it passes beneath the continental moho at 37 km depth below western vancouver island 3 an upper mantle reflector may correspond to the base of the subducting lithosphere and 4 a segment of high velocity material above the downgoing crust with velocity 7 7 km s and depth range 20 25 km may represent a remnant of subducted lithosphere perhaps detached when the subduction zone jumped westward to its present position

age of the bowen island group southwestern coast mountains british columbia a new u pb date of for foliated felsic metavolcanic rocks of the bowen island group from mount elphinstone in the southwesternmost coast mountains of british columbia indicates that there the age of this hitherto undated unit is early middle jurassic these rocks grade along strike to the north northwest into a more sedimentary facies which north of jervis inlet contains a probable sinemurian lower jurassic ammonite the bowen island group thus appears to include lower and middle jurassic rocks and to be coeval in part with volcanic rocks of the bonanza formation on vancouver island to the west and the harrison lake formation within the central coast mountains 75 km to the east

geometric test for late cretaceous paleogene intracontinental transform faulting in the canadian cordillera the tintina trench northern rocky mountain trench tt nrmt fault zone and the fraser river straight creek fr sc fault zone are separate en echelon concentric small circle fault segments of a composite intracontinental transform fault zone more than 2500 km long that cuts diagonally across the canadian cordillera from the outboard part of a tectonic collage of accreted foreign terranes in the south into the north american preaccretionary continental margin in the north most of the 450 km of right hand slip on the tt nrmt fault zone was transformed southward during the late cretaceous and paleocene into oblique convergence in the southern canadian rockies the remainder probably comprising less than 100 km was transformed southwestward during early and middle eocene time via a zone of distributed shear and east west crustal stretching into right hand slip on the en echelon fr sc fault zone these interpretations based on regional systematic mapping of geologic structures are in conflict with interpretations of paleomagnetic measurements that call for more than 1000 km of post mid cretaceous right hand displacement along the general locus of the tt nrmt fault zone involving foreign terranes and the parts of north america to which they had been accreted this paradox must be resolved

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

electromagnetic constraints on strike slip fault geometry the fraser river fault system magnetotelluric data from four profiles crossing the eocene strike slip fraser river fault in southwestern british columbia suggest that it penetrates the entire crust this conclusion is supported by seismic reflection observations of a 2 3 km step in the moho slightly to the east of the surface expression of the fault but is at variance with an interpretation of the seismic data in which the fault soles into mid crustal reflectors that seem to be continuous across the fault trace a crustal penetrating geometry supports the proposal that the fraser river fault forms part of a 2500 km long intracontinental transform fault system in northwestern north america modeling studies resolve a thin highly conducting mid crustal zone that is connected electrically to the conducting lower crust beneath the coast belt low 13 c values close to the fraser fault system suggest that the electromagnetic signature of this zone may be due to the presence of organic carbon

a geodynamic framework for interpreting crustal scale seismic reflectivity patterns in compressional orogens summary 2 d plane strain finite element models are used to calculate crustal deformation patterns within model compressional orogens and the results are compared with natural examples the fundamental driving mechanism for model deformation is provided by asymmetric detachment and underthrusting of mantle lithosphere with deformation being rooted at the stress singularity where the mantle detaches deformation steps up into the overlying crust and spreads laterally according to the rhcological properties assumed for the crust the crust is modelled using plastic frictional and viscous rheologies and incorporates the effects of compositional layering and variable geothermal gradients overall deformation is determined by balancing the internal strength of the crust against the sum of applied boundary stresses plus the gravitational stress induced by mass redistribution within the deforming orogen the amount of convergence in the models is limited to 150 km or less and so the results are not strictly comparable with larger orogens involving greater convergence nevertheless larger orogens seem to evolve through stages that may be understood in terms of the models provided that consideration is confined to smaller scale components that are limited in time and space the continuum deformation calculated by the finite element models is qualitatively converted to equivalent pattcrns of discrete faults and shear zones by associating these discrete features with the areas of highest cumulative strain using the results of sandbox experiments as guides significant styles of deformation include 1 coupling between step up shears and subhorizontal detachments at one or more levels 2 localization of upper crustal deformation by subduction of the lower crust and 3 pinning of deformation by surface denudation a partial catalogue of such model styles is presented in which the strength of basal coupling between crust and mantle the number of rhcological layers within the crust the thickness of subducted lower crust and the extent of surface denudation are varied systematically compressional orogens with a wide range of ages are characterized by crustal scale seismic reflectivity similar to patterns of fault shear zones represented in this catalogue of styles this similarity suggests that crustalscale seismic reflection data can be used to constrain the dynamic processes involved in compressional orogcnesis

lithoprobe southern vancouver island cenozoic subduction complex imaged by deep seismic reflections reply the lithoprobe seismic reflection project on vancouver island was designed to study the large scale structure of several accreted terranes exposed on the island and to determine the geometry and structural characteristics of the subducting juan de fuca plate in this paper we interpret two lithoprobe profiles from southernmost vancouver island that were shot across three important terrane bounding faults leech river san juan and survey mountain to determine their subsurface geometry and relationship to deeper structures associated with modem subduction the structure beneath the island can be divided into an upper crustal region consisting of several accreted terranes and a deeper region that represents a landward extension of the modern offshore subduction complex in the upper region the survey mountain and leech river faults are imaged as northeast dipping thrusts that separate wrangellia a large mesozoic paleozoic terrane from two smaller accreted terranes the leech river schist mesozoic rock

coast plutonic complex a mid cretaceous contractional orogen early late cretaceous east vergent thrusts deform much of the eastern margin of the coast plutonic complex in western british columbia similarities in timing and style suggest that the faults represent a system of backthrusts to a west vergent thrust belt on the west side of the complex this geometry and the rarity of mid cretaceous strike slip faults indicate that the coast plutonic complex was a strongly contractional orogen in mid cretaceous time

experiments on adsorption and molecular sieving and inferences on primary migration in upper jurassic claystone source rocks north sea fine pores primarily slit shaped micropores in upper jurassic claystone source rocks were studied by gas adsorption at 20 c approximately 80 of the mesopore and micropore volume is penetrable to water only because of constrictions approximately 3 a wide the pore surface is nonpolar and probably characterized by kerogen covering the clay mineral surfaces water is not structured in the mesopores and micropores but readily forms a liquid phase without distinct monolayer formation n alkanes probably enter the pores end on and become adsorbed parallel with the surface these results apply to all samples studied irrespective of the degree of clay mineral diagenesis three migration types proposed for these claystone source rocks are 1 type a migration which at experimental conditions permits entry and removal of n alkanes isobutane neohexane cyclohexane and benzene in approximately equal amounts 2 type b migration which permits entry and removal of n alkanes isobutane and neohexane in approximately equal amounts but where only 20 of the pore volume and surface area is also open to cyclohexane and benzene and 3 type c migration which is intermediate between type a and type b the occurrence of the migration type is related to the reservoir oil composition in the samples studied tectonics and clay mineral diagenesis appear to have no influence on the migration type migration types may be related to past overpressured conditions but do not appear to be related to current pressures

nature of the contact zone between the north cascades crystalline core and the methow sequence in the ross lake area washington implications for cordilleran tectonics previous analyses of the accretionary history of nw washington sw british columbia have suggested the possibility of large scale dextral slip faulting events to explain the present day regional outcrop pattern the contact zone between the crystalline skagit complex and the volcano sedimentary methow sequence has been considered to be a major fault named the ross lake fault by misch 1966 and has been considered to be a possible large scale strike slip fault by later workers detailed mapping of this contact zone in the ross lake area shows that the brittle faults and mylonites thought by misch to express dextral shearing along the contact are not continuous throughgoing structures and that the contact between skagit orthogneisses and methow sequence strata is primarily intrusive furthermore the mylonites show both left and right lateral shear the skagit methow contact is therefore not a major terrane boundary but rather a tectonized intrusive contact that has not accommodated significant motion between the two regions based on these observations and regional synthesis of timing relations deformation in the contact zone is interpreted to express regional ene wsw shortening not major dextral slip in the early tertiary since no terrane bounding fault exists the cretaceous tertiary history of the ross lake area can be interpreted as follows 1 jurassic early cretaceous forearc rift basin sedimentation deposition of the lower methow sequence 2 110 95 ma imbrication of the lower methow sequence and its basement of oceanic crustal rocks by east vergent thrusting with concomitant development of a west derived foredeep in the upper methow sequence 3 95 85 ma arc magmatism with genesis of the skagit migmatite from methow and older basement protoliths and 4 paleocene early eocene folding faulting uplift and exposure of a relatively intact 25 km crustal section termed the skagit methow crustal section by kriens and wernicke 1987

lithoprobe crustal reflection cross section of the southern canadian cordillera 1 foreland thrust and fold belt to fraser river fault seismic reflection data from the south central canadian cordillera covering the interval from the easternmost metamorphic core complexes near arrow lakes to the fraser river fault system along the fraser river reveal a highly reflective and complex crust the base of the crustal reflectivity interpreted as the reflection moho is clearly delineated by a continuous sharp boundary that is essentially planar and slopes uniformly over a distance of 250 km from about 12 0 s in the east to about 10 5 s in the west this virtual lack of relief at the base of the crust contrasts sharply with surface structures that involve 25 km or more of structural relief some of these surface structures can be readily correlated to structures that are outlined by the reflection data and that can be followed into the middle and lower crust even though part of this area was subjected to large amounts of eocene extension the crust is not divisible into transparent upper and reflective lower layers as it is in parts of the u s cordillera three structural culminations the monashee complex the vernon antiform and the central nicola horst are interpreted on the basis of the reflection configuration and the surface geological relationships to have formed initially during jurassic to eocene compression and then to have been modified and exposed during early and middle eocene extension an example of a compressional structure observed on the profiles is the monashee decollement which can be traced from the surface westward into the lower crust extension is manifested along a variety of normal faults including the regionally extensive low angle okanagan valley eagle river fault system moderately dipping faults such as the columbia river and slocan lake faults and high angle faults such as the quilchena creek and coldwater faults both jurassic to eocene compressional shear zones and early to middle eocene extensional shear zones are listric into the lower crust or moho under the intermontane belt

electromagnetic images of crustal structures in southern and central canadian cordillera data from more than 400 magnetotelluric soundings made since the early 1980 s in the canadian cordillera over a 300 000 km2 area between 49 and 53 5 n are used to image qualitatively regional three dimensional crustal variation in electrical conductivity by means of phase maps phase frequency sections and maps of resistivity at depth two hundred of the soundings were acquired as part of lithoprobe southern canadian cordillera transect activities and their locations were coordinated with the seismic reflection and refraction experiments the lower crust has a generally pervasive low resistivity 1 100 m throughout the cordillera west of the foreland belt within this canadian cordilleran regional conductor the magnetotelluric data reveal both two dimensional structures with highest conductivities along the coast belt and omineca belt and three dimensional variation along geological strike this conductor mapped over a volume in excess of 106 km3 is most probably caused by fluids saline wat

lithoprobe crustal reflection structure of the southern canadian cordillera 2 coast mountains transect the lithoprobe seismic reflection transect across the southern coast mountains of the canadian cordillera images fundamental crustal structures presumably related to collision of the intermontane and insular composite terranes and deep levels in the upper plate of the offshore cascadia subduction belt the eastern part of the coast mountains are characterized by east dipping upper crustal reflectors that project to exposed faults and east dipping lower crustal reflectors they are truncated by subhorizontal to west dipping middle and upper crustal reflectors these geometric relationships are interpreted to have formed during an early phase of primarily west directed contraction that created the east dipping structures of the upper and lower crust and a later phase of east directed shortening caused by wedging of the intermontane belt into the lower and middle crust of the tectonic stack subsequently the coast belt may have been displaced eastward on contractional faults that ascend from the lower crust beneath the intermontane belt and surface in the omineca and foreland belts extensional faults bounding the east flank of the coast mountains and west flank of the central nicola horst in the intermontane belt flatten into the middle and lower crust of the intervening region and geometrically outline crustal boudinage within the western coast mountains east dipping reflections spanning the middle crust to upper mantle are traced updip to vancouver island and the underlying cascadia subduction zone the c reflector on vancouver island is believed to separate wrangellia from underlying accreted terranes and is correlated to the mainland where it forms the upper boundary of a reflective lower crustal wedge that flattens into the moho if the moho is not a young feature then some accreted material appears to have wedged into the continental framework above the crust mantle boundary possibly causing shortening in the overlying crust and creating midcrustal ramps observed on the reflection data the structurally lower e reflections interpreted as shear zones originate at the subduction contact offshore and project landward into sub moho reflections within the upper plate on the mainland the region between the e reflector and the descending oceanic plate is interpreted to be subducted lower continental crust and mantle

enhanced crustal reflection continuity by estimation of staitcs from coherence filtered sections coherency filtered seismic sections provide excellent models for estimating residual statics especially for deep crustal data with low signal to noise a second coherency filter pass following residual statics collections provides even better structural clarity than is seen on sections with only a single coherency filter pass benefits of the technique include increased lateral extent of individual reflections resulting in fewer isolated events uniform wavelet shape throughout the section and an increase in the number of detected events over line drawings this processing flow results in appealing visual displays and may provide new information on structural complexities not recognized in line drawings based on the input data alone

the electrical conductivity distribution beneath vancouver island a region of active plate subduction magnetotelluric mt and geomagnetic depth sounding gds data were recorded at 25 locations across vancouver island canada over the subducting juan de fuca plate the gds data respond to a number of local conductive features at frequencies above 10 hz while at longer periods the in phase and quadrature induction arrows are colinear and are aligned approximately normal to the continental shelf with a maximum amplitude response near the southwest coast interpretation of the mt data show the presence of a conducting zone at depths greater than 20 km beneath vancouver island and correlating with a strong seismic reflector extensive testing with two dimensional models shows the mt and gds data are consistent with a proposed geoelectrical structure containing a conducting layer extending from the pacific ocean dipping beneath vancouver island and in electrical contact with the mainland conductive region the layer has a horizontal conductance of 200 s that may decrease to 100 s beneath the northeast side of vancouver island related geophysical studies suggest the conductive zone is above the actual thrust surface of the juan de fuca plate the conducting layer is most likely the result of cracks and pores filled with saline fluids which are supplied bymore water subducted with the oceanic crust and by dehydration reactions the presence of fluids has significant implications for thrust earthquakes and for metamorphic reactions that occur in subduction zones the conductance of the upper mantle between 90 and 390 km is best modeled at approximately 1 500 s less

seasonal variations of yellow sea fog observations and mechanisms sea fog is frequently observed over the yellow sea with an average of 50 fog days on the chinese coast during april july the yellow sea fog season is characterized by an abrupt onset in april in the southern coast of shandong peninsula and an abrupt basin wide termination in august this study investigates the mechanisms for such steplike evolution that is inexplicable from the gradual change in solar radiation from march to april over the northwestern yellow sea a temperature inversion forms in a layer 100 350 m above the sea surface and the prevailing surface winds switch from northwesterly to southerly both changes that are favorable for advection fog the land sea contrast is the key to these changes in april the land warms up much faster than the ocean the prevailing west southwesterlies at 925 hpa advect warm continental air to form an inversion over the western yellow sea the land sea differential warming also leads to the formation of a shallow anticyclone over the cool yellow and northern east china seas in april the southerlies on the west flank of this anticyclone advect warm and humid air from the south causing the abrupt fog onset on the chinese coast the lack of such warm moist advection on the east flank of the anticyclone leads to a gradual increase in fog occurrence on the korean coast the retreat of yellow sea fog is associated with a shift in the prevailing winds from southerly to easterly from july to august the august wind shift over the yellow sea is part of a large scale change in the east asian western pacific monsoons characterized by enhanced convection over the subtropical northwest pacific and the resultant teleconnection into the midlatitudes the

clay mineral transformations in tertiary and mesozoic sediments from north sea clay mineral transformations of 10 north sea wells have been studied and several transformation stages picked out and correlated with geothermal variations smectite disappears at 149 to 167 f 65 to 75 c whereas transformations in the mixed layer illite smectite clay minerals are observed between 113 and about 212 f 45 and about 100 c at temperatures above 113 to 149 f 45 to 65 c more than 30 illitic layers are found in the mixed layered clay minerals whereas temperatures from 140 to 167 f 60 to 75 c indicate the transition zone toward more than 50 dehydrated lattice positions temperatures above 176 to 212 f 80 to 100 c mark the lower limit for mixed layer clay minerals containing more than 70 illitic la ers the major part of the clay mineral transformations apparently takes place in the mesodiagenetic zone in which most of the hydrocarbons are also formed

the role of geochemical self organization in the migration and trapping of hydrocarbons abstract many sedimentary basins of the world contain abnormally pressured compartments surrounded by impermeable seals which may serve as hydrocarbon traps observations of the many types of seals that may exist point to an origin due to self organization self organization is the development of repetitive or other low symmetry patterns from an initially unpatterned system in the absence of an externally imposed template and involves feedback generated by the interaction of transport chemical reactions and grain growth and dissolution herein we focus on the self organizing mechanisms of reaction driven advection as they pertain to the formation of diagenetic traps

reconciliation of two sided thrusting burial metamorphism and diachronous uplift in the cascades of washington and british columbia several recently published data sets have shed new light on many of the fundamental kinematic aspects of mid cretaceous orogeny in the cascades of northwestern washington and southwestern british columbia specifically a it is now clear that contractional deformation associated with this orogeny affected rocks east of the crystalline core of the range to a greater degree than had previously been suspected and b geobarometric data from the crystalline core of the range now permit a quantitative reconstruction of the crustal thickening event responsible for core metamorphism to be attempted i propose a new kinematic model for mid cretaceous orogeny that reconciles these data with previously collected data sets that focused on deformation in the northwest cascades san juan islands thrust system the model derived from this analysis suggests that the cascades underwent a minimum of between 400 and 500 km of east west shortening between about 115 and 85 ma owing to the collision of the greater insular terrane which probably included rocks of the chilliwack nooksack terrane with the western edge of the greater intermontane terrane which included the methow basin and bridge river hozameen terrane on the basis of their relative and absolute times of uplift i assign the deepest part of the metamorphic core the skagit gneiss to the greater insular terrane and the structurally higher carapace of the core the settler nason metapelites and the cogburn creek mad river metabasalt metachert to the westernmost intermontane terrane the contact between the skagit gneiss and the overlying assemblages must represent a fault or suture across which at least 120 km of displacement took place this fault is also the root zone from which many of the nappes in the northwestern cascades and san juan islands were derived i concur with previous workers who suggested that the collisional event was not precipitated by the closure of a several thousand kilometer wide ocean but was rather due to a short lived margin normal convergence event that both followed and was followed by periods during which the continental margin was highly influenced by oblique subduction and strike slip faulting

accretion and recent deformation of sediments along the northern cascadia subduction zone new multichannel seismic reflection profiles acoustic imagery and swath bathymetric data from the vancouver island continental margin reveal the surface morphology cross sectional geometry and deformation style of this part of the cascadia accretionary prism the incoming 3 to 5 km thick sediment section fails most commonly along landward dipping thrusts that penetrate to or very close to the top of the underlying oceanic crust the faults are listric with approximately circular cross sections and hanging wall sediments are back tilted in a planar manner high near lithostatic pore pressures in the deeper part of the section are inferred from the flattening of the faults near the decollement and from the long distances over which the decollement has propagated seaward the faults dip more steeply at 40 45 near the surface where pleistocene turbidites are displaced similar folds have developed where the turbidites are particularly thick 4 km and near hydrostatic pore pressures are inferred to occur in the turbidite part of the section an increase in pore pressure with depth is expected as a consequence of sedimentation and tectonic loading particularly because the deeper hemipelagic sediments are probably far less permeable than are the overlying turbidites the top of the downgoing juan de fuca plate which defines the base of the accreted sedimentary wedge beneath the margin is well imaged in the new seismic reflection profiles and is further defined by land reflection data seismic refraction and earthquake hypocenters the landward dipping continental backstop to the prism is also well located if these constraints are used for the geometry of the accretionary prism a general balance is found between the present prism volume and the estimated total sediment supply over the approximately 42 m y accretion history this result along with the observation that deformation front faults penetrate most or all of the sediment section suggests that little or no sediment has been subducted since initiation of the present phase of subduction in the eocene application of the critically tapered wedge model of davis and others to the observed prism geometry suggests that high average pore pressures occur in the prism particularly the seawardmost part beneath the lower slope beneath the continental shelf the dip of the subducting slab increases to greater than 11 a dip that according to the critically tapered wedge model is too steep to allow upward growth of an accretionary prism this provides a simple explanation for ongoing subsidence of the tofino sedimentary basin over the older part of the accretionary complex to the southeast the juan de fuca plate dips much more gently beneath the olympic peninsula of northern washington allowing the accretionary prism to grow upward well above sea level to form the olympic mountains

quantitative modeling of organic matter connectivity in source rocks using fractal geostatistical analysis abstract numerical modeling of hydrocarbon expulsion requires accurate assessment of the 3 d geometry and connectivity of hydrocarbon pathways such as pore systems organic matter networks fractures and stylolites in source rocks in this paper a method combining scanning electron microscopy sem digital image analysis fractal geostatistical analysis and a renormalization algorithm is developed to determine the 3 d geometrical properties defined as organic matter connectivity factor ocf of these pathways in source rocks the method is applied to derive fractal geostatistical models and the ocfs of organic matter networks omn of fourteen source rocks with wide variation in total organic carbon toc content and texture the results show that the connectivity of the omns is affected by both the amount and distribution of organic matter in source rocks uniformly distributed omns lose 3 d connectivity when the toc content is below approx 6 whereas omns with preferred orientation may maintain lateral connectivity at 4 and perhaps lower toc content thus in shales such as the bakken in which vertical omn connectivity may not exist the fracture systems may provide not only primary migration pathway but hydrocarbon reservoirs that are recharged through the laterally connected omns the method developed in this paper can be used to quantify geological models and average geological properties over a wide range of scales and thereby provide reliable geometric parameters for basin modeling using a numerical technique

deep seismic reflection constraints on paleogene crustal extension in the south central intermontane belt british columbia following growth of the canadian cordillera during the mesozoic the southern cordillera was subject to extension during the paleocene and eocene that correlated with widespread volcanic activity in south central british columbia including across much of the nechako chilcotin plateau in 2008 geoscience bc acquired 330 km of deep vibroseis reflection profiles on the plateau mostly over the stikinia arc terrane but also over its eastern contact with the oceanic cache creek terrane all seven seismic reflection lines reveal a strongly reflective lower crust that extends from 7 to 9 s down to the moho which is defined by the downward termination of reflectivity at 11 12 s in the uppermost crust extension occurred by block faulting with faults soling into subhorizontal to shallowly dipping detachments above 10 km depth extension in the deeper upper and middle crust which was partly controlled by antiforms likely related to earlier shortening was accommodated on a network of anastomosing shear zones

marine boundary layer structure for the sea fog formation off the west coast of the korean peninsula marine boundary layer mbl structure for the formation of sea fogs off the west coast of the korean peninsula are examined for the investigation period from january 2002 to august 2006 using the meteorological data measured at a buoy and the vertical sounding data measured at an island in this region there is the total of 3 294 vertical soundings during the investigation period based on these vertical soundings the mbl structure is classified as convective boundary layer cbl when inversion exists aloft but at altitudes lower than 3 km 1 618 soundings stable boundary layer sbl when inversion base is at the surface 655 soundings or near neutral boundary layer nnbl when there is no inversion or inversion base is higher than 3 km altitude 1 021 soundings under the cbl condition the most frequently formed lower level cloud is stratocumulus but fogs do form in spring and summer months mostly as warm sea fogs tsst t sst 0 are the most frequently found lower level clouds the effects of turbulence advection and radiation on sea fog formation vary with turbulence strength represented by bulk richardson number r b for cold sea fog cases in the highly turbulent regime r b 0 30 regimes the effects of turbulence decrease dramatically and so do the advection effects but radiative cooling is still strong again making it the crucial reason for the successful formation of cold sea fogs on the other hand the turbulent moisture supply from the warmer sea surface is the crucial factor for the formation of warm sea fogs while turbulent warming and radiative cooling largely cancel each other out and the advection effects are negligibly small

recognizing and quantifying expulsion of oil from the woodford formation and age equivalent rocks in oklahoma and arkansas accumulations of oil in fractures stylolites burrows sandstone lenses and chert nodules deeply embedded within organic rich mature oil source beds of late devonian early mississippian age are considered prima facie evidence of internal migration and expulsion most oil migrated internally and was expelled as a separate phase within a given section in which chert and black shale are interbedded contain the same type of organic matter and have reached the same level of thermal maturity black shales typically contain less hydrocarbons per weight percent toc than cherts the observed differences represent the amount of oil expelled from the black shales and range from 10 to 15 mg g toc for total bitumen 7 to 8 mg g toc for saturated hydrocarbons and 11 mg g toc for volatile hydrocarbons approximately 27 33 of the oil generated in these source rocks was calculated to have been expelled in the main oil producing region of central and southern oklahoma 22 billion bbl of bitumen and 16 billion bbl of saturated hydrocarbons were estimated to have been expelled from the woodford formation relatively efficient separate phase oil expulsion may be characteristic of very rich oil source rocks like those reported here such rocks would reach effective oil saturation and begin to expel oil as a separate phase at a relatively early stage of generation timing and efficiency of oil expulsion must then be influenced by the concentration and type of organic matter in the source rock because these factors determine the volume of oil generated and hence the time when a source rock becomes oil saturated

interplay of plutonism and regional deformation in an obliquely convergent arc southern coast belt british columbia the coast plutonic complex is an extensive zone of continental growth that formed along the mesozoic convergent margin of northwestern north america the orogeny creating this belt involved terrane accretion and assembly massive upward transfer and emplacement of sial in the form of batholiths constituting a magmatic arc and transformation of broad tracts of sedimentary and volcanic rocks into crystalline continental crust all operating in more or less the same space and time the mechanisms and interplay of these orogenic processes are well displayed in the harrison lake area of the southern coast belt british columbia great structural relief across the area exhibits a present day architecture defined by thin thrust stacked terrane sheets and early concordant pluton sheets folded on a macroscopic scale all truncated by oblique dextral reverse faults and overlain by later floored plutons construction of this complex began with terrane assembly on orogen normal thrusts during a lull in plutonism in the early cretaceous low grade metamorphism during this event indicates only modest crustal thickening subsequent plutons intruded into the assembled terranes appear to be composites of sheets early pluton sheets are now steeply dipping due to folding but were likely intruded as horizontal bodies large ovoid post folding plutons are mostly subhorizontal floored bodies at least in part sheeted these plutons are underlain by barrovian mineralogic aureoles that indicate downward vertical displacement of 10 km or more during plutonism suggesting pluton emplacement by vertical inflation magmatic fabrics in these bodies and the discordant relation of plutons to regional structures preclude emplacement in active fault zones penetrative strain aureoles flanking plutons are mostly limited to zones a few hundred meters wide and regional tectonic structures are widely preserved tectonic deformation of the arc is characterized by contraction and strike slip not orogen normal extension plutons played a greater role than terrane accretion in causing crustal thickening and high grade metamorphism

mantle heterogeneities and their significance results from lithoprobe seismic reflection and refraction wide angle reflection studiesthis article is one of a series of papers published in this special issue on the theme lithoprobe parameters processes and the evolution of a continent lithoprobe contribution 1486 within lithoprobe s 10 transects data from more than 20 000 km of multichannel seismic mcs reflection profiling and 12 refraction wide angle reflection r war surveys were acquired while the

subsidence and thermal history of queen charlotte basin a tectonic model for the formation subsidence and thermal history of queen charlotte basin is developed based upon regional geological and geophysical data subsidence data from offshore wells in hecate strait and queen charlotte sound and thermal criteria derived from present heat flow and vitrinite reflectance information queen charlotte basin is seen to have resulted from two distinct mechanisms 1 during a period of broad regional uplift rifting and crustal extension occurred in queen charlotte sound up to about 17 ma ago and the queen charlotte islands were displaced northwards toward their present position by transcurrent motion along the louscoone inlet sandspit fault system the rifting generated a significant thermal anomaly and a restricted deep basin as a consequence of crustal thinning and subsequent thermal cooling 2 beginning about 6 ma ago oblique underthrusting commenced along the margin resulting in flexural uplift of the western part of the queen charlotte islands and comp

role of pressure solution in the formation of bedding parallel calcite veins in an immature shale cretaceous southern uk bedding parallel fibrous calcite veins in black shales cretaceous southern uk were investigated using a combined field stable isotopic geochemistry petrographic and crystallographic method to examine their formation mechanism calcite veins occur in all shale beds and are most abundant in the bituminous shales of the chief beef beds the calcite fibres in these veins exhibit either an antitaxial fibre growth with curvy stylolites as the median zone or a predominantly syntaxial upwards growth the calcite veins range from 0 49 to 1 78 of 13c values and 6 53 to 0 03 of 18o values which are both similar to those of their host shales our petrographic observations demonstrate that subhorizontal and interconnecting microstylolite networks commonly occur within the calcite veins equant calcite grains in the median zones exhibit indenting truncating and also interpenetrating grain contacts it is interpreted that the fibrous calcite veins were sourced by neomorphic calcite from their host shales with evidence from the 13c signatures pressure solution features stylolites microstylolites and grain contact styles and embedded fossil ghosts within the veins the diagenetic fluids from which calcite was precipitated were a mixing of the original seawaters and 18o depleted meteoric waters development of bedding parallel calcite veins is considered to have been enhanced by pressure solution as a positive feedback mechanism which was facilitated by the overburden pressure as the maximum principal stress calcite fibres with a predominant subvertical c axis orientation exhibit a displacive growth in porous shales and a replacive growth at vein limestone contacts this study highlights the critical role of pressure solution in the formation of bedding parallel calcite veins during burial and diagenesis of immature black shales

deep high amplitude reflections from a major shear zone above the subducting juan de fuca plate seismic reflection data show that a regionally extensive band of landward dipping reflections exists above the subducting juan de fuca plate at the western canadian continental margin the reflections truncate at depth a major terrane boundary mapped near the surface and must have a structural origin many reflections are very strong having reflection coefficients locally as high as 10 20 these amplitudes are consistent with theoretical calculations of reflections from sharp poirosity contrasts if the pores are very thin however seismic data from the accreted sedimentary melange farther seaward from which much of the deep reflective zone is derived suggest that significant porosity contrasts do not occur alone because higher reflection amplitudes are found in regions of inferred high strain both geometric and amplitude constraints imply that the deep reflective layering represents intensely sheared rocks possibly originating close to the subduction decollement

dolomite from clay in argillaceous or shale associated marine carbonates abstract postcompactional late stage ferroan dolomite commonly occurs as 1 finely disseminated rhombic microspar in argillaceous lime mudstone 2 sparry cement within voids in argillaceous carbonates and 3 sparry cement within carbonates adjacent to marine shales the distribution and abundance of these dolomites correspond with that of clay deposited in the marine environment and cannot easily be explained by alternative models of dolomite formation conversion of smectite to illite during burial is a common diagenetic process which is capable of releasing large amounts of fe mg ca na and si sandstone petrologists have emphasized the significance of this process in generating quartz cements in sandstone shale sequences however the potential of this conversion for producing postcompactional dolomite cement in limestone shale sequences or in argillaceous limestones has been neglected smectite illite conversion is here invoked as the source of ions that formed late stage postcompactional dolomites in examples of the pennsylvanian of oklahoma kansas missouri and iowa the devonian of iowa and the ordovician of oklahoma the smectite illite conversion model for generating dolomite may be widely applicable to many other ex mples of late stage dolomitization it should prove useful in predicting the distribution of late stage dolomite cement that reduces reservoir quality and may prove useful for estimating the timing of hydrocarbon migration relative to carbonate cementation

the northern cascadia subduction zone at vancouver island seismic structure and tectonic history the structure and tertiary tectonic history of the northern cascadia subduction zone have been delineated by a series of new multichannel seismic lines acquired across the continental shelf to the

seismic images of the continental moho of the indian shield abstract deep seismic reflection profiling has imaged different patterns of the moho across the indian shield with a variety of tectonic environments from archean to recent the character of the moho varies from a discrete strong event the base of strong coherent lower crustal sub horizontal reflections the base of dipping lower crustal reflections into mantle to no clear reflection boundary the seismic reflection data suggest a laminated lower crust in several places and offsets in the moho at others kinematic and dynamic modeling of wide angle reflection data across the mesoproterozoic south delhi fold belt and the central indian tectonic zone suggests a laminated lower crust for these regions in general the lower crust of the indian shield is heterogeneous a clear moho is identified in some of the precambrian orogenic belts and sedimentary basins along with reflective lower crust whereas the cratonic areas exhibit a diffused moho post collisional extensional process such as orogenic collapse delamination magmatic intrusions low viscosity ordering and underplating might have played a role in the generation of lower crustal laminated zone and formation of a younger moho the termination of lower crustal reflectivity at the moho with a transparent upper mantle need not necessarily indicate homogeneous upper mantle

the reflection moho beneath the southern canadian cordillera the transition from the crust to the mantle beneath the canadian portion of the north american cordillera varies in depth geometry and tectonic age across the orogen these variations are rarely spatially related to the positions of morphologic or tectonic belts based on surface geology nor to nearly 25 km of structural relief identified in outcrop and on seismic reflection data the moho in this region is thus interpreted to be a long lived feature perhaps as old as proterozoic in the eastern part of the cordillera that probably has been active as a structural boundary during periods of crustal contraction and subsequent crustal stretching recognition of the moho and lower crust as a zone of localized tectonic activity provides a partial explanation for the problem of where regional detachments that underlie the foreland thrust and fold belt go as they project westward to deep structural levels beneath the interior of the orogen they likely project to the base of the crust where they flatten and

fibrous calcite veins overpressures and primary oil migration the fibrous calcite veins found parallel to the bedding of certain shales may have been formed during burial as a consequence of overpressuring their presence could even be indicative of former overpressures this suggestion if it can be upheld carries implications for theories of primary oil migration

how the crust meets the mantle lithoprobe perspectives on the mohorovicic discontinuity and crust mantle transition application of regional geophysical and geological methods throughout two decades of canada s lithoprobe project provides new opportunities to analyze the mohorovicic discontinuity moho and crust mantle transition the transect format employed during lithoprobe in which 10 specified regions of canada were targeted for approximately a decade each between 1984 and 2003 permitted teams of scientists to focus on geological geophysical and tectonic issues for each transect as a primary objective was to enhance knowledge of the structure of the crust and lithosphere an obvious target in each transect was the nature and origin of the moho and crust mantle transition accordingly the combined results provide new perspectives on the moho and the relationship of the moho to the crust mantle transition perhaps the most important result is that the continental geophysical moho is a deceptively simple feature it has a variety of signatures at different scales that preclude a single universally applicable interpretation in methods that provide large scale information such as regional seismic studies it is a relatively abrupt refraction velocity contrast that often displays a dramatic downward decrease in seismic reflectivity however its origin in a geological or tectonic sense is perhaps best determined by careful analyses of structural details near the geophysical moho which are complex and varied in some areas within canada it appears that the geophysical moho may be old and perhaps remains from the time the crust formed in other areas it appears to be a relatively young feature that was superimposed onto older crustal fabrics

lithoprobe southern vancouver island seismic reflection sees through wrangellia to the juan de fuca plate multichannel seismic reflection profiles obtained on vancouver island show that above a zone of decoupling between the north american and juan de fuca plates wrangellia is underplated by two accreted terranes of probable oceanic origin both the zone of decoupling and wrangellia are disrupted by easterly dipping faults some of which are thrusts the crustal structure of wrangellia comprises paleozoic and mesozoic volcanic and sedimentary rocks disposed as roof pendants upon and large irregular masses within a ubiquitous jurassic plutonic and metamorphic complex

diagenesis of the kimmeridge clay formation onshore uk study of sedimentology carbonate geochemistry and clay mineralogy of four laterally continuous beds from the outcrop of the kimmeridge clay formation indicates strong lateral variations in the depositional and early diagenetic processes reflecting the basin and swell topography of the depositional basin the mudstones from the swell environment with low sedimentation and subsidence rates are shelly and carbonate rich with thin poorly developed oil shales they were deposited under dysaerobic conditions with consequent poor organic matter preservation early diagenetic processes were limited to the sulphate reduction and methanogenesis zones with the formation of discrete horizons of concretions the shallow burial depths attained are reflected by the immaturity of the organic matter in the mudstones although ordered illite smectites are present sediments from other locations comprise black organic rich mudstones the thick beds and good organic matter preservation indicating deposition under high sedimentation and subsidence rates with anoxic bottom waters in a basinal environment these indurated mudstones contain a few shell fragments and much pyrite indicating intense reaction in the sulphate reduction zone carbonates were precipitated in the methanogenesis and decarboxylation zones as ferroan calcites and dolomites the much greater burial depths are indicated by the higher maturity of the organic matter and by the ordered nature of the illite smectites and the loss of kaolinite

lithospheric structure in the southern canadian cordillera from a network of seismic refraction lines lithospheric velocity structure and its relationship to regional tectonics and development of the southern canadian cordillera are derived from a synthesis of interpretations from nine in line seismic refraction wide angle reflection profiles and broadside data recorded during the lithoprobe southern cordillera refraction experiment score and other refraction experiments across southern british columbia and one profile in northwestern washington consistency of the score two dimensional models at their intersection positions is achieved through application of a simultaneous inversion of all relevant traveltime data the cross sectional and map presentations demonstrate the strong degree of three dimensional heterogeneity within the crust and upper mantle a first order characteristic is the continuous increase in crustal velocities westward from the foreland belt to the insular belt the variations do not correlate with the morphogeological belts they do correspond with large scale geological and or

abnormal formation pressure and shale porosity an abnormally pressured jurassic shale from the north sea viking graben has a fluid pressure over burden ration close to 0 8 at a depth of more than 4 000 m and is associated with low porosity and high density the porosity and fluid pressure history of the shale involves three successive stages 1 normal gravitational compaction prevailed during the first few hundred meters of burial 2 the shale porosity was severely reduced by carbonate cementation in conjunction with a major break in sedimentation but the fluid pressure remained hydrostatic and finally 3 the porosity was further reduced by compaction and possibly cementation and the fluid pressure increased to above hydrostatic in response to renewed subsidence and the cretaceous and tertiary overburden lo d

an observational study of cloud topped mixed layers abstract the turbulence and mean structure of oceanic stratocumulus was studied using aircraft data collected during the summer of 1976 off the coast of california three cloud topped mixed layers were studied in detail they consisted of 1 a thin cloud capped by an inversion at a height of 1000 m 2 a relatively thick but broken cloud layer capped by a weak inversion at 600 m and 3 a solid cloud capped by a strong inversion at 600 m the mean temperature moisture liquid water and radiative characteristics obtained for these three cases were compared heat and moisture fluxes were also calculated and compared although there was considerable variation in the characteristics of the three cloud topped mixed layers studied all indicated the validity of the general approach used in simple mixed layer models of stratocumulus but for these models to be useful they should be generalized to allow clouds other than solid clouds to be modeled the measurements indicate that cloud microphysics may be impo

a numerical study of an extreme cold air outbreak over the labrador sea sea ice air sea interaction and development of polar lows in this paper the ability of the mm5 mesoscale forecast model to simulate the air sea interaction boundary layer development and mesoscale structure associated with a cold air outbreak over the labrador sea is investigated the case chosen was one for which research aircraft data and satellite imagery are available for validation the default surface layer parameterization included in the model is shown to grossly overestimate the magnitude of the air sea interaction resulting in forecasts of boundary layer growth and mesoscale development that differ substantially from observations it is also shown that a representation of the inhomogeneities in sea ice cover results in a significant improvement in simulations of the air sea interaction boundary layer development and mesoscale structure both within the marginal ice zone and downstream over the open ocean finally the mesoscale cyclones or polar lows observed in the wake of the cold air outbreak are shown to be coupled to the evolution of an upper tropospheric potential vorticity anomaly that was advected over the region the model simulations suggest that mm5 most probably due to inaccuracies in and the limited resolution of the analyzed fields that supply the initial and boundary conditions to the model was unable to correctly simulate the development and track of this anomaly and this ultimately led to an incorrect forecast of the polar lows finite amplitude behavior

eruptive history and k ar geochronology of the late cenozoic garibaldi volcanic belt southwestern british columbia the cenozoic garibaldi belt comprises 6 volcanic fields spaced at irregular intervals along an axis extending 240 km north northwest from the head of howe sound to the bridge river area 2 additional fields the franklin glacier and silvert lie 140 and 190 km west of the north end of the main volcanic belt the volcanoes erupted lavas ranging in composition from augite olivine basalt through hypersthene andesite hornblende andesite and hornblende biotite andesite to biotite rhyodacite many of the volcanic complexes are characterized by geomorphic features which indicate complex interactions between volcanism and the pleistocene ice sheets but preglacial and postglacial phases are also present whole rock samples from 18 volcanic complexes have been dated by the k ar method most of the results are internally consistent with stratigraphic relationships and with limited 14 c and paleomaguetic data they suggest that volcanic activity was episodic most of the analyzed andesitic and dacitic lavas were erupted in the intervals 2 3 to 1 7 ma and 1 1 ma to present in the northern part and in the intervals 1 4 to 1 0 ma and 0 7 ma to present in the southern part of the belt basaltic volcanism occurred only during the past 0 15 m y except in the salal glacier area where hawaiite and alkali olivine basalt which are perhaps an edge effect related to subduction of the juan de fuca plate were erupted as early as 0 97 ma the timing of garibaldi belt volcanism provides information bearing on the distribution of pre wisconsin glaciers in southwestern british columbia and constrains interpretations of late cenozoic changes in explorer juan de fuca north american plate configuration along the continental margin

coefficients for sea surface wind stress heat flux and wind profiles as a function of wind speed and temperature surface layer coefficients for wind profiles wind stress and heat flux in typical open sea conditions are briefly reviewed businger dyer flux gradient relationships and a charnock wind stress formula fit the empirical data and are dimensionally consistent these have been solved by an iterative method and the results are presented in a tabular form suitable for climatological calculations from marine wind and temperature data

cretaceous sedimentation and tectonics tyaughton methow basin southwestern british columbia the mesozoic tyaughton methow basin straddles the fraser yalakom pasayten straight creek fypsc strike slip fault zone between six tectono stratigraphic terranes in southwestern british columbia data from hauterivian cenomanian basin fill provide constraints for reconstruction of fault displacement and paleogeography the early cretaceous eastern margin of the basin was a region of uplifted jurassic plutons and active intermediate volcanism detritus shed southwestward from that margin was deposited as the marine jackass mountain group albian inner to mid fan facies of the jackass mountain group can be correlated across the yalakom fault suggesting 150 25 km of post albian dextral offset deposits of the jackass mountain group overlap the major strike slip zone fypsc if that zone represents the eastern boundary of the tectono stratigraphic terrane wrangellia then accretion of wrangellia to terranes to the east occurred before late early cretaceous time the western margin of the basin first b

regionally extensive mid cretaceous west vergent thrust system in the northwestern cordillera implications for continent margin tectonism the intermontane insular superterrane boundary zone represents a fundamental crustal boundary separating the two largest allochthonous crustal fragments in the north american cordillera structural stratigraphic and geochronologic relations along this boundary indicate that substantial west vergent compression and concomitant crustal thickening occurred there in mid cretaceous time this orogenic zone extends for more than 1200 km along strike length between southern southeast alaska and northern washington in southern southeast alaska and northwest british columbia rocks of the insular superterrane were imbricated along a series of west to southwest vergent thrust faults in northern washington and southwestern british columbia a wide zone encompassing the margins of the two superterranes as well as numerous intervening smaller fragments was shortened principally along west vergent thrusts known geologic relations do not discriminate among existing tectonic models that explain the origin of the mid cretaceous thrust system

an 1800 km cross section of the lithosphere through the northwestern north american plate lessons from 4 0 billion years of earth s history the lithoprobe slave northern cordillera lithospheric evolution snorcle study across northwestern north america in combination with related crustal studies has been synthesized into an 1800 km long cross section of the lithosphere that is constrained by high resolution geophysical data seismic reflection refraction electromagnetic potential fields and detailed bedrock geology the cross section offers one of the longest continuous profiles of the continental lithosphere anywhere in the world that is constrained by combined geophysical measurements and electromagnetic properties and exposed bedrock geological relationships the primary conclusion of the study is that during all major orogenic episodes recorded from archean to present in that part of earth s lithosphere the crust and perhaps much of the mantle was reorganized and redistributed rather than being differentiated from the mantle at the time of orogenesis the observed subsurface geometries of relict subduction zones accretion

diagenesis and primary migration in upper jurassic claystone source rocks in north sea carbonate bands are common in central graben kimmeridgian upper jurassic claystone that is mature for oil generation x ray diffraction thermal analysis mossbauer spectroscopy thin section studies scanning microscopy and electron microprobe investigations showed that the bands are composed of claystone fragments coarse grains of dolomite quartz and siderite and diagenetic layer silicates all cemented to a certain degree by ankerite the diagenetic layer silicates are kaolinite being neoformed into muscovite in claystones adjacent to the carbonate bands ankerite fills pores about 50 m in diameter however claystone further away from the bands contains little ankerite gas adsorption with n2 kr and h2o together with microscopy showed porosity in the claystone is composed of a large amount of micropores and mesopores possibly with inlet constrictions and a few macropores with diameters of about 50 m in the carbonate bands microporosity and mesoporosity are probably located in the claystone fragments whereas several pores with diameters of about 50 m are present in the carbonate matrix the presence of claystone fragments fluid release structures and large amounts of diagenetic carbonates indicates that carbonate bands formed through fracturing possibly as a result of overpressuring porosity parameters indicate that fluid transport occurred by diffusion in the claystone matrix to claystone macropores and further through macropores in the carbonate bands out of the source rock the diagenesis of carbonates and clay minerals in the carbonate bands and in the claystone points to two migration stages an early migration of fresh neutral fluids and a later migration in connection with hydrocarbon migration of saline alkaline fluids

relict subduction zones in canada 1 relict subduction zones that are interpreted on 10 lithoprobe deep seismic reflection profiles in canada provide key observational evidence that lithosphere plate interactions have operated with essentially the same resultant geometry for at least 2 7 gyr subduction zone reflections are generally found beneath known collisional belts and their orientations are often consistent with the locations of exposed arcs sutures and subduction complexes they project from the lower crust into the upper mantle and provide key geometric relationships between the crust moho and upper mantle the interpretation of subduction zone reflections as being syntectonic establishes a minimum age for the overlying lower crust and mantle wedge and precludes inferred formation of the moho and upper mantle by postorogenic delamination in these areas the orientation of subduction zone reflections may be synthetic or antithetic to exposed sutures indicating juxtaposition by subcretion or by delamination respectively the mantle wedge above the subduction zone reflections may exhibit sparse reflectivity subduction zone reflections commonly dip toward the craton indicating a preferred dip of subduction during the last stages of convergence within an orogen or else a higher likelihood of preservation beneath older domains interpreted ages of the canadian examples range from recent to neoarchean 2 7 ga providing observational evidence that plate tectonics or similar processes have been active since at least the neoarchean the locations and geometries of these relict subduction zones provide a snapshot of accretion boundaries in the mantle and establish a framework for the neoarchean recent accretionary architecture of the north american lithosphere

the southern coast mountains british columbia new interpretations from geological seismic reflection and gravity data the southern coast mountains of british columbia are characterized by voluminous plutonic and gneissic rocks of mainly middle jurassic to eocene age the coast plutonic complex as well as metamorphic rocks folds and thrust and reverse faults that mostly diverge eastward and westward from an axis within the present mountains and by more localized eocene and younger normal faults in the southeastern coast mountains mid cretaceous and younger plutons intrude bridge river cadwallader and methow terranes and overlap middle jurassic through early cretaceous marine clastic rocks of the tyaughton methow basin the combination of geological data with new or reanalyzed geophysical data originating from lithoprobe and related studies enables revised structural interpretations to be made to 20 km depth five seismic profiles show very cut up and chaotic reflectivity that probably represents slices and segments of different deformed and rearranged rock assemblages surface geology seismic interpretations ph

the near neutral marine atmospheric boundary layer with no surface shearing stress a case study abstract data from a marine coastal experiment over the baltic sea comprising airborne measurements and mast measurements have been used to highlight the turbulence dynamics of a case with most unusual flow characteristics the boundary layer had a depth of about 1200 m the thermal stratification was near neutral with small positive heat flux below 300 m and equally small negative heat flux above the entire situation lasted about 6 hours turbulence levels were unexpectedly high in view of the fact that momentum flux was negligible in fact positive in the layers near the surface and buoyancy flux was also small the turbulence was found to scale with the height of the boundary layer giving rise to velocity spectra having the shape of those characteristic of convectively mixed boundary layers analysis of the turbulence budget for the entire planetary boundary layer pbl revealed that energy was produced from shear instability in the uppermost parts of the pbl and was distributed to the lower par