e i corrected paleolatitudes for the sedimentary rocks of the baja british columbia hypothesis paleomagnetic inclinations from sediments of the western terranes of canada are consistently too shallow for their reconstructed paleogeographic positions two contradicting explanations for these discrepancies are 1 terranes have been displaced northward with respect to the stable american craton by several thousands of kilometres between the late cretaceous 75 ma and the eocene 50 ma and 2 sedimentary inclination error has caused a shallow bias in the paleomagnetic directions here we apply the elongation inclination e i method to paleomagnetic data sets from sedimentary rocks of supposedly allochtonous terranes of western north america to correct for inclination flattening our results indicate that the paleomagnetic directions from the continental silverquick sediments 95 92 ma of southern british colombia are not seriously affected by inclination error because the magnetic signal most likely concerns a chemical remanent magnetisation crm in contrast the marine sediments of the nanaimo group 84 72 ma of vancouver island region appear seriously affected by inclination flattening f 0 7 and the e i corrected mean inclinations are about 98 steeper than the original data we arrive at corrected inclinations paleolatitudes of i 578 k 388n for the silverquick and i 558 k 368n for the nanaimo sediments our corrected paleolatitudes indicate that the canadian terranes were indeed located adjacent to the baja californian margin during the late cretaceous thus supporting the baja bc hypothesis d 2005 elsevier b v all rights reserved

geochronology and tectonic implications of magmatism and metamorphism southern kootenay arc and neighbouring regions southeastern british columbia part i jurassic to mid cretaceous k ar dates and u pb zircon dates define three periods of igneous activity in the southern kootenay arc 1 emplacement of late synkinematic to post kinematic granodioritic plutons in mid jurassic time 170 165 ma accompanying amphibolite facies regional metamorphism 2 emplacement of post kinematic granitic plutons in mid cretaceous time 100 ma and 3 emplacement of small bodies of syenite in eocene time 50 ma in the western part of the area micas from mid jurassic plutons that yield the oldest k ar dates 158 166 ma also yield plateau shaped 40ar 39ar age spectra age spectra for biotites younger than these but older than 125 ma reflect thermal overprinting in southeastern british columbia the kootenay arc marks the transition from the north american rocks of the cordilleran miogeocline to the tectonic collage of allochthonous terranes that have been accreted to it deformation metamorphism and plutonism recorded in rocks of the southern kootenay arc commenced in mid jurassic time as a co

upper limit of docking time for stikinia and terrane i paleomagnetic evidence from the eocene ootsa lake group british columbia the middle eocene ootsa lake group is exposed in the central portion of the stikine terrane where it was sampled along the shoreline of tahtsa reach and whitesail reach the group consists of dominantly subaerial flows which range in composition from basalt to rhyolite that unconformably overly the jurassic hazelton group detailed alternating field and thermal stepwise demagnetizations were done on all specimens from the 21 sites collected the presence of a normal and reversed polarity remanence a positive fold test and high coercivities and unblocking temperatures indicate that a prefolding primary remanence has been isolated the mean tilt corrected direction of d 002 2 i 69 2 95 7 4 from 13 sites for which paleohorizontal is well known yields a pole position at 354 6 e 88 0 n a95 11 5 which is statistically indistinguishable from published 50 ma reference poles for cratonic north america this evidence demonstrates that the proposed large scale northward displacement of stik

cretaceous remagnetization in the sylvester allochthon limits to post 105 ma northward displacement of north central british columbia the sylvester allochthon of the slide mountain terrane in northern british columbia is a structurally interleaved assemblage of ocean floor lithologies ranging in age from late devonian to late triassic it is the most inboard of oceanic suspect terranes and rests as a vast klippe on miogeoclinal strata of the cassiar terrane the sylvester allochton and the cassiar terrane lie west of the northern rocky mountain trench fault both the sylvester allochthon and the cassiar terrane are intruded by mid cretaceous 105 ma granite of the cassiar batholith six oriented cores were collected at each of 12 sites in guadalupian parafusulina bearing limestone of the sylvester allochthon at a location 4 km from the batholith isothermal remanent magnetization irm acquisition and subsequent thermal demagnetization indicate that pyrrhotite is the dominant ferrimagnetic mineral least squares line fitting to four thermal demagnetization steps between 150 and 310 c was used to determine the characteristic natural re

paleomagnetism magnetic anisotropy and mid cretaceous paleolatitude of the duke island alaska ultramafic complex we report paleomagnetic results from layered igneous rocks that imply substantial post mid cretaceous poleward motion of the insular superterrane western canadian cordillera and southeast alaska relative to north america the samples studied are from the stratiform zoned ultramafic body at duke island which intruded rocks of the alexander terrane at the south end of the southeastern alaska archipelago at about 110 ma thermal and alternating field demagnetization experiments show that the characteristic remanence of the ultramafic rocks has high coercivity and a narrow unblocking temperature range just below the curie temperature of magnetite this remanence is likely carried by low ti titanomagnetite exsolved within clinopyroxene and perhaps other silicate hosts the duke island intrusion exhibits a well developed gravitational layering that was deformed during initial cooling but below 540 c into folds that plunge moderately to the west southwest the characteristic remanence clearly predates this early folding and is therefore primary the fisher parameter describing the concentration of the overall mean remanence direction improves from 3 to 32 when the site mean directions are corrected by restoring the layering to estimated paleohorizontal all samples exhibit a magnetic anisotropy that is strong but nonuniform in orientation across the intrusion and we show that it has no significant or systematic effect on the site mean directions of remanence at least some of the anisotropy derives from secondary magnetite formed during partial serpentinization the mean paleomagnetic inclination 56 10 corroborates paleomagnetic results from five coeval silicic plutons of the canadian coast plutonic complex to the south and southeast and implies 3000 km 1300 km of poleward transport relative to the north american craton between mid cretaceous and middle eocene time the insular superterrane and coast plutonic complex shared a common paleolatitude history with more poleward transport than coeval inboard terranes

paleomagnetism of the lower jurassic copper mountain intrusions and the geotectonics of terrane i british columbia the 198 ma lower jurassic copper mountain intrusions outcrop in the quesnellia subterrane of terrane i in the canadian cordillera thermal demagnetization at 550 10 c defines a single stable remanence component of 25 9 41 2 95 3 6 in 11 reliable sites the resulting pole position of 11 8 e 57 3 n p 2 7 m 4 4 is discordant for the north american craton and reflects 39 6 of clockwise rotation and 9 5 of northward translation combined with previous paleomagnetic and geologic data a consistent model for the geotectonic evolution of quesnellia and terrane i emerges

tillamook volcanic series further evidence for tectonic rotation of the oregon coast range paleomagnetic directions from the eocene tillamook volcanic series of the oregon coast range point 46 o clockwise from the expected eocene field direction potassium argon dating of six dikes and flows from this formation yields a mean age of 44 3 0 6 m y these results establish that the oregon coastal block of simpson and cox 1977 extends north to the oregon washington border and that this block has rotated clockwise 46 o 13 o during the past 44 m y the block has undergone no detectable north south translation a two phase model is developed to explain the tectonic history and anomalous magnetic field directions of the pacific northwest region phase i of the rotation active between 50 and 42 m y b p results from fragmentation of the farallon plate with rotation of a fragment during its accretion to north america phase ii of the rotation active between 20 m y b p and the present occurs in association with extension in the basin and range province

evidence of early flandrian tidal surges in lower strathearn scotland detailed stratigraphic palaeobotanical diatom and pollen and radiometric evidence from a sequence of buried estuarine deposits buried peat and overlying estuarine carse deposits at wester rhynd in lower strathearn suggests the occurrence of two brief marine incursions between the abandonment by the sea of a buried estuarine flat probably the low buried beach at about 8765 75 bp and c 8500 bp the first incursion shortly after 8565 85 bp caused bottom living marine diatoms to be thrown without clastic material onto the rapidly accumulating terrestrial peat the second bracketed by dates of 8485 80 and 8510 85 bp deposited an extremely thin 1 mm layer of fine sand that interrupts an otherwise unbroken buried peat succession covering the period 8765 75 to 7710 70 bp the marine diatom lithostratigraphic and 14c evidence together are consistent with a storm storm surge or tsunami origin for these events which are recognised principally from the diatom evidence having left no mark in the pollen record

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

a holocene tsunami deposit in eastern scotland a thin regionally extensive laterally persistent sand layer identified within the holocene coastal sequences of eastern scotland dated to 7000 years bp is suggested to be a tsunami deposit the likely source of the tsunami wave is the earthquake induced second storegga slide on the norwegian continental slope at least 750 km northeast of the deposit

tertiary paleomagnetism of the north cascade range washington we have obtained paleomagnetic data for the southern tip of the middle tertiary chilliwack composite batholith located on the canada united states border about 125 km e of vancouver b c thirty four separately oriented samples were collected along a road traverse 1 5 km long located along state highway 22 about 20 km ne of marblemount washington the mean direction after magnetic cleaning is d 182 8 i 65 0 95 1 5 this corresponds to a paleomagnetic pole at 87 5 n 267 5 e close to other poles for tertiary plutons from the north cascades and only slightly displaced from tertiary reference poles from the craton we conclude that the north cascades block has not been rotated or suffered major internal disruption since perhaps late eocene time in marked contrast to all the terranes that surround it

linking onshore and offshore structures mesozoic extension in the scottish highlands geological relationships in the offshore basins flanking northern scotland suggest that a regional caledonian control on the structure of these basins is far from proven but conversely mesozoic faults of the offshore set may extend onshore the strathconnon fault long held to be late caledonian may be mesozoic in age forming the principal kinematic link between the east and west coast basins of northern scotland the numerous outcrops of precambrian basement within the minch hebrides basin nearly all lie in the uplifted footwalls of mesozoic faults similar fault controls on the distribution of onshore outcrop within the precambrian may exist

major dextral transcurrent displacements along the northern rocky mountain trench and related lineaments in north central british columbia the northern rocky mountain trench and a number of other prominent lineaments along and east of the eastern margin of the intermontane belt mark faults along which dextral transcurrent movements have been dominant offsets of shelf to off shelf facies boundaries in lower paleozoic rocks indicate a cumulative displacement of at least 750 km and probably 900 km within the system of faults related to those in the northern rocky mountain and the tintina trenches farther west another system of faults appears to offset plutons and stratigraphic assemblages along the eastern margin of the intermontane belt by as much as 300 km these faults including the kutcho and the pinchi connect in part with the teslin suture zone in yukon territory and probably with the fraser river straight creek fault zone in southern british columbia although dextral transcurrent faulting may have taken place between the middle jurassic and early cenozoic the most convincing evidence points to middle cretaceous and particularly to early cenozoic eocene displacements the eocene movements were temporally related to plutonism volcanism lamprophyre dike emplacement high heat flow sedimentation in grabens and rapid uplift of northwesterly trending elongate ranges climactic episodes of granite emplacement particularly in and near the northern omineca crystalline belt at 100 m y 70 m y and 50 m y ago may have been facilitated by changes from dominantly compressional to dominantly transcurrent and related tensional strain

paleomagnetism and k ar isochron dates of early jurassic basaltic flows and dikes of atlantic canada k ar isochron dates of 193 2 189 3 and 191 2 ma are reported for the shelburne dike of nova scotia the avalon dike of newfoundland and the caraquet dike of new brunswick respectively these major tholeiitic dikes agree in radiometric date with the north mountain basalt of nova scotia and with other tholeiitic flows of the newark supergroup that have been paleontologically assigned to the hettangian however further work is needed to resolve the discrepancy between the triassic jurassic boundary date of 193 6 ma suggested by the newark supergroup flows and the boundary dates of 204 213 ma adopted in recent time scales the north mountain basalt flows at nine sites on the north shore of the bay of fundy are shown to have likely magnetized during initial cooling yielding an hettangian virtual paleopole at 66 n 72 e dp 9 dm 14 new paleomagnetic results are also reported for the caraquet and avalon dikes the virtual paleopoles from hettangian flows and dikes of atlantic canada lie on a

new paleomagnetic data for the triassic guichon batholith of south central british columbia and their bearing on terrane i tectonics the 198 ma guichon batholith outcrops in the southern end of the intermontane belt or composite terrane i of the western north american cordillera thermal demagnetization of specimens from 19 sites at 200 450 and 560 c isolates a stable primary component at 560 c in 13 sites giving a pole position of 347 w 52 n p 5 m 9 these data support earlier results obtained by the author that indicate the batholith has undergone a clockwise rotation about a vertical axis of 43 7 they also show that the batholith has undergone northward motion of 13 6 which supports recent arguments that the terrane underwent 14 2 of northward translation between late cretaceous and pre miocene time

northward translation of baja british columbia along the late cretaceous to paleocene margin of western north america paleomagnetic data suggest that a large part of british columbia and southern alaska was at the latitude of baja california mexico in early late cretaceous time this allochthonous block baja bc includes the insular talkeetna in alaska and intermontane composite terranes the miniterranes between them and possibly part of the omineca metamorphic belt assuming that baja bc was adjacent to north america by middle cretaceous an analysis using plate kinematics of the pacific basin produces a model of northward movement of baja bc which is compatible with the known geology of the reconstructed margin of western north america baja bc moved north 2400 km as part of the kuia plate along a transform margin with north america from 85 to 66 ma this time interval is marked by the cessation of igneous activity in the sierra nevada development of wrench faults and basins along coastal california and initiation of laramide style tectonics to the east within baja bc diminished igneous activity to the west was coeval with possible wrench tectonic basins along its eastern margin by the end of the cretaceous baja bc was positioned from oregon to northern british columbia between 66 and 56 ma baja bc became attached to north america in a dextral transpressive stage during which the kula north america plate boundary expanded to encompass the whole block with a series of northwest trending strike slip faults a fold and thrust belt in the east and large scale uplifts and the formation of an incipient volcanic arc on the west southern alaska was the site of convergence during the whole of the period of northward translation of baja bc a late cretaceous subduction zone in alaska evolved into a major compressional belt as the basin and miniterranes on the northern margin of baja bc collided with interior alaska the collision culminated in the paleocene with formation of the mckinley granites and coeval dextral slip on the denali fault system

cracking the fractures seismic anisotropy in an offshore reservoir the clair field lies west of the shetland islands on the u k continental shelf in 140 m of water figure 1

devonian extensional tectonics versus carboniferous inversion in the northern orcadian basin the old red sandstone middle devonian orcadian basin was formed as a consequence of extensional collapse of the caledonian orogen onshore study of these collapse basins in orkney and shetland provides directions of extension during basin development the origin of folding of old red sandstone sediments that has generally been related to a carboniferous inversion phase is discussed syndepositional deformation supports a devonian age and consequently some of the folds are related to basin formation large scale folding of devonian strata results from extensional and left lateral transcurrent faulting of the underlying basement spatial variation of extension direction and distribution of extensional and transcurrent tectonics fit with a model of regional releasing overstep within a left lateral megashear in nw europe during late caledonian extensional collapse later inversion probably during the upper carboniferous is characterized by e w to ne sw contraction it induced reactivation of extensional faults as thrusts development of small scale folds and thrusts and right lateral transcurrent movement of the major faults such as the great glen and walls boundary faults

paleomagnetic evidence for motions of parts of the canadian cordillera abstract paleomagnetic evidence from major terranes of the western cordillera in canada referred to collectively as baja british columbia indicates that they have moved as a whole about 2300 km from the south and rotated 60 clockwise relative to north america in the late cretaceous and earliest tertiary 85 50 ma sometime between the early jurassic and the mid cretaceous 190 100 ma these same terranes moved south over 1000 km and underwent irregular but where well constrained counter clockwise rotations the terranes amongst themselves seem to have shared much the same paleolatitude during and since the late triassic although they may have undergone relative rotations in the later jurassic and early cretaceous these motions are now known to be broadly consistent with the motions of oceanic plates to the west as calculated by independent procedures and indicate that the terranes of the western cordillera were for part of their existence coupled to oceanic plates first to the farallon plate during the late jurassic and early cretaceous and then to the kula plate during the late cretaceous and early tertiary it was this change of allegiance from farallon to kula that caused first the southerly and then the northerly motion the paleomagnetic evidence despite claims to the contrary is consistent with geologically inferred displacements along major faults in the canadian cordillera when due account is taken of the age constraints on those motions

devonian carboniferous sedimentary evolution of the clair area offshore north western uk impact of changing provenance abstract the clair group was deposited in a devonian carboniferous rift basin at the edge of the present day north west european shelf west of the shetland islands the west shetland basin in which the clair area lies therefore provides the most westerly record of devonian carboniferous environments in northern britain and allows comparison with the orcadian basin to the east palaeogeographical time slices are presented based on sedimentological studies of core electrical logs and heavy mineral assemblages the basin underwent two cycles of increasing endorheism internal drainage in a devonian continental rift followed by a cycle of increasing humidity as high sinuosity streams were succeeded by marginal marine environments in the carboniferous the two lower cycles of increasing endorheism are separated from the upper cycle by an important field wide unconformity this stratigraphic break is accompanied by a major change in provenance from small intra rift drainage networks and deserts depositing polycyclic minerals to much enlarged drainage systems transporting first cycle unstable minerals from catchments reaching far beyond the devonian rift

comparison of deterministic with stochastic fracture models in water flooding numerical simulations determination of multiphase flow properties considering the variation of fracture patterns i e number of fracture sets their orientation length distribution spacing and in situ aperture remains a key challenge in reservoirs in reservoir engineering one way is by studying outcrop analogs with comparable petrophysical properties and a similar geological history and incorporating these data into model building discretization and numerical simulation the limitation of directly incorporating attributes measured on outcrops is that this method is error prone because of postburial processes mineralized fracture vein attributes are good candidates to use as analogs for open fractures formed under in situ conditions to establish the relationship between fracture length and aperture and help to reveal the conditions at the time of their formation and to quantify fracture induced porosity in rock masses vein attributes determined from scan lines and window samples were combined to condition the stochastic generation of fractures using the discrete fracture network code fracman comparison of water breakthrough time and oil saturation at breakthrough was then determined by applying a constant pressure gradient for each realization to simulate water flooding numerical simulation using the combined finite element finite volume method the different stochastic realizations were compared with discrete fracture and matrix models and we show how the uncertainty in these fracture attributes affects multiphase flow behavior in naturally fractured rocks uncertainty in quantifying these attributes has a profound impact for predicting the oil recovery and water breakthrough time based on limited information from boreholes

the paleomagnetic effects of reheating the ecstall pluton british columbia abstract paleomagnetic data of plutons from the western canadian cordillera are currently interpreted to indicate thousands of kilometers of latitudinal transport in situ tilting or post intrusion folding for the ecstall pluton of british columbia the inclination of magnetic remanence directions steepens to the east from 16 to 81 butler et al j geophys res 107 2002 between 24 and 12 km west of a thermal boundary with the coast mountains batholith cmb the cmb was at 700 800 c between 60 and 52 ma the stable remanent magnetization is in ilmenohematite grains with exsolved lamellae of ferrian ilmenite it has the characteristic properties of lamellar magnetism robinson et al nature 418 2002 517 520 which is acquired with exsolution in ilmenohematite below 390 c ghiorso phys chem minerals 25 1997 28 38 thus it is thermal chemical remanent magnetization tcrm our heat flow calculations show that the thermal effects of eocene cmb on the adjacent 91 ma ecstall pluton were enough to reset the remanent magnetization directions reheating to the temperatures necessary for tcrm is supported by k ar and ar ar cooling dates on hornblende and biotite which young from west to east towards the cmb in concert with the change in inclinations thus the progressive steepening of magnetization inclinations is attributed to reheating during the eocene of the 91 ma ecstall pluton by the cmb this reheating followed post solidification northward latitudinal displacement of the pluton the amount of translational displacement of the coastal terranes of british columbia prior to 60 ma hinges on the interpretation of discordant magnetizations from plutons that may have cooled slowly after emplacement in the mid to lower crust as was the case for the ecstall pluton many of these plutons contain ilmenohematite as an accessory magnetic phase our interpretation for the low temperature acquisition of tcrm in the ecstall pluton may have far reaching implications for understanding enigmatic discordant paleomagnetic directions reported from plutons of the western canadian cordillera

pre development fracture modelling in the clair field west of shetland abstract the clair oilfield is a large fractured sandstone reservoir lying 75 km west of shetland on the uk continental shelf fracture analysis and modelling was carried out in preparation for the phase 1 development which started production early in 2005 fracture clusters and discrete fluid inflows observed in wells are associated with faults and other localized deformation features tens or hundreds of metres apart the reservoir has moderate to good matrix permeability but well flow rates and profiles are fracture dominated full field geological models were built using conventional object modelling approaches for matrix and discrete fracture networks for fractures and upscaled to populate a reservoir simulation grid dual porosity dual permeability dynamic modelling full field and well test was undertaken to understand the fracture and matrix flow contributions and their interaction fracture models were conditioned to wells and to seismic data including coherency and multi azimuthal velocity information from a four component ocean bottom cable three dimensional seismic survey at this early stage in field development there is insufficient calibration to select a single fracture model instead well and depletion plans have been tested against multiple fracture models chosen to encompass a wide range of plausible outcomes

block rotations along the strike slip finlay ingenika fault north central british columbia implications for paleomagnetic and tectonic studies structure developed in association with oblique motions on the dextral strike slip finlay ingenika fault fif in the mcconnell creek area north central british columbia is dominated by subvertical to vertical strike slip faults some of the faults cut the area into discrete fault bounded blocks several kilometres wide stress tensors for 24 sites were inverted from the regional cleavage which predates the block bounding faults the site mean stress tensors indicate that the fault bounded blocks were rotated clockwise about a subvertical axis during progressive oblique motions on the fif rotation varies systematically being maximal 58 7 3 3 close to the fif and minimal 0 0 1 6 about 20 km away paleomagnetic samples were collected from 13 sites in the widespread early jurassic to cretaceous plutonic rocks interpretable magnetic components of presumed late cretaceous age were obtained from six sites the observed paleopole is significantly different from the late cretaceous reference pole for cratonal north america cna after corrections for the local block rotations the precision is much improved k increased from 48 to 383 and the paleopole moves closer to the reference pole but is not coincident with it rotation about the eulerian pole for the best fitting small circle to the tintina trench and northern rocky mountain trench fault zone however brings the observed pole into coincidence with that for cna and requires 670 km of dextral displacement on the fault zone it is evident therefore that local structures associated with large dextral strike slip faults could account for at least part of the paleomagnetic disparity between some western parts of the canadian cordillera and cna

the holocene storegga slide tsunami in the united kingdom all currently known sites in the united kingdom with evidence for the holocene storegga slide tsunami are described information on the altitude distribution stratigraphical context age particle size profile and microfossil characteristics of the deposits is presented the tsunami involved a greater area than previously described reaching a coastline over 600 km long the ubiquitous sand layer which forms the main deposit associated with the event is shown to exhibit a consistent morphology and a particle size profile marked by fining upwards sequences an analysis of new and previously published radiocarbon dates indicates that from evidence in the united kingdom the event took place sometime around 7100 radiocarbon years bp 7900 calibrated years bp a new isobase model for mainland scotland and adjacent areas providing a preliminary estimate of land uplift since the tsunami is presented the model estimates contemporary sea surface level offshore at 14 m below the present day mean high water spring tides tsunami sediment run up is greatest in inlets where it reaches at least 25 m on shetland and at least 5 m along the mainland coastline to the south and run up of the tsunami would have exceeded these values the tsunami sediments identified here are considered particularly valuable as a synchronous marker horizon

heterogeneous exhumation in the inner moray firth uk north sea constraints from new afta and seismic data integration of regional seismic interpretation sonic velocity vitrinite reflectance and apatite fission track analysis afta studies has demonstrated that the western region of the moray firth rift arm uk north sea experienced pronounced exhumation during the cenozoic although this basin is usually considered to have experienced regionally uniform exhumation interpretation of new seismic data has revealed the presence of a major system of post jurassic normal faults with throws commonly in the range of 10 300 m and locally exceeding 1 km new high quality seismic data are used in combination with afta and vitrinite reflectance data to investigate the role of extensional faulting during exhumation of this basin results of this interpretation not only confirm the offsets across major faults but also show that greater exhumation and erosion occurred on their footwalls than on their hanging walls we conclude that the localized differential exhumation is the result of superposition of local or short spatial wavelength extensional tectonics upon regional long spatial wavelength exhumation these results suggest that differential exhumation might be characteristic of unroofed rift basins where normal faults subcrop the exhumation related unconformity and that in such cases thermal histories from footwall locations may yield inaccurate predictions of the burial history of hanging wall depocentres inaccurate burial histories will lead to a misrepresentation of the thermal history with an impact on the estimation of hydrocarbon source rock maturity for petroleum basins

paleomagnetic evidence for displacement from the south of the coast plutonic complex british columbia the mid cretaceous spuzzum and porteau plutons of the coast plutonic complex of british columbia have two magnetizations a and b the a magnetization eight sites 83 specimens d 30 3 i 56 7 95 4 9 paleolatitude 37 5 n paleopole 65 0 n 14 9 w a95 6 2 is considered to have been acquired in the age range 105 90 ma this result differs from the field established for cratonic north america in this time range the difference could be caused either by previously undetected tilting about a horizontal axis of the plutons or by their rotation about a vertical axis and lateral displacement relative to the craton previously observed mid cretaceous magnetizations from other rock units from the western canadian cordillera and the cascades of washington united states are similarly discordant with respect to the craton this similarity over such a large area indicates that although local undetected tilting could be partly responsible it is unlikely to be the prime cause and we argue ther

on determining paleohorizontal and latitudinal shifts paleomagnetism of spences bridge group british columbia the spences bridge group of late albian age palynology and u pb zircon date of 104 5 ma is situated in the intermontane belt of the southern canadian cordillera zeolite grade andesite lavas and interbedded volcaniclastic rocks have been sampled through a thickness of about 2900 m sampling has been confined to localities whose bedding attitudes are well defined and to rocks that have not undergone internal deformation of the 27 sites studied 25 gave single component magnetizations with well grouped directions high coercivities and high unblocking temperatures applying corrections for geological tilt to all 25 sites yielded minimum dispersion after 65 untilting analysis indicates that this is a consequence of the interaction of two modes of behavior one exhibited by y magnetizations at 8 sites in which minimum dispersion occurs after 35 untilting and one x magnetizations at 17 sites in which minimum dispersion occurs after 100 correction actually the dispersion is essentially constant in the range 88 to 100 correction the y magnetizations are uninterpretable in terms of the paleofield because no estimate of paleohorizontal can be made because of their positive response to the tilt test the x magnetizations were acquired before tilting and it is argued that geologically determined bedding planes are good estimators of paleohorizontal at the time of remanence aquisition there may be errors because of paleoslope but arguments are presented for believing that these are small on this basis the best estimate of the mean direction of the paleofield in spences bridge time is estimated to be d i declination inclination 38 7 63 9 17 sites k 44 compared with k 11 in situ 95 5 4 with a paleopole at 64 4 n 321 0 e k 24 compared with k 5 in situ a95 7 5 when compared with the cratonic reference field for mid cretaceous time this pretilting magnetization indicates a clockwise rotation of the study area of 66 3 11 8 p 0 05 and an apparent displacement from the south of 15 5 7 1 1725 790 km when these and other data previously obtained from cretaceous rocks of the pacific northwest are compiled they show an increase in apparent displacement from east to west across the cordillera this result is discussed in terms of three hypotheses 1 no translation but systematic tilts of about 30 to the southwest 2 translation of a substantial part of the pacific northwest referred to as baja british columbia and is defined more exactly in the text by variable amounts up to more than 2000 km from the south together with clockwise rotations and 3 lesser translation of baja british columbia by about 1500 km combined with variable tilting predominantly to the south it is concluded that paleomagnetic data as they are presently known are consistent with hypotheses 2 and 3 but unless serious sources of error are present are not consistent with hypothesis 1 the most likely candidate for such errors is the uncertainty in estimating initial dip of beds paleoslope in volcanic rock units

paleomagnetism of the mount stuart batholith revisited again what has been learned since 1972 we have collected 20 new paleomagnetic sites from the mount stuart batholith and the adjacent beckler peak stock using thermal and low temperature demagnetization and rock magnetic tests we have found that the remanence in most of the batholith is carried by single domain magnetite the mean of the new mount stuart batholith sites is d 354 2 i 46 2 k 87 2 a95 4 6 n 11 and is similar to those of the beck and noson 1972 and beck and others 1981 studies examination of ar geochronology of hornblende and biotite from the mount stuart batholith finds that the southern part of the batholith cooled through the blocking temperature of magnetite at 91 ma the northern part cooled through the blocking temperature of magnetite at 86 ma and of pyrrhotite at 83 ma from these combined results we conclude that the paleomagnetic directions from the southern part of the batholith were acquired within 0 5 to 1 0 ma of the time at which the ah barometers cooled below their closure temperature use of the ah barometry to establish paleohorizontal for these rocks is thus well justified correcting the mount stuart direction for the tilt indicated by the aluminum in hornblende ah barometry the mean becomes d 355 9 i 50 6 this result places the mount stuart batholith at a latitude of 31 3 3 8 3 4 n at 91 ma by identifying the carrier of remanence in the mount stuart batholith as being single domain sd magnetite we have removed the major remaining uncertainty in interpreting the paleomagnetism of these rocks the characteristic magnetization repeatedly found in the mount stuart rocks clearly supports the microplate tectonic model of beck and noson 1972 presently manifest as the baja british columbia baja bc hypothesis

seismic anisotropy as an indicator of reservoir quality in siliciclastic rocks improving the accuracy of subsurface imaging is commonly the main incentive for including the effects of anisotropy in seismic processing however the anisotropy itself holds valuable information about rock properties and as such can be viewed as a seismic attribute here we summarize results from an integrated project that explored the potential to use observations of seismic anisotropy to interpret lithological and fluid properties the sail project our approach links detailed petrofabric analyses of reservoir rocks laboratory based measurements of ultrasonic velocities in core samples and reservoir scale seismic observations we present results for the clair field a carboniferous devonian reservoir offshore scotland west of the shetland islands the reservoir rocks are sandstones that are variable in composition and exhibit anisotropy on three length scales the crystal grain and fracture scale we have developed a methodology for assessing crystal preferred orientation cpo using a combination of electron back scattered diffraction ebsd x ray texture goniometry xrtg and image analysis modal proportions of individual minerals are measured using quantitative x ray diffraction qxrd these measurements are used to calculate the intrinsic anisotropy due to cpo via voigt reuss hill averaging of individual crystal elasticities and their orientations the intrinsic anisotropy of the rock is controlled by the phyllosilicate content and to a lesser degree the orientation of quartz and feldspar the latter can serve as a palacoflow indicator our results show remarkable consistency in cpo throughout the reservoir and allow us to construct a mathematical model of reservoir anisotropy a comparison of cpo predicted velocities and those derived from laboratory measurements of ultrasonic signals allows the estimation of additional elastic compliance terms due to grain boundary interactions the results show that the cpo estimates are good proxies for the intrinsic anisotropy of the clean sandstones the more micaceous rocks exhibit enhanced anisotropy due to interactions between the phyllosilicate grains we then compare the lab scale predictions with reservoir scale measurements of seismic anisotropy based on amplitude variation with offset and azimuth avoa analysis and non hyperbolic moveout our mathematical model provides a foundation for interpreting the reservoir scale seismic data and improving the geological modelling of complex reservoirs the observed increases in avoa signal with depth can only be explained with an increase in fracturing beneath the major unit boundaries rather than a chan e in intrinsic cpo properties in general the style and magnitude of anisotropy in the clair field appears to be indicative of reservoir quality less

laser scanning and digital outcrop geology in the petroleum industry a review abstract the use of lidar light detection and ranging systems for modelling petroleum reservoir analogues has become increasingly popular over the past few years and there has been a proliferation of articles on the subject both on techniques and applications a review of the literature of recent years has been conducted focussing on the use of lidar data not only in petroleum geology related projects but also looking to the wider field of lidar usage to examine what other approaches may be of use to the petroleum geologist benefits of digital data acquisition are considered as well as a basic overview of data collection approaches use of a variety of attributes intensity colour dip azimuth co linearity co planarity among others is discussed as an aid to both manual and automated interpretation approaches integration of lidar data with other data types from traditional field data sedimentary logs for example and other digital data types such as multispectral and hyperspectral imagery and ground penetrating radar are discussed as a way of increasing the amount of information in the digital dataset the application of artificial intelligence approaches such as smart swarms and neural networks are considered as well as current developments in both hardware and software a variety of examples are given where lidar has been used in an innovative or interesting way showing the strength of this data acquisition approach when combined with appropriate interpretation and modelling techniques

canadian cordilleran displacement palaeomagnetic results from the early jurassic hazelton group terrane i british columbia canada summary the early jurassic telkwa formation comprising the base of the hazelton group was sampled at three areas in the central part of the stikine terrane british columbia detailed alternating field and thermal step demagnetization on samples from nine sites from the red canyon area and 10 sites from the zymoetz river area both of which are in the bulkley ranges and eight sites from the telkwa range area isolate stable remanence magnetization components the components are interpreted to be primary magnetizations because of the presence of two polarities and the much improved agreement of their inclinations after full tilt correction of the sites from the bulkley ranges within locality declinations agree well between locality declinations are discordant the expected cratonic declination is 340 whereas declinations from this study are 265 227 and 328 for the red canyon zymoetz river and telkwa range areas respectively these results are similar to those of monger irving 1980 and we concur that the discordant declinations are the result of differential rotation about vertical axes between sample localities our observed mean inclination of 52 is in good agreement with monger irving s 1980 result of 54 they interpreted this to indicate 1300 km of northward displacement since the early jurassic and their interpretation was substantiated by several later studies however with revisions to the geologic time scale and the early jurassic reference pole for north america the early jurassic canadian cordillera palaeomagnetic data base appears latitudinally concordant this indicates that terrane i and southern wrangellia were in much the same latitudinal position relative to the north american craton as they are now tectonic displacement models developed in view of discordant cretaceous palaeomagnetic data from the canadian cordillera must now consider latitudinally concordant permian to early jurassic data and middle eocene to recent data this tectonic senario appears more reconcilable with the regional tilt hypothesis however this hypothesis cannot account for discordant cretaceous data from bedded volcanic rocks in terrane i it is therefore probable that cretaceous cordilleran tectonics were characterized by both regional tilting and moderate latitudinal displacement

paleomagnetism of the eocene kamloops group and the cratonization of terrane i of the canadian cordillera the lower middle eocene 49 4 2 4 ma kamloops group is exposed in the middle of the quesnellia subterrane of terrane i the group consists of the siliciclastic tranquille beds and the overlying dewdrop flats plateau basalts and andesites detailed alternating field af and thermal step demagnetization was carried out on 282 specimens from 26 flow sites and one conglomerate site and saturation isothermal remanent magnetization sirm tests were performed to examine the remanence carriers the petrology of the gently dipping flows the presence of antiparallel normal and reverse remanence the conglomerate test and the fold test all indicate that a primary remanence has been isolated it resides in both magnetite and hematite over a broad range of af coercivities blocking temperatures and domain sizes its mean direction of 355 0 73 4 95 6 9 gives a pole position of 138 4 w 81 4 n dp 11 0 dm 12 3 that is statistically indistinguishable from the 50 ma reference pole for the north a

simulation of subseismic joint and fault networks using a heuristic mechanical model author s gillespie p casini g iben h o brien jf abstract 2018 the author s flow simulations of fractured and faulted reservoirs require representation of subseismic structures about which subsurface data are limited we describe a method for simulating fracture growth that is mechanically based but heuristic allowing for realistic modelling of fracture networks with reasonable run times the method takes a triangulated meshed surface as input together with an initial stress field fractures initiate and grow based on the stress field and the growing fractures relieve the stress in the mesh we show that a wide range of bedding plane joint networks can be modelled simply by varying the distribution and anisotropy of the initial stress field the results are in good qualitative agreement with natural joint patterns we then apply the method to a set of parallel veins and demonstrate how the variations in thickness of the veins can be represented lastly we apply the method to the simulation of normal fault patterns on salt domes we derive the stress field on the bedding surface using the horizon curvature the modelled fault network shows both radial and concentric faults the new method provides an effective means of modelling joint and fault networks that can be imported to the flow simulator

line sampling of fracture swarms and corridors abstract scanlines across a range of fracture networks are analysed using cumulative frequency plots spacing distribution and correlation integral plots synthetic samples from known distributions are used to distinguish uniform and random positioning of fractures from various types of clustering and the results used to interpret fracture corridors from the bergen area norway the kuiper test provides a means of establishing the statistical significance of clustering and the correlation integral allows assessment of clustering at different scales a simple workflow is proposed that uses quantitative measures for the definition and characterisation of the spatial organisation of fractures the form of fracture networks is shown to vary from uniform or random distributions through the development of simple corridors to clustering at various scales

cordilleria a newly defined canadian microcontinent palaeomagnetic data and geological field evidence indicate that most of the western canadian cordillera lay 1 500 km south of its present position in the early cretaceous we suggest that this region comprised a microcontinent termed cordilleria which moved on the kula plate and collided with the craton 100 myr ago to form first the mackenzie mountains and then the rockies

post folding remagnetization that passes the fold test summary the palaeomagnetism of folded cretaceous redbeds in the methow pasayten belt of washington was studied in an attempt to resolve the tilt versus translation origin of shallow inclinations found in most cretaceous plutonic rocks of the pacific northwest after elimination of results from apparently strained overturned beds correction to palaeohorizontal of the high temperature dominant components produced two distinct directions one from each of two areas treated separately the magnetizations from these two areas appear to pass the fold test both directions are anomalously shallow which is typical of the region but the discrepancy between them casts doubt that both could have been acquired when the strata were horizontal instead we propose that they date from at least two episodes of remagnetization after the planar strata were tilted but before development of the tighter folds observed today our caution is that a positive fold test only establishes that a magnetization likely was acquired when strata in an area were planar other arguments are required to demonstrate that this planar surface was in fact horizontal during magnetization

neogene tilting of crustal panels near wrangell alaska a late oligocene miocene igneous complex south and west of wrangell alaska contains mafic dikes that yield a discordant paleomagnetic direction inclination i 70 4 declination d 39 3 95 4 8 n 72 sites combined with local and regional geobarometric metamorphic and structural observations the discordant paleomagnetic direction indicates east side up tilt by 16 about a tilt axis with azimuth 8 neogene tilt of crustal blocks in the insular superterrane accounts for much of the paleomagnetic discordance in cretaceous plutons without the coastwise translation of 1000 km as suggested by the baja british columbia hypothesis

paleomagnetic reconnaissance of early mesozoic carbonates from williston lake northeastern british columbia canada evidence for late mesozoic remagnetization three classic sections of middle and late triassic fossiliferous limestones cropping out around williston lake in british columbia canada were sampled for paleomagnetic study the objective was to test the suitability of these units for detailed magnetobiostratigraphic study with the aim of improving the reference triassic geomagnetic polarity time scale the williston lake characteristic magnetizations differ however from any triassic north america cratonic reference directions a satisfactory agreement is found instead with cretaceous early cenozoic north america cratonic reference directions the exclusive occurrence of normal polarity suggests that remagnetization likely occurred during the cretaceous long normal superchron remagnetizations may have been triggered by connate brines which moved along aquifers of porous sandstones and carbonates in the early stages of laramide folding resume trois sections fossiliferes classiques de calcaires trias moyen et tardif affleurant autour du lac williston en colombie britannique ont ete echantillonnees pour une etude paleomagnetique l objectif etait de s assurer de la pertinence de ces unites pour une etude magneto bio stratigraphique detaillee visant a ameliorer l echelle referentielle de temps de la polarite geomagnetique au trias les magnetisations caracteristiques du lac williston different toutefois de toute direction cratonique referentielle au trias en amerique du nord toutefois une correlation satisfaisante est etablie avec les directions cratoniques referentielles du cretace cenozoique precoce en amerique du nord l occurrence exclusive d une polarite normale suggere qu il y eut probablement une remagnetisation au cours du long superchron normal du cretace les remagnetisations peuvent avoir ete declenchees par des saumures connees qui se sont deplacees le long d aquiferes de gres et de carbonates poreux dans les premieres phases du plissement laramide

the storegga slides evidence from eastern scotland for a possible tsunami abstract the second storegga slide on the continental slope off western norway has been dated at between 8000 and 5000 yrs b p a prominent sand layer in flandrian holocene deposits along the coast of eastern scotland and dated at approximately 7000 yrs b p may have been deposited by a tsunami generated by the slide the altitude and stratigraphy of the layer allow estimates to be made of the magnitude of the earthquake which initiated the slide

characterization and impact on reservoir quality of fractures in the cretaceous qamchuqa formation zagros folded belt abstract reservoir quality in tight fractured carbonate rocks is controlled by the fracture properties the tectonic origin of fractures the relationship of fractures to other sedimentary features within the rockmass and diagenesis in this study fracture analysis porosity and permeability of the qamchuqa formation in the miran west block of the zagros folded belt in kurdistan has been studied this was undertaken using core analysis micro resistivity image logs drill stem tests dst mud logging data repeat formation test rft drilled cutting samples and wireline log data the integrated analysis shows that the qamchuqa formation is characterized by heterogeneous sedimentary and tectonic features the sedimentary features include burial stylolites dissolution seams and some fractures which formed at early stages of burial and diagenesis phase 1 open fractures partially open mineralized fractures veins and tectonic stylolites were formed by later tectonic activity phase 2 the finding of this study highlight that the fracture properties including aperture length frequency and origin play an important role in controlling the reservoir s quality the open fractures and partially open mineralized fractures enhance permeability providing an inter connected fracture network leading to a high fracture permeability that controls fluid flow in this tight carbonate reservoir rock the fracture network had little impact on the volume of hydrocarbon storage which is controlled by the pore matrix in contrast structures including stylolites dissolution seams and veins generally have a negative impact on the reservoir quality by blocking the fluid flow this work emphasizes the importance of understanding the regional geological history and the role of sedimentary and tectonic features when investigating in tight carbonate reservoirs

paleomagnetism and tectonics of the cretaceous mt stuart batholith of washington translation or tilt abstract the mt stuart batholith is a composite pluton of late cretaceous age that intrudes the crystalline north cascades terrane of northwestern washington its paleomagnetic direction d 10 0 i 45 5 95 4 9 is markedly different from the direction expected for cretaceous rocks from northwestern washington d 330 5 i 73 0 which means that the mt stuart batholith either has moved relative to the north american interior or has been tilted through a substantial angle or both since it acquired its magnetism either tilt or translation are possible geometrically but translation is more likely because 1 local geology apparently does not support tilt in the required direction 2 it probably is not possible for a panel of rock the size of the mt stuart batholith to tilt through the necessary angle ca 35 after its deeper parts have cooled sufficiently to retain remanent magnetization 3 the sense of paleomagnetic discordance found in the mt stuart batholith clockwise rotation of declination flattened inclination is identical to that found in nearly every other allochthonous terrane in the western north american cordillera including every other cretaceous batholith studied except the sierra nevada

post breakup compression of a passive margin and its impact on hydrocarbon prospectivity an example from the tertiary of the faeroe shetland basin united kingdom the faeroeshetland basin is part of a passive continental margin that formed as a result of multiphase extension associated with north atlantic rifting during the mesozoic and paleocene breakup was followed by postrift subsidence during the latest paleocene to late eocene and the development of at least three 70 150 km 43 93 mi long broadly north south orientated slope canyons and linked terminal fans during the middle eocene the terminal fans filled northeast southwest striking basin floor bathymetric depressions that had formed above the hanging walls of underlying dormant northeast southwest trending mesozoic extensional faults and adjacent half graben depocenters compression during the middle and late miocene caused contractional reactivation of the mesozoic extensional faults and folding of the overlying uppermost paleocene to middle miocene postrift sediments into a series of 17 northeast southwest striking anticlinal domes the switch from hanging wall bathymetric depression during terminal fan deposition to anticlinal domal high during and after the middle to late miocene compression has led to the present day spatial coincidence of a potential hydrocarbon reservoir and an effective trap the anticlines also acted as the foci for gas migration during or after compression 15 ma to present however the timing of compression and differential uplift of the basin margins during the past 15 m y approximately 45 m y after the main phase of oil migration may be a critical negative factor for oil exploration in this part of the basin this hydrocarbon phase may have spilled during the structural reorganization either updip into shallower traps or out of the hydrocarbon system via seeps

tertiary compressional structures on the faroe rockall plateau in relation to northeast atlantic ridge push and alpine foreland stresses abstract a number of compressional anticlinal structures are identified in the western and northern part of the faroe rockall plateau these structures occur on that part of the faroe rockall plateau which was above sea level during the latest phase of paleocene plateau basalt extrusion three post basalt compressional phases have affected the plateau most of the compressional structures in the northern part of the plateau are related to ne sw to ene wsw oriented stress which we date to late paleocene early eocene the oligocene phase is interpreted as resulting from n s directed compressional stress which also mainly affected the compressional structures on the northern part of the plateau compressional stress from the northwest seemed to affect the whole of the faroe rockall plateau and we suggest it to be of miocene age it is proposed that during the late paleocene early eocene phase of compression local structure and anomalously oriented gravitational ridge push from the now extinct aegir axis contributed to a local ne sw compressional stress system the two later deformation phases were apparently connected to the regional northwest european stress system with small local modifications

testing terrane transport an inclusive approach to the baja b c controversy the baja british columbia hypothesis holds that a large segment of the western edge of northern north america baja b c was situated alongside california and northern mexico in middle cretaceous time was displaced northward in the late cretaceous and paleocene by north oblique convergence of the kula plate with north america and arrived near its present location by the early eocene a consistent body of paleomagnetic data supports this hypothesis however doubt persists and various crucial tests of a geologic nature have been proposed one such test concerns the provenance of zircons in cretaceous sedimentary basins of baja b c in this paper we use both paleomagnetic data and zircon occurrences to reconfirm the baja b c hypothesis we first argue that the only truly crucial tests yet performed have been paleomagnetic and that all such tests have been positive second we show that detrital zircon data from the upper cretaceous nanaimo group although not a crucial test provide valuable paleogeographic information available data demonstrate a change in detrital zircon provenance in the nanaimo group that closely matches the position of these rocks predicted by the baja b c hypothesis detrital zircons in the nanaimo group suggest a change from a southwestern north american source rich in grenville and 1 4 1 5 ga rocks to an increasing contribution from older parts of the craton such as the wyoming province together detrital zircons and paleomagnetic inclinations allow us to assemble a detailed schedule of northward tectonic transport of the baja b c terranes