paleomagnetism of coastal california and baja california alternatives to large scale northward transport paleomagnetic data from the santa lucia orocopia sloa and baja borderland bba allochthons of coastal california and baja california have been interpreted to indicate up to 2500 km of post mid cretaceous northward transport of these regions with respect to interior north america however with neogene strike slip offsets taken into account geological interpretations correlate basement rocks of the coastal allochthons with continental basement rocks directly across the san andreas and related fault systems we have examined paleomagnetic data from sloa and bba and conclude that apparent discordances can be explained without large scale pre neogene tectonic transport three major observations are fundamental to this analysis 1 paleolatitudes derived from volcanic rocks of the jurassic eugenia formation of bba and coast range ophiolite of sloa are concordant when compared to revised jurassic reference paleomagnetic poles from interior north america 2 isotopic and paleobarometric data from the peninsula ranges batholith in southern california indicate that the batholith has been tilted northeast side up by an amount that can account for discordant paleomagnetic directions observed in plutonic rocks of the batholith without large scale northward transport 3 literal interpretation of the paleolatitudes determined from paleomagnetic directions in upper cretaceous and paleogene marine sedimentary rocks of sloa and bba requires north then south then north transport and a complex motion history between the two allochthons however concordant paleolatitudes are indicated by some sedimentary rocks while coeval or younger sedimentary rocks of the same allochthon have discordant paleolatitudes coupled with recent documentations of compaction shallowing of paleomagnetic inclination in other marine sedimentary rocks these inconsistencies suggest that paleolatitudes derived from most of the marine sedimentary rocks of sloa and bba are biased towards low paleolatitudes by compaction shallowing

regional tilt of the mount stuart batholith washington determined using aluminum in hornblende barometry implications for northward translation of baja british columbia we have developed a new quantitative method to estimate paleohorizontal in granitic plutons using the aluminum in hornblende ah barometer the method is used to correct previously published paleomagnetic data from the 93 96 ma mount stuart batholith of the cascades mountains washington state for the effects of postemplacement tilting ah barometry was done on 46 samples from the batholith using the compositions of hornblende rims coexisting with the full mineral assemblage required for pressureestimation high contrastback scatteredelectronimagingwas usedtoensurethattheanalyzedhornblendeswerenotsignificantly affected by subsolidus alteration the success of the ah barometry is indicated by two observations first increases in the al content of the hornblendes are governed almost entirely by a pressure sensitive tschermak type substitution second amphibole plagioclase thermometry indicates that assemblage equilibration occurred at or very near magmatic conditions 650 c and that temperature has a negligible effect on our pressure estimates ah barometry results indicate that the depth of crystallization across the batholith decreases systematically from 0 3 gpa in the northwest to 0 15 gpa in the southeast consistentwithindependentbarometryforthecontactaureole ofthebatholithandregionalstructuralandstratigraphicrelations using a best fit planar tilt model and bootstrap analysis of uncertainties we estimate that the paleohorizontal plane has a strike of 43 630 4 and dip of 7 62 0 southeast 695 confidence our estimated paleohorizontal allows us to restore the paleomagnetic data of beck et al 1981 and to estimate the original paleolatitude of the mount stuart batholith beck et al found that the southern part of the batholith yielded a number of sites with a well defined high coercivity remanence the carrier of this remanence was not resolved but the following four lines of evidence stronglysuggestthatthepublisheddirectionswereacquiredshortly after emplacement of the batholith 1 the stable sites all came from the shallowest and most rapidly cooled portions of the batholith as indicated by our ah results and concordant k ar ages for hornblende biotite pairs 2 the high coercivity component was always normal in polarity which is consistent with emplacement of the mount stuart batholith at the end of the cretaceous long normal 3 sites from the batholith and the contact aureole gave similar directions 4 the directions show no indication of tilt related smearing after restoration the paleomagnetic data indicate 42 6 11 clockwise rotation and 3100 6 600 km of northward offset

discordant paleomagnetic data for middle cretaceous intrusive rocks from northern baja california latitude displacement tilt or vertical axis rotation 1 paleomagnetic results and u pb zircon dating from the san marcos dike swarm and the el testerazo pluton in the cretaceous peninsular ranges batholith of northern baja california are used to evaluate alternative pre neogene paleogeographic reconstructions of the baja california peninsula the san marcos dike swarm is a dense northwest striking regional dike swarm that is exposed over an 100 km long segment of the batholith and has yielded a u pb zircon crystallization age of 120 1 ma dike attitudes from the swarm suggest a regionally consistent average 320 e strike and 79 ne dip the el testerazo pluton is a younger tonalite intrusion that truncates the northern end of the dike swarm all but one of 36 sites sampled in this study show remanence of normal polarity paleopoles for the san marcos dike swarm and el testerazo pluton are indistinguishable and were combined into a paleopole at 248 1 e 86 6 n a95 4 8 which is displaced with respect to the 122 ma reference pole for stable north america at 198 2 e 72 3 n a95 3 3 the displacement may be described by an apparent clockwise rotation of 18 6 and an apparent northward shift of 8 5 restoring a northward shift of about 3 related to the separation of baja california from north america since 10 ma only a marginal northward displacement of 5 5 is left the clockwise rotation may be the result of crustal block rotations within the right lateral shear systems in northern baja california although there is no geological evidence that supports this possibility alternatively the difference between paleopole and reference pole may be due to tilting of the study area restoring a northeastward tilt of 11 based on the mean dip measured for the san marcos dike swarm in the study area yields a paleopole at 187 6 e 70 8 n a95 5 6 which is indistinguishable from the 122 ma north american reference pole the tilting hypothesis suggested previously as a potential explanation for low inclination of paleomagnetic data from baja california therefore seems to be viable for the discordant paleopoles from this segment of the batholith data obtained previously about 150 km further south and along the western edge of the batholith defined a concordant paleopole without any tilt correction indicating that regional tilting may not be valid for all of baja california

the elkhorn mountains revisited new data for the late cretaceous paleomagnetic field of north america the late cretaceous portion of north america s apparent polar wander apw path is poorly known due to a dearth of suitable post 85 ma reference poles a paleomagnetic re investigation of elkhorn mountains volcanics 80 ma was initiated to fill this void and to determine the degree to which the onset of an apparent rapid episode of apw during this time interval correlates with known late cretaceous tectonic events a total of 249 paleomagnetic samples 30 sites were collected from three separate areas within the elkhorn mountains using both alternating field and thermal demagnetization a characteristic direction of magnetization was isolate at 15 sites a95 15 which passes a fold test at the 95 confidence level the mean pole calculated from site virtual geomagnetic poles is located at 80 3 n 189 5 e n 15 a95 9 6 k 16 8 interestingly the elkhorn mountains pole is not concordant with the cretaceous stillstand poles but is nearly coincident with the paleocene reference pole and the recently published pole for the adel mountains dated at 76 ma these new data suggest the onset of apw which brought the pole from its cretaceous position to near its early tertiary position occurred prior to 80 ma and the transition was exceedingly rapid the onset of this rapid apw now appears to coincide more closely in time with many of the significant late cretaceous tectonic events e g the laramide orogeny however since the elkhorn mountains volcanics are floored by a major east directed thrust and have undergone crustal scale deformation the data should be viewed with caution until more results are available for this time interval

compaction corrected inclinations from southern california cretaceous marine sedimentary rocks indicate no paleolatitudinal offset for the peninsular ranges terrane paleomagnetic data have been used extensively to delineate the terrane displacement and accretion history of the western margin of north america however the anomalously shallow paleomagnetic inclinations used to indicate large scale northward translation might be alternatively interpreted as due to postmagnetization tilting of batholithic rocks and compaction of marine sediments to understand the magnitude of burial compaction effects on the post cretaceous motion history of the peninsular ranges baja borderlands terrane a rock magnetic compaction and paleomagnetic study of the ladd formation and the point loma formation from southern california was conducted the anhysteretic anisotropy of remanence of the characteristic remanence carrying grains and individual magnetic grain anisotropy were used to correct the inclinations of each formation individual magnetic grain anisotropy was determined by both compaction experiments and redeposition of a magnetic separate in a dc magnetic field standard paleomagnetic studies of the units indicated that previous ladd formation results could be reproduced and a correction was made at the sample level we were unable to adequately reproduce earlier results of the point loma formation so the average remanence anisotropy was used to correct the previously reported mean direction the mean inclination of the ladd formation was conected from 46 95 8 to 58 95 4 and the mean inclination of the point loma formation was conected from 39 5 5 4 normal and 36 4 16 6 reversed to 56 0 5 1 normal and 53 0 16 7 reversed these results suggest that the peninsular ranges baja borderland terrane has been part of the western north america since the late cretaceous and that clay containing sedimentary rocks may typically experience from 10 to 15 of inclination shallowing due to burial compaction

northward motion of the whitehorse trough paleomagnetic evidence from the upper cretaceous carmacks group reply the upper cretaceous carmacks group 70 4 2 4 ma comprises gently dipping basaltic and andesitic lava flows overlying volcaniclastic deposits of the intermontane belt in the whitehorse trough the sampling area is in southern yukon and northern british columbia it lies west of the tintina northern rocky mountain trench fault and teslin suture zone and east of the denali shakwak fault volcanic sections were sampled in three regions spread over 300 km providing the first paleomagnetic data from pre tertiary volcanic rocks in the northern canadian cordillera alternating field and thermal demagnetization revealed stable magnetization for 18 of the 27 sites collected the overall mean direction d 166 7 i 71 4 k 53 95 4 8 n 18 sites is pre folding and is most probably primary latest cretaceous this gives a paleopole at 109 4 e 82 1 n k 21 a95 7 8 a critical evaluation of north american cratonic data yields a reference paleopole for the latest cretaceous at 185 8 e 77

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

slope and deep sea fan facies and paleogeography of upper cretaceous chatsworth formation simi hills california the upper cretaceous chatsworth formation is a sand rich deep sea fan deposit consisting of thick channelized sequences and interchannel deposits typical of middle fan facies it has poorly developed outer fan lobes and slope facies petrographic and x ray diffraction xrd data indicate the arkosic deposits of the chatsworth formation were derived from an uplifted granitic terrane paleocurrent studies indicate northward sediment transport and an east trending slope regional comparisons of the simi hills with the santa monica and santa ana mountains suggest these terranes were once contiguous and covered part of a deep sea fan system that comprised much of the southern california area subsequently these terranes have been offset along the malibu cucamonga and elsinore faults and rotated in response to the opening of the los angeles basin and to other adjustments in the tectonic framework of the area the chatsworth formation is thought to be part of a forearc basin deposit similar to the great valley sequence and not part of the salinian borderland block the original geographic position of the forearc basin was to the south of the sierra nevada mountains and the great valley sequence

measurements of the cretaceous paleolatitude of vancouver island consistent with the baja british columbia hypothesis a previously unsampled outcrop of gently dipping or flat lying upper cretaceous sedimentary strata in the vancouver island region which contains unaltered aragonitic mollusk fossils yielded a stable remanent magnetization that is biostratigraphically consistent with cretaceous magnetochrons 33r 33n and 32r these results characterized by shallow inclinations indicate an upper cretaceous paleolatitude of about 25 3 degrees north which is equivalent to that of modern day baja california these findings are consistent with the baja british columbia hypothesis which puts the insular superterrane well south of the oregon california border in the late cretaceous

paleomagnetism of the mid cretaceous gem bearing pegmatite dikes of san diego county california usa pegmatite dikes in the peninsular ranges batholith of southwestern california have produced spectacular crystals of semiprecious and precious minerals for over a century aside from their economic importance these dikes straddle a major tectonic boundary and were used to test hypotheses related to the timing and development of this composite batholith paleomagnetic analysis of 252 specimens from 20 sites 12 and 8 sites in the western and eastern zones of the batholith respectively from 11 mines in five dike districts isolated a stable characteristic remanent magnetization direction at 19 sites the site mean directions for the western and eastern zones are statistically indistinguishable at 95 confidence supporting petrologic and geochemical arguments that the dikes of the two zones are coeval and cogenetic after correction for the neogene opening of the gulf of california the paleopole for all 19 site mean directions is indistinguishable from the 94 ma reference paleopole for north america and

paleomagnetism of the spences bridge group and northward displacement of the intermontane belt british columbia a second look the spences bridge group is a mid cretaceous 104 ma volcanic succession in the southern intermontane belt of the canadian cordillera 50 5 n 121 w it comprises the pimainus formation mafic to felsic lava volcaniclastic and interbedded epiclastic rocks and the overlying spius formation andesitic lava flows including previous work we have 55 sites distributed among 15 localities representing most of the 3000 m thickness forty seven sites 286 oriented cores 457 specimens mainly andesites yielded acceptable data the beds are gently to moderately tilted partly due to synvolcanic deformation samples taken from a sequence of flows at any one locality have with one exception well grouped magnetization directions polarities are all normal as expected for rocks laid down in the cretaceous normal superchron declinations always are clockwise of that expected of cratonic north america indicating 60 rotation of the spences bridge group as a whole however declinations differ from locality to locality implying relative interlocality rotations about vertical axes hence inclination only analysis has been used to estimate dispersion mean inclination and paleolatitude minimum dispersion for the spius formation 27 sites was achieved after 80 untilting but the changes between 80 and 100 untilting are insignificant indicating that magnetization was acquired predominantly before tilting by contrast minimum dispersion for the pimainus formation 20 sites was achieved after 50 untilting indicating that magnetization was acquired after synvolcanic tilting when buried beneath the overlying spius formation polished thin section studies show that magnetite in the pimainus formation has undergone extensive low temperature hydrothermal alteration whereas magnetite in the spius formation shows little alteration throughout the range of tilt correction from 0 to 100 the mean inclinations of both formations were less than expected from observations obtained from mid cretaceous rocks of cratonic north america the best estimate of paleolatitude from the spius formation is 50 8 5 0 p 0 05 which is 9 5 5 7 less than would be expected had the rocks had been rigidly attached to north america this corresponds to displacement from the south of 1100 600 km displacement between the northern intermontane belt and craton probably was accommodated along major strike slip faults northern rocky mountain trench finlay pinchi etc in the south our results require a major dextral fault the intra quesnellia fault to be situated during late cretaceous or paleocene time within or marginal to the omineca belt along which about 1000 km of dextral motion occurred this could be a southern extension of the pinchi fault whose trace is now obscured by eocene extension and tectonic denudation the results also indicate that the largest tectonic discontinuity in the canadian cordillera occurs not to the east of the intermontane belt as commonly assumed but to the west because the displacements relative to cratonic north america observed from the intermontane belt are only about one third of those observed from the coast belt

角閃石中のアルミニウム圧力計を使って決定された ワシントン州 stuart山バソリスの広域的傾動 バハ ブリティシュコロンビアの北方への転移に関する意味

a paleomagnetic constraint on the late cretaceous paleoposition of northwestern baja california mexico we present palaeomagnetic data for cretaceous sedimentary rocks from the el rosario formation of northwestern baja california which imply a northward displacement of 15 0 3 8 and a 30 8 4 2 clockwise rotation for the baja peninsula relative to the north american craton since late cretaceous time paired irm acquisition x ray diffraction and mossbauer spectra indicate that fine grained magnetite is the dominant magnetic mineral present with goethite and other more oxidized phases rare to absent biochemical evidence constrains the amount of diagenesis undergone by the sediments we subjected oriented samples to both progressive alternating field and thermal demagnetization and in general found univectorial magnetizations yielding a mean inclination of 44 6 and declination of 5 3 with an 95 of 2 0 the corresponding paleolatitude for these values is 26 3 1 6 most of the samples were of normal polarity which is consistent with their deposition within the upper campanian chron 33n we collected samples from younger maastrichtian sediments which yield consistent reversed directions

dinoflagellate cysts from the upper campanian upper cretaceous of hornby island british columbia canada with implications for nanaimo group biostratigraphy and paleoenvironmental reconstructions abstract thirty mudstone samples from coastal exposures of the northumberland formation on hornby island british columbia canada yielded diverse dinoflagellate cyst and terrestrial sporomorph assemblages a late campanian age for the formation has been well defined through magnetostratigraphy macrofossil biostratigraphy and geochemical studies of the hornby island section dinoflagellate cyst taxa corresponding to 61 genera are exceptionally well preserved and include specimens referable to at least 68 formally established species the earliest occurrences of canninginopsis maastrichtiensis druggidium cf discretum phanerodinium belgicum renidinium cf vitilaire senegalinium simplex spiniferella cornuta and xenicodinium delicatum sensu slimani et al are reported along with the most recent occurrence of senoniasphaera protrusa extending their stratigraphic ranges into the upper campanian the palynomorph assemblages support a late campanian age two dinoflagellate cyst ecozones are recognized ecozone 1 and ecozone 2 assemblages suggest sediment deposition in an inner shelf environment with moderate to high nutrient input and primary productivity

partitioning of sediment on the shelf offshore of the columbia river littoral cell this paper is not subject to u s copyright the definitive version was published in marine geology 273 2010 11 31 doi 10 1016 j margeo 2010 02 001

a compaction correction for the paleomagnetism of the nanaimo group sedimentary rocks implications for the baja british columbia hypothesis 1 a paleomagnetic and magnetic anisotropy study of the late cretaceous northumberland formation on hornby island british columbia was conducted to determine if burial compaction could have caused its anomalously shallow inclinations the shallow nanaimo group inclinations have been used to support the baja british columbia baja bc model of continental dynamics in which superterranes were transported thousands of kilometers northward along the active north american continental margin in the cretaceous a mean of the site means from the northumberland formation is d 5 8 i 50 9 95 7 9 n 8 anisotropy of magnetic susceptibility ams and anisotropy of anhysteretic remanence aar were measured to identify and correct for any inclination shallowing caused by depositional compactional processes both concretion and fine grained rock samples had typical depositional compactional ams and aar fabrics with bedding perpendicular minimum principal axes a revised correction equation was used to account for the effects of either triaxial magnetic fabrics or small angular deviations of principal axes from the bedding plane the average inclination was increased by 9 6 after the compaction correction d 6 1 i 60 5 95 7 1 n 8 and the mean inclination of concretion and fine grained rock sites was significantly steeper than ward et al s 1997 result i 42 5 placing hornby island and the insular superterrane at a paleolatitude of 41 n in the late cretaceous this paleolatitude indicates that baja bc did translate northward since the late cretaceous by about 1600 km but not by the 3500 km previously indicated

paleomagnetic evidence that the central block of salinia california is not a far traveled terrane new paleomagnetic results from late cretaceous 75 85 m y red beds on the central block of salinia indicate that salinia was located within 6 in latitude of its current cratonal north american position during the late cretaceous after correction for neogene san andreas fault transport the red beds formed as alluvial fan overbank deposits with hematite cement deposited directly on salinian granites in the la panza range paleomagnetic analysis shows two components of magnetization in the red beds a low blocking temperature present day overprint residing in goethite and a high blocking temperature 600 component residing in hematite the hematite magnetization is a chemical remanent magnetization which formed soon after deposition during pedogenesis the bedding corrected hematite remanence contains a magnetic polarity stratigraphy with antipodal normal and reversed directions twenty three class i sites 95 20 have an average hematite direction with inclination 54 4 and declination 18 2 95 6 1 after structural correction these paleomagnetic data suggest that salinia resided at about 35 n latitude during the late cretaceous within 6 of its current location adjacent to cratonal north america by contrast a summary of paleomagnetic data from the peninsular ranges terrane and the sur obispo terrane which are currently outboard of salinia shows northward transport of these terranes of 12 to 22 relative to their current locations in north america since the cretaceous the offsets increase systematically away from the craton with the most outboard sur obispo terrane which is composed of accretionary prism and distal forearc material showing the largest degree of northward translation

coastal and baja california paleomagnetism reconsidered systematic reappraisal of paleomagnetic data from upper mesozoic and lower cenozoic sedimentary rocks and igneous rocks of late mesozoic age in coastal and baja california indicates that pluton tilt and shallowing of paleomagnetic directions by sedimentary compaction resolve observed discordances with the north american apparent polar wander apw path when the best available reference paleopoles are used for comparison the hypothesis of major tectonic transport in excess of distances inherent in current models for evolution of the san andreas transform system is unnecessary and in conflict with geologic observations fresh insights derived from recent data sets and improved analysis include the following 1 the limited paleomagnetic data recording primary remanence for upper jurassic and lower cretaceous volcanic rocks in coastal california are concordant with the north american apw path 2 the tilt of the peninsular ranges batholith inferred from paleobarometric data eliminates its declination discordance and reduces its inclination discordance to a level where ovals of confidence for observed and expected paleomagnetic directions overlap 3 key cretaceous and paleogene red bed successions on the salinian block of coastal california and in baja california have yielded concordant paleolatitudes 4 the discordances of different apparent paleolatitudes inferred from cretaceous and paleogene marine sedimentary strata lie within a range that can be attributed to compaction shallowing on the basis of both experimental information and observations from elsewhere 5 turbidites are more susceptible to compaction shallowing than shelf and deltaic strata 6 the uniform rotation of paleomagnetic directions inferred previously for peninsular california is not supported by the full array of data now available from multiple localities 7 basement ties of the salinian block in california and of the baja california peninsula to the continental interior preclude any hypothesis for tectonic transport much in excess of san andreas transform slip

compaction corrected paleomagnetic paleolatitudes for late cretaceous rudists along the cretaceous california margin evidence for less than 1500 km of post late cretaceous offset for baja british columbia the paleolatitudinal distribution of bivalve rudists has important significance for the baja british columbia baja bc hypothesis that western canadian superterranes from british columbia have been displaced 3000 km since cretaceous time rudists are not observed in baja bc sedimentary rocks yet they are common in late cretaceous strata in california and baja california which have the same paleomagnetically determined paleolatitudes approximately 25 n as baja bc rocks of late cretaceous age in order to resolve this contradiction and to delimit more exactly the southern paleolatitudes of baja bc paleomagnetic inclinations corrected for the effects of burial compaction were used to determine the paleolatitudinal distribution of rudists along the california margin compaction corrected paleomagnetic data from the peninsular ranges and salinia terranes indicate that rudists were restricted to paleolatitudes between 34 and 40 n evidence of coastal upwelling in the latest cretaceous marca shale may explain the northern limit of the rudist distribution these data suggest that baja bc was no farther south than 40 n in the late cretaceous thus limiting its post cretaceous displacement to less than 1500 km and that burial compaction has also affected the paleomagnetism of nanaimo group sedimentary rocks from vancouver island this result also helps resolve the conflict between paleomagnetic results which show 1500 km of post late cretaceous offset between the insular coast plutonic complex superterrane and the intermontane superterrane and geologic observations which can allow only tens of kilometers of offset between these terranes in the methow tyaughton basin

exotic terranes of western california numerous distinct geological terranes compose the north american cordillera1 there may be as many as 50 terranes in california alone2 critical to deciphering the history of cordilleran tectonic assembly is an understanding of the displacement history of individual terranes it is therefore important to know 1 whether a terrane has undergone significant motion with respect to the stable craton that is whether it is allochthonous or exotic 2 if so when relative motion started and stopped 3 from where an individual terrane originated and 4 the nature of interterrane movements we consider here the problem of determining whether the now juxtaposed salinian and stanley mountain terranes of california became amalgamated at or near their present position with respect to cratonic north america or if they collided at a considerable distance from their present positions and were later accreted to north america as a composite package the palaeomagnetic data that we present indicate that the latter was the case

reconstruction of paleo wave conditions during the late pleistocene from marine terrace deposits monterey bay california the santa cruz coastal terrace fringes much of the northern monterey bay region california it consists mainly of a regressive sequence of high energy barred nearshore marine sediments deposited during the last sangamonian highstand of sea level this sequence can be sub divided into several depth dependent facies on the basis of paleo current data and vertical sequence of sedimentary structures these include a lower shoreface facies deposited in 10 16 m water depth an upper shoreface facies including both a storm dominated assemblage and a surf zone assemblage deposited in 0 10 m water depth and a foreshore facies deposited in the swash zone up to 3 5 m above high tide the magnitudes of the storm events responsible for depositing these sediments were estimated by calculating paleo wave heights using a variety of criteria e g critical threshold equations breaker depths berm heights in addition the climate and paleogeography during the deposition of these sediments were essentially the same as today allowing the use of present day wave statistics to estimate the frequency of these storm events the largest storms formed offshore flowing currents e g rip wind forced and possibly storm surge ebb currents that resulted in the deposition of approximately 30 of the sediments seaward of the surf zone however the magnitude and frequency of these events are unknown the remaining 70 of the sediment beyond the surf zone was deposited in response to smaller storm waves which were on the average at least 1 6 m high such waves presently occur no more than 15 of the time sediments deposited during fairweather conditions i e the remaining 85 of the time have a low preservation potential and are generally not preserved in this facies in contrast surf zone sediments were deposited by a variety of processes associated with waves whose maximum offshore heights were probably 2 2 m such waves presently occur up to 92 of the time sediments within the swash zone were deposited by waves up to 3 m high the largest of which presently occur approximately 2 of the time most of the sediments were deposited by storms of intermediate magnitude and frequency different facies however appear to preferentially record events of different recurrence intervals in particular surf zone sediments were deposited under relatively small storm and post storm conditions whereas sediments deposited farther offshore record increasingly larger less frequent storm events relatively rare events e g the 100 or 1000 yr events do not appear to have significantly affected sedimentation in these nearshore environments

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

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

discordant paleomagnetic poles from the canadian coast plutonic complex regional tilt rather than large scale displacement stratigraphic petrologic and isotopic data indicate that parts of the coast plutonic complex and the north cascade range have been tilted northeast side up by angles of approximately 30 degree about north northwest trending axes these tilts can account for discordant paleomagnetic directions observed in mid cretaceous plutons from these regions without large scale displacement relative to north america

deciphering shallow paleomagnetic inclinations 1 implications from correlation of albian volcanic rocks along the insular intermontane superterrane boundary in the southern canadian cordillera 1 geologic and paleomagnetic data lead to two contradictory hypotheses regarding the paleoposition of the insular and intermontane superterranes that presently constitute the western canadian cordillera paleomagnetic data from the insular and intermontane superterranes suggest a southerly origin coinciding with the latitude of mexico and the northwest united states respectively during the mid cretaceous geologic evidence points to a northerly origin for these same tectonic entities during this period both models cannot be correct geologic and paleomagnetic data from the empire valley churn creek area in south central british columbia 51 5 n 122 5 w are critical to resolving these contradictory hypotheses late cretaceous rocks correlated to the insular superterrane with large paleomagnetic displacements unconformably overlie mid cretaceous rocks correlative to the spences bridge group of the intermontane superterrane we provide paleomagnetic evidence of this correlation based on similar magnetic properties opaque mineral assemblages demagnetization behavior fold test results mean inclinations clockwise vertical axes rotations and statistically indistinguishable paleomagnetic poles and displacement estimates this correlation and the observed geologic relationships in the empire valley churn creek area indicate that the insular and intermontane superterranes were linked by the mid cretaceous sites from the two previous spences bridge group studies are combined with their correlatives in the empire valley churn creek area to give 81 sites that yield a paleomagnetic pole of 60 5 n 304 5 e dp 3 7 dm 5 5 which corresponds to 1050 450 km of displacement from the south this new displacement estimate suggests that the spences bridge arc formed at the latitude of southern oregon during the mid cretaceous

deciphering shallow paleomagnetic inclinations 2 implications from late cretaceous strata overlapping the insular intermontane superterrane boundary in the southern canadian cordillera 1 significant discrepancies exist between paleomagnetic and geologic estimates of the timing and magnitude of terrane displacement in the southern canadian cordillera lithostratigraphic palynological geochronologic geochemical and structural data to which we add paleomagnetic data demonstrate that upper cretaceous strata in churn creek are laterally equivalent facies of the silverquick powell creek spc succession these rocks therefore comprise a single overlap sequence linking the insular and intermontane superterranes by late albian cenomanian time 95 ma contradicting previous assertions based solely on paleomagnetic interpretation that major 2000 km latitudinal displacement separated the two regions the churn creek succession retains primary magnetic remanence as demonstrated by positive fold conglomerate and contact tests the sediments do not hold the anisotropy signature of compaction shallowed inclinations the mean inclination of all spc sites from both mount tatlow and churn creek is 55 6 2 3 n 36 sites corresponding to a paleolatitude of 36 1 2 4 this reflects northward translation of the composite insular intermontane superterrane of 3050 450 km between 85 and 50 ma the silverquick powell creek succession at churn creek unconformably overlies the northern end of the spences bridge group a late early cretaceous volcanic arc assemblage on the intermontane superterrane paleomagnetic data in the companion paper place it 1050 450 km south of its current position between 100 and 105 ma integration of these new data sets require that the insular and intermontane superterranes formed a single enormous crustal block that underwent complex episodic south north translation between circa 105 and 50 ma the timing rate and vectors of translation are problematic in terms of geologic constraints along the continental margin

a paleomagnetic transect of the mid cretaceous peninsular ranges batholith baja california mexico we report structural paleomagnetic and magnetic fabric data for midcretaceous plutons of the peninsular ranges batholith along a transect at 30 n latitude four plutons in the western sector are characterized by characteristic magnetizations residing in magnetite in this sector el milagro aguaje del burro la zarza and san telmo plutons yield a combined paleopole at 82 1 n 169 7 e k 137 6 a 95 7 9 n 4 38 sites which rotated for closure of the gulf of california falls at 79 3 n 179 5 e and it is concordant with the north america reference pole plutons in the transition zone between the eastern and western sectors of the peninsular ranges have magnetizations residing in hematite el potrero and san jose plutons yield highly discordant paleopoles indicating apparent clockwise rotation r and fl attening f of 33 0 5 1 and 27 6 6 1 respectively san jose and 46 1 5 9 and 31 0 7 0 el potrero the discordance is best explained by west down tilt of the crustal block between the main martir thrust and the rosarito fault which are major compressional structures parallel to the trend of the peninsular ranges the san pedro martir pluton a large la posta type pluton on the eastern sector of the transect has magnetizations that reside primarily in hematite the mean

new paleomagnetic rock magnetic and petrographic results from the valle group baja california mexico exploring the causes of anomalously shallow paleomagnetic inclinations 1 a detailed paleomagnetic rock magnetic and sedimentologic study was conducted on cenomanian age strata of the valle group at el campito baja california to examine the burial compaction effects on the paleomagnetic inclination of marine sedimentary rocks alternating field and thermal demagnetization isolated a characteristic remanence at 16 of 18 sites with a mean of dec 342 6 inc 19 1 and 95 3 4 the inclination is 38 7 shallower than that predicted by the reference paleopole for north america laboratory experiments indicate that compaction could account for only 7 5 of the inclination shallowing fold tests at different scales yield both positive and negative results making a tight constraint on the remanence s age impossible a primary postdepositional remanence is supported by bedding parallel foliations in the anisotropy of anhysteretic remanence fabric although primary anomalously shallow inclinations could indicate significant southerly then northerly paleolatitudinal offset a more likely scenario is a late cenozoic low temperature remagnetization which is suggested by alteration along the edges of some detrital silicate grains and a bimodal magnetic grain size distribution revealed by isothermal remanence data the synthesis of the data indicates that the vizcaino terrane was contiguous with the cordillera margin during remagnetization and underwent a subsequent 13 5 5 4 clockwise rotation we tentatively interpret that the remagnetization resulted from burial and or miocene volcanism which caused an acquisition of thermochemical remanent magnetization tcrm this study reveals a complicated remanence that resists easy interpretation and suggests caution in studies of similar rocks

sorted bedform pattern evolution persistence destruction and self organized intermittency 1 we investigate the long term evolution of inner continental shelf sorted bedform patterns numerical modeling suggests that a range of behaviors are possible from pattern persistence to spatial temporal intermittency sorted bedform persistence results from a robust sorting feedback that operates when the seabed features a sufficient concentration of coarse material in the absence of storm events pattern maturation processes such as defect dynamics and pattern migration tend to cause the burial of coarse material and excavation of fine material leading to the fining of the active layer vertical sorting occurs until a critical state of active layer coarseness is reached this critical state results in the local cessation of the sorting feedback leading to a self organized spatially intermittent pattern a hallmark of observed sorted bedforms bedforms in shallow conditions and those subject to high wave climates may be temporally intermittent features as a result of increased wave orbital velocity during storms erosion or deposition of bimodal sediment similarly leads to a spatially intermittent pattern with individual coarse domains exhibiting temporal intermittence recurring storm events cause coarsening of the seabed strengthening the sorting feedback and the development of large wavelength patterns cessation of storm events leads to the superposition of storm large wavelength and inter storm small wavelength patterns and spatial heterogeneity of pattern modes

a new late cretaceous paleomagnetic pole from the adel mountains west central montana north america s apparent polar wander path has been poorly defined between the mid cretaceous and paleocene reference pole positions existing data allowed 13 of apparent polar motion over about 22 m y 87 65 ma roughly coinciding with the beginning of laramide deformation 80 ma we report on a paleomagnetic study of the adel mountain volcanic rocks to refine the north american apparent polar wander path for this interval the shonkinite rocks of the adel mountain volcanic field are on the eastern edge of the cretaceous paleocene fold and thrust belt some of these structures disturb the western edge of the volcanic pile we obtained two new k ar dates from the adel rocks one date on biotite from a shonkinite dike that crosscuts most of the volcanic rocks is 71 2 2 7 ma the other a whole rock date from a flow deep in the volcanic pile is 81 1 3 5 ma we collected six to nine paleomagnetic samples from each of 34 sites in roadcuts and natural outcrops of flows dikes and laccoliths positive fold and conglomerate tests along with alternating field and thermal demagnetization indicate that our characteristic remanent directions are primary magnetizations acquired before late cretaceous to paleocene thrust belt deformation averaging the virtual geomagnetic poles from 26 reliable sites all of normal polarity yields a paleopole at 82 2 n 209 9 e 95 6 80 k 18 38 this pole is concordant with the paleocene reference pole 82 0 n 170 2 e 95 3 5 k 18 6 diehl et al 1983 and is 11 6 from the globerman and irving 1988 mid cretaceous pole at 71 n 196 e the youngest information in the cretaceous stillstand pole is from the niobrara formation shive and frerichs 1974 at about 85 89 ma if we take the average age of the adel mountain volcanics to be 76 ma then 12 of apparent polar motion occurred between 87 ma and 76 ma thus rapid apparent polar motion correlates well with the onset of laramide deformation

magnetostratigraphy of displaced upper cretaceous strata in southern california a magnetostratigraphic study of upper cretaceous marine strata from the santa ana mountains in southern california has identified a campanian reversed magnetozone this reversed interval corresponding to marine magnetic anomaly 33 34 chron 33r of campanian age can be correlated with a campanian reversed magnetozone that has been reported from strata of the great valley sequence in central california the late cretaceous paleolatitude of the santa ana mountains is estimated from this study to be 26 6 n this is significantly different from the region9s expected cretaceous paleolatitude of 43 8 n as part of the north american stable craton and indicates that this region part of the peninsular ranges terrane was 1900 km farther south in cretaceous time relative to the stable craton

a successful rock magnetic technique for correctng paleomagnetic inclination shallowing case study of the nacimiento formation new mexico the accuracy of an inclination shallowing correction technique was tested on the remanence of the paleocene nacimiento formation the correction assumes that changes in paleomagnetic inclination during deformation will be directly related to changes in remanence anisotropy the remanence anisotropy is also a function of the magnetic anisotropy of the individual magnetic grains the nacimiento formation was selected for this test because its inclination is shallow by 7 to 8 and previous paleomagnetic studies indicate that it has a primary remanence with a well constrained age and that magnetic overprints are minimal tectonics are an unlikely explanation for its shallow inclination these conditions allow the inclination corrected remanence to be compared to a well defined paleomagnetic pole to determine the accuracy of the technique the characteristic remanence from 20 nacimiento sites was isolated by alternating field and thermal demagnetization and was corrected using the anisotropy of anhysteretic remanence measured for three to five samples per site individual particle anisotropy was determined by drying a magnetic separate epoxy mixture in a 35 50 mt magnetic field laboratory compaction of disaggregated nacimiento material was also used to yield an effective individual magnetic particle anisotropy the two techniques resulted in similar values for individual particle anisotropy and similar inclination shallowing corrections both corrections were successful and the inclination corrected formation mean direction was indistinguishable from the direction predicted by north america s paleocene paleopole the inclination shallowing correction technique reported here should be applied routinely in paleomagnetic studies provided that the remanence is a primary depositional remanence that has been affected only by syndepositional or early postdepositional processes e g compaction

submarine fan deposystems and tectonics of a late cretaceous forearc basin along an accretionary convergent plate boundary maccoll ridge formation wrangell mountains alaska analysis of upper cretaceous sedimentary and volcanic strata in the wrangell mountains of south central alaska provides an opportunity to study the tectonics depositional systems and provenance of a forearc basin that developed along an accretionary convergent plate boundary new data from the 1150 m thick maccoll ridge formation indicate that deposition occurred during the campanian on a coarse grained submarine fan that was derived from an uplifted allochthonous terrane exposed in the hanging wall of a fault system that separated the forearc basin from the subduction complex new age controls include palynoflora indicative of a late middle to late campanian age and compatible radiometric age determinations of volcanic vitric crystal tuffs near the top of the formation which have 40ar 39ar isochron ages of 79 4 0 7 and 77 9 2 1 ma sedimentological and paleontological data show that sedimentation occurred on the inner portions of a sand and gravel rich submarine fan system evidence for this inte

el nino southern oscillation variability from the late cretaceous marca shale of california changes in the possible behavior of el nino southern oscillation enso with global warming have provoked interest in records of enso from past greenhouse climate states the latest cretaceous laminated marca shale of california permits a seasonal scale reconstruction of water column flux events and hence interannual paleoclimate variability the annual flux cycle resembles that of the modern gulf of california with diatoms characteristic of spring upwelling blooms followed by silt and clay and is consistent with the existence of a paleo north american monsoon that brought input of terrigenous sediment during summer storms and precipitation runoff variation is also indicated in the extent of water column oxygenation by differences in lamina preservation time series analysis of interannual variability in terrigenous sediment and diatom flux and in the degree of bioturbation indicates strong periodicities in the quasi biennial 2 1 2 8 yr and low frequency 4 1 6 3 yr bands both characteristic of enso forcing as well as decadal frequencies this evidence for robust late cretaceous enso variability does not support the theory of a permanent el nino in the sense of a continual el nino like state in periods of warmer climate

paleomagnetism of the upper cretaceous strata of mount tatlow evidence for 3000 km of northward displacement of the eastern coast belt british columbia this study contributes the first paleomagnetic data from dated cretaceous units of the coast belt 51 3 n 123 8 w in which paleohorizontal bedding surfaces can be identified with certainty we sampled 38 sites through a 1 5 km stratigraphic interval of cenomanian silverquick sedimentary strata and cenomanian to campanian powell creek volcanics in the tatlow syncline in the tyaughton methow basin magnetizations at 21 sites have high unblocking temperatures tub and pass the tilt test precision k 5 before untilting maximum k 48 after 100 untilting magnetic minerals of volcanics show original textures mean declinations in volcanic and sedimentary rocks are statistically identical and polarity is consistently normal the mean inclination 55 4 3 4 probability p 0 05 of this pretilting magnetization is 20 1 4 0 shallower than that expected if the rocks were deposited in their present position relative to cratonic north america field and laboratory observations rule out other causes for these anomalous shallow inclinations these rocks therefore have been displaced northward by 3000 500 km relative to cratonic north america since mid cretaceous time this displacement is almost 3 times greater than that estimated from mid cretaceous volcanics in the now adjacent intermontane belt evidently the two belts were not amalgamated until latest cretaceous or early tertiary time these results are inconsistent with all previous geologically based tectonic reconstructions of the cordillera magnetizations at eight sites in silverquick and powell creek beds have low tub and directional characteristics similar to those in three younger diorite intrusions reversed and normal polarities occur the rocks are commonly highly altered and maximum precision occurs after 40 untilting the magnetizations therefore are interpreted as overprints of latest cretaceous age acquired during folding

palaeolatitude drift history of displaced terranes in southern and baja california the delineation of microplate tectonic terranes1 which make up western north america the timing of their accretions to western north america and the identification of their original geological settings are all topics of debate2 3 the most recent addition to this family of terranes is the santa lucia orocopia allochthon4 5 sloa fig 1 which is made up of salinia6 7 and several other smaller terranes8 and is located in central and southern california this composite terrane amalgamated in the cretaceous and accreted to southern california by the early palaeogene4 5 we describe here new palaeomagnetic results from localities outboard from the sloa in southern california usa and baja california mexico these results are used to define a newly identified allochthonous terrane in southern and baja california peninsular ranges terrane9 prt which is outboard from the sloa estimate the prt s palaeolatitude drift history for the past 160 myr and infer its original geological setting prt and sloa palaeolatitude drift histories are then combined to produce a new perspective on the tectonic development of southern and baja california over the past 160 myr

regional tilt of the mount stuart batholith washington determined using aluminum in hornblende barometry implications for northward translation of baja british columbia discussion and reply

coastal evolution of late cretaceous and pleistocene rocky shores pacific rim of northern baja california mexico cretaceous on cretaceous and pleistocene on cretaceous unconformities are mapped throughout a 45 km 2 field area surrounding the village of erendira on the pacific coast of northern baja california mexico the unconformities represent a late pleistocene rocky shore 120000 130000 ka directly superimposed on a campanian early maastrichtian rocky shore 77 70 ma superb exposure and preservation of coastal features allow for precise paleogeographic restorations physical analysis includes a comparison of rocky shore composition configuration and overall length paleoecological analysis permits the recognition and comparison of preferred wave directions high intensity windward biotas during the late cretaceous included rock encrusting rudists and coralline red algae while low intensity leeward biotas were characterized by rock encrusting oysters scleractinian corals and bryozoans during the pleistocene the open coast was exploited by the byssate bivalve mytilus and boring bivalves including petricola and penitella while more protected settings were dominated by the gastropods olivella and saxidomus amino acid analysis of saxidomus nuttalli yielded an age estimate consistent with the last interglacial epoch oxygen isotope stage 5e wave impact was oblique to the paleoshore during the late pleistocene onshore winds were generated from the west in contrast wave movement was generated from the east to southeast and parallel to shore during the late cretaceous field data are integrated with paleogeographic reconstructions and predictive models including computer models for local and global oceanography where different paleogeographies and oceanographic models conflict field mapping of this sort adds a much needed element of ground truth

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

using leaf margin analysis to estimate the mid cretaceous albian paleolatitude of the baja bc block abstract the baja bc hypothesis which postulates that western washington state british columbia and southern alaska originated at the latitude of mexico has pitted paleomagnetic results against long held interpretations about the tectonic evolution of western north america in this paper we develop a new paleobotanical method for estimating paleolatitude and apply it to this problem we start by showing that the modern mat field for north america is well correlated with latitude demonstrating the feasibility of using mat to estimate paleolatitude a compilation of mat and floral data from 84 modern sites in central and north america is used to establish a new prediction relationship mat 1 32 28 99p where p is the proportion of smooth margined species within a floral sample at a site our analysis also includes a more complete estimate of the uncertainties associated with estimating mat from a measurement of p using modern data we show that mat and p can be used to estimate latitude as well we then apply this approach to resolve the paleolatitude of baja bc eleven floral sites from stable north america are used to establish the latitudinal mat profile for north america during the albian and cenomanian a floral site from the winthrop formation a mid cretaceous 110 100 ma fluvial unit in the methow basin of northern washington state is linked to the baja bc block and predates its proposed northward offset forty three morphospecies of dicotyledonous angiosperm leaves from the winthrop formation give p 0 76 which is equivalent to a mat of 23 4 c indicating a subtropical to tropical climate we use the north american mat profile to estimate a paleolatitude of 38 4 n for the winthrop flora indicating 2200 km of northward offset relative to stable north america

revisiting the baranof leech river hypothesis for early tertiary coastwise transport of the chugach prince william terrane abstract according to the baranof leech river hypothesis originally proposed in 1982 1 schists on southern baranof island in southeastern alaska were contiguous with the leech river schist on southern vancouver island until 40 ma and 2 both rock units were part of the 2200 km long chugach prince william terrane which was displaced northward about 1100 km after 40 ma isotopic data obtained since 1982 show that the syn magmatic metamorphism that produced the baranof and leech river schists occurred at 50 ma not at 40 ma large magnitude coastwise slip of the terrane is therefore post 50 ma igneous rocks in the baranof and leech river units are part of the sanak baranof magmatic belt of forearc magmatism which has been ascribed to the early tertiary subduction of an oceanic ridge the slab window also gave rise to early eocene near trench plutonic and volcanic rocks on north american basement in the north cascades of washington state and probably to coeval igneous rocks on the western coast of vancouver island these igneous suites in the forearc fix the location of the intersection of the ridge with the continental margin 50 myr ago at latitude ca 48 49 n present day coordinates paleomagnetic data obtained since 1982 imply that before 50 ma the parts of the chugach prince william terrane that were to become the baranof and leech river schists were south of 48 49 n from 61 to 50 ma the northward movement of the terrane relative to north america can be reconciled with the southward migration of forearc magmatism in the chugach prince william terrane if the ridge trench intersection was fixed at 48 n present day coordinates the border ranges fault system is the on land structure that most likely accommodated hundreds of kilometers of post early eocene displacement

paleomagnetic and geologic data indicating 2500 km of northward displacement for the salinian and related terranes california results of a pair of paleomagnetic studies of sedimentary rocks in the salinian terrane of westernmost california indicate a northward displacement of about 2500 km since cretaceous time stratigraphic relations suggest that the salinian terrane became amalgamated with several others by the late cretaceous and all underwent the same northward translation this composite terrane allochthon became sutured to cratonal north america by early tertiary time one paleomagnetic study involved upper cretaceous turbidites of the pigeon point formation fine grained thin bedded turbidites yielded the most reliable results whereas medium to coarse grained sandstones are not always stably magnetized contorted layers resulting from soft sediment deformation usually gave directional results parallel to those of undeformed sedimentary layers thereby implying a postdepositional remanence process there is no indication of inclination error or other processes affecting the fidelity of the remanent magnetization paleomagnetic results from four separate locations in the pigeon point formation gave positive fold tests and mean inclination values near 36 a mean geomagnetic latitude calculated from these results is 21 2 5 3 much more southerly than the value of 46 5 2 3 calculated for pigeon point using paleomagnetic pole data from late cretaceous rocks from cratonic north america declination values are not antipodal for normal and reversed polarity sites analysis of depositional current directions from sandstone beds of the same outcrops shows that the difference is the result of neogene rotations of small crustal blocks adjacent to the san gregorio fault in a sequence of paleocene turbidites that crop out at point san pedro four sample localities yielded positive fold tests with mean inclination values near 40 declination values however were spread over a range between 230 and 320 comparison with depositional current directions from the same outcrops indicates clockwise rotations related to neogene right slip on the pilarcitos fault the mean geomagnetic latitude calculated for the point san pedro sediments is 24 5 4 0 and is more southerly than the 43 3 2 5 latitude expected for that location for the salinian terrane and the west coast of cratonic north america absolute rates of latitudinal motion were 8 5 cm yr northward and 3 cm yr southward respectively

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

fracture zone scale variation of trace elements and stable isotopes in calcite in a crystalline rock setting abstract with an aim to increase the understanding about the isotopic and chemical heterogeneity of calcites in water conducting fracture zones with different crystalline wall rock compositions at different depths we present trace element chemistry isotopic composition 18o 13c 87sr 86sr and biomarkers of euhedral low temperature fracture coating calcite paleohydrogeological fluctuations and wall rock influence on the hydrochemistry in the deep groundwater are explored samples are from several fracture zone sub fractures at 360 to 740 m retrieved during an extensive core drilling campaign in sweden calcite generally showed fracture zone specific values of 13c 18o and 87sr 86sr which indicates precipitation from relatively homogeneous fluid similar to the modern groundwater at the site at the same event in each fracture zone 18o and 13c in the different fracture zones were consistent with precipitation from waters of different salinity and decreasing organic input with depth respectively the latter is also supported by biomarkers showing clear indications of srb related organic compounds e g iso and anteiso c17 0 branched fatty acids except in the deepest zone in contrast to the isotopes variation in trace elements within the fracture zones was generally up to several orders of magnitude manganese and ree as oppose to the other metals were higher in the shallow fracture zones 112 1130 and 44 97 ppm respectively than in the deeper 28 272 and 5 11 ppm respectively in agreement with the groundwater composition although the rock types varied between and within the different fracture zones this had insignificant influence on the trace element chemistry of the calcites co variation was generally relatively large for many trace elements with isometric logratio correlation generally better than 0 75 which indicates that their variation in the calcites is due to variation of ca in the fracture water but other local factors especially uptake in co precipitating minerals clay minerals barite pyrite and zeolites but also microbial activity and metal speciation may have influenced the metal incorporation into calcite these detailed studies of fracture calcite are of importance for the understanding of variation in fluid chemistry and trace metal uptake in fracture zones adding together with hydrochemical studies detailed information optimal for site characterisation

detrital remanence inclination errors and anhysteretic remanence anisotropy quantitative model and experimental results summary we suggest that inclination errors in detrital remanent magnetization drm may be recognized and corrected by measurement of the anisotropy of anhysteretic remanent magnetization arm arm anisotropy reflects directional variations in the remanence capacity of relatively fine grained magnetic particles in rocks or sediments generally the same particles that carry the stable component of drm relative vertical and horizontal drm magnitudes are controlled by this directional remanence capacity as well as by the alignment efficiency of the particle magnetic moments which in turn is governed by the relative intensities of the vertical and horizontal components of the ambient magnetic field thus the respective vertical and horizontal components of palaeointensity and therefore palaeofield inclination may be obtained by normalizing the measured drm components by parallel arm intensities synthetic sediments containing silica kaolin and sized magnetite powders have previously been found to acquire experimental drm with an inclination error that is a direct function of kaolin concentration further experiments have now shown that arm anisotropy in the synthetic sediments is also a direct function of kaolin content and thus a correlation exists between drm inclination errors and arm anisotropy multiplying the measured drm vector by the inverse of the arm anisotropy matrix yields an improved estimate of the actual laboratory depositional field in all cases for samples with acicular 0 5 m magnetite this procedure reduces a mean inclination error of over 5 to less than 0 5 samples with subequant magnetite of slightly larger grain size 0 75 m exhibit similar arm anisotropy 10 per cent but somewhat larger inclination errors 10 we interpret this in terms of stronger horizontal alignment but weaker particle anisotropies for the larger more equant magnetites

a compaction correction for the paleomagnetism of the cretaceous pigeon point formation of california the paleomagnetism of the cretaceous pigeon point formation turbidites was reexamined to determine whether the 25 of southerly paleolatitudinal offset originally observed champion et al 1984 for these rocks was all or in part due to compaction shallowing of their paleomagnetic inclination the study consisted of two parts 1 a standard paleomagnetic study including detailed thermal and alternating field demagnetization was conducted on oriented cores collected at pigeon point approximately 50 km south of san francisco california the results of this study were combined with the alternating field demagnetized results for samples provided by d champion from the initial pigeon point paleomagnetic study the combined data set has a mean direction for pigeon point i 41 6 d 346 9 similar to that originally obtained by champion et al 1984 2 material from the pigeon point formation was disaggregated given a laboratory analog of a postdepositional remanence and compacted to pressures as high as 0 13 mpa which caused volume losses up to 53 the laboratory compacted samples were alternating field demagnetized and their magnetic inclination and anisotropy of anhysteretic remanence were both measured these data were used to derive correction curves following jackson et al 1991 which describe the specific relationship between remanence anisotropy and inclination shallowing for the pigeon point formation two correction curves were determined one assuming that the magnetic particle orientation distribution experienced a prolate deformation after remanence acquisition and one assuming an oblate deformation these two different corrections were necessary because the anisotropy of anhysteretic remanence indicates a composite fabric due to both a prelithification technically caused lineation and a burial compaction foliation the anisotropy of anhysteretic remanence measured for each paleomagnetic sample and the correction curves determined from the laboratory compaction experiments indicate that the inclination of the pigeon point formation has been shallowed by burial compaction the compaction corrected pigeon point mean directions assuming either a prolate i 53 1 d 347 2 or an oblate i 49 8 d 346 8 deformation suggest only 13 to 16 of southerly paleolatitudinal offset for the pigeon point formation in the cretaceous not the 25 originally observed champion et al 1984 the resulting paleolatitude for the pigeon point formation could indicate that salinia served as a link between the cratonic sierra nevada arc to the north and the peninsula ranges baja borderlands allochthon to the south alternatively our results suggesting a 10 compaction inclination shallowing for the pigeon point turbidites may indicate that many of the paleomagnetic studies placing the peninsula ranges baja borderlands 15 to the south of north america in the cretaceous and tertiary may have suffered from a similar effect and that the allochthon has been nearly in place since the cretaceous

the role of summer monsoon typhoons in the formation of nearshore coarse grained ripples depression and sand ridge systems along the shimizu coast suruga bay facing the pacific ocean japan abstract coarse grained ripples cgrs develop within the seafloor depression sand ridge systems along the shimizu coast in the northwestern part of suruga bay facing the pacific ocean central japan in this paper we analyze data from high resolution bathymetry seafloor observation by an underwater video camera and high resolution seismic surveys and seafloor trenching of shallow strata obtained between 2005 and 2007 to describe their geomorphological and sedimentological characteristics in detail and to examine the formative processes and maintenance of the systems in water depths of 5 30 m cgrs occur in seafloor depressions that are approximately 40 70 cm deeper than the surrounding sandy seafloor in many cases the ripples develop in depressions between shore normal sand ridges composed mainly of fine sand

magnetic anisotropy scanning electron microscopy and x ray pole figure goniometry study of inclination shallowing in a compacting clay rich sediment anisotropy of anhysteretic remanence aar scanning electron microscopy sem and x ray pole figure goniometry studies of clay rich sediments were conducted to delineate the interactions between magnetite and clay particles which cause inclination shallowing during compaction these studies used synthetic sediments composed of kaolinite or illite and two grain sizes of magnetite 0 45 m and 2 3 m natural marine sediments which contained 40 50 clay were also used the sediments were compacted by pressures as high as 0 157 mpa the sediments porosity decrease suggests that the compaction experiments model burial depths up to 400 500 m the main result of this study is that inclination shallowing and void ratio versus pressure curves show two points where behavior changes a rapid decrease in inclination and void ratio occurs up to a pressure of 0 02 mpa this is accompanied by a magnetic intensity decrease of 20 30 compaction at pressures between 0 02 mpa and 0 05 mpa causes a further decrease in these parameters at moderate rates while compaction at pressures above 0 05 mpa causes very little change percent magnetic anisotropy and x ray pole figure intensity ratio versus pressure curves show only one point where behavior changes at 0 05 mpa with a rapid increase at lower pressures and little change at higher pressures a model to explain this behavior based on the sem observations as well as the magnetic anisotropy pole figure and inclination data suggests that compaction up to 0 02 mpa causes a decrease in pore volume with little reorientation of clay particles some magnetic particles are firmly attached to clay particles whereas other loosely attached particles are either randomized or subvertical ones are preferentially disturbed causing inclination shallowing and an intensity decrease at pressures between 0 02 mpa and 0 05 mpa magnetite particles have become firmly attached to clay particles and start to follow the reorientation of clay particles as the clay fabric develops at 0 05 mpa there is a major change in the clay microstructure with a horizontal fabric becoming evident compaction at higher pressures causes little further volume loss and clay particle reorientation and hence little additional inclination shallowing the randomization disturbance process suggested by this model causes slightly more than half of the inclination shallowing observed in the samples studied whereas magnetite clay attachment causes the remainder of the inclination decrease

constraining the travels of a suspect terrane paleomagnetism and geobarometry of two early cretaceous igneous complexes in the peninsular ranges batholith california paleomagnetic and rock magnetic measurements for 27 sites in the tonalitic ca 108 ma alpine and ca 100 ma ramona complexes in the suspect yuma terrane or western zone of the peninsular ranges batholith near san diego show that single and pseudosingle domain magnetite carries their characteristic remanence the alpine and ramona paleopoles agree with six published paleopoles from cretaceous igneous rocks in the yuma terrane but all eight paleopoles are discordant for north america al in hornblende geothermobarometric depth determinations at 16 sites plus published mapping and depth determinations suggest that the batholith is divided into blocks by orogen parallel faults or by orthogonal fault sets with large vertical displacements the paleomagnetic data show that the fault blocks in the terrane underwent on average ene side up tilting of 10 3 about an orogen parallel axis between ca 125 ma and ca 89 7 ma but they have not been translated northward as a suspect terrane by 500 km excluding neogene opening of the gulf of california the tilting is attributed to torque from ene shallow underthrusting of the farallon plate beneath the wsw overthrusting north american plate where subsequent extension has caused differential uplift of the fault blocks nonsignificant dextral displacement of 4 1 440 110 km between the eastern and western zones of the batholith suggests that this boundary represents an intraarc fault the large paleopole discordance found in younger sedimentary strata of baja california is attributed mainly to compaction shallowing of the remanence and or postdepositional remagnetization

geometry migration and evolution of wave orbital ripples at leo 15 observations of the temporal evolution of the geometric properties and migration of wave formed ripples are analyzed in terms of measured suspended sand profiles and water velocity measurements six weeks of bedform observations were taken at the sandy medium to coarse sized sand leo 15 site located on beach haven ridge during the late summer of 1995 with an autonomous rotary sidescan sonar during this period six tropical storms several of hurricane strength passed to the east of the study site ripples with wavelengths of up to 100 cm and with 15 cm amplitudes were observed the predominant ripples were found to be wave orbital scale ripples with ripple wavelengths equal to 3 4 of the wave orbital diameter although orbital diameters become larger than 130 cm during the maximum wave event it is unclear if a transition to non orbital scaling is occurring ripple migration is found to be directed primarily onshore at rates of up to 80 cm day suspended transport due to wave motions calculated by multiplying acoustic backscatter measurements of suspended sand concentrations by flow velocity measurements are unable to account for a sufficient amount of sand transport to force ripple migration and are in the opposite direction to ripple migration thus it is hypothesized that the onshore ripple migration is due to unobserved bedload transport or near bottom suspended transport bedload model calculations forced with measured wave velocities are able to predict the magnitude and direction of transport consistent with observed ripple migration rates sequences of ripple pattern temporal evolution are examined showing mechanisms for ripple directional change in response to changing wave direction as well as ripple wavelength adjustment and erosion due to changing wave orbital diameter and relative wave to current velocities

paleomagnetism of the late cretaceous early tertiary north central montana alkalic province paleomagnetic results have been obtained from the late cretaceous early tertiary igneous complexes of the north central montana alkalic province data from 94 sites in eocene volcanic and intrusive rocks give a paleomagnetic pole located at 82 0 n 170 2 e a95 3 5 k 18 6 while 36 sites in paleocene intrusions yield a paleomagnetic pole at 81 8 n 181 4 e a95 5 4 k 20 2 these poles differ by only 1 6 and are not significantly different statistically the 130 site virtual geomagnetic poles show no significant elongation and suggest no significant apparent polar wander apw during the period of magnetization of the igneous centers postmagnetization structural complications in these rocks are minimal the presence of a single predominant polarity in these intrusive complexes reinforces the radiometric age data that suggest that igneous activity within individual centers was of short duration the northcentral montana data together with other early tertiary cretaceous and mid tertiary paleomagnetic results require modification of our earlier apw chronology diehl et al 1980 it now appears that apw relative to north america since the early cretaceous consists of a polar still stand during much of the cretaceous 120 75 m y b p a period of rapid movement in latest cretaceous time 75 65 m y b p and a period of slow polar movement thereafter the onset of this period of rapid apw correlates well with a major change in plate motions at 80 m y and the beginning of the laramide orogeny

campanian maastrichtian stage boundary in southern california resolution and implications for large scale depositional patterns detailed paleomagnetic study of upper cretaceous predominantly deep sea fan deposits from the point loma formation san diego california situated within the allochthonous peninsular ranges terrane has produced a magnetic polarity stratigraphy with one reversed magnetozone foraminiferal and megafossil primarily molluscan occurrences demonstrate that these strata are late campanian to early maastrichtian in age and that the reversed magnetozone is almost certainly basal maastrichtian chron 32r recognition of this chron provides a direct correlation of the north pacific province biostratigraphic zonations to the standard cretaceous stages in europe the identification of chron 32r indicates that for the available biostratigraphic zonations the pacific slope megafossil campanian maastrichtian stage boundary shows the best accord with the standard european stage boundary improved age relations for these strata suggest that their large scale depositional patterns were strongly influenced by both local active plate margin tectonics and global eustatic factors during the late cretaceous

a revised kinematic model for the relative motion between pacific oceanic plates and north america since the late cretaceous 1 the convergence between the pacific farallon and kula oceanic plates and the north american plate has provided a driving force for tectonic processes that have shaped the western margin of north america yet reconstructions of plate motion in the pacific basin have traditionally relied on the assumption of fixed hot spots in the last decade substantial cretaceous to paleogene motion between the pacific and atlantic hot spots has been recognized providing motivation to reevaluate the history of relative motion between pacific oceanic plates and north america by means of plate circuit reconstructions this paper presents new kinematic models based on two alternative plate circuits linking the pacific plate to north america since late cretaceous time when compared to models relying on fixity of pacific and indo atlantic hot spots our reconstructions suggest that the pacific kula and pacific farallon ridges were 600 1000 km closer to the western margin of north america and hence that the farallon and kula plates were smaller in late cretaceous to middle eocene time these findings cast significant doubt on the viability of a configuration of the farallon kula ridge that juxtaposes the kula plate with the southern part of the paleo north american margin during this time interval the results of our new reconstructions also suggest more oblique convergence between the farallon or kula plate and north america from the late cretaceous to the middle eocene related to the combination of dominantly northwest motion of the pacific plate and steady southwest motion of north america this provides an efficient mechanism for the coast parallel translation of some accreted terranes of north america it may also explain the structure of geological units in western north america such as the central belt of the franciscan complex which show a dominant coast parallel fabric formed during an interval coeval with the episode of oblique convergence

reply to comment on paleomagnetism of the upper cretaceous strata of mount tatlow evidence for 3000 km of northward displacement of the eastern coast belt british columbia by p j wynne et al and on paleomagnetism of the spences bridge group and northward displacement of the intermontane belt british columbia a second look by e irving et al

correction of inclination shallowing and its tectonic implications the cretaceous perforada formation baja california abstract a paleomagnetic and magnetic fabric study of the aptian to albian perforada formation the oldest sedimentary unit of the cretaceous valle group was conducted to determine whether the perforada inclination had been shallowed by burial compaction and to correct the inclination for any shallowing the perforada formation is located on the vizcaino terrane of the vizcaino peninsula of west central baja california an accurate paleolatitude will indicate whether the vizcaino terrane is far travelled eighty eight specimens from 43 independently oriented hand samples and cores were collected from 11 sites a small 10 m fold was sampled in order to constrain the age of the magnetization with a fold test thermal and alternating field demagnetization was able to isolate characteristic magnetizations for most samples maximum unblocking temperatures near 580 c indicate that magnetite is the magnetic carrier the characteristic magnetization passes the fold test at the 99 confidence level anisotropy of anhysteretic remanence aar and anisotropy of magnetic susceptibility ams measurements show that five sites had well developed bedding parallel foliations while four sites had poorly developed aar fabrics but foliated ams fabrics the remaining two sites had poorly developed foliations for both ams and aar the mean inclination i 35 6 of the five sites with well developed aar foliations is 13 7 shallower than the mean inclination i 49 3 of the two sites with poorly developed aar and ams fabrics when the inclinations of the sites with well developed aar foliations are corrected using an individual particle anisotropy of 1 5 determined from magnetic extract epoxy samples dried in 30 50 mt dc magnetic fields the corrected mean inclination i 50 1 is indistinguishable from the mean inclination of the sites with poorly developed aar fabrics a corrected formation mean direction for the perforada formation d 311 8 i 47 0 95 9 3 indicates a 33 5 11 1 counterclockwise rotation and 5 6 7 7 of post cretaceous northward motion after 3 of neogene fault motion has been removed these results indicate that the vizcaino terrane has moved little with respect to the peninsular ranges terrane and cratonic north america since the cretaceous

eocene rotation of the coast plutonic complex and intermontane belt paleomagnetism of eocene plutons along the klondike highway paleomagnetic results are reported for the 59 ma skagway 54 ma fraser 53 ma summit lake and 48 ma clifton felsic plutons of the eastern coast plutonic complex cpc that outcrop along the south klondike highway in alaska and british columbia thermal and alternating field step demagnetizing methods yielded stable characteristic remanent magnetization chrm directions for all 29 sites of normal reversed and mixed polarity the chrm resides in single or pseudosingle domain magnetite and or pyrrhotite that is shown to be primary by contact tests with the 47 ma vertical white pass mafic dikes paleopoles from six 56 to 50 ma mean 52 2 ma intermontane belt yukon tanana terrane imb ytt units that cannot be explained by tectonic tilt are compared with nine clustered 59 to 46 ma mean 52 4 ma eastern cpc paleopoles both paleopole populations show nonsignificant poleward northward translation relative to north america imb ytt 3 7 5 3 n cpc 4 3 6 4 s overall 1 2 4 9 s ind

rethinking yellowstone in yukon and baja british columbia paleomagnetism of the late cretaceous swede dome stock northern canadian cordillera 1 paleomagnetic results obtained from the 69 8 ma swede dome stock emplaced into the pericratonic yukon tanana terrane ytt west of dawson yukon indicate a minimal northward translation of 360 575 km and a clockwise rotation of 20 23 with respect to north america in accord with the displacement of 425 km along the nearby tintina fault coeval carmacks group volcanics in contrast have previously indicated 1900 km northward translation and minimal rotation and have been proposed to be a displaced manifestation of the fixed yellowstone hot spot thus providing an independent estimate of the late cretaceous paleoposition of the baja british columbia terranes of western north america a compilation of recent mid and late cretaceous paleomagnetic results from the ytt and intermontane belt imb terranes reveals that the carmacks group paleomagnetic result is anomalous the ytt and imb terranes which form the bulk of baja british columbia appear instead to have experienced 1000 km northward translation with respect to north america since 70 ma consistent with geological estimates of motion along plausible accommodating faults in addition past mobility of the hawaii emperor hot spot implies that the pacific hot spots may have experienced 1200 km of southward motion from 81 to 47 ma if so then the paleoposition of the yellowstone hot spot if it existed at 70 ma would likely have produced the carmacks magmatism 1000 km north of yellowstone s current latitude consistent with a moderate 1000 km post 70 ma northward translation of the ytt and imb terranes to their present position in north america

sedimentology facies architecture and chemostratigraphy of a continental high latitude paleocene eocene succession the chickaloon formation alaska abstract the paleocene eocene chickaloon formation of southern alaska represents rapid deposition in a floodbasin setting contains abundant and diverse fossil plant material and spans the paleocene eocene thermal maximum petm sedimentologic lithofacies and chemostratigraphic analyses of exposures of the chickaloon formation were conducted in order to provide a contextual framework for this late paleocene early eocene high latitude sedimentary succession and to test if hyperthermal conditions are recorded in the unit at the main study area in the evan jones coal mine strata represent an alluvial sequence dominated by floodplain channel sandstone crevasse lobe crevasse channel and mire deposition floodplain environments are represented by medium gray commonly nodular and or carbonate cemented shaly siltstone and centimeter scale thick sheet sandstone interbeds most channel sandstone deposits are interpreted to be crevasse channels and are generally small 2 5 m thick rarely coarser than medium grained sandstone and sand grains are commonly coated with fe oxides carbonaceous shale and coal are localized and indicate a high rate of organic carbon accumulation in the area 13c analyses of bulk organic carbon from the succession at the evan jones mine are internally consistent with this interpretation they yield uniformly negative values that are typical of continental organic matter 21 7 to 28 5 x 25 4 fossil plant material is also very common and includes leaves wood seeds and resins from broad leaf angiosperms conifers ferns and sphenopsids considered together lithologic and paleontologic data suggest that these strata represent a floodbasin environment the observed crevasse channels probably originate from a main channel located within several kilometers of the depocenter ash fall tuffs punctuate the studied sequence and contain abundant reworked or recycled zircons indicating that the depocenter was proximal to a volcanic source across all of these chickaloon depositional environments a significant negative isotopic shift 5 8 occurs which we hypothesize to represent a short lived perturbation associated with a global hyperthermal event

paleomagnetism of cretaceous and eocene strata san miguel island california borderland and the northward translation of baja california the history of poleward motion of the baja california peninsula is a subject of continuing geologic investigations including paleomagnetic studies during the past decade geologic correlations seem not to necessitate northward movement while paleomagnetic data suggest movement of 1000 km or more we have made paleomagnetic measurements on cretaceous and eocene sedimentary rocks of san miguel island california which are western lithofacies of rocks cropping out on the baja peninsula a total of 97 drill cores taken from upper cretaceous turbidites though weakly magnetized were found to clean best in response to thermal demagnetization revealing a characteristic remanence the characteristic magnetization has an inclination 43 9 declination of 24 0 and an 95 of 3 9 this direction is 19 shallower and rotated 50 clockwise from the expected direction for the present site position and corresponds to a paleolatitude of 26 n a total of 117 drill cores of middle eocene rocks revealed characteristic magnetizations in response to either alternating field or thermal demagnetizations some samples suffer from a secondary thermal magnetization from early miocene volcanic activity requiring a thermal cleaning that incompletely removes the overprint a mean direction of magnetization can be derived from the intersection of planes fitted to the paths of demagnetization the characteristic magnetization for the eocene rocks has an inclination of 31 9 a declination of 71 0 and an 95 of 3 8 this direction is 19 shallower and rotated 79 clockwise from the expected eocene direction for this site and corresponds to a latitude of 17 n these paleomagnetic data in combination with recently published data from the baja peninsula and peninsular ranges of southern california indicate motion trajectories that mimic the north american craton for the period cretaceous to late eocene time during the oligocene the baja peninsula and adjoining regions to the west moved northward relative to the craton arriving at a pre gulf of california position not later than earliest miocene time a comparison of the northward motion of the baja peninsula with that of the santa lucia orocopia allochthon shows that both areas underwent rapid poleward translations but these motions occurred at different times

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

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