radiocarbon studies of latest pleistocene and holocene lava flows of the snake river plain idaho data lessons interpretations abstract latest pleistocene holocene basaltic lava fields of the snake river plain idaho have been dated by the radiocarbon method backhoe excavations beneath lava flows typically yielded carbon bearing charred eolian sediment this material provided most of the samples for this study the sediment typically contains less than 0 2 carbon charcoal fragments were obtained from tree molds but only from a few backhoe excavations contamination of the charred sediments and charcoal by younger carbon components is extensive the effects of contamination were mitigated but appropriate pretreatment of samples using acid and alkali leaches twenty of the more than 60 lava flows of the craters of the moon lava field have been dated their ages range from about 15 000 to about 2000 yr b p the ages permit assignment of the flows to eight distinct eruptive periods with an average recurrence interval of about 2000 yr the seven other latest pleistocene holocene lava fields were all emplaced in short eruptive bursts their 14 c ages yr b p are kings bowl 2222 100 wapi 2270 50 hells half acre 5200 150 shoshone 10 130 350 north robbers and south robbers 11 980 300 and cerro grande 13 380 350

frequent eruptions of mount rainier over the last 2 600 years field geochronologic and geochemical evidence from proximal fine grained tephras and from limited exposures of holocene lava flows and a small pyroclastic flow document ten 12 eruptions of mount rainier over the last 2 600 years contrasting with previously published evidence for only 11 12 eruptions of the volcano for all of the holocene except for the pumiceous subplinian c event of 2 200 cal year bp the late holocene eruptions were weakly explosive involving lava effusions and at least two block and ash pyroclastic flows eruptions were clustered from 2 600 to 2 200 cal year bp an interval referred to as the summerland eruptive period that includes the youngest lava effusion from the volcano thin fine grained tephras are the only known primary volcanic products from eruptions near 1 500 and 1 000 cal year bp but these and earlier eruptions were penecontemporaneous with far traveled lahars probably created from newly erupted materials melting snow and glacial ice the most recent magmatic eruption of mount rainier documented geochemically was the 1 000 cal year bp event products from a proposed eruption of mount rainier between ad 1820 and 1854 x tephra of mullineaux us geol surv bull 1326 1 83 1974 are redeposited c tephra probably transported onto young moraines by snow avalanches and do not record a nineteenth century eruption we found no conclusive evidence for an eruption associated with the clay rich electron mudflow of 500 cal year bp and though rare non eruptive collapse of unstable edifice flanks remains as a potential hazard from mount rainier

time lapse seismic monitoring some shortcomings in nonuniform processing conceptually repeat or time lapse seismic monitoring is straightforward seismic data sets acquired at different times are calibrated compared and the intersurvey differences analyzed and interpreted in terms of fluid changes or movement

late quaternary geomagnetic secular variation from historical and 14c dated lava flows on hawaii a paleomagnetic record of geomagnetic paleosecular variation psv is constructed for the last 4400 years based on 191 sites in historical and 14c dated lava flows from mauna loa kilauea and hualalai volcanoes on the island of hawaii the features of this new record are similar to those recorded by sediments from lake waiau near the summit of mauna kea volcano but overall mean inclinations for the lava flows 31 to 33 depending on window size are nearer the expected dipole field value 35 than is that for the sediments 27 divergence of the inclination records with increasing age suggests that the lake waiau values at depths below 2 m have been affected by compaction related inclination shallowing although magnetic terrain effects cannot be ruled out the rate of psv indicated by the record presented here is highly variable 20 century and a pronounced shift in inclination from 25 to 40 occurred between 1030 and 975 years b p paleomagnetic directions from undated materials can be correlated with our calibrated curve but the resolution is largely dependent on the psv rate and data densities for both the reference and unknown directions the upper part of the puna basalt 18 lava flows previously sampled for paleomagnetism along the northern wall of kilauea s caldera uwekahuna bluff was likely deposited sometime between 1030 and 750 years b p but the lowest two flows beneath the uwekahuna ash 2100 years b p are correlated with an age of 3034 years b p paleomagnetic data for 54 lava flows of the ka u basalt exposed in the northwest wall of mauna loa s summit caldera mokuaweoweo indicate that they probably accumulated over a relatively short time interval 200 years and are assigned to a 1000 to 1199 year b p time window the mean of ages within this window is 1030 years b p but mapping and other 14c dates indicate that these summit overflows are probably closer to 1200 years b p in age

a review of lacustrine paleomagnetic records from western north america 0 40000 years bp abstract a review of 16 lake sediment paleomagnetic records from western north america spanning time intervals over the last 40 000 yr bp provides evidence that many of these lacustrine records have recorded geomagnetic secular variation with wavelengths on the order of a few hundred years the younger studies 0 13 300 yr bp show general morphologic agreement among inclination records but most of the declination records are difficult to correlate among the older records there are major disagreements over the existence of the mono lake excursion specifically five studies contain evidence for the excursion but six studies do not show any record of it because errors in radiocarbon dating will distort down core time scales the younger records were rescaled with time scales that were constructed from extremal correlations of long wavelength 1000 2000 yr high amplitude 10 20 inclination features with these new time scales the excellent temporal and morphologic agreement between the fish lake oregon and blue lake idaho declination records confirms the existence of errors in the radiocarbon time scales the lack of agreement among the other rescaled declination records indicates that the records have been distorted or altered by sedimentary and geologic processes and or by sampling measuring and data analysis procedures in terms of the regional geomagnetic record fish lake and blue lake present a 3300 yr master curve of secular variation for northeastern oregon and southwestern idaho the lack of correlation among the other records however prevents us from drawing definite conclusions about the areal variation of the geomagnetic field in western north america over the past 40000 yr bp

geomagnetic intensity spike recorded in high resolution slag deposit in southern jordan article i nfo in paleomagnetism periods of high field intensity have been largely ignored in favor of the more spectacular directional changes associated with low field intensity periods of excursions and reversals hence questions such as how strong the field can get and how fast changes occur are still open in this paper we report on data obtained from an archaeometallurgical excavation in the middle east designed specifically for archaeomagnetic sampling we measured 342 specimens from 72 samples collected from a 6 1 m mound of well stratified copper production debris at the early iron age 12th 9th centuries bce site of khirbat en nahas in southern jordan seventeen samples spanning 200 yr yielded excellent archaeointensity results that demonstrate rapid changes in field intensity in a period of overall high field values the results display a remarkable spike in field strength with sample mean values of over 120 t compared to the current field strength of 44 t a suite of 13 radiocarbon dates intimately associated with our samples tight control of sample location and relative stratigraphy provide tight constraints on the rate and magnitude of changes in archaeomagnetic field intensities

paleomagnetic correlation of late quaternary lava flows in the lower east rift zone of kilauea volcano hawaii paleomagnetic data reflecting paleosecular variation psv of the geomagnetic field are used to correlate individual lava flows in the lower east rift zone of kilauea volcano this area has been recently mapped based on petrography stratigraphy soil development and degree of weathering of the flows eight 14c dates also provide a framework for the relative age assignments site mean directions of remanent magnetization for historic flows in this region indicate that local magnetic anomalies do not mask the psv signal that within flow angular differences are generally 5 and that temporal resolution of the paleomagnetic directions is of the order of 100 years the paleomagnetic correlations do not conflict with the observed stratigraphic relationships and psv reference curves from dated lava flows and lake sediments have also been used to help determine the sequence of directional groups paleomagnetic grouping of flows into eruptive events indicates a different and perhaps more refined eruptive history for the lower east rift zone than implied by the geologic mapping alone the number of individual flows based on petrographic distinctions is likely the same but the frequency of events including petrographically distinct flows is apparently lower than previously thought flows from ridge crest vents bifurcated by the rift indicate formation of the central graben in this region after 300 years ago possibly related to the 1790 eruptions along dual fractures

a 10 000 yr geomagnetic secular variation record from three australian maars summary detailed within lake magnetic stratigraphies enable composite declination and inclination versus depth curves to be derived for sets of 6m cores from each of three volcanic crater lakes in western victoria comprehensive radiocarbon chronologies for each sequence enable reliable timescales to be assigned to the variations in direction of the remanence the resultant time scaled curves are in satisfactory agreement and are therefore thought to provide an estimate of the geomagnetic secular variation in se australia during the last 10 000 yr amplitude attenuation occurs as an increasing function of age and probably results from long time scale remagnetization processes mean directions coincide with the geocentric axial dipole field directions at the three sites inclination oscillations are stronger and better resolved than those in declination whereas the opposite tends to be true for the european records reduction of records to a common virtual site suggests that the difference is largely of geometrical origin comparisons of vgp paths do not reveal a common dipole wobble component the sense of looping of the magnetic vector favours westward rather than eastward drift of features of the non dipole field relative field strength estimates based on normalization of nrm with respect to measures of the magnetic mineral content do not agree with australian and worldwide archaeointensity results

paleosecular variations of the geomagnetic field during the holocene from eastern asia abstract high resolution paleomagnetic secular variation psv records bear great information of dynamics processes of the earth s geomagnetic field and can be further used for inter profile correlation and for dating sediments however effects of changes in the depositional environment on psv records have not been fully determined this study constructed holocene psv records for the gravity piston core zsqd34 obtained from the northern south china sea rock magnetic and transmission electron microscope tem results indicate that single sd and psd domain magnetites are the main carrier of the natural remanent magnetization comparable to the records derived from the freshwater lakes and the modeling results we observed that direction curves from these two environments of contrasting salinity content are rather consistent the direction curves are independent of the constructed salinity however the gradual increasing trend of relative intensity since about 5 kyr might be related to the decreasing sea surface salinity furthermore on the centennial and millennial time scale the relative intensity and salinity show some positive relation suggesting a potential contribution of salinity to the paleomagnetic relative intensity recording processes

age and duration of volcanic activity at diamond craters southeastern oregon abstract diamond craters one of several young basalt lava fields dotted across southeastern oregon was active in the time between about 7320 and 7790 years ago calibrated ages this timing is determined by a two step analysis first new radiocarbon ages from samples that underlie the lava field and existing ages from overlying deposits constrain the volcanic activity to between 6130 and 7790 years ago second paleomagnetic directions specifically a steep inclination of about 71 further constrain the age of emplacement to the older part of that interval the time before 7320 years ago paleomagnetic directions for lava emplaced early and late in the eruptive activity are essentially the same the duration of diamond craters eruptive activity must have been at least 1 2 decades in order to account for the extrusion of 1 6 km 3 of dense rock equivalent magma at rates typical of long lived basaltic eruptions whether the duration was only that brief or persisted to a century or more is irresolvable from paleomagnetic directions although the coincidence of directions from beginning to end is evidence that the eruption certainly was not protracted over many centuries

tree ring dating of pre 1980 volcanic flowage deposits at mount st helens washington tree ring dating ring width pattern matching was used to determine emplacement dates for eight subfossil tree bearing pre 1980 pyroclastic flow and lahar deposits in stream valleys draining mount st helens washington limiting dates were also established for nine other pre 1980 flowage deposits from the ages of trees rooted on or near them or from exhumed trees the 17 new dates improve understanding of the chronology of events during and after mount st helens9s kalama eruptive period which extended from a d 1479 to the mid 1700s we assign bracketing dates to the three phases of the kalama eruptive period 1479 1510 to the early kalama during which mount st helens erupted explosive dacitic tephras pyroclastic flows and one or more domes 1489 1566 to the middle kalama during which mount st helens produced andesitic tephras pyroclastic flows and lava flows and 1489 1750 to the late kalama during which mount st helens again erupted dacite overlap of the brackets reflects the limits of our dating resolution the revised chronology confirms that little time perhaps 50 yr elapsed between the end of mount st helens9s kalama eruptive period and the start of the succeeding goat rocks eruptive period a d 1800 1857 eruptions apparently occurred sporadically during the entire 1479 1857 interval the record also indicates that a large pyroclastic flow occurred 7 10 yr after the explosive eruptions that began the kalama eruptive period the dates further imply that extrusion of the pre 1980 summit dome continued intermittently for 100 yr and limit the ages of two tephras these findings demonstrate the usefulness of relict tree bearing deposits to volcanic history studies

post depositional remanent magnetization lock in depth in precisely dated varved sediments assessed by archaeomagnetic field models accurate and precise chronologies are needed to evaluate the existence and effect of a post depositional remanent magnetization lock in process on sedimentary palaeomagnetic records here we present lock in modelling results of two palaeomagnetic records from varved lake sediments lakes kalksjon and gyltigesjon in sweden by using model predictions based on archaeomagnetic data we used the c 14 wiggle match dating technique to improve the precision of the kalksjon varve chronology in the period between 3000 and 2000 cal bp which is characterized by pronounced palaeomagnetic secular variation this method allowed us to infer an age model with uncertainties of 20 years 95 4 probability range furthermore we compared the palaeomagnetic record of kalksjon to gyltigesjon which has a corresponding 14c wiggle matched chronology the ages of palaeomagnetic features derived from the wiggle matched varve chronologies are older than those predicted by the archaeomagnetic models lock in modelling was performed with different filter functions to explain the temporal offset and the amplitude of the lake sediment palaeomagnetic data the analyses suggest that a linear lock in function with lock in depths the depth below which no more natural magnetic remanence is acquired that range between 30 and 80 cm in kalksjon and 50 and 160 cm in gyltigesjon are most appropriate to explain the data these relatively deep lock in depths in sediments without a bioturbated mixed zone can be attributed to the relatively high organic contents and low density of the lake sediments which contribute to a thick unconsolidated upper zone of the sediment sequence in which re alignment of magnetic particles can take place c 2014 elsevier b v all rights reserved

cross equalization data processing for time lapse seismic reservoir monitoring a case study from the gulf of mexico nonrepeatable noise caused by differences in vintages of seismic acquisition and processing can often make comparison and interpretation of time lapse 3 d seismic data sets for reservoir monitoring misleading or futile in this gulf of mexico case study the major causes of nonrepeatable noise in the data sets are the result of differences in survey acquisition geometry and binning temporal and spatial amplitude gain wavelet bandwidth and phase differential static time shifts and relative mispositioning of imaged reflection events we attenuate these acquisition and processing differences by developing and applying a cross equalization data processing flow for time lapse seismic data the cross equalization flow consists of regridding the two data sets to a common grid applying a space and time variant amplitude envelope balance applying a first pass of matched filter corrections for global amplitude bandwidth phase and static shift corrections followed by a dynamic warp to align mispositioned events and finally running a second pass of constrained space variant matched filter operators difference sections obtained by subtracting the two data sets after each step of the cross equalization processing flow show a progressive reduction of nonrepeatable noise and a simultaneous improvement in time lapse reservoir signal

regionally consistent western north america paleomagnetic directions from 15 to 35 ka assessing chronology and uncertainty with paleosecular variation psv stratigraphy abstract new paleomagnetic secular variation psv data from fish lake utah usa along with previously published regional records allow us to build an independently dated western north america psv stack wnam17 from about 35 to 15 ka that quantifies dating and paleomagnetic uncertainties in february 2014 we recovered a composite 11 m long sediment record from fish lake utah that retrieved glacially influenced and post glacial sediments computed tomography ct scans and magnetic susceptibility were used to build a precise depth scale while radiocarbon dating of terrestrial macrofossils and tephrostratigraphy provide tight age control glacially influenced sediments have well defined characteristic remanent magnetizations with all maximum angular deviation values

repeatability issues of 3 d vsp data increased repeatability is recognized as one major issue for improving the time lapse seismic technology as a reservoir management tool a 3 d vertical seismic profiling vsp data set acquired over a period of two days is used to analyze how repeatable a permanent installed geophone array can be and how repeatability changes with inaccuracies in source positioning it is found that for a frequency range between 3 5 and 50 hz the difference root mean square rms level between two recorded traces belonging to two different shots is about 8 this fact shows that there is a potential for acquiring very accurate time lapse seismic data by using a permanently installed downhole geophone array repeatability variation with increasing shot separation distances is analyzed showing a rapid decrease in repeatability as the accuracy of the positioning of the repeat survey decreases horizontal geophone components show approximately the same degree of repeatability compared to the vertical component but horizontal geophone data is slightly more sensitive to positioning errors the results show that repeated 3 d vsp surveys preferably using permanently installed geophone arrays might be an efficient tool for detailed and precise monitoring of fluid and pressure changes within a hydrocarbon reservoir

palaeomagnetic results from the indian heaven volcanic field south central washington summary palaeomagnetic data have been obtained from plio pleistocene rocks of the indian heaven volcanic field ihvf located in the high cascade province in southern washington alternating field demagnetization yielded well defined directions from 56 individual lava flows sites from 23 volcanic units all units sampled were normally magnetized suggesting that volcanic activity within the indian heaven region occurred primarily during the last 0 73 myr and not over the last 3 75 myr as suggested by k ar ages combining palaeomagnetically similar site mean directions from lava flows from the same volcanic unit resulted in n 35 the mean direction calculated from this data set is i 65 2 and d 0 2 095 3 3 k 56 4 while the palaeomagnetic pole calculated using virtual geomagnetic pole vgp data is located at 87 7 n 231 4 e or95 4 7 k 27 2 this pole is not significantly different from the pole determined from all data n 56 or the rotational axis and is slightly near sided with respect to the mean sampling site longitude the between site angular dispersion of the vgps about the mean for n 35 and n 56 although low is not statistically different at the 95 confidence level from the expected value predicted by model f of mcfadden mcelhinny 1984 our data together with other recent data from the western united states do not confirm the presence of a persistent standing non dipole field component in this region during the plio pleistocene as suggested by brown mertzman 1979 additionally these data suggest that vgp angular dispersion associated with the geomagnetic field has been decreasing over the last 5 myr

holocene secular variation in western north america paleomagnetic record from fish lake harney county oregon an 8 9 m composite section of lake sediment from fish lake steens mountain southeastern oregon has provided a high resolution record of holocene geomagnetic secular variation in western north america the section is composed of overlapping core segments with stratigraphic control based on six tephra layers and other thin distinct bands and with age control from 37 radiocarbon dates the 455 paleomagnetic samples possess a strong and stable magnetic remanence which is carried by pseudo single domain magnetite paleomagnetic records for individual core segments show low scatter and high serial correlation and where the segments overlap there is excellent agreement between records the azimuthal orientation of the composite section was recovered from the known direction of the geomagnetic field at the time of the climactic eruption of mount mazama tephra which is present in fish lake both internal and external evidence including the correspondence with an archaeomagnetic record from the southwestern united states support the conclusion that the fish lake record represents the history of geomagnetic field behavior during at least the last 10 000 years b p analysis of that record reveals that the average geomagnetic direction can not be distinguished from that of a geocentric axial dipole field and that the overall circularity of the field was clockwise but the detailed behavior was quite complex angular standard deviations of both field directions and virtual geomagnetic poles differ significantly from the values predicted from theoretical models of secular variation but are consistent with those of other holocene records when the record from fish lake is compared to the proposed type curve for east central north america there is excellent agreement for the past 6000 years provided the curves are offset by about 400 years this offset corresponds to a rate of westward drift of about 0 062 yr beyond about 6000 radiocarbon years ago good agreement between the two curves occurs when there is no offset suggesting that the field was standing rather than drifting during this time

deflection of paleomagnetic directions due to magnetization of the underlying terrain in the summers of 1989 and 1991 we made 344 near ground level measurements of the ambient geomagnetic field above recent basalts on the island of hawaii using a three component fluxgate magnetometer we studied 12 surface features including a lava pond lava channels long tilted blocks smooth sloping surfaces two fissures and a deep u shaped road cut we observed substantial differences up to 20 between the observed and expected international geomagnetic reference field igrf magnetic field directions over these features except those composed of shelly pahoehoe and a flat horizontally thin lava pond we also observed inclinations that were systematically shallower than the igrf field by up to 5 we show that these shallower inclinations can be explained by the magnetization of the regionally sloping surface of the southern side of the island we found that all of the observed inclination deflections can be explained by simple two dimensional models which assume uniform induced and remanent magnetization parameters in the local terrain our observations imply that the inclination deflections cannot be corrected without a complete knowledge of the preexisting terrain and the remanence in the underlying flows upon which the lavas cooled since this information is rarely available it is difficult or impossible to discriminate between dispersion of paleomagnetic directions caused by the magnetic terrain effect and dispersion due to other factors such as paleosecular variation psv we therefore conclude that psv dispersion parameters cannot be accurately determined from paleomagnetic measurements on highly magnetic volcanic flows we also suggest that some of the geomagnetic excursions inferred from measurements on volcanic rocks may be at least in part due to the magnetic terrain effect it is unnecessary to invoke ad hoc mechanisms such as clastic block or crustal rotations distortion of the top crust or flow deformation to explain the large between site dispersions or inclination anomalies observed in many of the paleomagnetic data from volcanic rocks our observations also bring into question the general reliability of paleomagnetic pole positions inferred from volcanic rocks as a systematic inclination deflection due to local and regional slopes and irregular terrain such as those we observed would lead to a corresponding error in the inferred paleolatitude the magnetic terrain effects also offer alternative explanations for anomalous paleomagnetically inferred plate motions

variable effects of cinder cone eruptions on prehistoric agrarian human populations in the american southwest abstract two 900 bp cinder cone eruptions in the american southwest affected prehistoric human populations in different ways mostly because of differences in the eruption styles and area affected primary pre eruption cultural factors that may have led to successful adaptation to the eruptions include decision making at the family or household level low investment in site structures dispersion of agricultural sites in varied environments and settlement spread over a large area so that those who were less affected could shelter and feed evacuees sunset crater near flagstaff arizona produced about 8 km 2 lava flow fields and a 2300 km 2 tephra blanket in an area that had been settled by prehistoric groups for at least 1000 years local subsistence relied on agriculture primarily maize and 30 cm tephra cover rendered 265 km 2 of prime land unfarmable this area was apparently abandoned for at least several generations a 500 km 2 area was probably marked by collapsed roofs and other structural damage from the fallout if the eruption occurred during the agricultural season the fallout would also have significantly damaged crops the eruption did have some benefits to local groups because lower elevation land which had previously been too dry to farm became agriculturally productive due to 3 8 cm of tephra mulch and some temporary soil nutrient improvements this previously uninhabited land became the site of significant year round settlement and farming eventually containing some of the largest pueblo structures ever built in the region new agricultural techniques were developed to manage the fallout mulch the eruption also affected ceramic production and trading patterns and volcano related ritual behavior the production of maize impressed lava spatter agglutinate was initiated little springs volcano about 200 km northwest of sunset crater is a small spatter rampart around a series of vents that produced about 5 km 2 of lava flow fields about 1 km 2 of land severely affected by ballistic fall and no significant tephra fall the small area affected resulted in much less disruption of human activities than at sunset crater farming was still possible right up to the edge of the lava flows which became attractive sites for settlements most sites along the lava flows have habitation and storage structures at the base of the flow and a series of small apparently little used structures on the blocky lava flow above these lava surface structures may have been defensive in nature in addition trails were constructed on the blocky lava flow surface these trails whose access points are difficult to recognize from below appear to have been used for rapid movement across the flows and may also have been defensive in nature spatter agglutinate blocks containing ceramic sherds within them similar to the maize impressed spatter agglutinate at sunset crater were made at little springs and carried to a nearby habitation site in arid and semiarid lands such as northern arizona tephra fall is a mixed blessing thick cinder blankets 20 30 cm render land uninhabitable but thinner 3 8 cm deposits can serve to conserve soil moisture regulate soil temperature thus lengthening the growing season and by lowering soil ph provide a temporary decades to a century or two increase in available phosphorus an important nutrient for growth the mulch opened up new lands for settlement but likely only lasted for a century or two before reworking reduced its effects

evidence from lava flows for complex polarity transitions the new composite steens mountain reversal record summary geomagnetic polarity transitions may be significantly more complex than are currently depicted in many sedimentary and lava flow records by splicing together paleomagnetic results from earlier studies at steens mountain with those from three newly studied sections of oregon plateau flood basalts at catlow peak and poker jim ridge 70 90 km to the southeast and west respectively we provide support for this interpretation with the most detailed account of a magnetic field reversal yet observed in volcanic rocks forty five new distinguishable transitional t directions together with 30 earlier ones reveal a much more complex and detailed record of the 16 7 ma reversed r to normal n polarity transition that marks the end of chron c5cr compared to the earlier r t n t n reversal record the new record can be described as r t n t n t r t n the composite record confirms earlier features adds new west and up directions and an entire large n t r t segment to the path and fills in directions on the path between earlier directional jumps persistent virtual geomagnetic pole vgp clusters and separate vgps have a preference for previously described longitudinal bands from transition study compilations which suggests the presence of features at the core mantle boundary that influence the flow of core fluid and distribution of magnetic flux overall the record is consistent with the generalization that vgp paths vary greatly from reversal to reversal and depend on the location of the observer rates of secular variation confirm that the flows comprising these sections were erupted rapidly with maximum rates estimated to be 85 120 m ka 1 at catlow and 130 195 m ka 1 at poker jim south paleomagnetic poles from other studies are combined with 32 non transitional poles found here to give a clockwise rotation of the oregon plateau of 11 4 5 6 with respect to the younger columbia river basalt group flows to the north and 14 5 4 6 with respect to cratonic north america 95 per cent confidence interval

archaeomagnetic research in the andean highlands abstract eleven archaeomagnetic samples were collected from several sites near porco bolivia as part of the proyecto arqueologico porco potosi these samples were collected in order to 1 explore the availability of appropriate sample materials in the bolivian andes and 2 assess the feasibility of pursuing reference curve research for this region in addition this research explored the archaeomagnetic dating application of reference curves constructed from the global geomagnetic field model gufm1 jackson et al 2000 which covers the period from ad 1590 1990 this model is particularly applicable to our project since many of the project sites are late prehispanic pre ad 1532 and early historic ca ad 1532 1825 in age of the 11 samples three appeared to contain an insufficient amount of ferromagnetic minerals to provide reliable results while eight samples produced acceptable to good results the data from the eight good samples were compared to a reference curve for the period of ad 1600 2000 that was calculated for this project from the global field model gufm1 the archaeomagnetic dates obtained for two of the samples agreed with archaeological expectations while those for four other samples marginally or greatly postdated the archaeological age expectations two additional samples produced significantly different directions and could not be dated against the reference curve it is likely that the age discrepancies for four of the samples stem from inaccuracies in the archaeomagnetic data the archaeological age expectations the calculated reference curve or some combination of these factors

episodic holocene eruption of the salton buttes rhyolites california from paleomagnetic u th and ar ar dating in the salton trough ca five rhyolite domes form the salton buttes mullet island obsidian butte rock hill north and south red hill from oldest to youngest results presented here include 40ar 39ar anorthoclase ages 238u 230th zircon crystallization ages and comparison of remanent paleomagnetic directions with the secular variation curve which indicate that all domes are holocene 238u 230th zircon crystallization ages are more precise than but within uncertainty of 40ar 39ar anorthoclase ages suggesting that zircon crystallization proceeded until shortly before eruption in all cases except one remanent paleomagnetic directions require three eruption periods 1 mullet island 2 obsidian butte and 3 rock hill north red hill and south red hill borehole cuttings logs document up to two shallow tephra layers north and south red hills likely erupted within 100 years of each other with a combined 238u 230th zircon isochron age of 2 83 0 60 ka 2 sigma paleomagnetic evidence suggests this age predates eruption by hundreds of years 1800 cal bp rock hill erupted closely in time to these eruptions the obsidian butte 238u 230th isochron age 2 86 0 96 ka is nearly identical to the combined red hill age but its virtual geomagnetic pole position suggests a slightly older age the age of aphyric mullet island dome is the least well constrained zircon crystals are resorbed and the paleomagnetic direction is most distinct possible mullet island ages include ca 2300 5900 6900 and 7700 cal bp our results constrain the duration of salton buttes volcanism to between ca 5900 and 500 years

paleomagnetic constraints on a time stratigraphic framework for the evolution of ohachidaira volcano and the summit caldera central hokkaido japan we present a revised stratigraphy of the proximal deposits around ohachidaira volcano and their paleomagnetic directions obtained from 21 sites 193 samples we identify four proximal pyroclastic members from ohachidaira volcano that were produced after the early edifice building effusive volcanism from older to younger 1 vent opening mafic pyroclastic density current pdc deposits kobachidaira ignimbrite 2 maar forming mafic tephra ring deposits mamiyadake tephra ring 3 mafic to silicic caldera forming deposits sounkyo member and 4 mafic pdc deposits kumonotaira ignimbrite well grouped paleomagnetic directions obtained from the kobachidaira ignimbrite and the sounkyo member indicate that each deposit was formed over a short time interval compared to geomagnetic secular variation that is less than a century conversely scattered paleomagnetic directions of the mamiyadake tephra ring record the secular variation of the geomagnetic field that took place over a longer time interval that is at least 750 yr probably more the kumonotaira ignimbrite which has a similar paleomagnetic direction to the underlying sounkyo member may have been produced during the sounkyo eruption from comparison between our data and the previously reported paleomagnetic directions of two petrologically distinct distal ignimbrites we conclude that the sounkyo member is a proximal correlative of the distal pyroxene rich ignimbrite and that the distal hornblende rich ignimbrite may not be of an ohachidaira origin the revised stratigraphy suggests that ohachidaira volcano is a maar caldera complex volcano and that the summit caldera is a flaring funnel formed incrementally by explosive erosion and syn eruptive collapse of the vent walls volume estimates imply that the sounkyo eruption fundamentally enlarged the vent and formed the caldera our data confirm that the comparison of paleomagnetic directions can offer a useful identification and correlation tool for the ohachidaira pyroclastic sequences

monogenetic origin of ubehebe crater maar volcano death valley california paleomagnetic and stratigraphic evidence abstract paleomagnetic data for samples collected from outcrops of basaltic spatter at the ubehebe crater cluster death valley national park california record a single direction of remanent magnetization indicating that these materials were emplaced during a short duration monogenetic eruption sequence 2100 years ago this conclusion is supported by geochemical data encompassing a narrow range of oxide variation by detailed stratigraphic studies of conformable phreatomagmatic tephra deposits showing no evidence of erosion between layers by draping of sharp rimmed craters by later tephra falls and by oxidation of later tephra layers by the remaining heat of earlier spatter this model is also supported through a reinterpretation and recalculation of the published 10be age results sasnett et al 2012 from an innovative and bold exposure age study on very young materials their conclusion of multiple and protracted eruptions at ubehebe crater cluster is here modified through the understanding that some of their quartz bearing clasts inherited 10be from previous exposure on the fan surface too old and that other clasts were only exposed at the surface by wind and or water erosion centuries after their eruption too young ubehebe crater cluster is a well preserved example of young monogenetic maar type volcanism protected within a national park and it represents neither a protracted eruption sequence as previously thought nor a continuing volcanic hazard near its location

paleomagnetic chronostratigraphy of holocene laguna minucua oaxaca mexico abstract full vector paleomagnetic secular variation psv records have been recovered from two cores mn1 mn2 collected from laguna minucua oaxaca mexico the sediments of laguna minucua are laminated probably varved to within 15 cm of the sediment water interface they may become a key paleoclimate record for southern mexico however radiocarbon dating has been equivocal at estimating the age of the lake sediments goman et al 2013 the psv records from cores mn1 and mn2 are correlatable between them and have a distinctive pattern of variability that can be correlated to well dated psv records from the western usa the psv correlations establish that the longest core mn2 extends back 4500 cal bp assuming the mn2 lamina are varves their average thickness 1 2 mm and core length provide an independent estimate of 4600 cal bp not significantly different one radiocarbon date with an age of 1120 60 cal bp occurs at a depth in core mn2 with an equivalent paleomagnetic age of 1140 50 cal bp again not significantly different therefore our estimate is that the laguna minucua sediments are varved and represent a remarkable high resolution repository of paleoclimate information for southern mexico for the last 4500 years

a 20 15 ka high resolution paleomagnetic secular variation record from black sea sediments no evidence for the hilina pali excursion abstract a comprehensive magnetostratigraphic investigation on sixteen sediment cores from the southeastern black sea yielded a very detailed high quality paleosecular variation psv record spanning from 20 to 15 ka the age models are based on radiocarbon dating stratigraphic correlation and tephrochronology further age constraints were obtained by correlating four meltwater events described from the western black sea ranging in age from about 17 to 15 ka with maxima in k ti ratios obtained from x ray fluorescence xrf scanning and minima in s ratios reflecting increased hematite content in the studied cores since the sedimentation rates in the investigated time window are up to 50 cm ka 1 the obtained psvs records enabled a stacking using 50 yr bins a directional anomaly at 18 5 ka associated with pronounced swings in inclination and declination as well as a low in relative paleointensity rpi is probably contemporaneous with the hilina pali excursion originally reported from hawaiian lava flows however virtual geomagnetic poles vgps calculated from black sea sediments are not located at latitudes lower than 60 n which denotes normal though pronounced secular variations during the postulated hilina pali excursion the vgps calculated from black sea data migrated clockwise only along the coasts of the arctic ocean from ne canada 20 0 ka via alaska 18 6 ka and ne siberia 18 0 ka to svalbard 17 0 ka then looping clockwise through the eastern arctic ocean

40ar 39ar single grain dating and mineral chemistry of hornblendes south of the red river shear zone vietnam new evidence for early proterozoic tectonothermal event abstract the pre mesozoic metamorphic belt runs parallel to the day nui con voi red river shear zone in vietnam to the south the belt is mainly composed of hornblende gneisses amphibolite lenses and mica schists five hornblendes from a gneiss and an amphibolite were analyzed chemically and chronologically by electron probe micro analysis epma and 40ar 39ar methods epma analyses show that hornblendes in the gneiss and the amphibolite have significant amount of edenite component and similar average composition however the recalculated fe3 content is significantly heterogeneous in a thin section while total fe is nearly the same among the analyses the rim of each crystal is higher in fe3 fe3 fe2 than the core these chemical and petrological features suggest that the hornblendes have suffered significant oxidation in particular largely in the gneiss 40ar 39ar analyses showed that the gneiss has a significant variation of plateau ages 2089 14 1977 19 and 1873 13 ma among three hornblende grains whereas the amphibolite gives the same plateau ages 2056 14 and 2044 21 ma for two grains all grains of both samples have excess ages in the first few fractions at low temperatures and partial loss ages between the excess and plateau spectra the ca k ratios indicate some disturbed phases for the lower temperature spectra but the partial loss ages are also derived from hornblende phase these facts suggest that hornblende in the gneiss has experienced partial argon loss by oxidation and or thermally activated argon diffusion process however the gneiss and the associated amphibolite have preserved the early proterozoic tectono metamorphic event in the hornblende crystals except for their rims giving new evidence for the early proterozoic event within the pre mesozoic metamorphic belt northern vietnam south of the red river shear zone in indochina

high resolution paleomagnetic secular variation and relative paleointensity records from the western canadian arctic implication for holocene stratigraphy and geomagnetic field behaviourthis article is one of a series of papers published in this special issue on the theme polar climate stability network geotop contribution 2008 0024 two piston cores recovered from the chukchi and the beaufort seas document arctic holocene geomagnetic field behaviour and highlight the potential of secular variation and relative paleointensity as a regional chronostratigraphic tool several centennial to millennial scale holocene declination and inclination features can be correlated in both cores with other high resolution western north american lacustrine and volcanic paleomagnetic records and with records of changes in earth s dipole moment supporting the geomagnetic origin of these features and implying that they are associ ated with changes in earth s dipole moment resume deux carottes sedimentaires prelevees dans les mers de beaufort et de chukchi ont permis de reconstruire les variations d intensiteet d orientation de haute resolution du champ magnetique terrestre au cours de l holocene afin de caracteriser le comportement du champ geomagnetique dans l arctique ainsi que d explorer la possibilited utiliser les variations du champ geomagnetique comme outil chronostratigraphique au cours de l holocene la declinaison et l incli naison magnetique des deux sequences etudiees peuvent etre correlees entre elles avec des enregistrements paleomagne tiques lacustres ou volcaniques de l ouest de l amerique du nord a des echelles de temps au moins seculaires les variations de paleointensiterelative des deux carottes analysees sont egalement coherentes avec des enregistrements des variations du dipole geomagnetique confirmant ainsi l origine geomagnetique de ces variations et suggerant leur nature di polaire

overburden complexity and repeatability of seismic data impacts of positioning errors at the oseberg field north sea repeatability of seismic data plays a crucial role in time lapse seismic analysis there are several factors that can decrease the repeatability such as positioning errors varying tide source variations velocity changes in the water layer marine data and undesired effects of various processing steps in this work the complexity of overburden structure as an inherent parameter that can affect the repeatability is studied a multi azimuth three dimensional vertical seismic profiling data set with 10 000 shots is used to study the relationship between overburden structure and repeatability of seismic data in most repeatability studies two data sets are compared but here a single data set has been used because a significant proportion of the 10 000 shots are so close to each other that a repeatability versus positioning error is possible we find that the repeatability decreases by a factor of approximately 2 under an overburden lens furthermore we find that the x and y components have approximately the same sensitivity to positioning errors as the z component for the same events in this three dimensional vertical seismic profiling experiment this indicates that in an area with complex overburden positioning errors between monitor and base seismic surveys are significantly more critical than outside such an area this study is based on a three dimensional three component vertical seismic profiling data set from a north sea reservoir and care should be taken when extrapolating these observations into a general four dimensional framework

secular variation of the intensity of the geomagnetic field in mexico during the first millennium bce in western eurasia the first millennium bce is characterized by the fastest secular variation of the earth magnetic field observed over the last millennia and by a geomagnetic anomaly centered on the middle east on the global scale the variation of the dipolar field during this period remains poorly constrained because of the lack of data in other geographical areas here we presented 23 new mean archaeointensity data on ceramic sherds dated between 1500 bce and 200 ce from chalcatzingo archaeological site in central mexico archaeointensities were determined using the classical thellier thellier protocol with corrections for trm anisotropy and cooling rate effects our work doubles the number of high quality archaeointensity data in mexico during the considered period using a bayesian approach a new secular variation curve was calculated at mexico city between 1500 bce and 200 ce after selection of mexican archaeointensity data after a period of oscillations of the intensity between 20 and 40 t from 1500 to 300 bce the curve shows a large maximum 65 t in the second century bce the corresponding vadm varied between 4 0 and 11 0 1022 am2 which highlights further that the intensity of the geomagnetic field could vary at regional scale over a larger range as previously thought however this amplitude variation may be overestimated as it does not take into account the fast directional variation observed at this time

pitfalls in three dimensional seismic interpretation footprints of an irregular source receiver layout abstract this paper shows how nonuniform source receiver spacing in a three dimensional 3 d land acquisition creates footprints that could easily be mistaken for geology in a 3 d time migrated seismic volume from the midcontinent united states amplitude extraction along the top of the mississippian limestone formation shows a sinkhole like feature which is justified from a depositional perspective however an inspection of the acquisition layout shows that the sinkhole is a replica of the fold distribution in land surveys where source and receivers seldom have a regular distribution and for unconventional plays that are not developed through patterned drilling a thorough review of processing and acquisition parameters is necessary before interpreting amplitude maps

a comparison of holocene paleomagnetic secular variation records from north america the comparison of nine holocene 0 12 000 years b p records of paleomagnetic field secular variation psv obtained from across north america indicates that distinctive field features in inclination and declination often can be traced for more than 4000 km without significant change in pattern independent age determinations corroborate these correlations while also suggesting that westward or eastward drift is not significant on the other hand northward drift may be a significant process at least between 1500 and 5500 years b p several methods of analyzing the overall psv character point to circularity vector looping as a preferred means of defining coherent space time vector variations which are termed waveforms a few distinctive waveforms each discernible for about 1400 years dominate psv across north america during the holocene 4 5 loops and 2 loops being associated with clockwise and counterclockwise circularity respectively the clockwise loops appear to be periodic occurring every 2400 years and most likely result from the recurrence of a distinctive regional dynamo source in the outer core the pattern of circularity noted in north america during the last 3000 years correlates in time with similar circularity changes seen globally this may indicate that there is some degree of coupling between different regional dynamo sources within the outer core the fact that some north american waveforms are almost identical to waveforms observed elsewhere around the world at different times may indicate that similar distinctive regional dynamo sources recur randomly throughout the outer core

paleomagnetic correlation of late holocene earthquakes among estuaries in washington and oregon 1 paleomagnetic directions of estuarine mud provide additional evidence that individual earthquakes or rapid series of earthquakes caused widespread coseismic land level changes during the past 2000 years in western washington and oregon most of the paleomagnetic measurements were made on mud dating from the first decades after coseismic subsidence from plate boundary earthquakes at the cascadia subduction zone mud deposited soon after the a d 1700 cascadia earthquake has similar remanent directions among all five sites k 171 sampled along 80 km of pacific coast between grays harbor and the mouth of the columbia river likewise internally consistent directions were obtained along this stretch of coast from mud deposited soon after a plate boundary earthquake or earthquake series in a d 340 410 and soon after another such event in a d 680 720 also analyzed were remanent magnetizations of mud deposited shortly before or shortly after land level changes from seismicity in the north america plate beneath puget sound a mean direction for sites on the snohomish river delta near everett from the time of an earthquake on the seattle fault in a d 900 930 is statistically identical 95 confidence level to a mean direction in mud that was uplifted in a d 800 1000 at potentially correlative sites near tacoma and olympia the paleomagnetic direction from everett for the upper plate earthquake of a d 900 930 differs substantially from that for a plate boundary earthquake in a d 810 1190 this difference implies that the upper plate earthquake preceded the plate boundary earthquake by a century or two on the basis of comparisons of their paleomagnetic poles with a previously reconstructed path of geomagnetic paleosecular variation in western north america

a case history of time lapse 3d seismic surveys at cold lake alberta canada time lapse 3d seismic surveys were acquired across a bitumen field at cold lake alberta canada during a production cycle 1990 and a steam injection cycle 1992 of a thermal enhanced oil recovery eor program we observed changes in interval traveltime and amplitude distributions between the processed surveys we interpret the increased traveltimes observed over most of the injection survey to be a result of lowered interval velocities in the reservoir caused primarily by higher temperature and lower effective pressure reflection strength variations within the reservoir are present in each data set and change spatially between the surveys in general we interpret the amplitude anomalies seen only on the production survey to be caused by local free gas and the amplitude anomalies seen only on the injection survey which are close to the perforation depths to be caused by thin vertically restricted steamed zones

secular variation in mexico during the last 40 000 years paleomagnetic data are available for mexico from various archives covering irregularly the last 40 000 years data obtained from lake sediments are affected by ambiguous conversion of age to depth and the paleomagnetic data themselves are not of high quality as samples were only demagnetized at one field intensity these lake sediment data are therefore considered as less reliable for construction of a secular variation curve although they may give some qualitative information for the last 25 000 years archeological samples provide data for the period 100 1200 a d their 14 c ages are some times not well constrained with unrecoverable analytical and statistical procedures and often ages were only inferred from the stratigraphic position and the paleomagnetic record the paleomagnetic record of these materials is of high quality with very low internal dispersion although no magnetic cleaning techniques have been applied variations of inclination and declination with time are hampered by large age uncertainties and thus of limited value for the construction of secular variation curves paleomagnetic data from an u th dated stalagmite provide reasonable directions for most of the last 1200 years being of lower quality in those parts with very low remanence intensity the u th age determinations were interpreted in terms of a constant growth rate which might be only valid as a first order approximation recent volcanic rocks from the trans mexican volcanic belt provide 19 paleomagnetic directions of reasonable to high quality and often also absolute paleointensities ages have been determined from 14 c analysis of charcoal or paleosols found below the lavas and extend over the last 40 000 years therefore volcanic rocks provide the most adequate archive for the construction of a secular variation curve but much more volcanic structures need to be dated to obtain a semi continuous secular variation curve comparison of the data from different archives is possible mainly for the last 2500 years and despite the aforementioned problems similar variations of declination and inclination are observed this holds as well when comparing them to data from holocene volcanic rocks from western north america 2002 elsevier science b v all rights reserved

a 17 000 yr paleomagnetic secular variation record from the southeast alaskan margin regional and global correlations high resolution sedimentary records on two cores from the gulf of alaska margin allow development of a 17 400 yr reconstruction of paleomagnetic secular variation psv general agreement between the two records on their independent chronologies confirms that local psv is recorded demonstrating that such archives notwithstanding complexities due to variable sedimentary regimes deposition rates and diagenetic conditions provide meaningful information on past changes of the geomagnetic field comparisons with other independently dated sedimentary paleomagnetic records from the ne pacific indicate largely coherent inclination records that in combination create a ne pacific sedimentary inclination anomaly stack nepsias capturing the common signal over an area spanning 30 longitude and latitude from alaska through oregon to hawaii comparisons of nepsias with high quality declination records from the northern north atlantic nna show that negative shallow inclination anomalies in nepsias are associated with eastward nna declinations while positive steep inclination anomalies in nepsias are associated with westward nna declinations comparison of these directional records to regional geomagnetic intensities over the past 3000 yrs in north america and back nearly 8000 yrs in the euro mediterranean region are consistent with a driving mechanism of oscillations in the relative strength of the north american and euro mediterranean flux lobes the persistence of these dynamics through the holocene implicates a long lived organizing structure likely imposed on the geomagnetic field by the lower mantle and or inner core these observations underscore a fundamental connection between directional psv in the north pacific with that of the north atlantic supporting the potential for long distance correlation of directional psv as a chronostratigraphic tool

duration of eruption at the giant crater lava field medicine lake volcano california based on paleomagnetic secular variation nearly 500 cores were collected from the postglacial giant crater lava field on the south flank of medicine lake volcano the basaltic lavas form a continuous set of lava flows which display strong chemical zonation from initially erupted calc alkaline basaltic andesite to final primitive basalt of tholeiitic affinity six chemical stratigraphic groups have been recognized and mapped the eruptive sequence was sampled at numerous sites both to determine the characteristic paleomagnetic direction of each chemical group and to estimate the duration of the eruption inferred from secular variation of the geomagnetic field well grouped mean directions of magnetization were obtained for 41 sites in the giant crater lava field mean directions of magnetization determined for the lava field are nearly identical the likelihood of any extended time interval for the eruption of the different lava types is extremely small and the data suggest an eruptive event of less than 30 years duration analogous to historic hawaiian eruptions however the average of groups 1 4 which cannot be distinguished paleomagnetically from each other is slightly different statistically from that of the average of groups 5 and 6 which have similar directions a time gap of 10 5 years is inferred between eruption of group 4 and 5 lavas based on analysis of the probability of the observed angular difference of 1 27 0 84 between their mean directions and by comparison of this angular difference to calculated field directions with similar declination and inclination determined from spherical harmonic models of the geomagnetic field for the time period 1945 1990 about 200 oriented cores were also collected from predecessor and successor basaltic lava flows on the upper flanks of the volcano together with remanent directions from lavas of the snake river plain the data define a clockwise loop of secular variation

dating of holocene western canadian arctic sediments by matching paleomagnetic secular variation to a geomagnetic field model a recently recovered w6 m long holocene sedimentary sequence piston core 2004 804 650 collected from the beaufort sea western canadian arctic was dated by combining the paleomagnetic secular variation psv and a time varying spherical harmonic model of the geomagnetic field cals7k 2 a u channel based paleomagnetic study reveals the presence of a stable single component of magnetization mad 5 carried by low coercivity ferrimagnetic minerals most likely magnetite in the pseudo single domain grain size range an age depth model spanning the last w6000 calbp was established from nine paleomagnetic tie points obtained by comparing the magnetic declination profiles of core 650 and the cals7k 2 model output in order to verify the robustness of the method both the magnetic inclination and the relative paleointensity rpi records of core 650 were then compared with western north american lacustrine and volcanic holocene psv records as well as with previously published rpi records from the beaufort and chukchi seas several common magnetic inclination features and similar millennial scale fluctuations are detected among the records supporting a common geomagnetic origin of the records and implying consistency of the derived age model these results show the potential of using both the cals7k 2 model output and psv of the geomagnetic field as a practical dating tool

quickly erupted volcanic sections of the steens basalt columbia river basalt group secular variation tectonic rotation and the steens mountain reversal 1 the steens basalt now considered part of the columbia river basalt group crbg contains the earliest eruptions of this magmatic episode lava flows of the steens basalt cover about 50 000 km2 of the oregon plateau in sections up to 1000 m thick the large number of continuously exposed quickly erupted lava flows some sections contain over 200 flows allows for small loops in the magnetic field direction paths to be detected for volcanic rocks this detail and fidelity are rarely found outside of the holocene and yield estimates of eruption durations at our four sections of 2 5 ka for 260 m at pueblo mountains 0 5 to 1 5 ka for 190 m at summit springs 1 3 ka for 170 m at north mickey and 3 ka for 160 m at guano rim that only one reversal of the geomagnetic field occurred during the eruption of the steens basalt the steens reversal at approximately 16 6 ma is supported by comparing 40ar 39ar ages and magnetic polarities to the geomagnetic polarity timescale at summit springs two 40ar 39ar ages from normal polarity flows 16 72 0 29 ma 16 61 and 16 92 0 52 ma 16 82 equals 2 error place their eruptions after the steens reversal while at pueblo mountains an 40ar 39ar age of 16 72 0 21 ma 16 61 from a reverse polarity flow places its eruption before the steens reversal paleomagnetic field directions yielded 50 nontransitional directional group poles which combined with 26 from steens mountain provide a paleomagnetic pole for the oregon plateau of 85 7 n 318 4 e k 15 1 a95 4 3 comparison of this new pole with a reference pole derived from crbg flows from eastern washington and a synthetic reference pole for north america derived from global data implies relative clockwise rotation of the oregon plateau of 7 4 5 0 or 14 5 5 4 respectively probably due to northward decreasing extension of the basin and range

the age of the tseax volcanic eruption british columbia canada a recent volcanic eruption occurred at tseax volcano that formed a series of tephra cones in northwestern british columbia canada the explosive to effusive eruption also formed a 32 km long seque

seismic time lapse imaging using interferometric least squares migration case study seismic time lapse surveys are susceptible to repeatability errors due to varying environmental conditions to mitigate this problem we propose the use of interferometric least squares migration to estimate the migration images for the baseline and monitor surveys here a known reflector is used as the reference reflector for interferometric least squares migration and the data are approximately redatumed to this reference reflector before imaging this virtual redatuming mitigates the repeatability errors in the time lapse migration image results with synthetic and field data show that interferometric least squares migration can sometimes reduce or eliminate artifacts caused by non repeatability in time lapse surveys and provide a high resolution estimate of the time lapse change in the reservoir

a proven method for acquiring highly repeatable towed streamer seismic data seismic reservoir monitoring has become an important tool in the management of many fields monitoring subtle changes in the seismic properties of a reservoir caused by production places strong demands on seismic repeatability a lack of repeatability limits how frequently reservoir changes can be monitored or the applicability of seismic monitoring at all in this paper we show that towing many streamers with narrow separation combined with cross line interpolation of data onto predefined sail lines can give highly repeatable marine seismic data results from two controlled zero time lag monitoring experiments in the north sea demonstrate high sensitivity to changing water level and variations in lateral positions after corrections by deterministic tidal time shifts and spatial interpolation of the irregularly sampled streamer data relative rms difference amplitude levels are as low as 12 for a deep structurally complex field and as low as 6 for a shallow structurally simple field reducing the deg

holocene paleosecular variation from dated lava flows on maui hawaii ow inclination and low secular variation seem to be present for at least the past 5 myear in central pacific the period covering the past 10 kyear is crucial to the study of the field variability and to fill the gap between historical field measurements and long term paleomagnetic records we have conducted a paleomagnetic study of 13 sites of basaltic lava flows from maui island with 14c ages between 10 3 and 0 2 ka two other sites dated at 45 and 730 ka were also sampled eight to 10 samples from each site were demagnetized using thermal treatment and companion specimens from the same samples were demagnetized by alternating fields af thermomagnetic and hysteresis measurements indicated that magnetite 575 c in fine grains was the dominant magnetic carrier although in many cases we also observed a low temperature phase which is likely carried by titanomagnetite with low titanium content the existence of relatively high coercivities associated with these two mineralogical phases generated overlapping components which could not be properly isolated using af demagnetization successful results were obtained after thermal demagnetization for 13 sites with a mean inclination of 36 9 4 the mean inclination inc 36 3 of the eleven sites younger than 10 5 ka is also very close to the value 37 of the geocentric axial dipole gad at the site latitude but the angular dispersion of the virtual geomagnetic poles vgps about the spin axis 9 with n 13 and 6 7 with n 11 is significantly lower than the predictions of the models of paleosecular variation at this latitude the inclination variations for the past 10 kyear are in excellent agreement with the very detailed dataset which has previously been obtained from the big island of hawaii the mean inclination of all volcanic records n 132 is 1 8 lower than expected but this is likely caused by the lack of records between 5 and 7 ka b p we note also that the inclinations from lake waiau sediments big island are shallower than those of the volcanic records mauna kea hawaii and were thus probably affected by compaction we infer that there is no striking evidence for an inclination anomaly under hawaii during this period being aware of the need for additional records covering at least the 5 7 ka b p time interval the absence of a systematic deviation going beyond the dispersion of the inclinations obtained for the past millions of years neither pleads for a significant long term persistent anomaly however all studies report a low dispersion of the vgps which must reflect low secular variation

the secular variation of earth s magnetic field models of the magnetic field at the core mantle boundary at selected epochs from 1715 0 to 1980 0 reveal novel features in the field at the core these suggest that the flow of core fluid is coupled to the mantle and that magnetic diffusion is significant

continuous geomagnetic field models for the past 7 millennia 1 a new global data compilation 1 a global data set of archeomagnetic and paleomagnetic data covering the past 7000 years has been compiled it consists of 16 085 results of inclination 13 080 of declination and 3188 of intensity for the time span 5000 bc to 1950 ad declination and inclination data come partly from existing databases and partly from original literature a new global compilation of intensity data for the millennial scale is included data and dating uncertainties are discussed as we attempted to obtain an internally coherent data set the global distribution of the data is very inhomogeneous in both time and space all the data are compared to predictions from the previous 3000 year global model cals3k 1 this collection of data will be useful for global secular variation studies and geomagnetic field modeling although southern hemisphere data are still underrepresented in particular we will use it in a further study to update and extend the existing global model cals3k 1 the huge increase in data compared to the previous compilation will result in significant changes from current models as we might have missed some suitable data we encourage the reader to notify us about any data that have not been included yet and might fit in as improving our global millennial scale models remains our aim for the future the data files described in this paper are available from the earthref digital archive erda at http earthref org cgi bin erda cgi n 331

lake sediment record of the geomagnetic secular variation in britain during holocene times summary a palaeomagnetic record of the geomagnetic secular variation during the last 10000 years has been obtained from 10 cores of sediment from loch lomond scotland lake windermere north england and llyn geirionydd north wales a time scale is provided by 30 radiocarbon age determinations and pollen analyses on several of the cores the main swings and much fine detail of both declination and inclination records repeat well between cores and between lakes and the overall record is much more detailed than previous european records the new record shows that neither declination nor inclination swings have been periodic over the past 10000 years but that the main swings have become progressively shorter in duration during that time each swing is characterized by fine detail which enables use of the record as a secondary method of dating other european sediments the motion of the geomagnetic vector has been predominantly clockwise throughout the time period spanned but confirms a period of anticlockwise motion from 1100 to 600 bp first discovered by british archaeomagnetic investigations the record agrees with british and czechoslovakian archaeomagnetic records but not with japanese archaeomagnetic or north american lake sediment records this suggests that the secular changes are controlled by local growing and decaying drifting sources rather than by wobbling of the main geomagnetic dipole

paleomagnetic results from the snake river plain contribution to the time averaged field global database 1 this study presents paleomagnetic results from the snake river plain srp in southern idaho as a contribution to the time averaged field global database paleomagnetic samples were measured from 26 sites 23 of which 13 normal 10 reverse yielded site mean directions meeting our criteria for acceptable paleomagnetic data flow ages on 21 sites range from 5 ka to 5 6 ma on the basis of 40ar 39ar dating methods the age and polarity for the 21 dated sites are consistent with the geomagnetic reversal time scale except for a single reversely magnetized site dated at 0 39 ma this is apparently the first documented excursion associated with a period of low paleointensity detected in both sedimentary and igneous records combining the new data from the srp with data published from the northwest united states between the latitudes of 40 and 50 n there are 183 sites in all that meet minimum acceptability criteria for legacy and new data the overall mean direction of 173 normally magnetized sites has a declination of 2 3 inclination of 61 4 a fisher concentration parameter of 58 and a radius of 95 confidence 95 of 1 4 reverse sites have a mean direction of 182 4 declination 58 6 inclination of 50 and 95 of 6 9 normal and reversed mean directions are antipodal and indistinguishable from a geocentric axial dipole field at the 95 confidence level virtual geomagnetic pole dispersion was found to be circularly symmetric while the directional data were elongate north south an updated and corrected database for the northwestern u s region has been contributed to the magnetics information consortium magic database at http earthref org

holocene break up and reestablishment of the petermann ice tongue northwest greenland abstract over the last decade two major calving events of the petermann ice tongue in northwest greenland have led to speculation on its future stability and contribution to further greenland ice sheet mass loss however it has been unclear if these events are anomalous or typical within the context of limited historical observations we extend the historical record of the floating ice tongue using the stratigraphy of petermann fjord sediments to provide a longer term perspective computed tomography ct scans x ray fluorescence xrf scans ice rafted debris ird counts and the magnetic properties of specific particle size fractions constrain changes in depositional processes and sediment sources at our core sites allowing for reconstructions of past behavior of the petermann ice tongue radiocarbon dating of foraminifera 210pb and paleomagnetic secular variation psv provide age control and help to address uncertainties in radiocarbon reservoir ages a floating ice tongue in petermann fjord formed in late glacial time as petermann glacier retreated from an advanced grounded position this paleo ice tongue broke up during the early holocene when high northern latitude summer insolation was higher than present after gradual regrowth of the ice tongue associated with regional cooling the ice tongue reached its historical extent only within the last millennium little or no ice tongue was present for nearly 5000 years during the middle holocene when decadal mean regional temperatures are estimated to be 0 8 2 9 c higher than preindustrial 1750 ce and seasonal sea ice in the lincoln sea was reduced this pre historical behavior shows that recent anthropogenic warming may already be in the range of ice tongue instability and future projected warming increases the risk of ice tongue break up by the mid 21st century

dating of quaternary basalts using the cosmogenic 3he and 14c methods with implications for excess 40ar concordant radiocarbon and cosmogenic sup 3 he dates of 3 and 11 ka on basalt flows and associated scoria deposits from the zuni bandera volcanic field in new mexico further substantiate published production rates and latitudinal and altitudinal corrections for sup 3 he identical sup 3 he concentrations in coexisting olivine and clinopyroxene confirm that these two minerals have very similar production rates a cosmogenic sup 3 he date of 57 ka on another flow is concordant with a u series date and is younger than two k ar dates suggesting that this flow contains excess sup 40 ar this excess sup 40 ar is also evident in gases released by vacuum crushing of olivine clinopyroxene fractions from all three flows 27 refs 3 figs 3 tabs

holocene geomagnetic secular variation recorded by volcanic deposits at mount st helens washington a compilation of paleomagnetic data from volcanic deposits of mount st helens is presented in this report the database is used to determine signature paleomagnetic directions of products from its holocene eruptive events to assign sampled units to their proper eruptive period and to begin the assembly of a much larger database of paleomagnetic directions from holocene volcanic rocks in western north america the paleomagnetic results from mount st helens are mostly of high quality and generally agree with the division of its volcanic deposits into eruptive episodes based on previous geologic mapping and radiocarbon dates the muddy river andesite s paleomagnetic direction however indicates that it is more likely part of the pine creek eruptive period rather than the castle creek period in addition the two fingers andesite flow is more likely part of the middle kalama eruptive period and not part of the goat rocks period the paleomagnetic data from mount st helens and mount hood document variation in the geomagnetic field s pole position over the last 2 500 years a distinct feature of the new paleosecular variation psv record similar to the fish lake record oregon indicates a sudden change from rapid clockwise movement of the pole about the earth s spin axis to relatively slow counterclockwise movement at 800 to 900 years b p

the influence of high latitude flux lobes on the holocene paleomagnetic record of iodp site u1305 and the northern north atlantic 1 paleomagnetic analysis and radiocarbon dating of an expanded holocene deep sea sediment sequence recovered by integrated ocean drilling program iodp expedition 303 from labrador sea site u1305 lat 57 28 5 n long 48 31 8 w water depth 3459 m provides insights into mechanisms that drive both paleomagnetic secular variation psv and magnetization acquisition in deep sea sediments seventeen radiocarbon dates on planktonic foraminifera define postglacial ca 8 ka sedimentation rates as ranging from 35 to 90 cm kyr alternating field af demagnetization of u channel samples show that these homogeneous sediments preserve a strong stable and consistently well defined component magnetization normalized remanence records pass reliability criteria for relative paleointensity rpi estimates assuming that the age of magnetization is most accurately defined by well dated psv records with the highest sedimentation rates allows us to estimate and correct for temporal offsets at site u1305 interpreted to result from postdepositional remanence acquisition at a depth of 20 cm comparisons indicate that the northern north atlantic psv and rpi records are more consistent with european than north american records and the evolution of virtual geomagnetic poles vgp are temporally and longitudinally similar to global reconstructions though with much larger latitudinal variation the largest deviations from a geocentric axial dipole gad are observed during times of the highest intensities in contrast to the usual assumption these observations are consistent with the idea that psv in the north atlantic and elsewhere during the holocene results from temporal oscillations of high latitude flux concentrations at a few recurrent locations

a refined age calibrated paleosecular variation and relative paleointensity stack for the nw barents sea implication for geomagnetic field behavior during the holocene abstract reconstruction of paleomagnetic secular variation psv of the geomagnetic field is fundamental both to assess geodynamo models and to obtain age constraints for rocks sediments and archaeological material we present refined age calibrated holocene psv and relative paleointensity rpi stack curves derived from arctic marine sediments northwestern barents sea the holocene sections of four sedimentary cores were correlated on the basis of paleomagnetic trends and age models and stacked the resultant composite psv and rpi holocene records nbs stack and the reconstructed holocene virtual geomagnetic pole vgp path were evaluated in comparison with the most recent paleomagnetic stack curves and geomagnetic field models the data indicate that during the holocene time the vgps moved within the superficial projection of the inner core tangent cylinder with the exception of short time intervals around 5600 and 3200 cal yr bp when vgps extended to lower latitudes these deviations might reflect regional geomagnetic features such as persistent geomagnetic flux lobes at core mantle boundary our data confirm that the large vgp shift observed around 5600 cal yr bp is the result of an increased radial magnetic field at the core mantle boundary over north america whilst the vgp shift around 3200 cal yr bp represents a major swing to middle latitudes toward the middle east and might be associated to a regional high paleointensity peak known as levantine iron age anomaly liaa

holocene paleomagnetic records from the st lawrence estuary eastern canada centennial to millennial scale geomagnetic modulation of cosmogenic isotopes two long holocene piston cores md99 2220 and md99 2221 were raised from the st lawrence estuary eastern canada because of the expanded holocene sediment sequence this location provides a u channel based paleomagnetic study supported by an accelerator mass spectrometry ams 14c chronology rock magnetic and sedimentological data indicates that these sediments provide a paleomagnetic directional secular variation psv and relative paleointensity rpi proxy records for the last 8500 cal bp sedimentation rates vary from 1 2 to 4 2 m kyr comparison of inclination and declination features with other north american holocene psv records are generally consistent and temporal offsets are within chronological uncertainties the normalized natural remanent magnetization intensity record a rpi proxy from the postglacial sediments of core 2220 compares favorably with north american and european holocene rpi records at millennial and even some centennial timescales comparisons between core 2220 rpi proxy and the 10be flux record from the greenland summit gisp2 ice core finkel and nishiizumi j geophys res 102 1997 26699 26706 and a 14c production rate record bond et al science 294 2001 2130 2136 suggest that geomagnetic modulation may control the millennial and even some centennial scale variability within cosmogenic isotope records this implies that the core 2220 rpi record reflects changes in global scale geomagnetic field at these timescales

archeomagnetic secular variation from korea implication for the occurrence of global archeomagnetic jerks abstract an archeomagnetic paleosecular variation psv was first defined in korea using baked materials collected from 26 kilns or hearths with ages ranging from 1100 bc to ad 1790 variations of geomagnetic declination and inclination from the korean peninsula are distinctively different from the prediction of a global model cals3k 3 or cals7k 2 for the past 3500 yr in particular a distinctive offset in magnitude and phase is noticeable between the observations and predictions at 745 bc ad 300 and ad 1400 1700 a bi plot of magnetic declination versus inclination displays three cusps at the corresponding time intervals these time intervals are nearly identical to or at least overlap with three of the four potential archeomagnetic jerks suggested by gallet et al 2003 from the european archeomagnetic data a comparison of the psv curves for neighboring countries regions revealed that european archeomagnetic jerks at 800 bc ad 200 ad 800 and ad 1400 were all preserved in east asia suggesting that the archeomagnetic jerks were global or at least northern hemispheric features

high resolution holocene paleomagnetic secular variation records from bay of bengal abstract we present high resolution paleosecular variation psv records up to 8 cal kyr bp from three piston cores md161 8 md161 11 and md161 13 acquired in the krishna godavari kg basin bay of bengal during the holocene period high sedimentation rates are recorded at md161 8 38 8 248 3 cm kyr md161 11 137 336 cm kyr and md161 13 573 cm kyr rock magnetic data analysis suggests that the remanence signal is carried by titanomagnetite titanohematite grains in stable single domain ssd pseudo single domain psd state the psv records of md161 11 and md161 13 show good correlation in the uppermost sediments despite significant variation in the sedimentation rates however poor correlation of psv records is observed for the core md161 8 probably due to local effects paleoinclination records of md161 8 md161 11 and md161 13 show a low between 2 4 and 2 0 cal kyr bp an increase between 2 0 and 1 4 cal kyr bp and a decrease towards the present to varying degrees these trends can be observed in the other asian psv records of shuangchiling scl and biwa lakes however the magnitude of the observed inclination anomaly in kg basin is higher 40 compared to those reported from scl 25 and biwa 10 lakes paleodeclination records of md161 11 and md161 13 show a decline between 4 0 and 2 9 cal kyr bp an increase between 2 9 and 2 1 cal kyr bp a substantial decrease between 2 1 and 1 0 cal kyr bp and an increase towards the present similar trends can be observed in the other asian psv records of scl and biwa lakes with a minor age offset of 0 2 0 5 kyr the available models cals7k 2 and cals10k 1 are evaluated for their capability in predicting the inclination and declination anomalies from the asian regions the cals7k 2 model can predict most of the inclination anomalies while the cals10k 1 is unable to predict many of them the cals7k 2 model shows that the observed inclination anomalies can be attributed to the presence of a strong non axial dipolar magnetic field over the bay of bengal more psv records need to be constructed to better understand the anomalous non axial dipolar field over the bay of bengal

a holocene paleosecular variation record from 14c dated volcanic rocks in western north america 1 a paleosecular variation psv curve for western north america is presented on the basis of 94 virtual geomagnetic poles vgps from dated volcanic rocks sampled at 446 sites approximately 60 of the paleomagnetic database has been previously published a curve defined by spherical smoothed splines is fitted to the vgps ranked by the quality of the age determinations where the data density is highest between 3690 and 30 years before present b p a d 1950 between 7800 and 7050 years b p and between 14 060 and 12 700 years b p the younger segments of the curve derived from volcanic rocks are similar but less complex than other high resolution psv curves derived from lacustrine sediments particularly the record at fish lake oregon the psv record from lava flows psvl however is perhaps more reliable in its general shape and chronology because of the higher fidelity of volcanic rocks as magnetic field recorders and because of the greater density of 14c dates the new psvl record provides a partial holocene master curve for western north america and will be of particular value in dating geological and archeological materials using paleomagnetic directions