geoforschungszentrum anomaly magnetic map gamma a candidate model for the world digital magnetic anomaly map the world digital magnetic anomaly map wdmam is an ongoing effort toward the mapping of worldwide available aeromagnetic data it is led by a task force of the international association for geomagnetism and aeronomy iaga and aims at distributing a global map in printed and digital forms in this paper we describe in detail our candidate model which has to be evaluated by the iaga task force together with five other candidate maps after discussing the quality of the available data we show a simple but effective method applied to successfully process reduce and merge together individual compilations the near surface data are corrected using global field models and further refined with two dimensional polynomial corrections after the upward continuation to 5 km altitude data are resampled to a 3 minute grid and merged together we then calculate a spherical harmonic model up to degree 199 and analyze the magnetic spectrum of the global map this helps us to confirm that wavelengths larger than 400 km are spurious at a global scale in aeromagnetic compilations therefore we substitute them using a satellite based lithospheric field model mf5 to degree 100 finally our proposed candidate map for wdmam is presented

the boron isotope geochemistry of the neogene borate deposits of western turkey abstract we have analyzed the boron isotope composition of 80 borate minerals major minerals borax colemanite and ulexite minor minerals veatchite a tunellite kernite terrugite probertite meyer hofferite inderite inyoite hydroboracite howlite and pandermite from the main deposits kirka bigadic and emet and two smaller deposits kestelek and sultancayir in the western turkish borate deposits forty three samples were also analysed for their sr isotope composition the data span a wide range in 11b values from 1 6 o to 25 3 o the 11b values of the main borate minerals are largely controlled by their mineralogy and the ph of the brines from which they precipitated an inverse correlation between the average 11b and 87 sr 86 sr ratios of colemanite in the different deposits suggests there is some variation in the sources of boron and sr to the deposits emet has the highest contribution from aluminosilicates and kirka the highest contribution from eocene carbonates with bigadic occupying an intermediate position the 11b values of the minor borate minerals distinguish between those which are primary precipitates from the original brines or formed from primary borates without boron loss from the system and those which formed from alteration of preexisting borate minerals with substantial loss of boron from the system

surficial geology of the continental shelf northwestern vancouver island abstract the vancouver island continental margin lies along the convergent boundary between the explorer and juan de fuca plates and the america plate off northwestern vancouver island this tectonic regime is manifested in major thrust faults and folds which dislocate volcanic and sedimentary rocks of tertiary age beneath a relatively undeformed wedge of late neogene mudstones surficial sedimentation reflects both the tectonic and high latitude settings of the area predominance of lithic arenites and graywackes high wave and current energy restricting modern sedimentation to the outer shelf deeper than 110 m and resulting in the formation of large oscillation bedforms to depths of 100 110 m trapping of terrigenous sediments in fjords leading to low sediment accumulation rates on the shelf which in turn favor the formation of abundant glauconie gravel lags and extensive areas of biogenic sediments dominated by molluscs and bryozoa and the presence of pleistocene glaciomarine sandy muds and muddy sands beneath the mid and outer shelf

rethinking turbidite paleoseismology along the cascadia subduction zone a stratigraphic synthesis of dozens of deep sea cores most of them overlooked in recent decades provides new insights into deepsea turbidites as guides to earthquake and tsunami hazards along the cascadia subduction zone which extends 1100 km along the pacific coast of north america the synthesis shows greater variability in holocene stratigraphy and facies off the washington coast than was recognized a quarter century ago in a confluence test for seismic triggering of sediment gravity flows that test compared counts of holocene turbidites upstream and downstream of a deep sea channel junction similarity in the turbidite counts among seven core sites provided evidence that turbidity currents from different submarine canyons usually reached the junction around the same time as expected of widespread seismic triggering the fuller synthesis however shows distinct differences between tributaries and these differences suggest sediment routing for which the confluence test was not designed the synthesis also bears on recent estimates of cascadia earthquake magnitudes and recurrence intervals the magnitude estimates hinge on stratigraphic correlations that discount variability in turbidite facies the recurrence estimates require turbidites to represent megathrust earthquakes more dependably than they do along a flow path where turbidite frequency appears limited less by seismic shaking than by sediment supply these concerns underscore the complexity of extracting earthquake history from deep sea turbidites at cascadia

glauconitic sediments on the continental shelf off vancouver island british columbia canada abstract the tectonically active vancouver island continental margin is characterized by a very narrow 80 km continental shelf and an extremely steep continental slope the shelf is marked by high wave and current energies on the inner nondepositional shelf and very slow rates of sediment accumulation on the outer shelf within the muddy sands of the outer shelf and slope glauconitic grains are frequently an important constituent of the sand fraction occurring in four principal forms a locally abundant pale green infillings of benthic foraminifera b very abundant pale to moderately dark green dull grains displaying varying degrees of fracturing of the external surfaces c scarce moderately dark green altered and expanded mica grains and d scarce very dark green small 200 m grains with polished highly fractured surfaces mineralogically the grains mainly reflect their origins as detrital sediments they consist most commonly of quartz plagioclase minerals chlorite smectite and illite also a mixed layer mineral smectite illite occurs in significant amounts in glauconitic grams but is absent in unaltered mud fragments and in the clay fraction of sediments from the outer shelf the appearance of this mineral reflects the first stages of glauconite authigenesis bulk analyses of glauconitic grains yielded k2o values of less than 2 reflecting their very early stage of evolution but 19 28 fe2o3 several times the level in the surrounding matrix sediments microprobe analyses and scanning electron microscopy show that glauconitic smectite forms in the pores and along fractures in the host grains commonly as a boxwork arrangement or rosette clusters of blades fe2o3 and k2o values at these sites can reach 32 5 and 7 5 respectively several lines of evidence including radiocarbon age determinations on glauconitized foraminifera tests indicate a recent age for the vancouver island shelf glauconitic grains

forecasting change of the magnetic field using core surface flows and ensemble kalman filtering 1 accurate forecasting of the change of the earth s internal magnetic field over short intervals of time e g less than five years has many applications for government academic and commercial users forecasting can be achieved by making a number of reasonable assumptions about how the main field interacts with the flow in the liquid outer core in particular the magnetic field can be considered to be entrained in the large scale flow along the core mantle boundary surface over short time periods giving rise to measurable change at the earth s surface the observed change or secular variation at or above the surface of the earth can thus be inverted to produce flow models these can be used to propagate fluid parcels threaded by the field forwards in time to forecast the non linear change of the magnetic field in addition to prediction of field change by flow models it would be advantageous to include observations of the field from satellite measurements or ground based observatories we therefore present a method using ensemble kalman filtering enkf to produce an optimal assimilation between magnetic field change as forecast from core flow models and direct observations of the field we show by assuming a steady flow and assimilating field observations annually it is possible to produce a forecast over five years with less than 30nt root mean square difference from the true field within an assumed error budget the enkf method also allows sensitivity analysis of the field models to noise and uncertainty within the physical representation

new way of processing near surface magnetic data the utility of the comprehensive model of the magnetic field in assembling near surface magnetic surveys e g airborne or marine data for regional geologic studies one often has a problem in properly merging different surveys without applying ad hoc leveling methods or warping the long wavelengths of individual data sets a new comprehensive long wavelength and long time span magnetic field model based on satellite and observatory data may at last resolve this problem the model the comprehensive model cm is developed by terry sabaka of raytheon itss nasa and nils olsen of the danish space research institute the present version of the model cm3 incorporates data from magnetic field satellites pogo 1965 1970 magsat 1979 1980 orsted 2000 to present and champ 2001 to present and magnetic observatory data from the early 1960s to 2002

the agulhas plateau structure and evolution of a large igneous province summary large igneous provinces lip are of great interest due to their role in crustal generation magmatic processes and environmental impact the agulhas plateau in the southwest indian ocean off south africa has played a controversial role in this discussion due to unclear evidence for its continental or oceanic crustal affinity with new geophysical data from seismic refraction and reflection profiling we are able to present improved evidence for its crustal structure and composition the velocity depth model reveals a mean crustal thickness of 20 km with a maximum of 24 km where three major units can be identified in the crust in our seismic reflection records evidence for volcanic flows on the agulhas plateau can be observed the middle crust is thickened by magmatic intrusions the up to 10 km thick lower crustal body is characterized by high seismic velocities of 7 0 7 6 km s 1 the velocity depth distribution suggests that the plateau consists of overthickened oceanic crust similar to other oceanic lips such as the ontong java plateau or the northern kerguelen plateau the total volume of the agulhas plateau was estimated to be 4 10 6 km 3 of which about 10 per cent consists of extruded igneous material we use this information to obtain a first estimate on carbon dioxide and sulphur dioxide emission caused by degassing from this material the agulhas plateau was formed as part of a larger lip consisting of the agulhas plateau itself northeast georgia rise and maud rise the formation time of this lip can be estimated between 100 and 94 5 ma

chronological constraints on cordilleran ice sheet glaciomarine sedimentation from core md02 2496 off vancouver island western canada chronology based on 46 radiocarbon dates has been generated for md02 2496 western vancouver island canada subsequent correlation between glaciomarine sedimentary sequences within the core and the terrestrial stratigraphy of the cordilleran ice sheet for the last 50 ka provide new insight into cordilleran ice sheet processes glaciomarine sedimentation associated with the most recent advance fraser glaciation of the cordilleran ice sheet began at 30 5 cal kyr bp 25 14 c kyr bp extremely high sedimentation rates indicate the ice sheet became proximal to the site at 19 5 cal kyr bp 16 14 c kyr bp deposition of ice rafted detritus ird began at 17 cal kyr bp 14 14 c kyr bp and abruptly terminated at 16 2 cal kyr bp 13 5 14 c kyr bp indicating rapid regional ice sheet retreat a minor ird event followed at 14 7 cal kyr bp 12 5 14 c kyr bp glaciomarine sediment deposition abruptly ended at 10 2 cal kyr bp 8 8 14 c kyr bp with the resumption of biogenic sedimentation the olympia interstade is represented by an interval of hemipelagic sedimentation between 43 and 31 5 ka prior to 45 ka sediment deposition is controlled by glaciomarine processes with evidence for a significant ird event at 47 cal kyr bp 44171 06 14 c kyr bp

on the use of calibrated relative paleointensity records to improve millennial scale geomagnetic field models current millennial scale time varying global geomagnetic field models suffer from a lack of intensity data compared to directional data because only thermoremanently magnetized material can provide absolute information about the past field strength the number of archeomagnetic artifacts that can provide such data diminishes rapidly prior to 3000 b c sediment cores provide time series of declination and inclination and of variations of magnetization the latter can reflect relative geomagnetic field variations if suitably normalized we propose a calibration technique based on predictions from global models and use the cals7k 2 model to calibrate relative paleointensity records from 22 globally distributed locations and assess whether they reflect actual field variations all except a few contain useful information for 0 to 7 ka and could be used to improve the existing models using synthetic data from a numerical dynamo simulation we show that with the existing directional data the distribution of intensity data has an important influence on model quality intensity data from a broad range of latitudes seem particularly important this study opens the possibility of extending global time varying geomagnetic field models further back in time than the current 7 kyr interval

regional modelling of the southern african geomagnetic field using harmonic splines summary over the southern african region the geomagnetic eld is weak and changes rapidly for this area series of geomagnetic eld measurements exist since the 1950s we take advantage of the existing repeat station surveys and observatory annual means and clean these data sets by eliminating jumps and minimising external eld contributions in the original time series this unique data set allows us to obtain a detailed view of the geomagnetic eld behaviour in space and time by computing a regional model for this we use a system of representation similar to harmonic splines initially the technique is systematically tested on synthetic data after systematically testing the method on synthetic data we derive a model for 1961 to 2001 that gives a detailed view of the fast changes of the geomagnetic eld in this region

effects of productivity glaciation and ventilation on late quaternary sedimentary redox and trace element accumulation on the vancouver island margin western canada variations in chalcophile and redox sensitive trace elements are examined at high resolution intervals from a 50 kyr long sediment core md02 2496 from the vancouver island margin enrichments of ag cd re u and mo above lithogenous levels signifying sedimentary suboxia and anoxia occurred during the early holocene and bolling allerod and during warm interstadial events of marine isotope stage mis 3 down core trace element profiles co vary with productivity proxy records opal caco3 and marine organic carbon and with sedimentary nitrogen isotope ratios which reflect variably enriched nitrate upwelled from intermediate waters that were transported northward from the eastern tropical north pacific the similarity of the md02 2496 record with records from the southern portion of the california current system ccs and to the greenland ice core oxygen isotope record during warm climate intervals suggests that sedimentary redox conditions along the california current responded to local productivity to north atlantic climate change and to tropical pacific surface water processes via long distance teleconnections concentrations of trace elements and productivity proxies were relatively depleted during the younger dryas cool stadial events of mis 3 and in two episodes of glaciomarine sedimentation from 14 7 to 30 5 kyr bp last glacial maximum lgm and from 44 to 50 4 kyr bp cordilleran ice sheet advancement onto the vancouver island continental shelf during the lgm led to intervals of increased terrigenous sedimentation and greatly reduced productivity not seen in the southern portion of the ccs and along with ventilation of north pacific intermediate waters resulted in brief sedimentary oxic conditions

longitudinal variation of the e region electric fields caused by atmospheric tides 1 polarization electric fields created by the e and f region dynamos cause the uplift of f region plasma the subsequent redistribution of that plasma along the magnetic field lines creates the equatorial ionospheric anomaly eia observations of the post sunset eia made by the image and timed satellites are compared here with champ orsted and sac c observations of the noontime equatorial electrojet eej during magnetically quiet periods around equinox the eia and eej show a remarkably similar four peaked wave like longitudinal variation its structure is consistent with the longitudinal variation in the strength of diurnal tides that drive the e region dynamo this indicates a strong vertical coupling between the ionosphere and troposphere because the four peaked tidal structure is driven by tropospheric weather furthermore the dayside ionospheric conditions are found to perform the global scale longitudinal structure of the post sunset ionosphere at low latitudes

cm5 a pre swarm comprehensive geomagnetic field model derived from over 12 yr of champ orsted sac c and observatory data a comprehensive magnetic field model named cm5 has been derived from champ rsted and sac c satellite and observatory hourly means data from 2000 august to 2013 january using the swarm level 2 comprehensive inversion ci algorithm swarm is a recently launched constellation of three satellites to map the earth s magnetic field the ci technique includes several interesting features such as the bias mitigation scheme known as selective infinite variance weighting sivw a new treatment for attitude error in satellite vector measurements and the inclusion of 3 d conductivity for ionospheric induction sivw has allowed for a much improved lithospheric field recovery over cm4 by exploiting champ along track difference data yielding resolution levels up to spherical harmonic degree 107 and has allowed for the successful extraction of the oceanic m2 tidal magnetic field from quiet nightside data the 3 d induction now captures anomalous solar quiet features in coastal observatory daily records cm5 provides a satisfactory continuous description of the major magnetic fields in the near earth region over this time span and its lithospheric ionospheric and oceanic m2 tidal constituents may be used as validation tools for future swarm level 2 products coming from the ci algorithm and other dedicated product algorithms

first scalar magnetic anomaly map from champ satellite data indicates weak lithospheric field 1 satellite magnetic anomaly maps derived by different techniques from magsat pogo data vary by more than a factor of 2 in the deduced strength of the lithospheric magnetic field here we present a first anomaly map from new champ scalar magnetic field data after subtracting a recent orsted main and external field model we remove remaining unmodeled large scale external contributions from 120 track segments by subtracting a best fitting uniform field in order to preserve n s trending features the data are not filtered along track direct integration of the spherically gridded data yields the final degree 14 65 spherical harmonic expansion of the total intensity anomaly at the mean satellite altitude of 438 km apart from enhanced long wavelength features and a smoother general appearance our initial map is strikingly similar to one of the lower strength magsat pogo maps

spatio temporal characterization of the equatorial electrojet from champ orsted and sac c satellite magnetic measurements received 4 may 2007 revised 20 june 2007 accepted 12 june 2007 published 13 september 2007 1 the equatorial electrojet eej is an eastward electric current on the day side flowing in a narrow band along the dip equator in the ionospheric e region recent magnetic observations from the champ orsted and sac c satellites comprising more than 95 000 dip equator crossings from 1999 to 2006 have provided an unprecedented longitudinal coverage of the eej magnetic signature we have used these data to construct an empirical model of the eej current climatological mean and day to day variability as a function of longitude local time season and solar flux our model has been successfully verified against vertical drift data from the julia radar at jicamarca we have also used the eej observations to estimate the self correlation of the eej confirming short longitudinal correlation lengths of 15 and finding a temporal correlation length of 2 4 h our model s predictions of the eastward electric field and its standard deviation may provide useful input to various kinds of ionospheric simulations coefficients and software are available online at http models geomag us eej html and http www earthref org

temperate skeletal carbonate sediments on scott shelf northwestren vancouver island canada abstract scott shelf 2000 km 2 centred at scott islands northwestern vancouver island is mainly shallower than 150 m topographically diversified and floored by bedrock outcrops and terrigenous lithic gravels and sands left stranded following the post glacial rise in sea level 13 000 yrs b p it lies in a zone of vigorous wind wave currents and strong tidal flows but is largely starved of modern terrigenous sediment as a consequence it is slowly accumulating a thin discontinuous blanket of clean skeletal carbonate sands and gravels admixed to varying degrees with the underlying terrigenous deposits principal skeletal contributors are infaunal bivalves on coarse sandy and gravelly substrates barnacles on low amplitude gravelly ridges bryozoans on bedrock outcrops and boulders and benthic foraminifera on fine sands in deep 100 m waters south of the scott islands living carbonate benthos are scattered and generally sparse occupying specific ecologic niches and the shelf wide rate of carbonate production is low skeletons are fragmented transported and mixed during storms and are concentrated within bedrock hollows and crevices and shallow depressions between gravel ridges where infaunal bivalves are abundant the carbonates are dominated by aragonite but otherwise the skeletal hashes are predominantly calcitic many grains and especially aragonitic ones are corroded and weakened by epilithic and endolithic bioerosion and probably also by marine and dissolution the most corroded shells have ages of only about 1000 yrs so that their preservation potential is low the character of scott shelf skeletal carbonate deposits reflects their temperate latitude cold water heritage

playa lake and sheetflood deposits of the upper cretaceous jindong formation korea occurrences and palaeoenvironments abstract lake model of the upper cretaceous jindong formation in korea was established on the basis of sedimentological and palaeobiological records of the playa lake and sheetflood deposits and their palaeoenvironmental implications the playa lake and sheetflood deposits of the jindong formation are characterized by the common presence of traces of vanished evaporites complicated polygonal desiccation cracks and rainprints the pedogenic carbonate development and the preservation of invertebrate traces and dinosaur and bird tracks the traces of vanished evaporites including halite and sulphate evaporite occur as evaporite pseudopmorphs and moulds the occurrence of all of the evaporite minerals as traces suggests that flooding stages persisted much longer than evaporation and desiccation stages invertebrates birds and dinosaurs inhabited the playa lake environment of the upper cretaceous jindong lake the jindong lake formed by the combination of humid source area and arid depositional site due to an orographic effect in fault bounded basin extensive development of the playa lake and sheetflood deposits with evaporite mineral casts and very limited association of shoreline deposits in the jindong formation are characteristic of closed lake and the jindong lake is compared to a lake formed in partly drained closed basin the aggradation of mudflat deposits indicates continued subsidence of the basin and continuation of an underfilled lake basin the jindong lake expanded and stabilized as a playa lake surrounded by dry to saline mudflats and palaeoclimate and subsidence rates changed little throughout the period of the jindong lake development

making ends meet in gondwana retracing the transforms of the indian ocean and reconnecting continental shear zones interpretation of the detailed patterns of ocean floor transforms revealed by satellite altimetry enables the creation of the indian ocean to be described quantitatively as four consecutive plate tectonic regimes separated at 200 136 89 and 43 ma each regime is reversed in turn by keeping transform termini coincident and colinear until conjugate points on the margins of pre existing plates regain their pre regime integrity progressive elimination of the indian ocean demonstrable as a smooth computer animation http www kartoweb itc nl gondwana leads to a refined re assembly of the continental fragments of central gondwana that is substantiated by new geological data a sequence of euler interval poles that describes the dispersal of the gondwana fragments time calibrated against available magnetic anomaly data is given the model requires a mid cretaceous position for india s southern tip about 1000 km south of madagascar prior to india s rapid northward migration

resolution of direction of oceanic magnetic lineations by the sixth generation lithospheric magnetic field model from champ satellite magnetic measurements the champ satellite continues to provide highly accurate magnetic field measurements from decreasing orbital altitudes 350 km at solar minimum conditions using the latest 4 years 2004 2007 of readings from the champ fluxgate magnetometer including an improved scalar data product we have estimated the lithospheric magnetic field to spherical harmonic degree 120 corresponding to 333 km wavelength resolution the data were found to be sensitive to crustal field variations up to degree 150 down to 266 km wavelength but a clean separation of the lithospheric signal from ionospheric and magnetospheric noise sources was achieved only to degree 120 this new mf6 model is the first satellite based magnetic model to resolve the direction of oceanic magnetic lineations revealing the age structure of oceanic crust

grimm the gfz reference internal magnetic model based on vector satellite and observatory data summary in this paper the new gfz reference internal magnetic model grimm is presented the model has been derived from nearly 6 yr of champ satellite data and 5 yr of observatory hourly means at high latitudes full vector satellite data are used at all local times which allows a separation between on one hand the fields generated by ionosphere and field aligned currents and on the other hand the fields generated in the earth s core and lithosphere this selection technique leads to a data set without gaps during the polar summers resulting in a core field model that has an unprecedented time resolution the modelled static core field secular variation and lithospheric field are all in good agreement with previously published magnetic field models order five b splines are used to model the variation in time of the core field the energy in the secular acceleration has therefore a smooth behaviour in time and increases continuously from 2003 5 mapping the field acceleration from 2001 5 to 2005 5 reveals its rapid and complex evolution over this time period at the earth s surface due to the applied regularization technique the acceleration energy in spherical harmonics 6 11 is significantly larger than for other models and we show that such a spectrum is acceptable

traces of evaporites in upper cretaceous lacustrine deposits of korea origin and paleoenvironmental implications abstract diverse types of halite and sulfate evaporite traces occur in the upper cretaceous lacustrine deposits of the jindong formation and the jangdong tuff in korea in which dinosaur tracks are common the halite traces usually occur as casts or moulds and they include traces of primary halite hoppers primary and intrasedimentary skeletal halite and intrasedimentary tiny halite the sulfate traces occur as intrasedimentary and displacive casts filled with sediments and sparry calcite and the casts occur as diverse modes from single crystal casts through nodular aggregates to massive aggregates some aggregates of the sulfate casts are aligned in crack pattern and selective occurrence of the laths in ripple troughs are observed soluble sulfate evaporite minerals such as gypsum glauberite or mirabilite are probable for the precursors of these traces these halite and sulfate traces are interpreted to have been formed in a saline lake and mudflats it is interpreted that meteoric water was responsible for the evaporite precipitation in the jindong lake and jangdong lake recycled brine produced by the repeated dissolution of evaporites might contribute to the evaporite precipitation in the paleo jindong lake and the paleo jangdong lake the development of saline lake deposits in the jindong formation and the jangdong tuff suggests that the southern part of the korean peninsula remained an inland continental area during the cretaceous resulting in semi arid paleoclimatic condition due to an orographic effect by the location of the korean peninsula on continental margin in mid latitude with topographic barriers during the cretaceous the occurrence of dinosaur tracks in the lake margin deposits of saline lake with frequent inflow of dilute meteoric water suggests that upper cretaceous dinosaurs inhabiting lakes on the korean peninsula might have drunken brackish water

climatic influences on sediment deposition and turbidite frequency in the nitinat fan british columbia abstract continental margins in regions influenced by temperate ice sheets experience climate dependent changes in sedimentary processes a new stratigraphy is presented for ocean drilling program hole 888b from the nitinat fan on the vancouver margin in which we examine the relationship between fluctuations in glacial sourced sediment delivered to the continental shelf and turbidite character and frequency glacial interglacial episodes are determined based on 1 core lithology where sandy coarse grained sediment and fine grained clay silty clay represents glacial and interglacial intervals respectively 2 18 o of planktonic foraminifera g bulloides in which higher values indicate warmer sea surface temperatures and lower global ice volume 3 magnetic susceptibility in which higher values indicate coarser grain sizes deposited during glacials and 4 ratios of sinistral n pachyderma to dextral n incompta in which higher proportions of n pachyderma are a sign of cooler sea surface temperatures finally using radiocarbon 14 c dates specific marine isotope stages mis within the top 240 m of core are assigned mis 2 4 2 118 mbsf mis 5 118 157 mbsf and mis 6 213 240 mbsf using this chronology sedimentation rates for the nitinat fan were greater 187 cm kyr during glacial mis 2 4 than interglacial mis 5 69 cm kyr additionally during glacial mis 2 4 thicker turbidites upwards of 150 cm were deposited relatively frequently 75 year periodicity compared with those from mis 5 which are relatively thin up to 27 cm and deposited more rarely 130 year periodicity these results indicate that turbidite frequency and thickness are linked to climate through ice sheet extent since transport of glacimarine sediment to the continental slope promotes turbidity currents that are responsible for the most significant amount of offshore sedimentation this study shows that geological processes influencing turbidite deposition can fluctuate over time and may not necessarily be represented by ongoing processes within the modern depositional setting

mapping geomagnetic secular variation at the core mantle boundary summary data from recent satellite missions have vastly increased the resolution of models of the geomagnetic field and itsfirst and second time derivatives secular variation sv and secular acceleration sa the spectra of both sv and sa are blue at the core mantle boundary both well fit by functions proportional to l l 1 where l is the spherical harmonic degree the ratio of the two spectra defines a timescale for geomagnetic variations of approximately 10 yrs for all resolvable harmonic degrees the blue spectra should prevent meaningful maps of the sv being generated nevertheless the coherence of the maps up to harmonic degree 13 suggests that it is possible to obtain useful insight from their examination low sv is confirmed under the pacific but also revealed under the north atlantic and antarctica these features are more readily explained in terms of dynamo control through thermal core mantle coupling than by electromagnetic screening comparison with maps from measurements prior to the recent satellites using the comprehensive model suggests that models back to at least 1970 are sufficiently good to enable direct comparison of the sv

sedimentology petrography and diagenesis of eocene oligocene evaporites the tuzhisar formation sw sivas basin turkey abstract the study area is situated in the southwestern part of the sivas basin sediments of the ortakoy formation middle upper eocene of flysch facies were deposited in a shallow marine environment and consist of interstratified sandstone shale and calcareous mudstone the karaziyaret basaltic dikes cut the ortakoy formation the ortakoy formation is comformably overlain by the evaporite dominated tuzhisar formation gradual transitions between these two stratigraphic units crop out between yenikoy and yenituzhisar villages the tuzhisar formation is composed mainly of secondary gypsum which originated from the hydration of precursor anhydrite rock the formation has been subdivided into three members yenikoy kullu and selimiye members yenikoy lower evaporite unit and kullu upper evaporite unit members contain gypsum sequences up to 70 m thick the selimiye member lower middle oligocene which consists mainly of red clastic units interrupt and gradationally overlies laterally and vertically these two members in the gypsum of the yenikoy member nodular nodular banded laminated banded lithofacies with enterolithic and chicken wire structures are distinguished these associations indicate a sabkha or shallow water setting of deposition such as a lagoon secondary gypsum in the tuzhisar formation generally displays alabastrine and porphyroblastic textures with corroded anhydrite relics associated minerals are dolomite calcite celestite and lutecite the kullu member is composed of irregular thick bedded massive locally brecciated secondary gypsum probably formed by multiple synsedimentary collapse after the dissolution of pre existing soluble minerals and or by paleoslumping related to synsedimentary tectonism however most of the evidence for the origin of the breccia has been destroyed by intense karstification

magnetic signatures of medium scale traveling ionospheric disturbances as observed by champ 1 in this work we analyze the global distribution and physical characteristics of nighttime midlatitude magnetic field fluctuations mmfs as observed by the champ satellite from 2001 to 2002 solar maximum and from 2006 to 2007 solar minimum mmfs are defined as medium scale magnetic fluctuations perpendicular to the mean field which are not accompanied by plasma density irregularities at the champ altitude 400 km mmfs occur at 15 40 invariant latitude in the ionospheric f region the occurrence is rare above the southern atlantic ocean and bears little connection to geomagnetic activity the global mmf occurrence rate depends on season the occurrence is generally low in equinox maximizes around east asia oceania and europe northern atlantic ocean in june solstice and peaks above the american continents in december solstice as the solar cycle declines the detected mmf occurrence rate also decreases the mmf occurrence peaks around 2100 lt and slowly decreases toward midnight in the postmidnight sector events are practically absent the mmf occurrence is generally consistent with known features of nighttime medium scale traveling ionospheric disturbances mstids such as the conjugate climatology and premidnight occurrence peak in the east asia oceania region but differences in their distributions also exist implying that factors other than mstids e g ionospheric conductivity sporadic e layer or plasma instabilities may play a nonnegligible role in generating mmfs mmfs have a preferred direction of polarization which is consistent with that of mstids and again corroborates the close connection between these two phenomena we interpret the observed magnetic deflections in terms of field aligned currents facs the estimated wavelength range 200 500 km of associated fac pairs also agrees well with the size of mstid density structures

sea level change and paleogeographic reconstructions southern vancouver island british columbia canada abstract forty eight new and previously published radiocarbon ages constrain deglacial and postglacial sea levels on southern vancouver island british columbia sea level fell rapidly from its high stand of about 75 m elevation just before 14 000 cal bp 12 000 radiocarbon yrs bp to below the present shoreline by 13 200 cal bp 11 400 radiocarbon years bp the sea fell below its present level 1000 years later in the central strait of georgia and 2000 years later in the northern strait of georgia reflecting regional differences in ice sheet retreat and downwasting direct observations only constrain the low stand to be below 11 m and above 40 m analysis of the crustal isostatic depression with equations utilizing exponential decay functions appropriate to the cascadia subduction zone however places the low stand at 30 5 m at about 11 200 cal bp 9800 bp the inferred low stand for southern vancouver island when compared to the sea level curve previously derived for the central strait of georgia to the northwest generates differential isostatic depression that is consistent with the expected crustal response between the two regions morphologic and sub bottom features previously interpreted to indicate a low stand of 50 to 65 m are re evaluated and found to be consistent with a low stand of 30 5 m submarine banks in eastern juan de fuca strait were emergent at the time of the low stand but marine passages persisted between southern vancouver island and the mainland the crustal uplift presently occurring in response to the late pleistocene collapse of the southwestern sector of the cordilleran ice sheet amounts to about 0 1 mm yr the small glacial isostatic adjustment rate is a consequence of low viscosity mantle in this tectonically active region

late quaternary stratigraphy and seafloor geology of eastern juan de fuca strait british columbia and washington abstract a combination of shallow sediment cores and high resolution seismic reflection data were used to identify and map four main surficial geologic units in eastern juan de fuca strait these units comprise bedrock unit 1 till diamict unit 2 glacial marine unit 3 and post glacial sediments unit 4 bedrock crops out only in nearshore environments off vancouver island diamicton forms the numerous morainal and drumlin like banks in the region a series of banks including middle and hein banks and the offshore extension of dungeness spit divide the strait into two major areas based on the dominant surficial sedimentary units post glacial sediments are most common to the east and glacial marine sediments to the west glacial marine sediments are represented by several seismo lithologic subunits that suggest progression from ice proximal to ice distal depositional environments radiocarbon dates indicate these sediments are a product of the last phase of glacier retreat there is relatively little modern sediment input to eastern juan de fuca strait so most post glacial sediments are thought to consist of material reworked from glacial outwash or eroded from shallow bank deposits this conclusion is supported by radiocarbon ages from the post glacial sediments most of which are early holocene or younger also there are sandwave fields sediment drifts and barrier spits that appear to be actively maintained the source of sediment to these features is probably the pre existing deposits that occur in banks and extensive coastal exposures

mercury s internal magnetic field constraints on large and small scale fields of crustal origin abstract messenger and mariner 10 observations of mercury s magnetic field suggest that small scale crustal magnetic fields if they exist are at the limit of resolution large scale crustal magnetic fields have also been suggested to exist at mercury originating from a relic of an internal dipole whose symmetry has been broken by latitudinal and longitudinal variations in surface temperature if this large scale magnetization is confined to a layer averaging 50 km in thickness it must be magnetized with an intensity of at least 2 9 a m fits to models constrained by such large scale insolation variations do not reveal the predicted signal and the absence of small scale features attributable to remanence further weakens the case for large scale magnetization our tests are hindered by the limited coverage to date and difficulty in isolating the internal magnetic field we conclude that the case for large and small scale remanence on mercury is weak but further measurements by messenger can decide the issue unequivocally across the terrestrial planets and the moon magnetization contrast and iron abundance in the crust show a positive correlation this correlation suggests that crustal iron content plays a determining role in the strength of crustal magnetization

earth s lithospheric magnetic field determined to spherical harmonic degree 90 from champ satellite measurements summary the champ magnetic field mission is providing highly reliable measurements from which the global lithospheric magnetic field can be determined in unprecedented resolution and accuracy using almost 5 yr of data we derive our fourth generation lithospheric field model termed mf4 which is expanded to spherical harmonic degree and order 90 after subtracting from the full magnetic field observations predicted fields from an internal field model up to degree 15 an external field model up to degree two and the predicted magnetic field signatures for the eight dominant ocean tidal constituents we fit and remove remaining external fields and polar electrojet signatures in a track by track scheme from a subset of least disturbed tracks we estimate the mf4 model by least squares damping ill determined coefficients by regularization the resulting mf4 model provides a good representation of the lithospheric field down to an altitude of about 50 km at lower latitudes with reduced accuracy in the polar regions crustal features come out significantly sharper than in previous models in particular bands of magnetic anomalies along subduction zones become visible by satellite for the first time

an improved geomagnetic data selection algorithm for global geomagnetic field modelling a spherical harmonic degrees 60 global internal field model is described called bgs g l 0706 this model includes a degree 15 core and piecewise linear secular variation model and is derived from quiet time orsted and champ satellite data sampled between 2001 0 and 2005 0 for the satellite data selection a wide range of geomagnetic index and other data selection filters have been used to best isolate suitably quiet magnetospheric and ionospheric conditions only a relatively simple degree one spherical harmonic external field model is then required it is found that a new vector magnetic disturbance index vmd the existing longitude sector a indices the auroral zone index ie and the polar cap index pc are better than kp and dst at rejecting rapidly varying external field signals at low middle auroral and polar latitudes the model quality is further enhanced by filling spatial and temporal gaps in the quiet data selection with a second selection containing slightly more disturbed data it is shown that vmd provides a better parametrization than dst of the large scale rapidly changing external field the lithospheric field model between degrees 16 and 50 is robust and displays good coherence with other recently published models for this epoch bgs g l 0706 also shows crustal anomalies consistent with other studies although agreement is poorer in the southern polar cap intermodel coherency reduces above about degree 40 most likely due to incompletely filtered signals from polar ionospheric currents and auroral field aligned currents the absence of the pc index for the southern hemisphere for 2003 onwards is a particular concern

longitudinal and seasonal structure of the ionospheric equatorial electric field 1 the daytime eastward equatorial electric field eef in the ionospheric e region plays an important role in equatorial ionospheric dynamics it is responsible for driving the equatorial electrojet eej current system equatorial vertical ion drifts and the equatorial ionization anomaly due to its importance there is much interest in accurately measuring and modeling the eef in this work we propose a method of estimating the eef using champ satellite derived latitudinal current profiles of the daytime eej along with h measurements from ground magnetometer stations magnetometer station pairs in both africa and south america were used for this study to produce time series of electrojet current profiles these current profiles were then inverted for estimates of the eef by solving the governing electrostatic equations we compare our results with the ion velocity meter ivm instrument on board the communication navigation outage forecasting system satellite we find high correlations of about 80 with the ivm data however we also find a constant offset of about 0 3 mv m between the two data sets in africa further investigation is needed to determine its cause we compare the eef structure in africa and south america and find differences which can be attributed to the effect of atmospheric nonmigrating tides this technique can be extended to any pair of ground magnetometer stations which can capture the day to day strength of the eej

improved horizontal wind model hwm07 enables estimation of equatorial ionospheric electric fields from satellite magnetic measurements 1 horizontal neutral winds play an important role in low latitude ionospheric e and f region dynamics in particular the zonal winds have strong effects on the local structure of the low latitude ionospheric current system accurate wind specification is therefore essential for modeling these currents in order to investigate the retrieval of eastward electric fields from satellite derived equatorial electrojet eej profiles we consider a provisional horizontal wind model hwm07 and its implications for the meridional structure of the eej we find that eej current profiles predicted using hwm07 agree better with champ magnetometer derived current profiles than eej profiles predicted using the older hwm93 model the improved wind model opens exciting new possibilities of determining the day side eastward electric field in the equatorial ionosphere from satellite magnetic field measurements

unusually well preserved casts of halite crystals a case from the upper frasnian of northern lithuania abstract upper frasnian carbonate siliciclastics of the stipinai formation northern lithuania comprise a bed of calcareous silty arenite with casts of halite crystals including hopper crystals unusually well preserved casts occur on the lower surface of the bed while poorly preserved casts are present on the upper bedding surface the casts originated as the result of the dissolution of halite crystals which grew in the sediment the dissolution took place during early stages of diagenesis when host sediment was soft unstable cavities after crystal dissolution were filled by overlying sediment forming their casts the collapsing sediment form sink hole deformation structures which disturb wave ripple cross lamination from the upper part of the bed dewatering pipe structures are also present the casts and accompanying sink hole and dewatering pipes are classified as the postdepositional deformation structures caused by haloturbation

can core surface flow models be used to improve the forecast of the earth s main magnetic field 1 geomagnetic main field models used for navigation are updated every 5 years and contain a forecast of the geomagnetic secular variation for the upcoming epoch forecasting secular variation is a difficult task the change of the main magnetic field is thought to be principally due to advection of the field by flow at the surface of the outer core on short timescales and when large length scales are considered with accurate secular variation sv and secular acceleration sa models now available from new satellite missions inverting for the flow and advecting it forward could lead to a more accurate prediction of the main field however this scheme faces two significant challenges the first arises from the truncation of the observable main field at spherical harmonic degree 13 this can however be handled if the true core flow is large scale and has a rapidly decaying energy spectrum the second is that even at a given single epoch the instantaneous sv and sa cannot simultaneously be explained by a steady flow nevertheless we find that it may be feasible to use flow models for an improved temporal extrapolation of the main field a medium term 10 years hindcast of the field using a steady flow model outperforms the usual extrapolation using the presently observed sv and sa on the other hand our accelerated toroidal flow model which explains a larger portion of the observed average sa over the 2000 2005 period fails to improve both the short term and medium term hindcasts of the field this somewhat paradoxical result is related to the occurrence of so called geomagnetic jerks the still poorly known dynamical nature of which remains the main obstacle to improved geomagnetic field forecasts

comment on can core surface flow models be used to improve the forecast of the earth s main magnetic field by stefan maus luis silva and gauthier hulot

magnetic field gradients from the st 5 constellation improving magnetic and thermal models of the lithosphere received 20 august 2007 revised 17 october 2007 accepted 6 november 2007 published 25 december 2007 1 we report the development of a new technique magnetic gradiometry for satellite based remote sensing of the lithosphere the measurements reported here represent the first systematic measurements of lithospheric magnetic field gradients and were collected from a spinning spacecraft the three satellite st 5 mission collected vector magnetic field observations at 300 800 km altitudes over mid and high northern latitudes in 2006 away from the auroral oval and over the continents the gradients of the low altitude 400 km total anomaly field are dominated by lithospheric magnetic fields using a seismic starting model and magnetic field observations from st 5 and other recent satellite missions we demonstrate how these techniques can be used to improve our knowledge of the processes involved in the thickened crust of the colorado plateau and the sierra madre occidental citation purucker m t sabaka g le j a slavin r j strangeway and c busby 2007 magnetic field gradients from the st 5 constellation improving magnetic and thermal models of the lithosphere geophys res lett 34 l24306 doi 10 1029 2007gl031739

the geomagnetic power spectrum summary combining champ satellite magnetic measurements with aeromagnetic and marine magnetic data the global geomagnetic field has now been modelled to spherical harmonic degree 720 an important tool in field modelling is the geomagnetic power spectrum it allows the comparison of field models estimated from different data sets and can be used to identify noise levels and systematic errors a correctly defined geomagnetic power spectrum is flat white for an uncorrelated field such as the earth s crustal magnetic field at long wavelengths it can be inferred from global spherical harmonic models as well as from regional grids marine and aeromagnetic grids usually represent the anomaly of the total intensity of the magnetic field appropriate corrections have to be applied in estimating the geomagnetic power spectrum from such data the comparison of global and regional spectra using a consistently defined azimuthally averaged geomagnetic power spectrum facilitates quality control in field modelling and should provide new insights in magnetic anomaly interpretation

extraction of magnetic anomalies of crustal origin from magsat data over the area of the japanese islands three component data along the magsat paths in the area of 110 e 170 e and 8 n 68 n were fitted by polynomial series of the coordinates of the satellite position along the path the coefficients decrease sharply up to the sixth degree and become almost constant the fields represented by the sixth degree polynomials were subtracted from the data to remove the core and the external fields for the altitude correction a rectangular harmonic analysis was applied to the residuals thus obtained by employing local cartesian coordinates the residual fields were expanded into double fourier series of the maximum order of n m 3 over areas of 4000 4000 km and 2000 2000 km and anomaly fields were computed for the satellite altitude it was revealed that 1 an intense positive anomaly of the vertical component ran along the kuril trench 2 the japan sea was covered with a negative vertical anomaly in the northeastern part and with a positive in the southwestern part 3 there was a pair of positive and negative vertical anomalies covering the area from northern korea to the east china sea suggesting the existence of an extremely localized magnetization like a dipole near the surface in the southwestern tip of the korean peninsula

pleistocene glacimarine sedimentation on the continental slope off vancouver island british columbia abstract cordilleran ice sheet activity has had a significant influence on glacimarine sediment transport and deposition on the western canadian continental slope resulting in distinct sediment facies here we present lithogenic sediment grain size distributions grains 250 m g 1 63 m 10 to 60 m and 2 to 4 m and mass accumulation rates mar from a marine core md02 2496 collected 50 km offshore of vancouver island british columbia the lithogenic fraction of sediment deposited on the slope increased as grain size decreased and sediment sorting increased at 30 ka when the cordilleran ice sheet grew into southern british columbia during the fraser glaciation as the ice sheet advanced onto the continental shelf near core md02 2496 between 19 and 17 ka the proximal ice margin dramatically increased lithogenic sediment mars glacimarine sedimentation at this time was associated with cyclic deposition of generally coarse poorly sorted sediment an 80 year cyclicity suggests the influence of 1 outburst floods 2 lunar or 3 solar cycles on tidewater outlet glacier discharge rapid ice sheet retreat at 17 ka is indicated by ice rafted debris ird deposition followed by the deposition of fine well sorted silt suggestive of iceberg discharge followed by rock flour in a meltwater plume lithogenic sediment mars decreased dramatically at the bolling with a brief return to coarse poorly sorted sediments during the younger dryas glacimarine sedimentation decreased by 10 ka as the cordilleran ice sheet extent diminished to the areal extent of modern ice fields

identifying fluvio lacustrine intervals in thick playa lake successions an integrated sedimentology and ichnology of arenaceous members in the mid late triassic mercia mudstone group of south west england uk abstract a complete triassic succession is exposed in the cliffs of the devon coast in south west england uk where it forms part of the dorset east devon world heritage site the upper part of the succession the middle to late triassic mercia mudstone group consists of c 450 m of predominantly red mudstones and associated evaporites that were deposited in playa lakes in hot deserts the group has an extensive onshore and offshore outcrop and subcrop in the u k where it locally comprises over 3000 m of red beds with thick halites the devon coast section is the type for the group and is the most complete exposure of the keuper marl facies in north west europe in its middle part the dunscombe mudstone formation comprises a 25 to 40 m thick laterally variable succession of green purple and grey laminated mudstones with thin interbeds of calcareous siltstone sandstone and thicker beds of autobreccia related to gypsum anhydrite and halite dissolution it represents a fluvio lacustrine and probably cooler climatic interval that is thought to have lasted on the basis of palaeontological and magnetostratigraphic evidence for most of the carnian stage c 12 ma elsewhere in europe the carnian stage is represented by fluvial deposits including the esterienschichten and schilfsandstein formations in germany at the type section on the devon coast the dunscombe mudstone includes a lenticular unit of bioturbated predominantly fine grained sandstone up to 4 m thick the lincombe member that has not been recorded in inland sections in the county when traced northwards into somerset thin lenticular sandstones the north curry and sutton mallet sandstone members are locally present at similar stratigraphical levels in the lower part of the dunscombe mudstone a detailed analysis of the sedimentology of the three principal occurrences of these arenaceous units revealed 13 lithofacies and 6 ichnofabrics that suggest deposition in similar fluvio lacustrine settings their palaeoenvironmental interpretation and correlation is more complex than previously thought the lincombe member is interpreted as a geographically isolated sedimentary body that was deposited in a shallow oxygenated freshwater lake in devon it passes upwards and laterally into lake margin and lake delta plain deposits the north curry sandstone was deposited in a series of broad shallow channels that crossed a low relief topography laterally along strike the channel sands either pass into or terminate against more argillaceous lacustrine deposits in contrast the depositional environment of the sutton mallet sandstone is interpreted as relatively small scale channels with low flows and possible channel switching fluvio lacustrine intervals are relatively common within playa lake successions but there are few published accounts of ancient examples that are sufficiently detailed to allow the complex interactions of these ephemeral shallow water environments to be understood the sedimentological and ichnological descriptions and analyses of the triassic example presented here will be applicable to other fluvio lacustrine sediments deposited in dryland environments

emag2 a 2 arc min resolution earth magnetic anomaly grid compiled from satellite airborne and marine magnetic measurements 1 a global earth magnetic anomaly grid emag2 has been compiled from satellite ship and airborne magnetic measurements emag2 is a significant update of our previous candidate grid for the world digital magnetic anomaly map the resolution has been improved from 3 arc min to 2 arc min and the altitude has been reduced from 5 km to 4 km above the geoid additional grid and track line data have been included both over land and the oceans wherever available the original shipborne and airborne data were used instead of precompiled oceanic magnetic grids interpolation between sparse track lines in the oceans was improved by directional gridding and extrapolation based on an oceanic crustal age model the longest wavelengths 330 km were replaced with the latest champ satellite magnetic field model mf6 emag2 is available at http geomag org models emag2 and for permanent archive at http earthref org cgi bin er cgi s erda cgi n 970

late quaternary deglaciation and sea level history of eastern juan de fuca strait cascadia abstract eastern juan de fuca strait of southwestern british columbia northwestern washington state is near the western and southern terminus of late wisconsinan glaciation in north america seismic reflection profiles bathymetric data sediment core data and 41 new radiocarbon dates provide insight into the history of ice retreat and sea level change in the eastern portion of the strait the retreating ice margin appears to have passed through the area between 14 460 200 and 13 595 145 14c yr glacial marine sediments date between 12 889 50 and 11 110 50 14c yr bp wave eroded unconformities drowned prograded deposits and a partially isolated low stand basin are evidence attributed to low stand sea levels following deglaciation and five new control points on the local eustatic sea level curve are assigned based on radiocarbon dating of these features sea level change was rapid from 75 m immediately after deglaciation to possibly 60 4 m at 9920 60 14c yr bp after this time gradual sea level transgression took place relative sea level reached its approximate present position by 5470 115 14c yr bp since then relative sea level has remained constant suggesting eustatic rise is balanced by crustal uplift

lacustrine carbonates of iberian karst lakes sources processes and depositional environments abstract carbonates are the main components of iberian quaternary lake sediments in this review we summarize the main processes controlling carbonate deposition in extant iberian lakes located in mesozoic and tertiary carbonate dominated regions and formed through karstic activity during the late quaternary the lakes relatively small 1 ha to 118 ha and relatively shallow zmax 11 to 40 m provide examples of the large variability of sedimentary facies depositional environments and carbonate sources hydrology is dominated by groundwater inflow except those directly connected to the fluvial drainage nine lakes have been selected for this review and the main facies in palustrine littoral and profundal environments described and interpreted clastic carbonates occur in all iberian lakes due to the carbonate composition of the bedrocks surface formations and soils of the watersheds low temperatures and dilute meteoric waters seem responsible for the low carbonate content of sediments in high elevation lakes in the glaciated terrains in the pyrenees and the cantabrian mountains clastic carbonates are dominant in small karst lakes with functional inlets where sediment infill is dominated by fining upward sequences deposited during flood events re working of littoral carbonates is common in shallow environments and during low lake level stages in most lakes endogenic carbonate production occurs in two settings i littoral platforms dominated by chara and charophyte meadows and ii epilimnetic zone as biologically mediated calcite precipitates continuous preservation of varves since the mid holocene only occurs in one of the deeper lakes montcortes lake up to 30 m where calcite laminae textures massive fining upward and coarsening upward reflect seasonal changes in limnological conditions however varves have been formed and preserved in most of the lakes during short periods associated with increased water depth and more frequent meromictic conditions most iberian lakes are in a mature stage and karstic processes are not very active an outstanding example of a lake with intense karstic activity is banyoles lake where increased spring discharge after long rainy periods causes large remobilization and re suspension of the sediments accumulated in the deepest areas leading to the deposition of thick homogeneous layers homogeinites the iberian karst lake sequences underline the large variability of facies carbonate sources and depositional environments in small lake systems they illustrate how lake types evolve through the existence of a lake basin at centennial or even smaller time scales hydrology is the paramount control on facies and depositional environment patterns distribution and lake evolution and consequently a lake classification is proposed based on hydrology and sediment input a correct interpretation of carbonate sources and depositional history is a key for using lake sequences as archives of past global changes

magnetic anomaly map for northern western and eastern europe all of the available data describing the earth s magnetic field in northern western and eastern europe c 3 106 data points are compiled and presented at a scale of 1 20 400 000 the compilation meets two requirements i that the total field intensity anomalies reflect a survey acquired at an altitude of 3000 m above m s l and during the same epoch 1980 0 and ii that the anomalies are residuals after subtracting the common reference field dgrf1980 as the data span many epochs geomagnetic data recorded at observatories and repeat stations were used to determine the best model for estimating the secular variation in all data up to 1980 this yielded magnetic anomalies with wavelengths up to the order of 2000 km the precision of the resultant anomalies amplitudes about 1700 nt to 8000 nt differ between 10 nt in central europe and 20 nt in the outer parts of the compilation the resultant anomaly map contains a wealth of information to geoscientists studying global tectonic processes and the deep crustal composition of major continental crusts it clearly shows the different anomaly patterns between the palaeozoic and precambrian crusts of central and eastern europe these anomalies are interpreted as lateral changes of magnetization in a horizontal plate a comparison between the low level compilation and maps derived from the magsat satellite at about 360 km altitude allows the description of the two different crust types in europe

fifth generation lithospheric magnetic field model from champ satellite measurements 1 six years of low orbit champ satellite magnetic measurements have provided an exceptionally high quality data resource for lithospheric magnetic field modeling and interpretation here we describe the fifth generation satellite only magnetic field model mf5 the model extends to spherical harmonic degree 100 as a result of careful data selection extensive corrections filtering and line leveling the model has low noise levels even if evaluated at the earth s surface the model is particularly suited for inferring large scale structure and composition of the lithosphere it is also meant to serve as the long wavelength part of continental and global scale marine and aeromagnetic anomaly maps

an ellipsoidal harmonic representation of earth s lithospheric magnetic field to degree and order 720 1 while high degree models of the earth s gravity potential have been inferred from measurements for more than a decade corresponding geomagnetic models are difficult to produce the primary challenge lies in the estimation of the magnetic potential which is not completely determined by available field intensity measurements and cannot be computed by direct integration described here is the methodology behind the third generation of the national geophysical data center s degree 720 magnetic model key issues are 1 the ellipsoidal harmonic representation of the magnetic potential 2 the reduction of ambiguities by a suitable penalty function and 3 the use of an iterative method to estimate the model coefficients the ngdc 720 model provides the lithospheric magnetic field vector at any desired location and altitude close to and above the earth s surface anticipated uses are in geological and tectonic studies of the lithosphere as a local correction for magnetic navigation and heading systems and the calibration of ground marine airborne and spaceborne magnetometers the ngdc 720 model is available at http geomag org models ngdc720 html and for long term archive at http earthref org cgi bin er cgi s erda cgi n 989

satellite observations of magnetic fields due to ocean tidal flow the ocean is an electrically conducting fluid that generates secondary magnetic fields as it flows through earth s main magnetic field extracting ocean flow signals from remote observations has become possible with the current generation of satellites measuring earth s magnetic field here we consider the magnetic fields generated by the ocean lunar semidiurnal m2 tide and demonstrate that magnetic fields of oceanic origin can be clearly identified in satellite observations

global equivalent magnetization of the oceanic lithosphere abstract as a by product of the construction of a new world digital magnetic anomaly map over oceanic areas we use an original approach based on the global forward modeling of seafloor spreading magnetic anomalies and their comparison to the available marine magnetic data to derive the first map of the equivalent magnetization over the world s ocean this map reveals consistent patterns related to the age of the oceanic lithosphere the spreading rate at which it was formed and the presence of mantle thermal anomalies which affects seafloor spreading and the resulting lithosphere as for the age the equivalent magnetization decreases significantly during the first 10 15 myr after its formation probably due to the alteration of crustal magnetic minerals under pervasive hydrothermal alteration then increases regularly between 20 and 70 ma reflecting variations in the field strength or source effects such as the acquisition of a secondary magnetization as for the spreading rate the equivalent magnetization is twice as strong in areas formed at fast rate than in those formed at slow rate with a threshold at 40 km myr in agreement with an independent global analysis of the amplitude of anomaly 25 this result combined with those from the study of the anomalous skewness of marine magnetic anomalies allows building a unified model for the magnetic structure of normal oceanic lithosphere as a function of spreading rate finally specific areas affected by thermal mantle anomalies at the time of their formation exhibit peculiar equivalent magnetization signatures such as the cold australian antarctic discordance marked by a lower magnetization and several hotspots marked by a high magnetization

magnetic anomaly map of the world merging satellite airborne marine and ground based magnetic data sets abstract we report here a simple but practical method to combine systematically the magnetic surveys of disparate specifications from marine ground aeromagnetic and satellite platforms that aims to be helpful in the framework of the world digital magnetic anomaly map project because the satellite coverage and data quality is more uniform than near surface surveys it is adopted as the base map for wavelengths larger than 400 km and up to spherical harmonic degree inclusive of 16 2500 km after checking that satellite models and large aeromagnetic wavelengths are not consistent we filter out wavelengths longer than 400 km in aeromagnetic compilations existing regional grids and when available individual surveys are merged to give a more uniform spatial variation of the magnetic anomalies the effects of merging the grids are examined by plotting profiles and difference maps of the overlapping regions a preliminary global map is obtained after combining the magnetic anomaly map with the downward continued champ satellite derived magnetic anomaly map forthcoming availability of new datasets as well as improvements in the procedure will help to produce increasingly reliable maps

glaciation and post glacial history of the continental shelf off southwestern vancouver island british columbia abstract bathymetry sediment distribution and seismic stratigraphy are used to interpret the pattern of glaciation of the continental shelf off southwestern vancouver island canada four seismostratigraphic units are distinguished and mapped in relation to sediments and sedimentary rocks present on the shelf they are 1 undivided tertiary bedrock 2 a unit composed mainly of pleistocene outwash 3 pleistocene morainal deposits and 4 holocene marine sediments a large piedmont glacier is envisaged formed by the coalescence of glaciers emanating from juan de fuca strait and barkley sound it cut a system of deep troughs into the tertiary bedrock built up a complex of morainal ridges and built out an extensive outwash plain on the unglaciated shelf to the northwest during glacial maxima the piedmont glacier extended right across the shelf particularly high discharge of debris from the seaward ends of the glacial troughs may have caused the erosion of adjacent submarine canyons during the final deglaciation the ice withdrew somewhat faster than the sea advanced although masses of downwasting ice may have persisted in many of the troughs the glacial topography including moraines and tertiary bedrock were levelled by the advancing sea but many of the troughs were preserved from burial perhaps because they were still ice filled or because the coastal system was sediment starved strong currents sweep the present shelf redistributing sand and mud winnowed from the tops of the truncated moraines into low lying areas and leaving concentrations of gravel behind

holocene coastal carbonates and evaporites of the southern arabian gulf and their ancient analogues abstract the holocene sediments of the coast of the united arab emirates in the southeastern arabian gulf are frequently cited in the literature as type examples for analogous assemblages of carbonates evaporites and siliciclastics throughout the geologic record this paper is intended as a convenient single source for the description of sediments of this region providing information on how to reach the classic localities and some of the analogs the holocene sediments of the region accumulate over an area that is 500 km long and up to 60 km wide the sediments collecting offshore are predominantly pelecypod sands mixed with lime and argillaceous mud with these latter fine sediments increasing as the water deepens the pelecypod rich sediments also collect east of abu dhabi island both in the deeper tidal channels between the barrier island lagoons and in deeper portions of the protected lagoons west of abu dhabi island the shallow water margin is the site of coral reefs and coralgal sands whereas to the east oolites accumulate on the tidal deltas of channels located between barrier islands grapestones accumulate to the lee of the reefs and the oolite shoals where cementation becomes more common they are particularly common on the less protected shallow water margins of the lagoons west of abu dhabi island pelleted lime muds accumulate in the lagoons in the lee of the barrier islands of the eastern abu dhabi lining the inner shores of the protected lagoons of abu dhabi and on other islands to the west are cyano bacterial mats and mangrove swamps landward of these a prograding north facing shoreline is formed by supratidal salt flats sabkhas in which evaporite minerals are accumulating this paper describes the localities associated with 1 the mangrove swamps of the west side of the al dhabaiya peninsula 2 the indurated cemented carbonate crusts cyanobacterial flats and sabkha evaporites on the shore of the khor al bazam south of qanatir island 3 the reef and oolitic sand flats on the coast just east of jebel dhana and 4 the marine travertine and aragonite coats associated with the beach sediments in a small bay south of jebel dhana and 5 the sabkha mutti between jebel barakah and al sila similar sedimentological associations of carbonate and evaporites to those of the holocene of the united arab emirates are to be found in the tertiary and mesozoic sedimentary rocks of the immediate subsurface in the arabian gulf other analogs to this setting include the paleozoic carbonates of the western usa europe and asia mesozoic carbonates of the gulf of mexico europe and middle east and tertiary sedimentary rocks in the middle east

vulnerability of the cordilleran ice sheet to iceberg calving during late quaternary rapid climate change events 1 we present the first high resolution record of iceberg calving on the continental slope of vancouver island british columbia md02 2496 48 58n 127 02w 1243 m water depth through the last glacial from the cordilleran ice sheet cis these previously unknown ice rafted debris ird events representing significant retreat of the western margin of the cis out of marine waters show little correspondence with local climate change high resolution radiocarbon dating indicates that the younger ird events coincide with global radiocarbon age plateaus that allow direct correlation with distal climate records where the same plateaus have been identified the coincidence of episodic shedding of ird from the cis with north atlantic climate events i e north atlantic deep water shutdown and heinrich events begs the question what drove cis destabilization forcing appears to be external to cis dynamics perhaps resulting from either eustatic sea level rise or episodes of atmospheric warming over the north american continent

a global lithospheric magnetic field model with reduced noise level in the polar regions 1 due to persistent ionospheric current systems at high latitudes satellite magnetic measurements have high noise levels in the polar regions consequently small scale lithospheric features are much more difficult to resolve there than at lower latitudes using linear combinations of spherical harmonics sh we define localized functions which are band limited to a given maximum degree thus a model s sh resolution can be varied over the globe we produce a lithospheric field model from champ satellite data which resolves features to sh degree 90 at low latitudes but only to sh degree 60 in the polar regions the new model can be downward continued from satellite altitude to the earth s surface without generating spurious high latitude anomalies citation lesur v and s maus 2006 a global lithospheric magnetic field model with reduced noise level in the polar regions geophys res lett 33 l13304

deglacial ocean warming and marine margin retreat of the cordilleran ice sheet in the north pacific ocean abstract a new high resolution planktonic foraminiferal mg ca based ocean temperature record has been generated for deep sea core md02 2496 sited offshore of vancouver island western canada during the last deglaciation 21 12 ka the relationship between cordilleran ice sheet cis retreat and changing regional ocean temperatures has been reconstructed through glaciomarine sediments in md02 2496 that capture tidewater glacier response to surface ocean thermal forcing at cis maximum extent the marine margin of the ice sheet advanced onto the continental shelf during this interval ocean temperatures recorded by surface dwelling globigerina bulloides remained a relatively constant 7 5 c while subsurface dwelling neogloboquadrina pachyderma s recorded temperatures of 5 c these ocean temperatures were sufficiently warm to induce significant melt along the tidewater ice terminus similar to modern alaskan tidewater glacial systems during the deglacial retreat of the cis the n pachyderma temperature record shows two distinct warming steps of 2 and 2 5 c between 17 2 16 and 15 5 14 ka respectively coincident with ice rafting events from the cis while g bulloides records an 3 c warming from 15 to 14 ka we hypothesize that submarine melting resulting from relatively warm ocean temperatures was an important process driving ice removal from cis tidewater glaciers during the initial stages of deglaciation

ice streams of the late wisconsin cordilleran ice sheet in western north america abstract the late wisconsin cordilleran ice sheet cis of western north america is thought to have reached its maximum extent 2 5 106 km2 as late at c 14 5 ka most 80 of the ice sheet s bed consists of high mountains but its core zone sited on plateaux of the intermontane belt of british columbia and coterminous parts of the usa shows broad swaths of subglacially streamlined rock and sediment broad scale mapping from new digital imagery data identifies three subglacial bed types 1 hard beds of variably streamlined bedrock 2 drumlinized soft beds of deformation till reworked from antecedent sediment and 3 mixed beds of variably streamlined bedrock protruding through drumlinized sediment drumlins on soft beds appear to be erosional features cut into till and antecedent sediments and identify the catchment areas of paleo ice streams expressed downglacier as flow sets of megascale glacial lineations msgls grooved and cloned drumlins appear to record the transition from drumlins to msgls the location of paleo ice streams reflects topographic funneling of ice from plateau surfaces through outlet valleys and a soft bed that sustained fast flow rock cut msgls are also present locally on the floors of outlet valleys cis disintegrated in

electric fields and zonal winds in the equatorial ionosphere inferred from champ satellite magnetic measurements 1 the equatorial electrojet eej produces a strong magnetic signal in measurements of the low orbiting champ satellite six years of data with more than 30 000 dayside equator crossings provide a unique data basis to study this current system in addition to scalar measurements used in previous studies we have also inverted vector magnetic field measurements to gain accurate meridional profiles of the eastward current in the equatorial region by solving the relevant differential equation the champ derived current profiles can be inverted for the driving zonal electric fields and zonal winds as a result of this feasibility study we suggest an inversion of the complete set of individual champ eej current profiles which will provide valuable new information on dayside electric fields and thermospheric winds at low latitudes citation maus s p alken and

extending comprehensive models of the earth s magnetic field with orsted and champ data summary a new model of the quiet time near earth magnetic field has been derived using a comprehensive approach which includes not only pogo and magsat satellite data but also data from the orsted and champ satellites the resulting model shows great improvement over its predecessors in terms of completeness of sources time span and noise reduction in parameters with its well separated fields and extended time domain of 1960 to mid 2002 the model is able to detect the known sequence of geomagnetic jerks within this frame and gives evidence for an event of interest around 1997 because all sources are coestimated in a comprehensive approach intriguing north south features typically filtered out with other methods are being discovered in the lithospheric representation of the model such as the s atlantic spreading ridge and andean subduction zone lineations in addition this lithospheric field exhibits significantly less noise than previous models as a result of improved data selection the f region currents through which the satellites pass are now treated as lying within meridional planes as opposed to being purely radial results are consistent with those found previously for magsat but an analysis at orsted altitude shows exciting evidence that the meridional currents associated with the equatorial electrojet likely close beneath the satellite besides the model a new analysis technique has been developed to infer the portion of a model parameter state resolved by a particular data subset this has proven very useful in diagnosing the cause of peculiar artefacts in the magsat vector data which seem to suggest the presence of a small misalignment bias in the vector magnetometer

national geophysical data center candidate for the world digital magnetic anomaly map marine and airborne magnetic anomaly data have been collected for more than half a century providing global coverage of the earth furthermore the german champ satellite is providing increasingly accurate information on large scale magnetic anomalies the world digital magnetic anomaly map project is an international effort to integrate all available near surface and satellite magnetic anomaly data into a global map database teams of researchers were invited to produce candidate maps using a common pool of data sets here we present the national geophysical data center ngdc candidate to produce a homogeneous map the near surface data were first line leveled and then merged by least squares collocation long wavelengths were found to agree surprisingly well with independent satellite information this validates our final processing step of merging the short wavelength part of the near surface data with long wavelength satellite magnetic anomalies

study on crustal magnetic anomalies and curie surface in southeast tibet abstract in this paper the potsdam model pomme 6 2 is used to investigate the distributions of crustal magnetic anomalies and curie surface in southeast tibet the curie surface is compared with the regional heat flow bouguer anomaly moho depth and seismicity the results show that the magnetic anomalies and curie surface are both consistent with the geological structure sichuan basin exhibits a high positive anomaly while orogenic belts such as the longmenshan northwestern sichuan and western yunnan exhibit weak positive or negative anomalies the distribution of magnetic anomaly confirms that escape flow from east tibet branches into northeastward part and southward part on west sichuan basin due to resistance by the rigid basin the depth of curie surface ranges from 20 to 34 km the curie surface beneath the longmenshan xiaojiang and lijiang xiaojinhe faults is shallow with the uplift strike consistent with the faults the curie surface beneath sichuan basin and the central bayan har massif is deep with sheet like depressions strong earthquakes primarily occurred in the areas with the uplift of curie surface the heat flow values near tengchong lijiang dali and kunming are high and the curie surface there is shallow

ergodicity of the recent geomagnetic field the geomagnetic field is a fundamental property of our planet its study would allow us to understand those processes of earth s interior which act in its outer core and produce the main field knowledge of whether the field is ergodic i e whether time averages correspond to phase space averages is an important question since if this were true it would point out a strong spatio temporal coupling amongst the components of the dynamical system behind the present geomagnetic field generation another consequence would be that many computations usually undertaken with many difficulties in the phase space can be made in the conventional time domain we analyse the temporal behaviour of the deviation between predictive and definitive geomagnetic global models for successive intervals from 1965 to 2010 finding a similar exponential growth with time also going back in time at around 1600 and 1900 by using the gufm1 model confirms the same findings this result corroborates previous chaotic analyses made in a reconstructed phase space from geomagnetic observatory time series confirming the chaotic character of the recent geomagnetic field with no reliable prediction after around 6 years from definitive values and disclosing the potentiality of estimating important entropic quantities of the field by time averages although more tests will be necessary some of our analyses confirm the efforts to improve the representation of the geomagnetic field with more detailed secular variation and acceleration

interpretation of an aeromagnetic survey of the spanish mainland abstract an aeromagnetic survey of the spanish mainland was carried out in 1987 a first interpretation of this survey is given here with particular reference to the structure and tectonic development of the spanish part of the iberian peninsula this involves the integration of the geophysical interpretation where possible with the current understanding of the tectonic framework as determined from previous geological and geophysical investigations of particular interest is the apparent structural symmetry and the possible manner in which this might be associated with the generally acknowledged structural units of spain this gross structural symmetry even seems to extend to the northern and southern coastlines where the magnetic responses are somewhat similar in character from a magnetic point of view the spanish mainland appears to be dominated by a series of sub circular structures about an ese wnw axis centered on the gredos mountains and remaining open in the axial direction into portugal

interaction between local tectonics and glacial unloading on the pacific margin of canada abstract variations in late quaternary coastal deformation along the pacific margin of canada reflect not only differences in glacial history but also local non glacial tectonics a forebulge developed to the north in the queen charlotte basin qcb from 13 2 until after 9 7 ka bp resulting in exposure of the currently submerged shelf whereas similar exposure was not evident to the south in the georgia basin a semi quantitative effective elastic lithosphere thickness of between 10 and 20 km is estimated for the qcb we propose that this warm relatively thin lithosphere combined with tectonic movement influenced crustal displacement particularly the decoupling of the north american plate along the queen charlotte qc fault which may have allowed the qcb to behave like a hinge in response to glacial unloading this would explain large magnitude crustal tilting 2 1 m km 1 observed adjacent to the qc fault the 50 m of depression observed in the early and mid holocene may imply that the western edge of the north america plate flexed down below present elevation producing a second wave of response to ice loading and unloading

third generation of the potsdam magnetic model of the earth pomme the potsdam magnetic model of the earth pomme is a geomagnetic field model providing an estimate of the earth s core crustal magnetospheric and induced magnetic fields the internal field is represented to spherical harmonic sh degree 90 while the secular variation and acceleration are given to sh degree 16 static and time varying magnetospheric fields are parameterized in geocentric solar magnetospheric gsm and solar magnetic sm coordinates and include disturbance storm time dst index and interplanetary magnetic field imf by dependent contributions the model was estimated from five years of champ satellite magnetic data all measurements were corrected for ocean tidal induction and night side ionospheric f region currents the model is validated using an independent model from a combined data set of orsted and sac c satellite measurements for the core field to sh degree 13 the root mean square rms vector difference between the two models at the center of the model period is smaller than 4 nt at the earth s surface the rms uncertainty increases to about 100 nt for the predicted field in 2010 as inferred from the difference between the two models

the satellite along track analysis in planetary magnetism summary many physical characteristics of planets such as their topography magnetic and gravitational fields are routinely detected and measured by spacecrafts at satellite altitudes even if little is known about the measured signal it is possible to separate the large scale components from other contributions by a spectral analysis carried out along the spacecraft orbit this procedure which dates back to the early age of the satellite era is routinely applied with spherical harmonics analysis for the study of large scale planetary magnetic fields particularly those that vary rapidly in time in this paper we review the approximations of this procedure for investigating internal and external magnetic fields of planets we show that the magnetic field analyses along the orbits are limited by a finite frequency resolution that is known to introduce a spectral leakage this leakage may lead to artificial spatio temporal variations of the magnetic field such as an apparent internal field secular variation an asymmetry of the magnetospheric field and a regional distortion of the lithospheric field structures we quantify the errors for the earth s lithospheric field and display its distribution in the spatial and the spectral domains we also discuss these limits for the moon and mars lithospheric magnetic fields our analytical results illustrate the pros and cons of the orbit by orbit analyses and should allow us to avoid the pitfall of geophysical overinterpretation of some artificial magnetic field variations

the origin of major incisions within the pleistocene deposits of the north sea a seismic survey to resolve the geometry of major incisions within the upper pleistocene has been run over an area of 1600 km2 in the mid north sea twelve separate incisions have been identified ranging up to 5 km wide and 25 km long with incised depths from 100 to 350 m deposits categorised into four recurring types infill the incisions to form a flat sea bed the surveyed features are comparable to others widely found beneath the northern continental shelves and lowlands of europe asia and america such incisions have a similar range of sizes and shapes were cut during at least three separate periods in the pleistocene and are down cut into substrates of various lithologies ranging from precambrian to pleistocene in age the major incisions are believed to be the product of a singular mechanism the outburst of intra ice sheet lakes forming jokulhlaup plunge pools except for late stage hollow infills which have interglacial temperate deposits the incision infills are periglacial the former deposits are similar to the sediments accumulating in the present day bathymetric enclosed deeps such as the lambay deep and devil s hole found on continental shelves it is suggested that the enclosed deeps are large kettle holes which resulted from the thawing of ice formerly buried in the incision infills