origin of magnetic anomalies in the large ebersbrunn diatreme w saxony germany the ebersbrunn diatreme is a deeply eroded 1 km diatreme structure in western saxony germany at current erosion levels this ultramafic to carbonatitic diatreme is about 2 1 5 km in map view which makes it a large one based on shallow drill cores the diatreme contains coarse unbedded volcaniclastic rocks with up to 80 country rock fragments the diatreme is characterised by positive and negative magnetic anomalies which are controlled mostly by the changing proportions of magnetic minerals in the rocks the magnetic minerals are themselves contained in the juvenile fraction rock magnetic studies on three drill cores one from the magnetic low and two from magnetic highs including bulk susceptibility and its anisotropy temperature dependent susceptibility various remanence measurements natural remanent magnetisation anhysteretic remanence and isothermal remanent magnetisation and alternating field demagnetisation have been performed additionally scanning electron microscope imaging and energy dispersive x ray spectroscopy were performed to better characterise the magnetic minerals magnetisation is caused by titanomagnetite with slightly varying ti contents within all cores samples from the positive magnetic anomalies have a relatively high degree of anisotropy but no preferred orientation of one of the principal axes can be seen the magnetic highs are caused by non bedded volcaniclastic rocks comparatively rich in juvenile particles the negative magnetic anomaly is associated with a compaction like magnetic fabric but without macroscopically visible bedding hence the magnetic low is caused by rocks with a lower content of juvenile material to the authors knowledge this is the first time rock magnetic methods have been applied to diatreme rocks

discovery of the first quaternary maar in the bohemian massif central europe based on combined geophysical and geological surveys abstract based on results of previous investigations of tephra tuff volcaniclastic deposits and a geophysical survey in the surroundings of the elezna h rka quaternary volcano west bohemia we performed detailed geophysical surveys using gravimetry magnetometry and electrical conductivity techniques striking anomalies were revealed in a morphological depression near m tina west bohemia as a strong evidence of the assumed maar diatreme structure the sharp isometric gravity low of 2 30 mgal as well as the corresponding positive magnetic anomaly of 200 nt with a negative rim on its northern side indicate a steeply dipping geological body of low density and containing magnetic rocks minerals magnetic survey also showed pronounced local anomalies outside the depression that can reflect relicts of the tephra rim of the maar this geophysical evidence was then proven by an exploratory drilling near the centre of the gravity anomaly macroscopic on site evaluation of the core and more detailed sedimentological petrochemical palynological and microbiological laboratory analyses further confirmed the existence of a maar structure filled by 84 m of lake sediments reflecting a succession of several warm and cold climatic periods results of palynological analyses confirm the presence of a continuous palaeoclimate archive with at least three successive warmer periods of most probably interstadial character from the upper quaternary saalian complex therefore the recovered sediment sequence holds strong potential for in depth paleoclimate reconstruction and deep biosphere studies at the bottom of the m tina 1 my 1 borehole 84 85 5 m country rock debris was found containing also volcanic bombs and lapilli the discovered volcanic structure is considered to be the first known quaternary maar diatreme volcano on the territory of the bohemian massif because of hidden active magmatic processes in combination with earthquake swarm seismicity ca 20 30 km north of the m tina maar reconstruction of the palaeovolcanological evolution is important for evaluation of hazard potential of the ne and e part of the cheb basin

magnetism in rocks rock magnetism is the study of induced and remanent magnetization of ferrimagnetic mineral grains in rocks sediments soils and organisms its applications include environmental magnetism magnetic anisotropy sources of continental and oceanic magnetic anomalies records of geomagnetic field variations and polarity reversals and the paleomagnetic record of plate motions and the wilson cycle this paper reviews the beginnings of rock magnetism and then traces the development of six particularly interesting areas pseudo single domain behavior magnetic domains and micromagnetic structures diagnostic tests of the type and stability of remanent magnetization magnetic microanalysis thermoviscous remagnetization and chemical remanent magnetization other areas including sediment and soil magnetism are covered in a companion paper by verosub and roberts on environmental magnetism

magnetic properties and emplacement of the bishop tuff california anisotropy of magnetic susceptibility ams and characteristic remanence were measured for 45 sites in the 0 76 ma bishop tuff eastern california thirty three sites were sampled in three stratigraphic sections two in owens gorge south of long valley caldera and the third in the adobe lobe north of long valley the remaining 12 sites are widely distributed but of limited stratigraphic extent weakly indurated highly porous to dense welded ash flow tuffs were sampled saturation magnetization vs temperature experiments indicate two principal iron oxide phases low ti magnetites with 525 570 c curie temperatures and maghemite with 610 640 c curie temperatures af demagnetization spectra of isothermal remanent magnetizations are indicative of magnetite maghemite predominantly in the multidomain to pseudo single domain size ranges remeasurement of ams after application of saturating direct fields indicates that randomly oriented single domain grains are also present the degree of anisotropy is only a few percent typical of tuffs the ams ellipsoids are oblate with kmin axes normal to subhorizontal foliation and kmax axes regionally aligned with published source vents for 12 of 16 locality means kmax axes plunge sourceward confirming previous observations regarding flow sense topographic control on flow emplacement is indicated by the distribution of tuff deposits and by flow directions inferred from kmax axes deposition east of the benton range occurred by flow around the south end of the range and through two gaps benton notch and chidago gap flow down mammoth pass of the sierra nevada is also evident at least some of the adobe lobe in the northeast flowed around the west end of glass mountain eastward flow directions in the upper owens gorge and southeast directions in the lower owens gorge are parallel to the present canyon suggesting that the present drainage has been established along the pre bishop paleodrainage characteristic remanence directions from 45 sites 267 samples yield an overall mean of d 348 i 53 for the bishop tuff a correlation is found in two of the three profiles between density and remanence inclination a mean remanence direction based on 13 localities together with data from uncompacted xenoliths and data from the ash fall tuff at lake tecopa is d 353 i 54 k 172 95 2 9 n 15

magnetic susceptibility zonation of the melilititic riedheim dyke hegau volcanic field germany evidence for multiple magma pulses the olivine melilitic riedheim dyke complex is related to the tertiary alkaline magmatism within the hegau volcanic field magnetic susceptibility measurements and the mineral composition of oxides together with petrographic observations imply two phases of magma intrusion for the emplacement of this dyke the first intrusion forms the eastern and western margins of the dyke section with high magnetic susceptibility values of up to 75 10 3 si which are related to ferrimagnetic mg al cr bearing titanomagnetites with a magnetite component between 0 59 and 0 75 mol a generally lower magnetic susceptibility of up to 45 10 3 si and a significantly lower and homogeneous magnetite component of the titanomagnetites xmt 0 38 mol are recorded for the second intrusion into the central part of the dyke furthermore a dependence of magnetic susceptibility on the amplitude of the ac field was measured which is more pronounced in the second intrusion hd 25 than in the first one 6 hd 10 confirming the magneto mineralogical data secondary pervasive alteration is more pronounced in the first intrusion phase characterised by a very fine grained and glassy matrix that is more receptive to hydrothermal overprint than the well crystallised matrix of the second intrusion localised thermally induced alteration at the intimately fractured contact between the first and second intrusion phase has oxidised the titanomagnetite of the first intrusion phase but did not significantly effect the second intrusion differences between the dyke sections are also documented by the anisotropy of magnetic susceptibility ams which reflects a magmatic flow fabric with long axis of the ams ellipsoids magnetic lineation parallel to the flow direction and short axis normal to the n s trending dyke boundary the orientation of the magnetic fabric for the individual magma pulses is different with a more moderate plunge of the magnetic lineation within both the western 177 57 and eastern parts 181 50 of the first dyke intrusion compared to a nearly vertical orientation in the second central dyke intrusion 180 78 we suggest that the primary crystallisation history of the two intrusion phases caused the magnetic susceptibility zonation in the riedheim dyke complex

curie temperatures of synthetic titanomagnetites in the fe ti o system effects of composition crystal chemistry and thermomagnetic methods 1 the present study is aimed at improving the calibration of the compositional dependence of the curie temperature tc of titanomagnetite tmt on the basis of temperature dependent magnetic susceptibility c t curves measured on synthetic tmts in the fe ti o system in order to assess the possible influence of high temperature cation vacancies onto the tc values we have synthesized two types of assemblages in subsolidus conditions at 1 bar 1100c and 1300c under controlled oxygen fugacity conditions tmts synthesized in equilibrium with ilmenite hematitess ilmss are expected to have the highest vacancy concentrations those in equilibrium with wustite wus the lowest the composition and homogeneity of the synthetic tmts were carefully checked with a scanning electron microscope sem and an electron microprobe emp tc was determined from c t curves using a kappabridge and for comparison from ms t curves measured with a variable field translation balance our data set shows systematically higher tc values for tmt coexisting with ilmss than for tmt coexisting with wus most c t curves are nonreversible whereby the largest dtc 40 k concern tmt ilmss o f intermediate compositions synthesized at 1300c nonreversibility is interpreted as reflecting cation reordering in tmt during the high temperature c t measurements tc values obtained from ms t curves are higher than those obtained from the c t curves whereby the difference regularly increases up to 40 k with increasing ti content up to xusp 0 6 our new calibration curves are suitable to retrieve tmt compositions in basalts that were rapidly cooled and not oxidized by deuteric or hydrothermal fluids citation lattard d r engelmann a kontny and u sauerzapf 2006 curie temperatures of synthetic titanomagnetites in the fe ti o system effects of composition crystal chemistry and thermomagnetic methods j geophys res 111 b12s28

evidence for ascending upper mantle derived melt beneath the cheb basin central europe 1 we present new 3he 4he data of co2 rich gas exhalations of three presently nonvolcanic areas in europe the 3he 4he ratios from the cheb basin czech republic are clearly higher than data obtained ten years ago whereas the 3he 4he ratios from the other areas laacher see germany and marianske lazn cr have remained nearly constant no other locality showing such high 3he 4he ratios in free gases supplied by continental mantle degassing is known in the european cenozoic rift system at the northeastern edge of the cheb basin swarm earthquakes repeatedly occur in the context of contemporaneous periods of seismicity the increased 3he 4he ratios are interpreted as the first geochemical evidence for ascending mantle derived melt beneath the cheb basin which is related to the triggering of earthquake swarms

field dependence of ac susceptibility in titanomagnetites abstract ac susceptibility measurements as a function of field amplitude hac and of frequency show a strong field dependence for a set of synthetic titanomagnetites fe3 xtixo4 and for certain basalts from the soh 1 hawaiian drill hole and from iceland in phase susceptibility is constant below fields of about 10 100 a m and then increases by as much as a factor of two as hac is increased to 2000 a m both the initial field independent susceptibilities and the field dependence of susceptibility are systematically related to composition initial susceptibility is 3 si for a single crystal sphere of tm0 x 0 and decreases with increasing titanium content field dependence is nearly zero for tm0 and increases systematically to a maximum near tm60 x 0 6 this field dependence can in some cases be mistaken for frequency dependence and lead to incorrect interpretations of magnetic grain size and composition when titanomagnetite is present

emplacement temperatures of pyroclastic and volcaniclastic deposits in kimberlite pipes in southern africa palaeomagnetic techniques for estimating the emplacement temperatures of volcanic deposits have been applied to pyroclastic and volcaniclastic deposits in kimberlite pipes in southern africa lithic clasts were sampled from a variety of lithofacies from three pipes for which the internal geology is well constrained the cretaceous a k1 pipe orapa mine botswana and the cambrian k1 and k2 pipes venetia mine south africa the sampled deposits included massive and layered vent filling breccias with varying abundances of lithic inclusions layered crater filling pyroclastic deposits talus breccias and volcaniclastic breccias basalt lithic clasts in the layered and massive vent filling pyroclastic deposits in the a k1 pipe at orapa were emplaced at 570 c in the pyroclastic crater filling deposits at 200 440 c and in crater filling talus breccias and volcaniclastic breccias at 560 c although the interpretation of these results is hampered by the presence of mesozoic magnetic overprints these temperatures are comparable to the estimated emplacement temperatures of other kimberlite deposits and fall within the proposed stability field for common interstitial matrix mineral assemblages within vent filling volcaniclastic kimberlites the temperatures are also comparable to those obtained for pyroclastic deposits in other silicic volcanic systems because the lithic content of the studied deposits is 10 30 the initial bulk temperature of the pyroclastic mixture of cold lithic clasts and juvenile kimberlite magma could have been 300 400 c hotter than the palaeomagnetic estimates together with the discovery of welded and agglutinated juvenile pyroclasts in some pyroclastic kimberlites the palaeomagnetic results indicate that there are examples of kimberlites where phreatomagmatism did not play a major role in the generation of the pyroclastic deposits this study indicates that palaeomagnetic methods can successfully distinguish differences in the emplacement temperatures of different kimberlite facies

pyroclastic flow deposits from a kimberlite eruption the orapa south crater botswana abstract the orapa diamond mine republic of botswana exposes a bi lobate kimberlite pipe that erupted during the late cretaceous epoch 93 ma through archaean basement and volcano sedimentary rocks of the karoo supergroup geological mapping of the crater zone of the south pipe has revealed a 15 25 m thick in situ kimberlite pyroclastic flow deposit the pyroclastic deposit fills in the crater and completely drapes lower units indicating that the parent flow originated from an adjacent kimberlite pipe the unit comprises a basal coarse lithic concentration layer exhibiting imbricated clasts which grades upwards into massive poorly sorted lapilli tuff the tuff contains abundant sub vertical degassing structures defined by lithic enrichment and depletion in fine grained material degassing structures commonly emanate from blocks in the basal layer the presence of degassing structures and a coarse basal layer distinguishes this deposit from pipe filling massive volcaniclastic kimberlite which is typically homogeneous in terms of texture and clast size over distances on the order of 100s of metres studies of the thermal remanent magnetism in basalt clasts from the deposit together with serpentine diopside assemblages indicate that it was emplaced at elevated temperatures on the order of 200 440 c consistent with deposition from a pyroclastic flow the lithofacies characteristics can be explained by the interaction of the pyroclastic flow with the complex topography of a pre existing crater

co2 discharge in an active non volcanic continental rift area czech republic characterisation δ13c 3he 4he and quantification of diffuse and vent co2 emissions abstract in the western eger rift er area along the pocatky plesna fault zone ppz co 2 degassing occurs predominantly within two mofette fields bublak and hartousov we studied 27 wet mofettes belonging to these mofette fields for gas emission rates repeatedly between 2007 and 2009 and selected mofettes for gas composition and isotope ratios 13 c 3 he 4 he detailed ground mapping along the ppz provided further two separated diffuse degassing structures dds within the mofette fields hartousov and bublak the dds hartousov was studied in detail by measurements of 682 co 2 soil gas concentrations 762 co 2 soil gas fluxes max 10 grid spacing and partly by analyses of isotope ratios 13 c 12 c 3 he 4 he of soil gas at the dds hartousov the total co 2 soil flux yielded 1 559 t m 2 d 1 in spring 2009 and the co 2 emission rate at the wet mofettes of hartousov mofette field yielded 0 62 t d 1 the total co 2 discharge of the 27 wet mofettes was 3 75 t d 1 at sites with high co 2 soil flux the portion of mantle derived helium is in the same range as the releasing at wet mofettes both cover the signature of the subcontinental mantle also the 13 c values analysed in the gas releasing from wet mofettes and those analysed in soil gas are nearly the same taking in account a biogenic soil co 2 flux of 25 g m 2 d 1 as background the mantle derived co 2 flux yielded approximately 1566 t m 2 d 1 as a result of the co 2 flux mapping of the dds hartousov it could be proved that 97 4 of the released soil co 2 1 518 t m 2 d 1 stems from sites with co 2 fluxes higher than 500 g m 2 d 1 pointing to dominantly fault related co 2 release at the central mofette bublak b2 the gas emission rate was determined for the first time in 1993 measurements repeated between 2007 and 2009 showed a clear increase in the gas emission rate of more than 40 correlating well with the increase of the 3 he 4 he ratios from 5 ra to approximately 6 ra between 1993 and 2008 at this location brauer et al 2009 the bublak mofette field is characterised by the highest co 2 emission rate along the ppz and in combination with the helium isotope signature of the european subcontinental mantle this area was identified as a deep reaching fluid injection zone

investigation of the inner structure of la crosa de sant dalmai maar catalan volcanic zone spain abstract la crosa de sant dalmai volcano is the largest volcanic edifice of the catalan volcanic zone ne spain it is a very well preserved maar type structure 1 5 km in diameter excavated at the contact between a hard substrate and a soft substrate formed by palaeozoic granites and pliocene and quaternary gravels respectively in order to infer the uppermost inner structure of la crosa de sant dalmai maar and to characterise its main geological and tectonic constraints we have performed a multiparametric geophysical study including gravimetry magnetometry self potential and electrical resistivity tomography the results obtained together with a field geology revision and additional geological data from two drill cores provide a detailed picture of the post eruptive maar infill sequence as well as of the uppermost part of the maar diatreme structure this information helps in understanding the origin and subsequent evolution of the volcano which included an alternation of phreatomagmatic and strombolian phases geophysical data show that the last strombolian phase which culminated with the formation of a scoria cone inside the maar was associated with a nw se trending regional fault the little erosion and degradation of the original tephra ring suggest a much younger age of la crosa de sant dalmai maar than was previously stated

detailed study on the anisotropy of magnetic susceptibility of arctic marine sediments summary five sediment cores from three different areas the jan mayen fracture zone in the greenland sea the fram strait and the makarov basin in the arctic ocean have been subjected to a detailed analysis of the magnetic fabric by analysing their anisotropy of magnetic susceptibility ams as a supplementary parameter to already existing palaeo and rock magnetic data sets intervals of reversed inclinations documented within the five cores can be interpreted as geomagnetic excursions because all the investigated sediments are characterized by an undisturbed magnetic fabric as expected for layered sediments that is an oblate anisotropy ellipsoid with its short principal axis oriented vertically excursional directions are also not associated with significant changes in rock magnetic parameters however cores from the arctic ocean in particular exhibit a strong cyclicity in their anisotropy parameters here sand rich layers are characterized by a low anisotropy whereas clay rich layers yielded highest anisotropy degrees of up to 9 per cent indicating an ams mainly controlled by the matrix properties of the sediment a simple three axis determination of the anisotropy of anhysteretic remanent magnetization aarm on one of these cores surprisingly yielded an even higher degree of anisotropy of the ferrimagnetic fraction of up to 18 per cent i e twice as high as determined for the susceptibility which is also influenced by the paramagnetic fraction this implies a strong contribution of this sediment fraction to the overall magnetic susceptibility of the investigated arctic ocean deposits

lithofacies succession of maar crater deposits in the eifel area germany maar craters often contain exceptionally preserved fossils and maar sediments may reflect detailed environmental changes volcanosedimentary processes in a middle eocene maar crater lake are illustrated by the deposits of eckfeld maar in the tertiary hocheifel volcanic field rhenish massif germany the maar origin of the basin is evident from a circular negative gravity anomaly which indicates a low density funnel shaped basin filling from the facies analysis of an eocene eckfeld and a pleistocene dottingen maar we develop a lithozone classification for the interpretation of maar sediments syn post eruptive breccias are followed by a fining upwards sequence of lacustrine mud with coarse layers and final swamp deposits from the facies analysis and regional geological data we reconstruct the pre to post eruptive history of a maar crater prior to post eocene uplift these observations can be used for the interpretation of tertiary and quaternary maar craters that are ideal fossil and sediment traps

rock magnetism of late neogene and pleistocene deep sea sediments relationship to sediment source diagenetic processes and sediment lithology we use bivariate scatter plots to illustrate variations in selected rock magnetic properties low field susceptibility anhysteretic and isothermal remanence of late neogene and pleistocene deep sea sediments from 16 sites in the arctic ocean north atlantic equatorial atlantic and north pacific ocean and the arabian sea our intention is to examine the ability of the rock magnetic properties to differentiate the sediments according to factors such as lithology geographical area and the dominant mode of terrigenous sedimentation which at these sites is via ice rafting via bottom currents or via eolian processes overall correlations between sediment magnetic properties and gross lithology is poor and factors such as the source and transport path of terrigenous sediment and detrital magnetic minerals together with the action of reductive diagenetic processes are the major controls on the magnetic properties on the bivariate scatter plots sites with major ice rafted contributions tend to have high sedimentary ferrimagnetic mineral concentrations relatively coarse ferrimagnetic grain sizes and scattered sample point distributions in contrast sites where we infer significant bottom current supply of terrigenous material have tightly grouped sample point distributions carbonate sediments in which the terrigenous component is supplied by eolian processes tend to have a broad range of magnetic mineral concentration caused by glacial interglacial fluctuations in carbonate accumulation and eolian activity sediments containing significant volcanogenic material have high concentrations of relatively coarse grained ferrimagnetic material reductive diagenesis is a significant determinant of sediment magnetic properties in high productivity areas and has the effect of preferentially removing the fine grained ferrimagnetic fraction causing a coarsening of the ferrimagnetic grain size distribution and a rise in the antiferromagnetic ferrimagnetic ratio

maar diatreme volcanoes a review maar diatreme volcanoes are produced by explosive eruptions that cut deeply into the country rock a maar is the crater cut into the ground and surrounded by an ejecta ring while the diatreme structure continues downward and encloses diatreme and root zone deposits here we attempt an evenhanded review of maar diatreme volcanology that extends from mafic to kimberlitic varieties and from historical maar eruptions to deeply eroded or mined diatreme structures we conclude that maar diatreme eruptions are episodic ejecta rings provide invaluable insight into eruption processes and sequence but are incomplete records of diatreme formation deposits within the diatreme structure include in varying proportions lower unbedded deposits sometimes typified by subvertical contacts among domains of debris emplaced sequentially and upper bedded deposits formed by sedimentation on surfaces open to the atmosphere a basal root zone comprises the transition from coherent magmatic feeder dike to clastic deposits formed by fragmentation of magma and enclosing country rock root zones are irregular in form and the clastic deposits are typically intruded by contorted dikes irregular root zone like chaotic breccias cut by contorted dikes are also present within diatreme deposits where they represent intra diatreme fragmentation zones and record changes in the location of the explosion locus during eruption

detailed investigation of preserved maar structures by combined geophysical surveys the detection of completely preserved maar structures is important not only for underground mapping but also for paleoclimate research because laminated maar lake sediments may contain a very detailed archive of climate history objective evidence for the existence of such structures can only be provided by geophysics and boreholes the combination of gravity and magnetic ground surveys appears to be an excellent tool to detect and identify buried maar structures their prominent properties are an almost circular gravity minimum corresponding to a crater filled with limnic sediments of low density and a magnetic anomaly caused by a pyroclastic or basaltic body in the diatreme which indicates the volcanic character seismic measurements provide the most detailed information about the internal structure of the maar sediments zones of low seismic reflectivity and very low density represent sediments of the late maar lake period the early lake period is indicated by debris flow deposits and turbidites represented by seismic reflectors the seismic sections clearly reveal the bowl like structure of the maar outside this bowl like structure there are only a few reflections which represent the basement taking into account the shape of the gravity anomaly seismic information allows geometrical modelling of the maar structure optimal drilling sites can be selected based on the results of geophysical surveying comparing the results of combined geophysical surveys above two maar structures of different ages yields a marked similarity in their geophysical pattern

emplacement of magma in eastern iceland dikes insights from magnetic fabric and rock magnetic analyses abstract the anisotropy of magnetic susceptibility ams coupled with mineral magnetic identification has been investigated in about 640 samples from 27 basaltic dikes of tertiary age in eastern iceland the dikes are a few meters thick and they have been sampled all across three types of magnetic fabrics with well defined mean principal axes of anisotropy are recognized in the first one the maximum axis is vertical and the minimum axis coincides with the pole of the dike plan geometrically normal fabric the second fabric shows opposite orientation geometrically inverse fabric the third type is when these two fabrics coexist with the normal one at the margins and the inverse one in the center of the dike mixed fabric no relationship is observed between the type of fabric and the width of the dikes each fabric is carried by clear magnetic assemblages made of low x 0 15 ti content fine grained magnetites for the normal one and high ti content around tm60 coarse magnetite grains for the inverse fabric upon heating the magnetic properties and the orientation of the anisotropy ellipsoid characterizing the inverse fabric in the mixed dikes change and evolve toward the normal type these two geometrically normal and inverse fabrics are interpreted as primary ones representing different physico chemical conditions during the emplacement of the magma the ams results indicate that during the volcanic events occurring about 10 myr ago the extrusion of the magma was vertical at the depth of the studied sites in eastern iceland

monitoring aseismic tectonic processes via hydrologic responses an analysis of log periodic fluid flow events at the costa rica outer rise a log periodic series of fluid inflow events from the outer rise off the nicoya peninsula costa rica was recorded on a flow meter deployed at the sediment surface similar periodic series have been seen in many failure processes in laboratory and field research including seismic and chemical records preceding earthquakes each cycle has the appearance of an impulse and subsequent decay the hypothesis that the recorded flow pattern is a result of a series of relatively small strain events resulting from aseismic extensional faulting of the outer rise basement is explored and analytical results supporting this hypothesis are presented

greigite detected as dominating remanence carrier in late pleistocene sediments lisan formation from lake kinneret sea of galilee israel summary a rock magnetic investigation of three sedimentary cores of lisan formation of late pleistocene age from lake kinneret sea of galilee northern israel demonstrates that the magnetization of these sediments is controlled by various degrees of a secondary chemical remanent magnetization crm carried by greigite fe3s4 this crm is superimposed on a primary detrital remanent magnetization drm that resides in ti magnetite this finding is independently confirmed by x ray diffraction xrd measurements performed on magnetic extracts of the sediments the domain state of the greigite is largely single domain behaviour sd thus dominating the magnetization therefore the magnetic record retrieve from of these sediments is not reflecting geomagnetic variations but rather chemical rock magnetic properties resulting from diagenetic processes the results of our study suggest that paleomagnetic record of greigite bearing sediments should be interpreted with caution because of the following reasons 1 geomagnetic secular variations can be biased due to large coercivity overlap between magnetite and greigite 2 alternating field af demagnetization can produce erroneous directions due to vector distortion by acquisition of a gyro remnant magnetization grm 3 estimation of relative paleointensity can be hampered by large scale variations in natural remnant magnetization nrm intensity caused by the acquisition of a secondary crm of unknown age and unknown extent superimposed on the drm the precipitation of greigite requires reducing conditions at the sediment water interface and or interstitial water associated with the presence of sulphur and iron oxides reducing conditions are typical of stratified lakes and other stratified water bodies such as the dead sea paleo lake lisan temporarily the eastern mediterranean sea the caspian sea the black sea and many other marine basins according to our findings paleomagnetic records from such environments carried dominantly by greigite therefore should be treated with care