geomagnetic field for 0 3 ka 2 a new series of time varying global models 1 steadily increasing numbers of archeomagnetic and paleomagnetic data for the holocene have allowed development of temporally continuous global spherical harmonic models of the geomagnetic field extending present and historical global descriptions of magnetic field evolution the current work uses various subsets of improved data compilations details of which are given in a companion paper by donadini et al 2009 and minor modifications of standard modeling strategies using temporally and spatially regularized inversion of the data and cubic spline parameterizations for temporal variations to produce five models with enhanced spatial and temporal resolution for 0 3 ka spurious end effects present in earlier models are eliminated by enforcing large scale agreement with the gufm1 historical model for 1650 1990 a d and by extending the model range to accommodate data older than 3 ka age errors are not considered as a contribution to data uncertainties but are included along with data uncertainties in an investigation of statistical uncertainty estimates for the models using parametric bootstrap resampling techniques we find common features but also significant differences among the various models indicating intrinsic uncertainties in global models based on the currently available holocene data model cals3k 3 based on all available archeomagnetic and sediment data without a priori quality selection currently constitutes the best global representation of the past field the new models have slightly higher dipole moments than our previous models virtual axial dipole moments vadms calculated directly from the data are in good agreement with all corresponding model predictions of vadms these are always higher than the spherical harmonic dipole moment indicating the limitations of using vadms as a measure of geomagnetic dipole moments

could the conventionally known abu roash g reservoir upper cenomanian be a promising active hydrocarbon source in the extreme northwestern part of egypt palynofacies palaeoenvironmental and organic geochemical answers abstract in different areas of the western desert of egypt the abu roash g member exhibits either a reservoir or source affinity thus thirteen cutting samples covering the abu roash g member were selected from the nest 1a well at matruh basin to investigate its hydrocarbon source potential palynological age dating of the section that is calibrated with foraminifera and ostracodes enabled a proper identification of the g member detailed analysis of the vertical distribution of particulate organic matter of this member shows two palynofacies types pf 1 reflects an outer middle shelf depositional environment of prevailed reducing suboxic anoxic conditions for the organic rich shales of the lower g member samples 1 8 while pf 2 reflects a minor regression that resulted in deposition of another organic rich shales of the upper g member samples 9 13 in an inner middle shelf setting under the same prevailing reducing suboxic anoxic conditions organic geochemical analysis reveals good to very good potential of the g member as a hydrocarbon source rock 1 8 2 41 avg 2 15 total organic content wt it also shows good to very good petroleum potential pp 4 8 11 avg 8 mg hc g rock pyrolsis and palynofacies analyses show kerogen type ii for the lower g member samples 1 8 which is characterized by high hydrogen index hi 396 and 329 mg hc g toc at depths 1500 and 1560 m and very high dominance of oil prone material amorphous organic matter aom marine palynomorphs and sporomorphs and very rare occurrence of gas prone material brown phytoclasts the upper g member samples 9 13 shows kerogen type ii iii which is characterized by a lower hi value of 213 mg hc g toc at depth 1340 m and it contains fewer amounts of gas prone material and relatively lower aom and marine palynomorphs in comparison to the upper g member maturation parameters t max 430 433 c production index pi 0 1 mg hc g rock and thermal alteration index tai 2 indicate the lower g member has already entered the early oil window kitchen and it is expected to produce oil the upper g member is expected to produce only oil with no gas shows because it is marginally mature t max 426 c pi 0 2 tai 2 the source potential index spi 5 3 t hc m 2 of the g member shows it as currently generating moderate quantities of oil in the area of nest 1a well consequently the organic rich shales of the g member are suggested here as a promising active oil source rock in that extreme northwestern part of the western desert of egypt however for commercial oil recovery from the abu roash g member it is highly recommended to explore the depocentre of matruh basin at about 150 km east the nest 1a well

palynological palaeoenvironmental and sequence stratigraphical analyses of a turonian coniacian sequence beni suef basin eastern desert egypt implication of pediastrum rhythmic signature abstract sixteen samples from the e to b members of the abu roash formation encountered in the beni suef basin eastern desert of egypt were palynologically analyzed for palaeoenvironmental and sequence stratigraphic investigations the integrated palynofacies and lithofacies analysis of the studied section indicates deposition of five alternating regressive and transgressive sequences in well oxygenated proximal shelf settings the abu roash e and the upper d to the lower c members were deposited during pronounced regressive phases in oxic shallow marginal marine settings the upper b member was deposited during a recurring regressive phase but of a lower magnitude in oxic shallow inner neritic conditions the lower d member was deposited during a minor transgression phase in dysoxic shallow inner neritic settings while the upper c to the lower b section was deposited during a stronger transgressive episode in a relatively deep inner neritic environment of prominent dysoxic conditions this interchange in the depositional setting was documented by the pronounced and concurrent cyclic nature of the freshwater algae peridinioid dinoflagellate cysts pteridophyte spores and reworked sporomorphs with variable intensities their increasing and conversely their diminishing trends clearly reflect alternating regressive transgressive periods of reduced and relatively normal salinity conditions respectively overall sedimentation of the studied abu roash section indicates a recurring rise in sea level which accentuated during the earliest santonian time the analogous peaking in the pediastrum signals with those of the pteridophyte spores and reworked taxa indicate a good connection between these pediastrum signals and the pronounced fluviatile influxes of terrigenous sediments during regressive phases accordingly this can be used to identify regressive sequence boundaries and hence the clastic reservoirs even with the small counts recorded herein we believe high ratios of peridinioid gonyalulacoid dinocysts are significantly paralleled by peaking signals of freshwater algae and regressive sedimentation phases this must be preliminary documented here probably future palynological studies will be able to fully interpret and address this important pediastrum rhythmic event in different sequence stratigraphic settings the palynological parameters age controlled sporomorph marker taxa lithology and gamma ray data were used to differentiate the abu roash members into three distinctive 3rd order depositional sequences ar sq1 ar sq2 and ar sq3 these sequences match well with the global stratigraphic sequences tu 3 tu 4 and co 1 and connect the local rise in sea level to the global eustatic sea level rise

palaeoenvironmental analysis of late cretaceous dinoflagellate cyst assemblages using high resolution sample correlation from the western interior basin usa abstract the cretaceous geological record of the western interior seaway of north america is one of the most thoroughly studied in the world extensive work on the lithostratigraphy biostratigraphy and geochemistry has resulted in a high resolution chronostratigraphic framework allowing precise bed by bed correlation between sections hundreds of kilometres apart late cenomanian to early turonian marine strata from five sites along a transect from arizona to kansas have been analysed for their palynological assemblages at the time of deposition the sites are thought to have been palaeoenvironmentally very different in terms of shoreline proximity bathymetry and salinity precise correlation of samples between the sites using the high resolution stratigraphy has provided a valuable testing ground for a comparison of the dinoflagellate cyst assemblages a number of species are determined to have palaeoenvironmental preferences in terms of salinity and shoreline proximity and this is supported by integration with the lithostratigraphy macropalaeontology micropalaeontology and geochemistry previous palaeoenvironmental interpretations suggest that one kansas site had comparatively much higher levels of primary productivity and this is reflected in the high ratio at this site of peridinioid to gonyaulacoid cysts the high resolution correlation also shows that a number of the biostratigraphically useful dinoflagellate cyst taxa had synchronous or near synchronous range tops and bases across the basin this integrated high resolution study with tight chronostratigraphic control supports the use of dinoflagellate cysts not only as biostratigraphic tools but also for palaeoenvironmental and palaeoecological interpretation

integrating palynological and geochemical data in a new approach to palaeoecological studies upper cretaceous of the banterwick barn chalk borehole berkshire uk abstract the dinoflagellate cyst record from an upper cretaceous uppermost cenomanian upper coniacian chalk core drilled at banterwick barn berkshire is described and statistically correlated with elemental and stable isotope bulk sediment geochemical data from the same core seventy two dinocyst species and subspecies are recorded and stable carbon and oxygen isotopic 13 c 18 o trends are documented lithostratigraphy and chemostratigraphic correlation of the 13 c curve with an expanded section at dover kent are used to identify stratigraphically significant marls and determine the positions of macrofossil zones and stage boundaries in the banterwick barn core these data indicate that 30 m of chalk at dover are represented by senoniasphaera rotundata alveolata is proposed which has a fad in the lower turonian and last appears lad in the lower coniacian senoniasphaera rotundata rotundata autonym herein has its fad in the middle turonian first common occurrence in the uppermost turonian and lad in the upper coniacian an extremely impoverished assemblage of dinocysts in the highest cenomanian to lowest turonian is considered to be largely a preservational artefact of intraclastic nodular and calcarenitic chalks and is not related directly to the well documented global oceanic anoxic event oae2 occurring at that time 93 5 ma a sharp increase in dinocyst abundance in the lower turonian corresponds with a change in lithology to more marly chalks a gradual decrease in the number of species is observed through the middle turonian to upper coniacian 18 o records show that this was associated with global climatic cooling cluster analysis of the dinocyst abundance record with geochemical data indicates four distinct species groups with characteristic geochemical associations i e groups 1 4 groups 1 and 2 are associated with phases of increased siliciclastic supply a positive correlation with higher 13 c values differentiates the latter group 3 is independent of carbonate and detrital input and group 4 is associated with high carbonate flux and low detrital supply these groupings suggest that cyst forming dinoflagellates exhibited a range of ecological niches in the late cretaceous although the relationship between the encystment process and the geochemical associations is unclear key environmental factors are likely to be sea level and climate related including water depth turbidity nutrient supply sea surface temperature and environmental stability predictability integrated geochemical and palynological studies have great potential for inter regional correlation and palaeoenvironmental interpretation

archaeomagnetic results from southern italy and their bearing on geomagnetic secular variation archaeodirectional results from kilns and other baked structures in southern italy are presented they are generally compatible with the much larger data sets from france and bulgaria in particular a summary of all the results associated with the well known eruption of vesuvius that destroyed pompeii n 9 d 355 i 5 8 95 1 5 provides a reliable archaeomagnetic anchor point supporting the french and bulgarian master curves it is extremely well constrained in time and it comprises independent studies carried out in four different countries furthermore it is derived from a diverse set of features agreement amongst which argues strongly against significant perturbations due to magnetic refraction structural disturbance or depositional shallowing in terms of geomagnetic secular variation we interpret the western european archaeomagnetic data summarized here in terms of an open loop caused by westward drift followed by an inclination low spanning the first few centuries ce representing the signal of a static flux pulse that reaches a maximum magnetic moment of a few percent of the earth s main central dipole 2005 elsevier b v all rights reserved

detection and extraction of fault surfaces in 3d seismic data we propose an efficient method for detecting and extracting fault surfaces in 3d seismic volumes the seismic data are transformed into a volume of local fault extraction lfe estimates that represents the likelihood that a given point lies on a fault surface we partition the fault surfaces into relatively small linear portions which are identified by analyzing tilted and rotated subvolumes throughout the region of interest directional filtering and thresholding further enhance the seismic discontinuities that are attributable to fault surfaces subsequently the volume of lfe estimates is skeletonized and individual fault surfaces are extracted and labeled in the order of decreasing size the ultimate result obtained by the proposed procedure provides a visual and semantic representation of a set of well defined cleanly separated one pixel thick labeled fault surfaces that is readily usable for seismic interpretation

abnormal shallow palaeomagnetic inclinations from the 1950 and 1972 lava flows hawaii summary high precision palaeomagnetic sampling and measurements of 1950 mauna loa lava flows hawaii show as noted by other workers a significantly low inclination compared to the geomagnetic direction expected from available observatory data such shallow inclinations appear related to the unusually high intensity of magnetization of the 1950 basalt resulting in a high magnetic refraction for the lava flows considered other altered palaeomagnetic directions both inclination and declination on kilauea 1972 flows possibly result from displacements during and or after cooling erroneous palaeomagnetic direction imprints do not appear to be the rule

integrated palynological organic geochemical and sequence stratigraphic analyses of the middle to upper cenomanian hydrocarbon reservoir source abu roash g member a depositional model in northwestern egypt abstract the current investigation provides further insight into the petroliferous characteristics of the abu roash g member which is regarded as an important rock unit for the egyptian oil industry forty seven samples covering the g member were selected from the bed 14 1 and bed 2 4 wells in the abu gharadig basin and from the abu tunis 1x well in the matruh basin both of which are located in the north western desert an independent dating of the g rocks of bed 2 4 by benthic foraminifera and ostracods in addition to palynological dating suggests a middle late cenomanian age and provides the biochronostratigraphic framework for the sequence stratigraphic analysis analysis of the vertical distribution of particulate organic matter defines three palynofacies types pf pf 1 represents the basal g where shales of the bed wells and calcareous shale of abu tunis 1x were deposited during a relative sea level rise in an outer middle shelf environment that experienced a notable high primary productivity prevailing reducing suboxic anoxic conditions supported preservation of very high amounts of amorphous organic matter aom in pf 1 pf 2 is equated to shales of the middle g of bed 14 1 and bed 2 4 and to calcareous shales and limestone of the upper g in abu tunis 1x pf 2 was deposited during a relative sea level fall in an inner middle shelf setting under better developed suboxic anoxic conditions pf 3 corresponds to the upper g of bed 14 1 and bed 2 4 and represents the shallowest setting where sandy and silty shales were deposited during a pronounced sea level fall in an inner shelf environment the same suboxic anoxic conditions were prevailing during deposition of pf 3 three bioevents were recorded which could be of palaeoecological and or biostratigraphic significance these are senegalinium aenigmaticum dinopterygium cladoides peak dinopterygium cladoides dinopterygium alatum peak and an acme of classopollis brasiliensis sequence stratigraphy of a transect of the four studied sections was carried out to understand the response of the particulate organic matter distribution and depositional system to the sea level changes three third order depositional genetic sequences were recognized and correlated with the global sea level curve kce 2 kce 3 and kce 4 the early highstand systems tract ehst of the genetically related kce 3 in all wells is characterized by relatively rich organic matter where combined remarkably low water circulation and insignificant dilution of organic matter with coarse terrigenous material probably supported good preservation of organic matter spatial distribution of the g rocks shows lateral facies changes this was inferred from sedimentation of an organic poor avg 0 8 toc wt coarse clastic sandy shales facies in the studied area in abu gharadig basin sedimentation changes laterally into a northeast and northwest organic rich finer clastic shale calcareous shales and argillaceous limestone facies in the western matruh basin the robust anoxic conditions and very low dilution of organic matter by terrigenous influx enhanced the organic richness avg 2 4 toc wt of these rocks which resulted in the formation of promising hydrocarbon source rocks thus for a successful hydrocarbon exploration in the north western desert the promising source section of the g member would be associated with shales calcareous shales and argillaceous limestone lithologies its depositional environment is mainly confined to outer middle and inner middle shelf settings that have widespread suboxic anoxic conditions and show ehst pattern in contrast the regressive intervals that are denoted by the lowstand systems tract lst and or the late hst lhst typify the relatively coarse clastics as good quality reservoir rocks that are characterized by poor organic richness due to dilution with terrigenous influx

the use of cyclic stratigraphic pattern of peridinioid and gonyaulacoid dinoflagellate cysts in differentiating potential thick monotonous carbonate reservoirs a possible ecostratigraphic tool under test abstract the current work used the conventional peridinioid gonyaulacoid ratio p g to devise a new concept of dinoflagellate cyst zonation called the dinoflagellate ecological zone dez which is based here on the peridinioid ecological zone pez and gonyaulacoid ecological zone gez the pez and gez were used successfully to further divide the thick monotonous carbonate succession mid cenomanian to campanian in q 72 1x well in the eastern desert of egypt into smaller ecozones pez and gez are practical and easy to use in subdividing large conventional biozones of the carbonate reservoirs into distinguishable smaller ecozones when a finer resolution is necessary on a reservoir scale for production demands this tool is suggested to be used in the hydrocarbon exploration industry with minimum knowledge of the taxonomy of the dinoflagellate cysts the proposed pez and gez are related to local ecological conditions within the basin hydrocarbon field i e can be traced out laterally in an intra basinal scale this tool can be applied to any carbonate reservoirs in any petroliferous basin worldwide moreover the p g ratio the relative abundances of the dinoflagellate cyst assemblages and other palynological parameters were used successfully to reveal the palaeodepositional settings of the identified pez and gez alternating transgressive and regressive phases were identified although a dissimilar species composition is observed in each of these ecozones environments were interchanging between the regressive marginal marine to proximal inner neritic and the transgressive distal inner to middle shelf settings three peridiniacean dinoflagellate cyst peaks were recorded the middle cenomanian subtilisphaera peak the middle coniacian isabelidinium chatangiella and manumiella peak and the middle santonian isabelidinium peak

dinoflagellate cysts paleoproductivity and upwelling systems a late cretaceous example from israel abstract diverse assemblages of dinoflagellate cysts occur in coniacian maastrichtian sedimentary sequences in israel which represent the inner shallower and outer deeper seaward belt of a late cretaceous upwelling system along the margin of the southern tethys the assemblages are composed mainly of peridinioid p and gonyaulacoid g cysts in varying concentrations it is suggested that the observed fluctuations in the numerical peridinioid gonyaulacoid p g cyst ratio reflect mainly changes in upwelling intensity and productivity in the studied area high p g values represent a higher productivity and vice versa thep g curve indicates a generally high productivity during the campanian followed by a decrease during the maastrichtian the inner part of the upwelling region is characterized by higherp g values representing a higher productivity the similarity between thep g ratio curve and the foraminiferal based paleoproductivity curve from the same sections supports the utility of thep g ratio as a reliable productivity indicator applied here for the first time to upper cretaceous sediments

ensembles of low degree archeomagnetic field models for the past three millennia abstract we introduce ensembles of time varying archeomagnetic field models consisting of a reference model a mean model and a thousand individual models we present a set of three such ensembles built from archeomagnetic volcanic and sedimentary data sets that cover the past three millennia these ensembles can be used to describe the field at any location from the core surface to the magnetosphere and assess the way uncertainties due to the limited distribution and quality of the data affect any of its component or parameter such as individual gauss coefficients they provide alternative and we argue more complete descriptions of the archeomagnetic field to those provided by previously published archeomagnetic field models being better suited to existing and emerging needs such as those of geomagnetic data assimilation we present the data sets we rely on essentially the same as those used by other recent archeomagnetic field models and describe how errors affecting the data and errors due to non modelled small spatial scales of the field are taken into account we next explain our modeling strategy and motivation for building low degree spherical harmonic degree ensembles of models we carry on a number of end to end simulations to both illustrate the usefulness of such ensembles and point at the type of errors one should expect practical illustrations of what can be done with these three ensembles of models with examples of geomagnetic inferences are also described northern high latitude flux patches for instance appear to be the most robust features of all these patches tend to fluctuate but clearly have some favored locations resulting in the same clear signature with three tongues over northern america europe and asia in the time averaged field at the core mantle boundary similar to what had been found in earlier models inferences about the field behavior in the southern hemisphere are more difficult to draw still some suggestions that the well known present south atlantic reversed patch could have arisen as early as in 1500 a d are found in some of the ensembles we otherwise confirm that most of the current archeomagnetic field model limitations are related to a number of sediment cores identified as producing frequent outliers in the modeling process we provide evidence that such cores are likely affected by timing errors and timing delays between magnetization lock in and sediment deposition that future more advanced treatment should be able to handle all source files for the three ensembles of models together with appropriate matlab applications can be downloaded from http geomag ipgp fr download archeo fm zip

3 d seismic attributes using a semblance based coherency algorithm seismic coherency is a measure of lateral changes in the seismic response caused by variation in structure stratigraphy lithology porosity and the presence of hydrocarbons unlike shaded relief maps that allow 3 d visualization of faults and channels from horizon picks seismic coherency operates on the seismic data itself and is therefore unencumbered by interpreter or automatic picker biases we present a more robust multitrace semblance based coherency algorithm that allows us to analyze data of lesser quality than our original three trace cross correlation based algorithm this second generation semblance based coherency algorithm provides improved vertical resolution over our original zero mean crosscorrelation algorithm resulting in reduced mixing of overlying or underlying stratigraphic features in general we analyze stratigraphic features using as narrow a temporal analysis window as possible typically determined by the highest usable frequency in the input seismic data in the limit one may confidently apply our new semblance based algorithm to a one sample thick seismic volume extracted along a conventionally picked stratigraphic horizon corresponding to a peak or trough whose amplitudes lie sufficiently above the ambient seismic noise in contrast near vertical structural features such as faults are better enhanced when using a longer temporal analysis window corresponding to the lowest usable frequency in the input data the calculation of reflector dip azimuth throughout the data volume allows us to generalize the calculation of conventional complex trace attributes including envelope phase frequency and bandwidth to the calculation of complex reflector attributes generated by slant stacking the input data along the reflector dip within the coherency analysis window these more robust complex reflector attribute cubes can be combined with coherency and dip azimuth cubes using conventional geostatistical clustering and segmentation algorithms to provide an integrated multiattribute analysis

dinoflagellate biostratigraphy and sequence stratigraphy of the type maastrichtian upper cretaceous enci quarry the netherlands abstract the upper maastrichtian strata in enci quarry contain rich assemblages of marine palynomorphs especially dinoflagellate cysts a quantitative study shows that a marked change from dinoflagellate dominated assemblages to assemblages dominated by the acritarch genus paralecaniella occurs at the base of the lanaye member indicating a change from open marine to marginal marine conditions a sequence stratigraphic breakdown into systems tracts based on an interpretation of the changes in the palynological assemblages and lithology suggests the presence of parts of four sedimentary cycles in the enci section three of the cycles may be correlated with the third order cycles uza 4 5 ta 1 1 and ta 1 2 of haq et al 1988 the fourth cycle is probably of higher order three dinoflagellate cysts are new laciniadinium aquiloniforme schioler et al sp nov leberidocysta verrucosa schioler et al sp nov and pulchrasphaera minuscula schioler et al gen et sp nov the description of rottnestia wetzelii is emended and the new combination cribroperidinium wilsonii slimani schioler et al comb nov is proposed the triblastula utinensis zone isabelidinium cooksoniae zone and the palynodinium grallator zone with its two subzones tanyosphaeridium magdalium subzone and thalassiphora pelagica subzone can be recognized in the enci section

the april 2007 eruption and the dolomieu crater collapse two major events at piton de la fournaise la reunion island indian ocean abstract after 10 years of high activity and 24 eruptions piton de la fournaise pdf produced on april 2 to may 1 2007 one of its most voluminous and intense eruption since at least one century the eruption focused at 590 m elevation in the grand brule on the south east flank of piton de la fournaise 7 km away from summit it was located close to the southern cliff of the grand brule volcano tectonic collapse the rempart du tremblet and to the nearby village called le tremblet and it highly rattled and incommoded the inhabitants there eleven hours after the beginning of the eruption the lava flows reached the sea and created 0 45 km 2 of new land until the end of eruption in the night of april 5 the rock column beneath dolomieu crater started to collapse with a piston like mechanism into the magma chamber forming within less than 24 h the most recent and well documented caldera we report in this paper the chronology of these two related major events in the recent activity of pdf seen by the scientific networks of the volcanological observatory ovpf ipgp and field observations which allowed to back up the scenario of the caldera formation and to quantify these two exceptional episodes

anatomy of piton de la fournaise volcano la reunion indian ocean the aim of this work is to propose a general model of piton de la fournaise volcano using information from geological and geophysical studies firstly we make a graphical compilation of all available geophysical information along a w e profile secondly we construct a geological section that integrates both the geophysical information and the geological information the lithosphere beneath piton de la fournaise is not significantly flexed and the crust is underlain by an underplating body which might represent the deep magma reservoir for la reunion volcanism piton de la fournaise is a relatively thin volcano lying on a huge volcanic construction attributed mostly to les alizes volcano indeed if the differentiated rocks observed at the bottom of the riviere des remparts are the top of les alizes volcano the interface with piton de la fournaise may be located at about sea level beneath the summit area the endogenous constructions intrusive complexes related to les alizes and piton de la fournaise volcanoes represent a large volume the huge intrusive complex of les alizes volcano probably rests on the top of the oceanic crust and appears to have a buttressing effect for the present eastern volcano tectonic activity of piton de la fournaise the early piton de la fournaise edifice was built around a focus located beneath the plaine des sables area the center subsequently moved 5 6 km eastward to its current location the dense high velocity body beneath the plaines des sables and the western part of the enclos probably corresponds to the hypovolcanic intrusive complex that developed before the volcanic center shifted to its present day position magma reservoirs may have existed and may still exist as illustrated by the march 1998 crisis at the mechanical and density interface between the oceanic crust and the les alizes edifice strong evidence also exists for the presence of a shallower magma reservoir located near sea level beneath the summit the march 1998 pre eruptive seismic pattern location and upward migration seems to be evidence for a transfer of magma between the two reservoirs the dominant structural feature of the central zone is a collapse structure beneath the summit craters above the inferred magma reservoir near sea level the collapsed column constitutes a major mechanical heterogeneity and concentrates most of the seismic intrusive and hydrothermal activity because of its higher permeability and weaker mechanical strength

magma transport and storage at piton de la fournaise la reunion between 1972 and 2007 a review of geophysical and geochemical data abstract since the middle of the 20th century improvement in volcano monitoring techniques has provided large data sets that can be used to evaluate the evolution of magma plumbing systems at piton de la fournaise volcano abundant eruptive activity and a dense monitoring network are especially conducive to such research analysis of the extensive set of geophysical and geochemical data associated with the last 35 years of activity provides new insights into magma transport and storage at piton de la fournaise two periods of frequent eruptions separated by 6 years of inactivity can be distinguished 1972 1992 and 1998 2007 considering these two periods we show evidence of major changes in the shallow plumbing system in 2000 during 1972 1992 and 1998 2000 lava compositions and weak long term eruptive precursors lasting few days to three weeks characterized by no significant summit inflation and about ten volcano tectonic earthquakes per day suggest that eruptions were fed by the progressive drainage of an occasionally recharged shallow magma reservoir geophysical evidence of shallow magma reservoir recharge was only recorded in 1986 and 1998 in contrast from 2000 to 2007 geophysical data highlight the appearance of long term precursors 1 to 5 months of summit inflation and strong seismicity up to one hundred events per day preceding cycles of successive eruptions each cycle of eruptions was characterized by a sequence 3 to 10 months in duration of summit and near summit proximal eruptions and ended with a distal low altitude oceanite olivine abundances 20 vol eruption on the eastern flank of the volcano within each of these eruptive cycles lavas became progressively more magnesian over time the preferential motion of the eastern flank caused by continuous recharging of the shallow reservoir since 2000 would favour the occurrence of distal eruptions towards this flank at the end of a cycle

archeomagnetism of piton de la fournaise bearing on volcanic activity at la reunion island and geomagnetic secular variation in southern indian ocean historical and other recent lavas from piton de la fournaise la reunion island are studied using the large sample archeomagnetic method which provides here paleodirections of the earth magnetic field with confidence cones between 0 9 and 2 5 thus offering a precise record of the geomagnetic field and potential dating constraints ages of the lavas are known thanks to historical chronicles from 1708 or 14c dating and their analysis give information about the directional secular variation sv in a region where observatory measurements are scarce and not available before the end of the 19th century for the past 250 yr we find a high value of inclination 50 to 55 with respect to the geographic latitude 21 s connected with a very restricted directional sv conversely the older volcanic units present a larger sv with magnetic inclinations of between 31 and 46 and declinations from 16 w to 10 e these results which are in reasonable agreement with instrumental measurements made on ships in the vicinity of la reunion allow us to infer that undated lavas of the northern part of the caldera emanated from eruptions during the second half of the 1700s other volcanic products e g mare longue flow piton chisny cone and flows and pointe langevin despite their fresh morphology are necessarily older than about 1500 ad further knowledge of the path of the sv in the more distant past and therefore further archeomagnetic dating is hampered by the lack of a precise chronology through radiometric or other similar methods available models of the geomagnetic field during the last millennium which suffer from the scarcity of data in the southern hemisphere are discussed in the light of our results

timing and progression of climatic tectonic and glacioeustatic influences on the messinian salinity crisis abstract new palynological analysis of the continuous upper neogene sequence from the rifian corridor at sale morocco permits the deconvolution of climatic tectonic and eustatic control on the messinian salinity crisis via two indices 1 a distance from shore index based on dinoflagellate cyst versus pollen distribution and 2 a land climate index based on detailed pollen analysis this new pollen analysis indicates that the messinian salinity crisis 6 8 ma to 5 3 ma was not associated with major climate change detailed analyses of dinoflagellate cyst ecology at sale correlated to the sale 18o record show that initial shoaling of the rifian corridor after 7 3 ma primarily resulted from tectonic uplift however from 6 5 ma to 5 4 ma the rifian corridor was sufficiently shallow to have experienced significant restriction of atlantic inflow during at least four small amplitude glacioeustatic lowstands at 5 4 ma abrupt increase in the ratio of continental versus marine derived palynomorphs indicates that restriction intensified as tectonic uplift significantly outpaced gradual glacioeustatic rise despite eustatic rise at 5 32 ma the sale palynological data show that the rifian corridor experienced a second major drop in relative sea level tectonic uplift or increased sedimentation therefore termination of the messinian salinity crisis was probably associated with a breach elsewhere along the gibraltar arc

archeomagnetic dating in western north america an updated reference curve based on paleomagnetic and archeomagnetic data sets 1 a robust database of paleomagnetic pm and archeomagnetic am data for western north america covering the past 4 millennia is assembled from three data sets 1 published pm data for dated lava flows 2 recently published am data generated by r l dubois and 3 published am data generated by j l eighmy chronologic information for the am data sets has been reassessed and the data points have been assigned to age ranges depending on their archeological contexts we have selected the computer program archeocourbe available from m le goff http www ipgp fr legoff or the auxiliary material see also http earthref org to construct am reference curves and to quantitatively estimate am dates for archeological and geological samples the updated curve provides a more detailed record of prehistoric secular variation for western north america than was previously available and shows a short interval of rapid secular variation sv in the 10th or 11th centuries at near excursional rates similar and coeval features in the hawaiian and to a lesser extent arkansan sv data sets possibly indicate a rapid amplitudinal shift in the regional nondipole field at that time

enhanced structural interpretation from 3d seismic data using hybrid attributes new insights into fault visualization and displacement in cretaceous formations of the scotian basin offshore nova scotia abstract meta or hybrid attributes extracted from seismic data through artificial neural networks enhance structural details in subsurface strata cretaceous units within the penobscot prospect are devoid of such interpretations although these units are plausible zones for hydrocarbon generation and accumulation the role of geologic structures responsible for such entrapment is poorly understood the present study enlightens these latter geological structures through a case study that uses 3d time migrated seismic data from the penobscot prospect in the scotian basin a modern data conditioning approach used together with multi attribute analyses and a supervised neural network have brought out the minute details of subsurface geologic structures through a hybrid attribute called the fault probability cube fpc the present fault displacement analysis reveals that the major fault of the prospect has evolved by the coalescence of different fault segments grown over space and time and has demonstrated a predominant nnw sse structural trend such a geometry has structurally modulated the cretaceous units the logan canyon the dawson canyon and the wyandot formations giving rise to different horst graben structures and fracture networks as shown by the fpc attribute this generates complicated structural deformation and accommodation space thereby enabling different trapping zones for hydrocarbon accumulation within these units such a detailed structural understanding will provide significant input to the future exploration and development programme in the penobscot prospect

geomagnetic field for 0 3 ka 1 new data sets for global modeling 1 paleomagnetic and archeomagnetic records are used in both regional and global studies of earth s magnetic field we present a description and assessment of five newly compiled data sets also used in the companion paper by korte et al 2009 to produce a series of time varying spherical harmonic models of the geomagnetic field for the last 3000 years data are drawn from our compilation of lake sediment records and from the online database geomagia50v2 the five selections are available from the earthref digital archive at http earthref org cgi bin erda cgi n 944 data are grouped according to the source of material and we conducted separate assessments of reliability for archeomagnetic artifacts and lava flows the arch3k dat data set and for sediments sed3k dat the overall number of data is 55 greater than in previous compilations constrained data sets were selected using different criteria for each group winnowing of archeological data was based on uncertainties supplied by the original data providers the lake sediment data assessment relied on preassigned age uncertainties and one or more of the following comparisons with archeomagnetic data from the same region regional consistency among several lakes and consistency with global archeomagnetic models we discuss relative merits of a larger unconstrained data set or a smaller possibly more reliable one the constrained data sets eliminate a priori up to 35 of the available data in each case and rely on potentially subjective assessments of data quality given the limited data available our analyses indicate that iterative rejection of a small number 1 1 5 of outlying data during global field modeling is a preferable approach specific regional comparisons among the models and data support the conclusion that korte et al s outlier free cals3k 3 model based on all available measurements from sediments and archeological artifacts currently provides the best global representation of the 0 3 ka field the arch3k 1 model provides a better fit to the denser european archeomagnetic data and may be better in that region

la reunion an example of channeled hot spot plume la reunion a large intraplate volcanic system in the mascarene basin indian ocean is widely considered as the expression of a mantle plume or hotspot it lies in a region of the mascarene basin bounded by 2 major transform faults and an extinct rift the bathymetry suggests the presence of a positive topographic anomaly around la reunion we have compared the bathymetry with a theoretical bathymetry based on the thermal subsidence of the oceanic lithosphere as a function of its age a bathymetric anomaly of several hundreds of meters is shown but it is confined to the la reunion zone analogue models have been carried out to explore the deformation resulting from a mantle plume rising beneath a faulted lithosphere they show that the plume and the associated deformation are channeled into the area enclosed by the transform faults and the paleo rift the deformation is virtually nil outside the zone fault bounded zone we have analyzed the surface features and the available gravity and magnetic data in order to find evidence of the deformation predicted by the presence of the bathymetric anomaly and by the analogue models no clear pattern of deformation has been recognized but we demonstrate the complex organization of the oceanic crust in the la reunion zone the fact that the plume head focuses on the restricted area of the zone may amplify the dynamic support of the lithosphere beneath la reunion where not flexure is observed we also suspect that some seamounts near la reunion could correspond to a recent magmatic activity distinct from that of the island the mantle plume lithosphere interaction model presented here is a new to the oceanic domain and it will have to be confirmed by subsequent observations in the la reunion area and possibly in other similar sites on earth

generating a relative geologic time volume by 3d graph cut phase unwrapping method with horizon and unconformity constraints abstractconstruction of a relative geologic time rgt volume is vital to seismic geomorphological and sedimentological interpretation seismic instantaneous phase unwrapping provides an excellent approach for generating an rgt volume although several 2d or 3d seismic phase unwrapping results have been published there is a clear need for discussions on concrete methods for seismic phase unwrapping we have developed the graph cut phase unwrapping method which performs well in the interferometric synthetic aperture radar image processing it has advantages of strong discontinuity preserving ability and high computing efficiency to make it suitable for 3d seismic phase unwrapping the method is improved by extending it from 2d to 3d and by introducing the seismic horizon and unconformity constraints the strong and continuous conformable seismic events which can be easily tracked by certain autopicking methods are introduced as horizon constraints for guiding the phase unwrapping to ensure a constant

a texture based region growing algorithm for volume extraction in seismic data we present a novel approach to automated volume extraction in seismic data and apply it to the detection of allochthonous salt bodies using a genetic algorithm we determine the optimal size of volume elements that statistically according to the u test best characterize the contrast between the textures inside and outside of the salt bodies through a principal component analysis approach this information was used to implement a seeded region growing algorithm to directly extract the bodies from the cube of seismic amplitudes we present the resulting three dimensional bodies and compare our final results to those of an interpreter showing encouraging results

dinoflagellate based sea surface temperature reconstructions across the cretaceous tertiary boundary abstract quantitative analysis of organic walled dinoflagellate cyst dinocyst assemblages from closely spaced samples across the cretaceous tertiary boundary ktb at el kef nw tunisia caravaca se spain and stevns klint e denmark allows for reconstructions of sea surface temperature sst trends the combined dinocyst based sst curves indicate relatively stable warm conditions during the latest maastrichtian in contrast to strongly fluctuating and on average cooler conditions during the earliest danian in detail the results indicate cooling across the ktb immediately followed by an interval of pronounced warming the latter recorded in all studied sections two more cooling pulses may be recognized in the overlying interval followed by a gradual return to stable relatively warm conditions our data furthermore show that these ktb related climatic changes invoked distinct migration among organic walled cyst producing dinoflagellates a group not pushed to extinction at the ktb recordable in both hemispheres recent models predict periods varying between several months to 8 13 yr of global cooling impact winter and reduced solar transmission as a direct result of the chicxulub ktb impact followed by relatively long term excess co 2 related global warming our results are in line with such models but suggest that the impact related cooling phase may have lasted longer and that marked climatic instability continued to some 100 000 yrs following the ktb event s

three millennia of directional variation of the earth s magnetic field in western europe as revealed by archeological artefacts directional secular variation of the geomagnetic field over the last 2000 years has been defined in western europe from numerous archeomagnetic studies however the number of archeomagnetic results for older periods is much more limited for this reason we present new data obtained from fired archeological structures found in two french sites loupiac and aspiran dated within the first millennium b c latest bronze earliest iron age transition 850 700 b c and iron age 525 475 b c respectively from a compilation of archeomagnetic results from western europe great britain italy and france and northern africa tunisia we propose a directional secular variation curve for western europe that covers the entire first millennium b c this curve exhibits a large clockwise motion with rapid changes during the first half of the millennium while the last four centuries b c are characterized by weak variations

april 2007 collapse of piton de la fournaise a new example of caldera formation collapse calderas are frequent in the evolution of volcanic systems but very few have formed during historical times piton de la fournaise is one of the world s most active basaltic shield volcanoes the caldera collapse which occurred during the april 2007 lateral eruption is one of the few large documented collapse events on this volcano it helps to understand the mode and origin of caldera collapses in basaltic volcanoes field observations gps and seismic data show that the collapse occurred at an early stage of the eruption the cyclic seismic signal suggests a step by step collapse that directly influenced the lateral eruption rate likely the caldera results from the combined effect of i the progressive collapse of the plumbing system above the magma chamber since 2000 and ii the large amount of magma withdrawal during the early stage of the eruption by both a significant intrusion within the edifice and an important emission rate

explosive activity of the summit cone of piton de la fournaise volcano la reunion island a historical and geological review summit explosive activity and collapses that form pit craters and calderas represent major volcanic hazards on a dominantly effusive frequently active volcano like piton de la fournaise only three summit collapse events 1986 2002 2007 have been recorded since the foundation of the piton de la fournaise volcano observatory ovpf in 1979 and two of them 1986 and 2007 were associated with weak phreatic activity at piton de la fournaise the normal explosive activity consists of short lived and mild 20 m high lava fountains which quickly evolve into strombolian activity during the eruptions based on comprehensive literature review and high resolution image analysis of surface outcrops and summit caldera walls we reconstructed the time distribution of recent explosive events phreatomagmatic phreatic and their link with summit collapses and lateral flank effusive eruptions in historical time post 1640 ce we recognise two main clusters of explosive events frequent and violent phreatomagmatic to phreatic explosions occurred during the oldest cluster 1708 1878 and alternated with long lasting periods years to decades of summit effusive activity in contrast scarce and on average weak explosions occurred during the youngest cluster 1897 2012 when discrete and short lived 6 months effusive eruptions represent the main eruptive dynamics historical summit collapses pit craters and caldera all localised at the top of the summit cone were related to voluminous lateral eruptions and were followed by a significant decrease in eruptive rate however magma draining during lateral eruptions was not systematically associated with summit collapses or explosions the long lasting occurrence of magma at very shallow depth below the volcano summit followed by a rapid lateral drainage apparently represents a critical condition favouring magma groundwater interaction to produce explosive activity the prehistoric growth of the piton de la fournaise summit cone results chiefly from long lasting to continuous activity centred below its western side bory crater containing lava lakes high lava fountains long lasting effusive activity lava lakes ash plumes and block ejections were common types of eruptive dynamics in the historical past between 1640 and 1878 in this perspective short lived small volume eruptions and long pauses up to six years during the last century of activity of piton de la fournaise can be considered as a lull despite the high frequency of eruption 1 eruption 9 months on average temporal and spatial variations in recurrence rate and eruptive dynamics of basaltic volcanism such as those recognised at piton de la fournaise should be considered in the formulation of hazard assessments and in the interpretation of precursory patterns

deflation in the dustiest place on earth the bodele depression chad the bodele depression in chad is the largest single source of dust on earth because of a combination of strong near surface winds and a large reservoir of readily eroded and easily entrained low density sediment during the holocene and late pleistocene the bodele depression was host to a great lake palaeolake megachad that is now completely desiccated leaving the lake bed sediments exposed to deflation deflation in the bodele depression is revealed in erosional remnants of lake bed deposits exposed as yardangs on the lake floor erosional remnants indicate that locally up to 4 m of sediment has been removed by deflation optically stimulated luminescence dating shows that this occurred in less than 2400 years giving a rate of deflation of at least 1 6 mm yr 1 a range of other geomorphological features indicate that in some areas rates of deflation may be greater than or equal to 10 mm yr 1 deflation appears to be greatest in an arc around the northeastern margins of the lake basin where the diatomite deposits have been removed and revealed an underlying network of distributary channels preserved as gravel capped ridges the ridges which are part of an inverted topography are interpreted as deltaic distributary channels from an inland delta similar to the okavango delta examples of barchan dunes exist that were flooded by the palaeolake and which have now been exhumed from beneath layers of diatomite the distribution of extensive deflation around the northeasterly upwind end of the bodele depression probably results from a combination of large wind velocities an upwind source of abrasive sand and thinner diatomite deposits around the lake margin satellite image analysis shows that outcropping diatomite covers 24 049 km2 of the bodele depression furthermore the area from which diatomite has been removed by deflation is around 14 000 km2 combining this information with the ages and rates of deflation mentioned above indicates that some 61 000 km3 of diatomite has been eroded from the bodele depression during the past 1000 years

3 d seismic discontinuity for faults and stratigraphic features the coherence cube seismic data are usually acquired and processed for imaging reflections this paper describes a method of processing seismic data for imaging discontinuities e g faults and stratigraphic features one application of this nontraditional process is a 3 d volume or cube of coherence coefficients within which faults are revealed as numerically separated surfaces figure 1 compares a traditional 3 d reflection amplitude time slice with the results of the new method to our knowledge this is the first published method of revealing fault surfaces within a 3 d volume for which no fault reflections have been recorded

a workflow to skeletonize faults and stratigraphic features abstractimproving the accuracy and completeness of subtle discontinuities in noisy seismic data is useful for mapping faults fractures unconformities and stratigraphic edges we have developed a workflow to improve the quality of coherence attributes first we apply principal component structure oriented filtering to reject random noise and sharpen the lateral edges of seismic amplitude data next we compute eigenstructure coherence which highlights the stratigraphic and structural discontinuities we apply a laplacian of a gaussian filter to the coherence attribute that sharpens the steeply dipping faults attenuates the stratigraphic features parallel to the seismic reflectors and skeletonizes the unconformity features subparallel to the reflectors finally we skeletonize the filtered coherence attribute along with the fault plane the filtered and skeletonized seismic coherence attribute highlights the geologic discontinuities more clearly and precisely these discontinuous features can be colo

first archeomagnetic data from kenya and chad analysis of iron furnaces from mount kenya and guera massif abstract the variation of the earth s magnetic field over the last millennia is poorly known in africa especially in sub saharan africa that represents less than 1 of the global archeomagnetic dataset fourteen iron furnaces from kenya and chad have been studied here for archeomagnetic purposes these structures were dated by 14c from the 14th century in kenya and from the 18 19th centuries in chad samples oriented with the plaster cap technique have been subjected to thermal and alternating field demagnetization rock magnetic analysis and paleointensity experiment with the classical thellier thellier technique corrected for anisotropy and cooling rate effects new directional data 4 from kenya and 10 from chad and one new paleointensity estimate from kenya 43 5 1 8 t were obtained the kenyan declinations are in good agreement with the geomagnetic global models but the inclinations are lower and the intensity higher than predicted for chad the new results prove the efficiency of the archeomagnetic dating with a precision that is better than radiocarbon for the 18 19th centuries

an updated archeomagnetic directional variation curve for france over the past two millennia following 25 years of additional data acquisition abstract nearly 40 years ago emile thellier published an article summarizing the archeomagnetic data he had obtained during his career which had allowed him to recover the main features of the directional variations of the geomagnetic field in france for the last two millennia this database went on to be significantly completed 25 years ago by ileana bucur who had taken over thellier s work on archeomagnetism this forms the current basis of our knowledge of the directional evolution of the geomagnetic field in france since then archeomagnetic studies have been continued at thellier s historical laboratory in saint maur this article presents the directional archeomagnetic data obtained in france over the past 25 years in this same laboratory a total of 528 new data are presented which together with the 170 results obtained on the french territory previously listed in bucur 1994 constitute the french directional database 698 data in all all but two of these data were obtained using the experimental protocol developed by e thellier based on the analysis of large samples and on a magnetic viscosity test that has proved its reliability on numerous occasions the directions from the entire french database have been precisely defined with 95 of the 95 values being less than 1 9 and 50 being less than 0 8 the selection of 286 data with dating uncertainties of 50 years allowed us to compute a new reference directional variation curve for france since the first century bc using sliding windows the variable durations and shifts of which were adapted to the time distribution of the available data and the bivariate extension of the fisher statistics this shows ample and smooth variations fairly similar to those previously determined from a much smaller database the resulting secular variation curve is particularly well suited for use in archeomagnetic dating

dating young 1000 yr lava flow eruptions of piton de la fournaise volcano from size distribution of long lived pioneer trees dating recent lava flows is a critical issue to assess the volcanic hazards for nearby human populations but traditional methods such as radiocarbon dating are often not applicable we propose here a simple statistical method that relates the age of lava flows of the piton de la fournaise volcano pdf to the size of agarista salicifolia ericaceae a long lived pioneer tree that quickly establishes after eruption and able to live 600 years we measured the diameter at base of 711 trees on 20 dated lava flows between 1401 ce and 2007 ce we used a log log linear model to assess the relationship between maximum diameter at base of agarista salicifolia and the age of lava flows and showed a very strong correlation r2 0 987 p 2 2e 16 we then used this calibrated model to estimate the age of 11 lava flows between 1447 ce ci 1349 1531 and 1823 ce ci 1806 1839 these new ages combined with existing radiocarbon ages and historical records indicate three clusters of eruptions 1460 1630 1690 1840 since 1970 ce affecting both the caldera and the flanks of pdf we interpret such discontinuous dynamics made of periods of intense and low activity as evidencing pulses of high magma supply since at least the 11th century overall our work shows that dating lava flow with calibration based on the size distribution of long lived pioneer trees represents an accurate alternative method to redefine the hazard map of lava flow inundation the existence of long lived pioneer trees in several volcanic areas provides the opportunity to use the same framework in order to better understand eruption recurrence patterns

delineation of tectonic features offshore trinidad using 3 d seismic coherence seismic coherence allows interpreters to quickly visualize and map complex fault systems calibration to well control adds the ability to recognize important stratigraphic features and potential gas water contacts applying coherence technology to an offshore trinidad 3 d survey reduced exploration cycle time and improved understanding of tectonic elements in the area the following shows some ways in which coherence may be used to identify complex fault systems and speed up interpretation

use of a computational fault extraction process with calibrations to characterize a fractured basement reservoir yufutsu japan the yufutsu oil and gas field located in hokkaido northern japan produces hydrocarbon from a typical fracture type reservoir composed of very tight cretaceous granitic basement and overlying conglomerate of the eocene here delineations of faults accompanying large open fractures are essential for optimal developments to capture fault distribution objectively various seismic attribute estimates ascribed to fault distributions are derived from three dimensional seismic data by computational procedures however to use the estimates properly calibrating them with independent observations other than seismic data is important we present a calibration scheme by coupling seismic data with microseismic data and in situ stress data to delineate active faults under a strike slip faulting stress regime in the yufutsu field active faults are interpreted to be fluid pathways formed by shear dilation in the calibration two kinds of parameter sets are tuned one controls linkages of fault responses fragmented by artificial noises caused by seismic acquisition and processing to adjust spatial continuities of fault surfaces properly another limits extracted fault strikes with respect to mohr coulomb failure criterion to highlight active faults the calibrated seismic attribute estimates show a qualitative consistency with the microseismic hypocenter distribution observed during a massive hydraulic stimulation in addition a large difference in gas productivity observed at four wells from very high productivity to no gas flowing is clearly related to an existence of distinct lineation with strong magnitudes of the calibrated seismic attributes it suggests that the calibrated estimate becomes a criterion to judge an economic viability of a well

distortion of the geomagnetic field in volcanic terrains an experimental study of the mount etna stratovolcano abstract the inclination i declination d and total intensity f of the geomagnetic field were measured on mount etna in 1989 1991 at a dozen sites previously sampled for archeomagnetic studies the purpose of the work was to determine the variations of these parameters at 30 cm above ground level and how the distortion from the main field can affect the archeomagnetic record of volcanic rocks ten measurements were usually performed at each site with a three component flux gate magnetometer whose estimated precision is 0 2 on direction and 50 nt on intensity this was considered sufficient on volcanic areas with highly magnetized rocks and where the geomagnetic gradient may be in excess of 1000 nt m results averaged for each site generally show small variations in intensity 3 of the total field and direction 1 5 the averaged values of the 12 sites i 52 6 d 0 3 f 44010 nt are very close to those measured in sedimentary terrain away from the volcano i 52 9 d 0 35 f 44110 nt themselves consistent with the interpolated igrf in eastern sicily the largest deviations of the geomagnetic direction have been observed on four sites three of them located on the south flank between 1900 and 700 m elevation it is suggested that these anomalies are mainly related to dyke swarms which are common within the south rift zone of mount etna our findings show that reliable archeomagnetic results can be obtained from volcanic rocks provided that lavas of the same eruption are sampled on several sites distributed over the largest possible area