catalogue of palaeomagnetic directions and poles from fennoscandia archaean to tertiary abstract palaeomagnetic data from fennoscandia ranging from the archaean to the tertiary have been compiled into a catalogue the data are presented in table format listing precambrian data according to tectonomagmatic blocks and late precambrian phanerozoic data according to geological periods each pole is graded with the modified briden duff classification scheme the catalogue complete to the end of 1988 contains 350 entries from 31 tectonomagmatic blocks and or geological periods normal and reversed polarity data are listed separately to allow polarity asymmetries to be studied each entry also has an indexed abstract summarizing relevant information such as the age of the rock the age of the natural remanent magnetization and the basis for the assigned reliability grade all the data are stored in the palaeomagnetic data bank which will be updated annually with new data the catalogue is the basic source of data for the microcomputer based palaeomagnetic database for fennoscandia now being compiled

effects of asteroid and comet impacts on habitats for lithophytic organisms a synthesis asteroid and comet impacts can have a profound influence on the habitats available for lithophytic microorganisms using evidence from the haughton impact structure nunavut canadian high arctic we describe the role of impacts in influencing the nature of the lithophytic ecological niche impact induced increases in rock porosity and fracturing can result in the formation of cryptoendolithic habitats in some cases and depending upon the target material an increase in rock translucence can yield new habitats for photosynthetic cryptoendoliths chasmoendolithic habitats are associated with cracks and cavities connected to the surface of the rock and are commonly increased in abundance as a result of impact bulking chasmoendolithic habitats require less specific geological conditions than are required for cryptoendolithic habitats and their formation is likely to be common to most impact events impact events are unlikely to have an influence on epilithic and hypolithic habitats except in rare cases where for example the formation of impact glasses might yield new hypolithic habitats we present a synthetic understanding of the influence of asteroid and comet impacts on the availability and characteristics of rocky habitats for microorganisms

shatter cones at the keurusselka impact structure and their relation to local jointing shatter cones are the only distinct meso to macroscopic recognition criterion for impact structures yet not all is known about their formation the keurusselka impact structure finland is interesting in that it presents a multitude of well exposed shatter cones in medium to coarse grained granitoids the allegedly 27 km wide keurusselka impact structure was formed about 1150 ma ago in rocks of the central finland granitoid complex special attention was paid in this work to possible relationships between shatter cones and local as well as regionally occurring fracture or joint systems a possible shatter cone find outside the previously suggested edge of the structure could mean that the keurusselka impact structure is larger than previously thought the spacing between joints fractures from regional joint systems was influenced by the impact but impact induced fractures strongly follow the regional joint orientation trends there is a distinct relationship between shatter cones and joints shatter cones occur on and against joint surfaces of varied orientations and belonging to the regional orientation trends planar fractures pf and planar deformation features pdf were found in three shatter cone samples from the central most part of the impact structure whereas other country rock samples from the same level of exposure but further from the assumed center lack shock deformation features pdf occurrence is enhanced within 5 mm of shatter cone surfaces which is interpreted to suggest that shock wave reverberation at preimpact joints could be responsible for this local enhancement of shock deformation some shatter cone surfaces are coated with a quasi opaque material which is also found in conspicuous veinlets that branch off from shatter cone surfaces and resemble pseudotachylitic breccia veins the vein filling is composed of two mineral phases one of which could be identified as a montmorillonitic phyllosilicate the second phase could not be identified yet the original composition of the fill could not be determined further work is required on this material observed joints and fractures were discussed against findings from barringer impact crater they show that impact induced joints in the basement rock do not follow impact specific orientations such as radial conical or concentric

impact craters and craterform structures in fennoscandia abstract sixty two nearly circular topographic morphological or geophysical structures in fennoscandia and estonia were studied to discover their origin the structures were divided into five classes fifteen were caused by meteorite impacts class a and a four of them lappajarvi janisjarvi mien and dellen contain large volumes of impact melt the age of the recognized impact craters varies from pre historic 3500 b c to 700 ma and their diameters from 0 04 km to 55 km the majority of the other structures are probable class b or possible class c craters for which there is not yet sufficient proof of impact origin there is increasing evidence that some of the large arcuate morphological or geophysical structures class e represent the deeply eroded scars of very old craters but owing to the lack of identified shock metamorphic features or impact generated rocks e g allogenic breccias they cannot so far be classified as impact craters so far no craterform structure or ejecta layer of archaean or early proterozoic age has been found in fennoscandia although statistically remnants of ancient cratering events should be found in the fennoscandian shield new ways of searching for these structures are proposed the impact cratering rate in fennoscandia is 2 4 10 14 km 2a 1 n 12 the very small craters are omitted which corresponds to about two events per 100 ma for the last 700 ma this is a minimum estimate and is higher than the global cratering rate

how well do precambrian paleomagnetic data agree with the phanerozoic apparent polar wander path a baltica case study abstract precambrian paleomagnetic data are crucial for various tectonic and geophysical applications the reconstructions of fusion and fission of supercontinents in particular due to many objective reasons the variety of stability tests for these data are abridged in comparison to phanerozoic results and is further hindered by the rather common refusal to consider the resemblance between precambrian and younger poles in this paper we selected precambrian paleomagnetic data with ages of

hubble space telescope observations of the martian aphelion cloud belt prior to the pathfinder mission seasonal and interannual variations the presence of a globally extant equatorial belt of water ice clouds on mars is quantitatively investigated using data from three seasons of our hubble space telescope synoptic monitoring program 1993 1997 a subset of the 1996 1997 images covers the landing site of the mars pathfinder including a set of images taken after touchdown using multicolor imaging from the wide field planetary camera and the wide field planetary camera 2 we characterize both water ice cloud and dust optical depths as a function of latitude at several local times for each observing epoch the analysis technique models calibrated data using a multiple scattering radiative transfer code our results support the initial results of clancy et al 1996a regarding changes between the aphelion and perihelion climate of mars and provide a more detailed look at the development and decay of the cloud belt comparing our dust optical depths to those of the viking landers for the same seasons we note a trend toward lower dust loading in late northern winter and in spring our observations of the pathfinder site in july 1997 reveal a dust opacity in good agreement with that reported by pathfinder smith et al 1997b in addition the serendipitous occurrence of a dust storm in valles marineris in late june 1997 allows us to derive a set of dust single scattering albedos for use in more accurately modeling the dust s radiative properties and effects

interpretation of magnetic fabrics in the early proterozoic diabase dykes of keuruu central finland abstract magnetic fabrics petrophysics petrography and chemical compositions are described for 14 diabase dykes located in the keuruu area central finland these early proterozoic 1880 ma dykes sharply cut both low density granodiorites and high density diorites and gabbros the diabase dykes with a nw se strike and an almost vertical dip have a maximum length of a few kilometers and widths of about 1 m strongly developed magnetic fabrics of deformation type anisotropy degree up to 1 4 were observed in six of the dykes and weakly developed fabrics of flow type anisotropy degree below 1 1 in eight dykes no systematic differences in the dyke widths mean densities palaeomagnetic poles mineral compositions degrees of alteration or chemical characteristics were observed between the two types of dykes suggesting that the dykes had a common magma source all the fabrics of deformation type are dominantly ferrimagnetic with tightly aligned horizontal foliations and well grouped lineations which in most cases are parallel to the dyke trends it is suggested that the deformation fabrics were generated as tholeiitic magma was forced to intrude laterally along its level of neutral buoyancy lnb which may have been close to the present erosion level pel in the low density granodiorite environment ferri and paramagnetic fabrics of flow type characterize the dykes located in the denser mafic parts of the crust in these parts the lnb was possibly somewhat higher in the crust so that magma flow passed the pel and formed weakly developed flow fabrics with gently plunging lineations and vertical or variable magnetic foliations

geophysical research on the kardla impact structure hiiumaa island estonia the 4 km wide and 500 m deep circular kardla impact structure in hiiumaa island estonia of middle ordovician age 455 ma is buried under upper ordovician and quaternary sediments to constrain the geophysical models of the structure petrophysical properties such as magnetic susceptibility natural remanent magnetization nrm density electrical conductivity porosity and p wave velocity were measured on samples of crystalline and sedimentary rocks collected from drill cores in different parts of the structure and the surrounding area the results were used to interpret the central gravity anomaly of 3 mgal and the magnetic anomaly of 100 nt and also the surrounding weak positive anomalies revealed by high precision survey data the unshocked granitic rocks outside the structure have a mean density of 2630 kgm 3 their shocked counterparts have densities of 2400 kgm 3 at a depth of 500 m increasing up to 2550 kgm 3 at a depth of 850 m porosity and electrical conductivity decrease but p wave velocity increases as density increases away from the impact point thus the gradual changes in the physical properties of the rocks as a function of radial distance from the crater centre are consistent with an impact origin for kardla as in many other impact structures the magnetization of the shocked rocks are also clearly lower than those of unshocked target rocks a new geophysical and geological model of the kardla structure is presented based on geophysical field measurements and data on gradual changes in petrophysical parameters of the shocked target and overlying rocks together with structural data from numerous boreholes an important feature of this model is the lack of an observable geophysical signature of the central uplift observed in drillcores

gusev crater wind related features and processes observed by the mars exploration rover spirit 1 wind related features observed by the rover spirit in gusev crater mars include patches of soil on the surface some of which are organized into bed forms windblown grains include dust inferred to be 2 mm in diameter microscopic imager data show the sands and granules to be rounded and relatively spherical typical of grains transported long distances by the wind the interior of bed forms exposed by rover operations suggests the infiltration of dust among the grains indicating that these sands are not currently experiencing saltation orientations of 1520 features such as bed forms and ventifacts along spirit s traverse from the landing site the columbia memorial station to west spur in the columbia hills suggest primary formative winds from the north northwest which correlate with measurements of features seen in orbiter images and is consistent with afternoon winds predicted by atmospheric models a secondary wind from the southeast is also suggested which correlates with predictions for nighttime early morning winds wind abrasion is indicated by ventifacts in the form of facets and grooves cut into rocks the orientations of which also indicate prevailing winds from the north northwest orientations of many aeolian features in the west spur area however have more scatter than elsewhere along the traverse which is attributed to the influence of local topography on the patterns of wind active dust devils observed on the floor of gusev from the columbia hills demonstrate that dust is currently mobile sequential images of some dust devils show movement as rapid as 3 8 m s consistent with wind velocities predicted by atmospheric models for the afternoon when most of the dust devils were observed sands accumulated on the rover deck in the same period suggest that some sands in the columbia hills experience active saltation two toned rocks having a light band coating at their bases are considered to represent partial burial by soils and subsequent exposure while perched rocks could represent materials lowered onto other rocks by deflation of supporting soils measurements of the heights of the light bands and the perched rocks range from 1 cm to 27 cm indicating local deflation by as much as 27 cm

preservation and detectability of shock induced magnetization preservation and detectability of shock induced magnetization abstract an understanding of the effects of hypervelocity impacts on the magnetization of natural samples is required for interpreting paleomagnetic records of meteorites lunar rocks and cratered planetary surfaces rocks containing ferromagnetic minerals have been shown to acquire shock remanent magnetization srm due to the passage of a shock wave in the presence of an ambient magnetic field in this study we conducted pressure remanent magnetization prm acquisition experiments on a variety of natural samples as an analog for srm acquisition at pressures ranging up to 1 8 gpa comparison of the alternating field af and thermal demagnetization behavior of prm confirms that af demagnetization is a more efficient method for removing srm overprints than thermal demagnetization because srm may persist to unblocking temperatures approaching the curie temperatures of magnetic minerals the blocking of srm to high temperatures suggests that srm could persist without being eradicated by viscous relaxation over geologic timescales however srm has been rarely observed in natural samples likely because of two factors 1 other forms of impact related remanence e g thermal remanent magnetization from impact related heating or chemical remanent magnetization from post impact hydrothermal activity are often acquired by target rocks that overprint srm and 2 low srm acquisition efficiencies may prevent srm from being distinguished from the underlying primary remanence or other overprints due to its low magnetization intensity sonia m tikoo 1 2 jerome gattacceca 3 4 nicholas l swanson hysell 1 benjamin p weiss 1 4 clement suavet 4 and cecile cournede 3 department of earth and planetary science university of california berkeley ca 94720 usa berkeley geochronology center 2455 ridge road berkeley ca 94709 usa cnrs aix marseille university cerege um34 aix en provence france department of earth atmospheric and planetary sciences massachusetts institute of technology mit 77 massachusetts avenue cambridge ma 02139 usa final version for publication in journal of geophysical research planets accepted 07 24 2015 doi 10 1002 2015je004840

initial results from the mini tes experiment in gusev crater from the spirit rover the miniature thermal emission spectrometer mini tes on spirit has studied the mineralogy and thermophysical properties at gusev crater undisturbed soil spectra show evidence for minor carbonates and bound water rocks are olivinerich basalts with varying degrees of dust and other coatings dark toned soils observed on disturbed surfaces may be derived from rocks and have derived mineralogy 5 to 10 of 45 pyroxene 20 ca rich pyroxene and 25 pigeonite 40 sodic to intermediate plagioclase and 15 olivine forsterite 45 5 to 10 two spectrally distinct coatings are observed on rocks a possible indicator of the interaction of water rock and airfall dust diurnal temperature data indicate particle sizes from 40 to 80 microm in hollows to approximately 0 5 to 3 mm in soils

temporal constraints on the paleoproterozoic lomagundi jatuli carbon isotopic event the paleoproterozoic lomagundi jatuli positive 13c excursion in sedimentary carbonates represents an event whose magnitude and duration is unique in earth history although precise absolute chronology of this event remains poorly constrained in northeastern fennoscandia an 1300 m thick sedimentary volcanic succession of the pechenga greenstone belt records decline of this isotopic excursion zircons from sedimentary rocks that occur within the decline have yielded 207pb 206pb dates at 2058 2 ma 6 ma including u decay constant uncertainties and provide the first maximum age constraint on the termination of the lomagundi jatuli event combined with existing constraints these data indicate an 140 m y interval characterized by 13c rich carbonate accumulation

overview of the microscopic imager investigation during spirit s first 450 sols in gusev crater the microscopic imager mi on the mars exploration rover spirit has returned images of mars with higher resolution than any previous camera system allowing detailed petrographic and sedimentological studies of the rocks and soils at the gusev landing site designed to simulate a geologist s hand lens the mi is mounted on spirit s instrument arm and can resolve objects 0 1 mm in size or larger this paper provides an overview of mi operations data calibration processing and analysis of mi data returned during the first 450 sols mars days of the spirit landed mission the primary goal of this paper is to facilitate further analyses of mi data by summarizing the methods used to acquire and process the data the radiometric and geometric accuracy of mi data products and the availability of archival products in addition scientific results of the mi investigation are summarized mi observations show that poorly sorted soils are common in gusev crater although aeolian bedforms have well sorted coarse sand grains on their surfaces abraded surfaces of plains rocks show igneous textures light toned veins or fracture filling minerals and discrete coatings the rocks in the columbia hills have a wide variety of granular textures consistent with volcaniclastic or impact origins case hardening and submillimeter veins observed in the rocks as well as soil crusts and cemented clods imply episodic subsurface aqueous fluid movement which has altered multiple geologic units in the columbia hills the mi also monitored spirit s solar panels and the magnets on the rover s deck

karst landscapes of new south wales australia abstract karst in new south wales has developed on proterozoic to permian limestones and in quaternary limestones on lord howe island karst features seen today have been controlled by the geotectonic setting of the limestone its topographic position climatic regime and in many areas a history of repeated episodes of karstification extending back at least to devonian times

quaternary climatic instability in south east australia from a multi proxy speleothem record milankovitch scale quaternary climatic oscillations within south east australia are known to be characterized by relatively arid glacial and wet interglacial stages however terrestrial proxy records of environmental change are scarce based largely on river terraces dune sediments and pollen sequences here we present a speleothem based palaeoclimate record from yarrangobilly caves south east australia the oxygen isotopic composition of calcite 18ocalcite is taken to represent rainfall amount and used as an aridity index high resolution trace element profiles and uv fluorescence support interpretations based on 18ocalcite allowing further designation of key phases of speleothem growth into periods of relative aridity and moisture excess a hiatus of approximately 37 ka duration divides the record into two key phases of growth which can be mapped onto marine isotope stages 5c a and 3 respectively increasing aridity in the latter half of mis 5 led to cessation of speleothem growth for the duration of mis 4 growth recommences during mis 3 associated with greater moisture availability enhanced vegetation and augmented biogeochemical cycling this speleothem record provides a unique context of terrestrial environmental change and depicts hydrological conditions which fluctuate markedly over the 70 ka period covering the time of megafauna extinction and human arrival on the continent

alpha particle x ray spectrometer apxs results from gusev crater and calibration report 1 the chemical composition of rocks and soils on mars analyzed during the mars exploration rover spirit mission was determined by x ray analyses with the alpha particle x ray spectrometer apxs details of the data analysis method and the instrument calibration are presented measurements performed on mars to address geometry effects and background contributions are shown cross calibration measurements among several instrument sensors and sources are discussed an unintentional swap of the two flight instruments is evaluated new concentration data acquired during the first 470 sols of rover spirit in gusev crater are presented there are two geological regions the gusev plains and the columbia hills the plains contain soils that are very similar to previous landing sites on mars a meteoritic component in the soil is identified rocks in the plains revealed thin weathering rinds the underlying abraded rock was classified as primitive basalt one of these rocks contained significant br that is probably associated with vein filling material of different composition one of the trenches showed large subsurface enrichments of mg s and br disturbed soils and rocks in the columbia hills revealed different elemental compositions these rocks are significantly weathered and enriched in mobile elements such as p s cl or br even abraded rock surfaces have high br concentrations thus in contrast to the rocks and soils in the gusev plains the columbia hills material shows more significant evidence of ancient aqueous alteration

palaeomagnetism of the lappajarvi impact structure western finland abstract palaeomagnetic and rock magnetic results are presented for rocks from the lappajarvi meteorite impact structure western finland oriented samples were collected from the melt rocks in the central island of the crater and of the palaeoproterozoic svecofennian target rocks at the crater rim the natural remanent magnitization nrm of the melt rocks is generally weak and metastable during demagnetization the characteristic nrm component carried by pyrrhotite yields a palaeomagnetic pole latitude 55 4 n longitude 152 6 e dp 6 2 dm 8 7 dg 6 sites suggesting an age of 195 ma for the impact the results from a deep core drilled from the impact melt rock display similar palaeomagnetic directions but with slightly shallower inclinations the palaeomagnetic age differs from the 40ar 3939ar age of 77 ma for the impact assuming that the 40ar 39ar age is correct the discrepancy between palaeomagnetic and radiometric ages is best explained by post impact and post cooling tilting of the melt layer the tilting 15 may be due to isostatic rebounds along joints in the melt impact remanence has also been isolated in a few target rocks at the rim this poorly defined overprint could be a mild shock remanent magnetization superimposed on the 1 9 ga old svecofennian direction this interpretation is supported by the observation that the nrm intensity is enhanced in specimens having the impact overprint the palaeomagnetic results are consistent with earlier interpretations based on geophysical morphological mineralogical and geochemical data that the lappajarvi structure is a complex meteorite impact site less than 200 ma old

correspondence and least squares analyses of soil and rock compositions for the viking lander 1 and pathfinder landing sites correspondence analysis is a dual q and r mode factor analysis that allows simultaneous visualization of relationships between normalized variables and samples the usefulness of the technique is first illustrated with an analysis of a simulated feldspar compositional data set and then applied to analysis of patterns among variables and samples for compositions obtained for viking lander 1 soils and pathfinder rocks and soils for the martian data the first two factors capture 90 of the variance data projected onto the plane defined by these two factors fall within a mixing triangle defined by three geologically plausible end members basaltic shergottite andesite and a halide kieserite evaporite however examination of data projected onto the second and third factors shows that the compositions are systematically displaced from the mixing triangle plane in the same general direction as the fe vector inclusion of a fe oxide e g hematite or maghemite as a reasonable fourth end member forms a mixing tetrahedron that encapsulates the data least squares mixing analysis of the data with these four end members and the elemental suite measured at both landing sites si al ti fe mg ca s cl implies that aeolian dust on rocks is a physical mixture of basalt and andesite derived materials in approximately equal proportions soil components at the two landing sites are similar to each other and less basalt like than the aeolian dust and viking 1 soils are more andesite rich than the pathfinder soils

physical properties of the mars exploration rover landing sites as inferred from mini tes derived thermal inertia 1 the miniature thermal emission spectrometer mini tes on board the two mars exploration rovers provides the first opportunity to observe thermal properties from the martian surface relate these properties to orbital data and perform soil conductivity experiments under martian conditions the thermal inertias of soils bedforms and rock at each landing site were derived to quantify the physical properties of these features and understand geologic processes occurring at these localities the thermal inertia for the gusev plains rock target bonneville beacon 1200 j m 2 k 1 s 1 2 is consistent with a dense basaltic rock but the rocks at the columbia hills have a lower thermal inertia 620 j m 2 k 1 s 1 2 suggesting that they have a volcaniclasic origin bedforms on the floors of craters at both landing sites have thermal inertias of 200 j m 2 k 1 s 1 2 consistent with a particle diameter of 160 m this diameter is comparable to the most easily moved grain size in the current atmosphere on mars suggesting that these bedforms may have formed under current atmospheric conditions along the meridiani plains the thermal inertia is lower than that derived from tes and thermal emission imaging system themis orbital data this discrepancy is not well understood mini tes derived thermal inertias at gusev along a 2 5 km traverse follow trends in thermal inertia measured from orbit with tes and themis however along the traverse there are variability and mixing of particle sizes that are not resolved in the orbital thermal inertia data due to meter scale processes that are not identifiable at larger scales

overview of the spirit mars exploration rover mission to gusev crater landing site to backstay rock in the columbia hills spirit landed on the floor of gusev crater and conducted initial operations on soil covered rock strewn cratered plains underlain by olivine bearing basalts plains surface rocks are covered by wind blown dust and show evidence for surface enrichment of soluble species as vein and void filling materials and coatings the surface enrichment is the result of a minor amount of transport and deposition by aqueous processes layered granular deposits were discovered in the columbia hills with outcrops that tend to dip conformably with the topography the granular rocks are interpreted to be volcanic ash and or impact ejecta deposits that have been modified by aqueous fluids during and or after emplacement soils consist of basaltic deposits that are weakly cohesive relatively poorly sorted and covered by a veneer of wind blown dust the soils have been homogenized by wind transport over at least the several kilometer length scale traversed by the rover mobilization of soluble species has occurred within at least two soil deposits examined the presence of monolayers of coarse sand on wind blown bedforms together with even spacing of granule sized surface clasts suggests that some of the soil surfaces encountered by spirit have not been modified by wind for some time on the other hand dust deposits on the surface and rover deck have changed during the course of the mission detection of dust devils monitoring of the dust opacity and lower boundary layer and coordinated experiments with orbiters provided new insights into atmosphere surface dynamics

unsaturated zone hydrology and cave drip discharge water response implications for speleothem paleoclimate record variability summary high frequency spatially dense discharge monitoring was conducted over fifteen months to characterise unsaturated zone flow at harrie wood cave hwc in the snowy mountains yarrangobilly se australia the cave was formed in the late silurian yarrangobilly limestone a fractured rock associated with very low primary porosity due to past diagenesis over our monitoring period we simultaneously measured rainfall soil moisture saturation and drip discharge rate at fourteen sites to characterise infiltration discharge relationships all drip discharge sites exhibited non gaussian distributions indicating long periods where low discharge predominates punctuated by short infrequent periods of high discharge however there was significant variability in discharge between sites and consequently no spatial correlation in the cave we investigated the depth discharge relationship at hwc and found a moderate relationship between depth and drip discharge lag response times to soil moisture content but only weak relationships between depth and mean and maximum discharge this highlights that the karst architecture plays an important role in controlling drip discharge dynamics principal component analysis pca and agglomerative hierarchal clustering ahc were used to classify similar drip types revealing five unique drip regimes two phase flow and non linear response to recharge behaviour were observed suggesting secondary porosity is controlling unsaturated zone flow in mature limestone environments with low primary porosity using the data presented here the first coupled conceptual and box hydrological flow model was developed this study highlights the heterogeneous nature of hydrological flow in karst and the need to understand unsaturated zone hydrology at the individual drip discharge level to inform speleothem studies for high resolution paleoclimate reconstruction

mars exploration rover geologic traverse by the spirit rover in the plains of gusev crater mars the spirit rover completed a 2 5 km traverse across gently sloping plains on the floor of gusev crater from its location on the outer rim of bonneville crater to the lower slopes of the columbia hills mars using the athena suite of instruments in a transect approach a systematic series of overlapping panoramic mosaics remote sensing observations surface analyses and trenching operations documented the lateral variations in landforms geologic materials and chemistry of the surface throughout the traverse demonstrating the ability to apply the techniques of field geology by remote rover operations textures and shapes of rocks within the plains are consistent with derivation from impact excavation and mixing of the upper few meters of basaltic lavas the contact between surrounding plains and crater ejecta is generally abrupt and marked by increases in clast abundance and decimeter scale steps in relief basaltic materials of the plains overlie less indurated and more altered rock types at a time stratigraphic contact between the plains and columbia hills that occurs over a distance of one to two meters this implies that regional geologic contacts are well preserved and that earth like field geologic mapping will be possible on mars despite eons of overturn by small impacts

the keurusselka impact structure finland impact origin confirmed by characterization of planar deformation features in quartz grains although the meteorite impact origin of the keurusselkaimpact structure central finland has been established on the basis of the occurrence of shatter cones no detailed microscopic examination of the impactites from this structure has so far been made previous microscope investigations of in situ rocks did not yield any firm evidence of shock features raiskila et al 2008 kinnunen and hietala 2009 we have carried out microscopic observations on petrographic thin sections from seven in situ shatter cone samples and report here the discovery of planar fractures pfs and planar deformation features pdfs in quartz and feldspar grains the detection and characterization of microscopic shock metamorphic features in the investigated samples substantiates a meteorite impact origin for the keurusselkastructure the crystallographic orientations of 372 pdf sets in 276 quartz grains were measured using a universal stage u stage microscope for five of the seven distinct shatter cone samples based on our u stage results we estimate that investigated shatter cone samples from the keurusselkastructure have experienced peak shock pressures from approximately 2 gpa to slightly less than 20 gpa for the more heavily shocked samples the decoration of most of the pdfs with fluid inclusions also indicates that these originally amorphous shock features were altered by postimpact processes finally our field observations indicate that the exposed surface corresponds to the crater floor it is however difficult to estimate the exact diameter of the structure and the precise amount of material that has been eroded since its formation

rethinking eastern australian caves there are some 300 bodies of cavernous limestone in eastern australia extending from precipitous bluff in southeastern tasmania to the mitchell palmer region in north queensland these impounded karsts developed in palaeozoic limestones of the tasman fold belt system contain many caves the caves have a suite of features in common that allows them to be thought of as a major group the tasmanic caves the tasmanic caves include multiphase hypogene caves such as cathedral cave at wellington and multiphase multiprocess caves such as jenolan with carboniferous hypogene and younger paragenetic and fluvial elements active hypogene caves occur at wee jasper and possibly at five other localities the tasmanic caves are one of the most complex suites of caves in folded palaeozoic limestones in the world field techniques developed to study these caves are now being applied to complex caves in central europe in the czech republic hungary poland slovakia and slovenia andrews 1911 recognized that there was a geographical unity of eastern australia although this may appear to be a quaint early 20th century idea later geologists recognized the tasman fold belt system as a continental scale tectonic fea ture in eastern australia similarly late 20th century geomorphologists such as ollier 1978 1982 recognized the existence of continental scale landforms such as the great escarpment running the length of eastern australia the tasman fold belt system in eastern australia has two palaeozoic sections the western lachlan thompson fold belt and the eastern new england fold belt both containing cavernous palaeozoic limestones if we take a continental scale view of the karst in these palaeozoic lime stones we find that despite some obvious climatic influences on surface landforms the caves have many characteristics in common caves in palaeo zoic limestones from the southeasternmost tip of tasmania to northern queensland are sufficiently similartobeviewedasacohesivegroup thetasma nic caves fig 1 the focus here is on caves because caves are the prominent features in many eastern australian karsts this paper begins by reviewing ideas about eastern australian caves from 1830 to 1995 the latter part of the paper dealing with developments in understanding eastern australian caves from 1996 onwards concentrates on the author s own work

preliminary results of a palaeomagnetic and rock magnetic study of the proterozoic tsuomasvarri intrusions northern fennoscandia abstract preliminary palaeomagnetic results are presented for the proterozoic tsuomasvarri central ultramafic intrusion and surrounding older gabbro diorite intrusion in the northeastern fennoscandian shield in the ultramafic intrusion five remanence components reflecting different geological processes were isolated in the alternating field af and thermal demagnetization of 55 samples from ten sites a reversed polarity remanence component c pole plat 26 n plon 245 e dp 5 dm 9 n 32 samples dominates in the ultramafic intrusion the normal polarity pole a plat 44 n plon 232 e dp 4 dm 6 n 9 samples corresponds to an age of 1 88 ga on the apparent polar wander path apwp and is probably a thermochemical remanence acquired during the svecokarelian orogeny or in the late stages of magma cooling pole b plat 35 n plon 158 e dp 9 dm 15 n 5 samples normal polarity corresponds to the 1 75 ga old post orogenic activity in the area and is also seen in results of k ar whole rock isotopic age determinations from the vicinity the normal polarity pole d pole plat 25 s plon 285 e dp 12 dm 19 n 11 samples has a palaeomagnetic age of 2 44 ga which is in contrast with the isotopic age determination of 1 93 ga u pb age on zircon of the gabbro diorite intrusion pole f plat 3 n plon 212 e dp 10 dm 18 n 5 samples indicates an age of 0 5 0 4 ga on the palaeozoic apwp segment of fennoscandia and probably reflects a weak caledonian overprint in northeastern finland in the gabbro diorite intrusion two remanence components were isolated in 46 samples from eight sites the palaeomagnetic age 1 93 ga of the dominant normal polarity component a pole plat 40 n plon 247 e dp 5 dm 8 n 28 samples is consistent with the isotopic age of 1 93 ga u pb determination on zircon the normal polarity component d pole plat 20 s plon 285 e dp 14 dm 23 n 5 samples which was also isolated in the ultramafic intrusion contradicts the u pb isotopic age determination

early proterozoic palaeomagnetic data from the pechenga zone north west russia and their bearing on early proterozoic palaeogeography summary an early proterozoic palaeomagnetic signature c 2125 ma verified by a positive conglomerate test is recorded in the kuetsyarvi formation pechenga group north west russia but the majority of the palaeomagnetic directions observed in the pechenga group lithologies reflect a low grade remagnetization event probably linked with the late precambrian baikalian orogeny which affected north west russia and northern norway secondary pyrrhotite is the dominant remanence carrier in the uppermost formations of the pechenga group palaeomagnetic poles from the kuetsyarvi formation differ somewhat or partially overlap with coeval palaeomagnetic poles from other tectonomagmatic provinces in northern fennoscandia but it is premature at this stage to speculate on intraplate movements during the early proterozoic besides the kuetsyarvi formation probably developed during an early phase of intracontinental rifting along the northern margin of fennoscandia similar to the present day east african rift hence younger intercontinental rifting possible seafloor spreading and subsequent convergence would remain undetected by our palaeomagnetic data palaeolatitude estimates from the kuetsyarvi formation suggest that the pechenga region was located in latitudes of around 20 to 30 during the 2100 2200ma interval these low latitude estimates are supported by the sedimentary record in the pechenga region which is characterized by red beds and evaporites comparison of fennoscandian palaeomagnetic poles with coeval poles from the slave and superior cratons laurentia questions previously publicized supercontinental configurations a close relationship between fennoscandia and early proterozoic laurentian provinces is conceivable from palaeomagnetic data but given the lack of longitudinal control as well as the choice of hemisphere such postulates are tentative at best on purely palaeomagnetic grounds

in flight calibration and performance of the mars exploration rover panoramic camera pancam instruments 1 the mars exploration rover panoramic camera mer pancam instruments have acquired more than 60 000 high resolution multispectral stereoscopic images of soil rocks and sky at the gusev crater and meridiani planum landing sites since january 2004 these images combined with other mer data sets have enabled new discoveries about the composition mineralogy and geologic geochemical evolution of both sites one key to the success of pancam in contributing to the overall success of mer has been the development of a calibration pipeline that can quickly remove instrumental artifacts and generate both absolute radiance and relative reflectance images with high accuracy and precision in order to influence tactical rover driving and in situ sampling decisions this paper describes in detail the methods assumptions and models algorithms in the calibration pipeline developed for pancam images based on new measurements and refinements performed primarily from flight data acquired on mars major calibration steps include modeling and removal of detector bias signal active and readout region dark current electronic shutter smear and pixel to pixel responsivity flatfield variations pancam images are calibrated to radiance w m2 nm sr using refined preflight derived calibration coefficients or radiance factor i f using near in time measurements of the pancam calibration target and a model of aeolian dust deposition on the target as a function of time we are able to verify that the absolute radiance calibration of most pancam images is accurate to within about 10 or less and that the filter to filter and pixel to pixel precision of the calibrated relative reflectance data both based on measurements of the pancam calibration target are typically about 3 and 1 or less respectively examples are also presented of scientific applications made possible by the high fidelity of the calibrated pancam data these include 11 color visible to near ir spectral analysis calculation of true color and chromaticity values and generation of super resolution image data products this work represents a follow on and enhancement to the pancam preflight calibration process described by bell et al 2003

laser argon dating of melt breccias from the siljan impact structure sweden implications for a possible relationship to late devonian extinction events in earlier studies the 6575 km diameter siljan impact structure in sweden has been linked to the late devonian mass extinction event the siljan impact event has previously been dated by kar and ar ar chronology at 342368 ma with the commonly quoted age being 362 7 2 2 ma 2 recalculated using currently accepted decay constants until recently the accepted age for the frasnian famennian boundary and associated extinction event was 364 ma which is within error limits of this earlier siljan age here we report new ar ar ages extracted by laser spot and laser step heating techniques for several melt breccia samples from siljan interpreted to be impact melt breccia the analytical results show some scatter which is greater in samples with more extensive alteration these samples generally yield younger ages the two samples with the least alteration yield the most reproducible weighted mean ages one yielded a laser spot age of 377 2 2 5 ma 95 confidence limits and the other yielded both a laser spot age of 376 1 2 8 ma 95 confidence limits and a laser stepped heating plateau age over 70 6 39ar release of 377 5 2 4 ma 2 our conservative estimate for the age of siljan is 377 2 ma 95 confidence limits which is significantly different from both the previously accepted age for the frasnian famennian f f boundary and the previously quoted age of siljan however the age of the f f boundary has recently been revised to 374 5 2 6 ma by the international commission for stratigraphy which is within error the same as our new age however the currently available age data are not proof that there was a connection between the siljan impact event and the f f boundary extinction this new result highlights the dual problems of dating meteorite impacts where fine grained melt rocks are often all that can be isotopically dated and constraining the absolute age of biostratigraphic boundaries which can only be constrained by age extrapolation further work is required to develop and improve the terrestrial impact age record and test whether or not the terrestrial impact flux increased significantly at certain times perhaps resulting in major extinction events in earths biostratigraphic record

rock magnetic and paleomagnetic study of the keurusselka impact structure central finland abstract there are 31 proven impact structures in fennoscandia one of the most densely crater populated areas of the earth the recently discovered keurusselka impact structure 62 08 n 24 37 e is located within the central finland granitoid complex which formed 1890 1860 ma ago during the svecofennian orogeny it is a deeply eroded complex crater that yields in situ shatter cones with evidence of shock metamorphism e g planar deformation features in quartz new petrophysical and rock magnetic results of shocked and unshocked target rocks of various lithologies combined with paleomagnetic studies are presented the suggested central uplift with shatter cones is characterized by increased magnetization and susceptibility the presence of magnetite and pyrrhotite was observed as carriers for the remanent magnetization four different remanent magnetization directions were isolated 1 a characteristic svecofennian target rock component a with a mean direction of d 334 8 i 45 6 95 14 9 yielding a pole plat 51 1 plon 241 9 a95 15 1 2 component b d 42 4 i 64 1 95 8 4 yielding a pole plat 61 0 plon 129 1 a95 10 6 3 component c d 159 5 i 65 4 95 10 7 yielding a pole plat 21 0 plon 39 3 a95 15 6 and 4 component e d 275 5 i 62 0 95 14 4 yielding a pole plat 39 7 plon 314 3 a95 19 7 components c and e are considered much younger possibly neoproterozoic overprints compared with the components a and b the pole of component b corresponds with the 1120 ma pole of salla diabase dyke and is in agreement with the 40ar 39ar age of 1140 ma from a pseudotachylitic breccia vein in a central part of the structure therefore component b could be related to the impact and thus represent the impact age

erosion isostatic rebound models for uplift an application to south eastern australia summary a mountain s history includes two distinctive phases one of active tectonism and construction followed by one of erosion and passive isostatic rebound in the first phase uplift is driven by tectonic mechanisms while in the second phase base levels of the terrain are regionally uplifted it is this latter phase that is modelled here the starting model is a mountain range initially in isostatic equilibrium on a viscoelastic plate defined by the effective flexural rigidity d and relaxation time 7 the rate of erosion at any time t is assumed to be proportional to the elevation at that time with an erosional time constant 7 for a given present day topography the uplift erosion gravity and stress can be computed through time as functions of d 7 7 and the time to at which the erosional rebound mechanism became the dominant landscaping process the model has been applied to the highlands of south eastern australia which we assume to be an erosional residue of the palaeozoic lachlan fold belt observations of rivers cutting through cainozoic basalts and other geomorphological indicators of uplift can then be interpreted in terms of the isostatic rebound and there is no need to invoke active tectonic uplift mechanisms the model parameters that fit the observations are t 150 3 50myr dt 2 5 x ioz4nmmyr and to 180 200myr the predicted late palaeozoic fold belt topography is about 75 per cent greater than the present day values topographic depressions are predicted to have occurred along the margins of the formerly elevated areas and the model is relevant to understanding the evolution of basins flanking the highlands within the highland area erosion generally exceeds uplift but in some regions the two are approximately equal in keeping with recent geomorphological observations the flexural stresses associated with the erosion initially increase with time and maximum values in south eastern australia are predicted to occur in late cainozoic time with the stress state near the surface being mainly tensional

cambrian palaeomagnetic data from baltica implications for true polar wander and cambrian palaeogeography a reliable early cambrian c 535 ma and a preliminary late cambrian c 500 ma palaeomagnetic pole from baltica sweden overlap within uncertainty and they are also broadly compatible with vendian c 583 ma palaeomagnetic data apparent polar wander for baltica amounts to less than 25 between 583 and 500 ma and therefore negates recent speculations that the earth tipped 90 during the early cambrian true polar wander throughout vendian and cambrian times baltica lay at southerly latitudes c 30 60 s baltica was geographically inverted and present day northern baltica faced the nw margin of gondwana which covered the south pole laurentia eastern baltica and laurentia west gondwana were separated by the iapetus ocean while the aegir sea separated western baltica from the taimyr region of siberia during the cambrian baltica probably moved eastward along the gondwana margin and by c 515 520 ma subduction in the aegir sea was initiated a major event is recognized in late cambrian or early ordovician times c 500 478 ma when baltica must have undergone a 55 counter clockwise rotation in c 22 million years 3 ma we relate this to the early caledonian finnmarkian orogeny which involved arc continent collision following subduction

baltica a synopsis of vendian permian palaeomagnetic data and their palaeotectonic implications torsvlk t h smethurst m a van der voo r trench a abrahamsen n and halvorsen e 1992 baltlca a synopsis of vendlan permmn palaeomagnetic data and their palaeotectonlc implications earth sci rev 33 133 152 in light of recent additions to the palaeozoic palaeo magnetlc data base particularly for the ordovlclan era a revised apparent polar wander apw path for baltica has been constructed following a rigorous synthesis of all late precambrlan perm lan data the apw path is characterized by two prominent loops firstly a late precambrlan camb rlan loop probably relating to a rifting event and secondly a younger loop relating to a mid silurian scandlan colhsion event these features imply major change in plate tectonic reconfiguratlon baltlca probably represented an individual continental unit m early palaeozoic times and was positioned m high southerly latitudes in an inverted geographic orientation in such a reconstruction baltlca was separated from the northern margin of gondwana by the tornqulst sea and from laurentla by the iapetus ocean the tornqulst zone is thus interpreted as a passive or dextral transform margin during the early palaeozoic while undergoing counter clockwise rotations up to 1 6 ma baltica drifted northward through most ol the palaeozoic except for a short period of southerly movement in late silurian early devonian times after colhslon with laurentla rapid movements in latitude up to 9 cm yr are noted m late precambrlan earl y palaeozoic times and slgmficant decrease in velocities throughout palaeozoic time probably reflect the progressive amalgamation of a larger continent by early devonian euramerlca and permian pangea times the tornqulst sea had a principal component of palaeo east west orientation hence it is difficult to be precise in the timing of when micro continents such as eastern avalonla and the european masslfs ultimately collided along the southwestern margin of baltica these micro continents are considered to have been peripheral to gondwana m high southerly latitudes during the early ordovlclan eastern avalonla clearly had rifted off gondwana by llanvlrn llanded o times and may have collided with baltlca during late ordovlclan times although the present available sdunan palaeomagnetlc data from eastern avalonia may suggest colhslon in late silurian times across the lapetus facing margin of baltica laurentla was s tuated in equatorml to southerly latitudes during most of the lower palaeozoic these continents collided in mid silurian times l e a first collision between southwestern norway and greenland scotla nd which gave rise to the early scandlan orogeny 425 ma in southwestern norway possible followed by a later but less dramatic scandlan event in northern norway at around 410 ma since baltlca was geographically reverted m early palaeozoic times the colhsional margin could not have been a margin that once rifted off laurentm as assumed in a number of plate tectonic models

the size frequency and areal distribution of rock clasts at the spirit landing site gusev crater mars 1 size frequency and nearest neighbor spacing measurements derived from the mars exploration rover spirit s panoramic camera images of the gusev landing site reveal that rock clasts on the intercrater plains are smaller better sorted and more evenly spaced than clasts found near the crater rims the even clast spacing is interpreted to be due to wind transport which acts to minimize surface roughness during periods of high velocity wind

geochemical and mineralogical indicators for aqueous processes in the columbia hills of gusev crater mars 1 water played a major role in the formation and alteration of rocks and soils in the columbia hills the extent of alteration ranges from moderate to extensive five distinct rock compositional classes were identified the order for degree of alteration is watchtower clovis wishstone peace backstay the rover s wheels uncovered one unusual soil paso robles that is the most s rich material encountered clovis class rocks have compositions similar to gusev plains soil but with higher mg cl and br and lower ca and zn watchtower and wishstone classes have high al ti and p and low cr and ni peace has high mg and s and low al na and k backstay basalts have high na and k compared to plains adirondack basalts and paso robles soil has high s and p some rocks are corundum normative indicating that their primary compositions were changed by loss and or gain of rock forming elements clovis materials consist of magnetite nanophase ferric oxides npox hematite goethite ca phosphates ca and mg sulfates pyroxene and secondary aluminosilicates wishstone and watchtower rocks consist of fe oxides oxyhydroxides ilmenite ca phosphate pyroxene feldspar mg sulfates and secondary aluminosilicates peace consists of magnetite npox mg and ca sulfates pyroxene olivine feldspar apatite halides and secondary aluminosilicates paso robles consists of fe3 mg ca and other sulfates ca phosphates hematite halite allophane and amorphous silica columbia hills outcrops and rocks may have formed by the aqueous alteration of basaltic rocks volcaniclastic materials and or impact ejecta by solutions that were rich in acid volatile elements

pancam multispectral imaging results from the spirit rover at gusev crater panoramic camera images at gusev crater reveal a rock strewn surface interspersed with high to moderate albedo fine grained deposits occurring in part as drifts or in small circular swales or hollows optically thick coatings of fine grained ferric iron rich dust dominate most bright soil and rock surfaces spectra of some darker rock surfaces and rock regions exposed by brushing or grinding show near infrared spectral signatures consistent with the presence of mafic silicates such as pyroxene or olivine atmospheric observations show a steady decline in dust opacity during the mission and astronomical observations captured solar transits by the martian moons phobos and deimos as well as a view of earth from the martian surface

the tempo of geomorphological change evidence from southeastern australia a revised denudational chronology based on k ar dating of basalts for much of southeastern australia shows that many major topographic features are far older than was previously realized some upland surfaces originated in the mesozoic and others in the early tertiary in some areas the last major uplift and onset of canyon cutting occurred prior to the mid oligocene apart from the slow headward extension of canyons and localized high level stripping much of the region had taken on approximately its present day form by the mid miocene paradoxically however none of the mechanisms that have been proposed to explain the survival of paleoforms hold here these instances may well be typical of large parts of the interior of tectonic plates and a revision of widely held estimates of modal rates of denudation seems required

a late mesoproterozoic 40ar 39ar age for a melt breccia from the keurusselka impact structure finland field investigations in the eroded central uplift of the 30 km keurusselka impact structure finland revealed a thin dark melt vein that intersects the autochthonous shatter cone bearing target rocks near the homestead of kirkkoranta close to the center of the impact structure the petrographic analysis of quartz in this melt breccia and the wall rock granite indicate weak shock metamorphic overprint not exceeding 8 10 gpa the mode of occurrence and composition of the melt breccia suggest its formation as some kind of pseudotachylitic breccia 40ar 39ar dating of dark and clast poor whole rock chips yielded five concordant late mesoproterozoic miniplateau ages and one plateau age of 1151 10 ma 11 ma 2 mswd 0 11 p 0 98 considered here as the statistically most robust age for the rock the new 40ar 39ar age is incompatible with 1 88 ga svecofennian tectonism and magmatism in south central finland and probably reflects the keurusselka impact followed by impact induced hydrothermal chloritization of the crater basement in keeping with the crosscutting relationships in the outcrop and the possible influence of postimpact alteration the late mesoproterozoic 40ar 39ar age of 1150 ma should be treated as a minimum age for the impact the new 40ar 39ar results are consistent with paleomagnetic results that suggested a similar age for keurusselka which is shown to be one of the oldest impact structures currently known in europe and worldwide

palaeomagnetism and the siljan impact structure central sweden summary the siljan impact structure diameter c 52 km located in central sweden is considered the largest meteorite crater in western europe the time of impact has been estimated to be 368 ma from ar ar dating of an impact melt a palaeomagnetic study of rocks from inside and outside the impact structure has been carried out with the aim of identifying natural remanent magnetizations nrms related to the impact event primary magnetizations are partly preserved within the impact area however the directions of these original magnetizations are disturbed due to tectonic movements related to the impact three different directions of magnetizations not recognized elsewhere were identified within the central part of the structure these three magnetizations are defined in order of increasing coercivity hc and blocking temperature tb the origin of a high hc chemical remanent magnetization crm c of late palaeozoic time carried by haematite can be interpreted as due to oxidation caused by circulating meteoric water in cracks and fractures caused by the impact another component b identified in a lower temperature range 40d 580dc is probably carried by magnetite in pseudotachylite this magnetization is considered as a thermal remanent magnetization while in other rocks its pre tectonic character and occurrence also in the low coercivity range implies a shock remanent origin the palaeomagnetic pole for this remanence corresponds to a silurian devonian age which gives an age of impact which is not very diffirent from that estimated by radiometric data a third low hc and tb component a is interpreted to be a crm carried by slowly growing goethite the direction of this crm implies it to be a recent post impact magnetization

fluid inclusions in microstructures of shocked quartz from the keurusselka impact site central finland granitoid rock samples from the assumed center of the keurusselka impact site were subjected to a systematic study of fluid inclusion compositions and densities in various microstructures of the shocked quartz the results are consistent with the following impact induced model of formation after cessation of all major regional tectonic activity and advanced erosional uplift of the fennoscandian shield a meteorite impact approximately 1 1 ga caused the formation of planar fractures pfs and planar deformation features pdfs and the migration of shock liberated metamorphic fluid co2 h2o to the glass in the pdfs postimpact annealing of the pdfs led to the formation of co2 h2o fluid inclusion decorated pdfs the scarce fluid inclusion implosion textures ips suggest a shock pressure of 7 6 10 gpa the postimpact pressure release and associated heating initiated hydrothermal activity that caused re opening of some pfs and their partial filling by moderate salinity high temperature 200 c h2o chlorite quartz and moderate density co2 the youngest postimpact endogenic sub and nonplanar microfractures mfs are characterized by low density co2 and low salinity low temperature 200 c h2o

fido prototype mars rover field trials black rock summit nevada as test of the ability of robotic mobility systems to conduct field science 1 the field integration design and operations fido prototype mars rover was deployed and operated remotely for 2 weeks in may 2000 in the black rock summit area of nevada the blind science operation trials were designed to evaluate the extent to which fido class rovers can be used to conduct traverse science and collect samples fido based instruments included stereo cameras for navigation and imaging an infrared point spectrometer a color microscopic imager for characterization of rocks and soils and a rock drill for core acquisition body mounted belly cameras aided drill deployment and front and rear hazard cameras enabled terrain hazard avoidance airborne visible and infrared imaging spectrometer aviris data a high spatial resolution ikonos orbital image and a suite of descent images were used to provide regional and local scale terrain and rock type information from which hypotheses were developed for testing during operations the rover visited three sites traversed 30 m and acquired 1 3 gigabytes of data the relatively small traverse distance resulted from a geologically rich site in which materials identified on a regional scale from remote sensing data could be identified on a local scale using rover based data results demonstrate the synergy of mapping terrain from orbit and during descent using imaging and spectroscopy followed by a rover mission to test inferences and to make discoveries that can be accomplished only with surface mobility systems

paleomagnetism and petrophysics of the janisjarvi impact structure russian karelia paleomagnetic rock magnetic and petrophysical results are presented for impactites and target rocks from the lake janisjarvi impact structure russian karelia the impactites tagamites suevites and lithic breccias are characterized by increased porosity and magnetization which is in agreement with observations performed at other impact structures thermomagnetic hysteresis and scanning electron microscope sem analysis document the presence of primary multidomain titanomagnetite with additional secondary titanomaghemite and ilmenohematite the characteristic impact related remanent magnetization chrm direction d 101 5 i 73 1 95 6 2 yields a pole lat 45 0 n long 76 9 e dp 9 9 dm 11 0 additionally the same component is observed as an overprint on some rocks located in the vicinity of the structure which provides proofs of its primary origin an attempt was made to determine the ancient geomagnetic field intensity seven reliable results were obtained yielding an ancient intensity of 68 7 7 6 t corresponding to vdm of 10 3 1 1 x 10 22 am 2 the intensity however appears to be biased toward high values mainly because of the concave shape of the arai diagrams the new paleomagnetic data and published isotopic ages for the structure are in disagreement according to well defined paleomagnetic data two possible ages for magnetization of jnisjrvi rocks exist 1 late sveconorwegian age 900 850 myr or 2 late cambrian age 500 myr however published isotopic ages are 718 5 myr k ar and 698 22 myr 39ar 40ar but such isotopic dating methods are often ambiguous for the impactites

a late paleoproterozoic key pole for the fennoscandian shield a paleomagnetic study of the keuruu diabase dykes central finland abstract we present an updated paleomagnetic pole and a new isotope age for the late paleoproterozoic svecofennian diabase dykes from keuruu central finland the paleomagnetic results reveal a dual polarity remanent magnetization with asymmetry which we explain by an unremoved secondary component contaminating both normal n and reversed r vectors the chrm is carried by magnetite most of which are primary grains crystallized from basaltic magma the primary nature of the chrm is further supported by positive baked contact tests an r polarity dyke shows a u pb concordia age of 1870 9 ma zircons from another dyke of n polarity reveal a mean pb pb age of 1867 8 ma the combined n and r mean chrm direction is d 340 4 i 35 2 95 5 8 k 31 3 n 21 dykes yielding a paleomagnetic pole of plat 45 7 plon 230 9 a 95 5 5 this positions the fennoscandian shield at low latitudes 19 4 and aligns with superior craton in a way that would naturally proceed into the 1 8 1 2 ga nena north europe north america configuration paleosecular variation analysis of n polarity dykes is consistent with the low latitude position of baltica

experimental evaluation of magnetic interaction in pyrrhotite bearing samples pyrrhotite bearing metamorphic limestones have recently experienced an increasing relevance in paleomagnetic research simple univectorial remanences document the metamorphic uplift whereas more complex multicomponent ptrms may constrain its age for a successful application of the latter it is important to estimate the degree of magnetic interactions to ensure the additivity of individual ptrm segments we therefore have subjected the sized dispersed suite 5 250m of tte pyrrhotite to forc analysis and

evidence of phyllosilicates in wooly patch an altered rock encountered at west spur columbia hills by the spirit rover in gusev crater mars 1 on its traverse to columbia hills the mars exploration rover spirit investigated an outcrop designated wooly patch that exhibited morphological mineralogical and geochemical characteristics at the extreme ends of ranges observed among rocks studied at west spur a westward projecting salient near the foot of the columbia hills gusev crater the major element composition and fe mineralogy as determined by the alpha particle x ray spectrometer and mossbauer spectrometer are inconsistent with any reasonable assemblage of basaltic minerals in that there is an excess of si and al the combined data are best explained by the presence of 14 17 phyllosilicate minerals phyllosilicates that account for the composition and cation ratios include members of the kaolinite serpentine chlorite and septechlorite groups the potential existence of kaolinite type al rich phyllosilicates within the wooly patch outcrop suggests a mildly acidic environment ph 4 6 in the past and an open hydrologic system with good drainage conditions in the environment where these rocks were altered

palaeomagnetic and rock magnetic investigations of the sipoo subjotnian quartz porphyry and diabase dykes southern fennoscandia abstract the sipoo quartz porphyry dyke swarm u pb zircon age 1 63 ga in southern finland carries an intermediate to high coercivity remanent magnetization a n d 22 2 i 1 8 k 34 2 95 13 3 n 5 dykes which is regarded as primary the sipoo diabase dykes emplaced slightly before the granite porphyries yield a highly scattered antiparallel direction a r d 198 0 i 6 5 k 6 2 95 40 1 n 4 dykes isolated in intermediate to high coercivities based on positive contact test results remanence a r is primary in the diabases the best preserved diabase dyke as determined by petrographic and bulk magnetization properties carries both the a r magnetization and the a n magnetization as a secondary component in some samples the most altered diabase dyke is almost completely overprinted by a n the overprinting has taken place as a result of hydrothermal alteration and formation of new magnetite during the emplacement of quartz porphyry dykes and rapakivi granite the quartz porphyries and diabases carry mixed sd and md magnetic grain sizes the large md grains being responsible for a relatively large present earth s field pef magnetization in addition a high coercivity magnetization b d 23 9 i 52 2 k 215 8 95 6 3 n 4 dykes presumably a chemical overprint has been isolated in the quartz porphyries the b magnetization is interpreted to be either an intermediate direction between a n and pef with no geological significance or to represent a separate reactivation of the crust at about 1 32 ga ago

palaeomagnetism of the lower ordovician orthoceras limestone st petersburg and a revised drift history for baltica in the early palaeozoic summary palaeomagnetic investigation of lower ordovician limestone in the vicinity of st petersburg yields a pole position at latitude 34 7 n longitude 59 1 e dp dm 5 7 6 4 a probable primary remanence origin is supported by the presence of a field reversal the limestone carries one other remanent magnetization component associated with a mesozoic remagnetization event an apparent polar wander path is compiled for baltica including the new result ranging in age from vendian to cretaceous ages of the published lower to midpalaeozoic palaeomagnetic pole positions are adjusted in accordance with the timescale of tucker mckerrow 1995 the new arenig result is the oldest of a series of ordovician and silurian palaeomagnetic pole positions from limestones in the baltic region there are no data to constrain apparent polar wander for the tremadoc cambrian and latest vendian if the fen complex results previously taken to be vendian in age c 565 ma are reinterpreted as permian remagnetizations an early ordovician cambrian vendian cusp in the polar wander path for baltica is eliminated the apparent polar wander curve might then traverse directly from poles for vendian dykes on the kola peninsula c 580 ma towards our new arenig pole c 480 ma the consequence of this change in terms of the motion of baltica in cambrian times is to reduce significantly a rotational component of movement the new arenig pole extends knowledge of ordovician apparent polar wander an increment back in time and confirms the palaeolatitude and orientation of baltica in some published palaeogeographies exclusion of the fen complex result places baltica in mid to high southerly latitudes at the dawn of the palaeozoic consistent with faunal and sedimentological evidence but at variance with some earlier palaeomagnetic reconstructions

integrated geophysical analysis supporting the impact origin of the mjolnir structure barents sea abstract gravity magnetic and seismic traveltime anomalies observed at the 40 km diameter mjolnir impact structure reveal a distinct spatial correspondence with the radially zoned seismic structure the gravity anomaly is dominated by a 2 5 mgal 14 km wide centrally located high superimposed on a 45 km diameter low that attains minimum values of 1 5 mgal the magnetic anomaly field exhibits several local low amplitude anomalies within the 100 nt range located towards the periphery while seismic mapping of a prominent originally planar reflector beneath the structure brings out a central pull up traveltime anomaly on the order of 80 ms in terms of impact origin the integrated geophysical modelling based on the characteristic bowl shaped seismic disturbance beneath the structure supports the differentiation into a central uplift and a peripheral region interaction of several impact cratering processes such as impact induced porosity increase due to brecciation mass transport during collapse and structural uplift explains the modelled physical properties associated with the disturbance the modelling further substantiates the interpretation of the mjolnir structure as an impact crater and demonstrates the incompatibility of alternative geological origins such as salt or clay diapirism and igneous intrusions

secondary magnetizations in shear and fault zones in southern finland abstract studies on remanent magnetization of shear and fault zones of crystalline rocks in southern finland have been carried out to test juvenile fluid activity that can be dated paleomagnetically locating in the central part of baltica the area has been tectonically relatively quiet since the precambrian however tectonism at the margins of the craton during the caledonian hercynian and uralian orogenies probably reactivated faults and resulted in low temperature hydrothermal activity also within the craton we identified two consistent remanent magnetization components in four out of five studied localities one remanence component has an intermediate to high coercivity nnw directed magnetization d 334 7 i 35 2 k 92 1 95 9 6 and unblocking temperatures suggest that it resides in titano magnetite the direction is similar to the remanence that is commonly observed in svecofennian age ca 1 9 ga rocks all over the precambrian fennoscandian shield and probably represents the primary svecofennian magnetization preserved in the host rocks another common component is directed ne i 30 8 d 35 3 k 264 5 95 5 7 and is carried by hematite and maghemite its resulting paleomagnetic pole compares well with phanerozoic paleopoles of baltica and is suggested to represent a permian remagnetization we interpret that this remanence reflects the reactivation of the svecofennian crust in the late paleozoic due to tectonic events related to the formation of the supercontinent pangea in addition remagnetizations due to mesoproterozoic rapakivi magmatism and younger mesozoic to present events were identified

in situ and experimental evidence for acidic weathering of rocks and soils on mars experimental data for alteration of synthetic martian basalts at ph 0 1 indicate that chemical fractionations at low ph are vastly different from those observed during terrestrial weathering rock surface analyses from gusev crater are well described by the relationships apparent from low ph experimental alteration data a model for rock surface alteration is developed which indicates that a leached alteration zone is present on rock surfaces at gusev this zone is not chemically fractionated to a large degree from the underlying rock interior indicating that the rock surface alteration process has occurred at low water to rock ratio the geochemistry of natural rock surfaces analyzed by apxs is consistent with a mixture between adhering soil dust and the leached alteration zone the chemistry of rock surfaces analyzed after brushing with the rat is largely representative of the leached alteration zone the chemistry of rock surfaces analyzed after grinding with the rat is largely representative of the interior of the rock relatively unaffected by the alteration process occurring at the rock surface elemental measurements from the spirit opportunity pathfinder and viking 1 landing sites indicate that soil chemistry from widely separated locations is consistent with the low ph low water to rock ratio alteration relationships developed for gusev rocks soils are affected principally by mobility of fe and mg consistent with alteration of olivine bearing basalt and subsequent precipitation of fe and mg bearing secondary minerals as the primary control on soil geochemistry copyright 2006 by the american geophysical union

crustal evolution of fennoscandia palaeomagnetic constraints abstract palaeomagnetic poles from fennoscandia ranging in age from archaean to tertiary are compiled and graded using a modified briden duff classification scale an new filtering technique is applied to select only the most reliable poles for analysis the filtering takes into account the following information 1 1 source block of rock unit 2 2 age of rock 3 3 age of magnetization component 4 4 scatter of palaeomagnetic directions 5 5 information from multicomponent analysis of natural remanent magnetization nrm 6 6 whether the pole considered belongs to a cluster or subcluster of poles 7 7 magnetic polarity and 8 8 the author s original assignment of results data are still insufficient for the drawing of separate apparent polar wander paths apwp for different blocks or cratons of fennoscandia treating fennoscandia as a single plate a new apwp from archaean to permian is constructed from the five previously drawn apwp loops or hairpins only one the jatulian loop 2200 2000 ma disappears in filtering the loops during 1925 1700 ma and during 1100 800 ma ago are linked to svecofennian and sveconorwegian orogenies respectively palaeomagnetic data support the concept that these orogenies took place episodically three distinct orogenic pulses early middle and late can be distinguished in the cluster plots of palaeopoles the drift history of fennoscandia from archaean to permian is presented during most of geological history fennoscandia has occupied low to moderate latitudes and undergone considerable latitudinal shifts and rotations the svecofennian and sveconorwegian orogenies have different kinematic characteristics during the svecofennian orogeny fennoscandia drifted slowly while rotating a large amount in an anticlockwise sense during the sveconorwegian orogeny it drifted rapidly and rotated first clockwise and then anticlockwise the most striking feature in the drift velocity curves is however the pronounced maxima in the latitudinal drift and rotation rates 9 cm yr and 0 8 ma respectively during the late subjotnian jotnian anorogenic magmatism and rifting phase 1450 1250 ma ago possibly reflecting the passage of fennoscandia across a thermal upwelling hotspot at equatorial latitudes the use of palaeomagnetism in delineating and dating movements between blocks is demonstrated with three examples from the polar profile area the northernmost section of the european geotraverse

spectral variability among rocks in visible and near infrared multispectral pancam data collected at gusev crater examinations using spectral mixture analysis and related techniques 1 visible and near infrared vnir multispectral observations of rocks made by the mars exploration rover spirit s panoramic camera pancam have been analyzed using a spectral mixture analysis sma methodology scenes have been examined from the gusev crater plains into the columbia hills most scenes on the plains and in the columbia hills could be modeled as three end member mixtures of a bright material rock and shade scenes of rocks disturbed by the rover s rock abrasion tool rat required additional end members in the columbia hills there were a number of scenes in which additional rock end members were required the sma methodology identified relatively dust free areas on undisturbed rock surfaces as well as spectrally unique areas on rat abraded rocks spectral parameters from these areas were examined and six spectral classes were identified these classes are named after a type rock or area and are adirondack lower west spur clovis wishstone peace and watchtower these classes are discriminable based primarily on near infrared nir spectral parameters clovis and watchtower class rocks appear more oxidized than wishstone class rocks and adirondack basalts based on their having higher 535 nm band depths comparison of the spectral parameters of these gusev crater rocks to parameters of glass dominated basaltic tuffs indicates correspondence between measurements of clovis and watchtower classes but divergence for the wishstone class rocks which appear to have a higher fraction of crystalline ferrous iron bearing phases despite a high sulfur content the rock peace has nir properties resembling plains basalts

spirit rover localization and topographic mapping at the landing site of gusev crater mars 1 by sol 440 the spirit rover has traversed a distance of 3 76 km actual distance traveled instead of odometry localization of the lander and the rover along the traverse has been successfully performed at the gusev crater landing site we localized the lander in the gusev crater using two way doppler radio positioning and cartographic triangulations through landmarks visible in both orbital and ground images additional high resolution orbital images were used to verify the determined lander position visual odometry and bundle adjustment technologies were applied to compensate for wheel slippage azimuthal angle drift and other navigation errors which were as large as 10 5 in the husband hill area we generated topographic products including 72 ortho maps and three dimensional 3 d digital terrain models 11 horizontal and vertical traverse profiles and one 3 d crater model up to sol 440 also discussed in this paper are uses of the data for science operations planning geological traverse surveys surveys of wind related features and other science applications

density and magnetic susceptibility of rocks from the lockne and tvaren marine impact structures the lockne and tv ren impact craters in sweden formed in a marine environment during the ordovician the contrast in density between the impact breccias and the surrounding target rock of these two craters is significantly lower than what has been found in craters formed in crystalline targets on land another marine target structure the estonian k rdla structure demonstrates intermediate contrast in impact breccia and target rock which we attribute to the interpreted shallowness of the sea at the k rdla impact site we conclude that the main cause for these low density contrasts is pore and fracture filling of calcite with subordinate quartz and fluorite calcite is the most abundant cement and its density differs most from that of fractured and brecciated bedrock with a low degree of cementation furthermore from the studied cases it is concluded that the target rock to impact rock contrast is generally the highest in craters formed on land in crystalline targets and the lowest in craters formed at sea while craters formed on land in sedimentary targets are intermediate the low density contrasts should decrease the negative gravity anomalies of marine craters

the tornquist sea and baltica avalonia docking early ordovician late arenig limestones from the sw margin of baltica scania bomholm have multicomponent magnetic signatures but high unblocking components predating folding and the corresponding palaeomagnetic pole latitude 19degreesn longitude 051degreese compares well with arenig reference poles from baltica collectively the arenig poles demonstrate a midsoutherly latitudinal position for baltica then separated from avalonia by the tomquist sea tornquist sea closure and the baltica avalonia convergence history are evidenced from faunal mixing and increased resemblance in palaeomagnetically determined palaeolatitudes for avalonia and baltica during the mid late ordovician by the caradoc avalonia had drifted to palaeolatitudes compatible with those of sw baltica and subduction beneath eastern avalonia was taking place we propose that explosive vents associated with this subduction and related to andean type magmatism in avalonia were the source for the gigantic mid caradoc c 455 ma ash fall in baltica i e the kinnekulle bentonite avalonia was located south of the subtropical high during most of the ordovician and this would have provided an optimum palaeoposition to supply baltica with large ash falls governed by westerly winds in scama we observe a persistent palaeomagnetic overprint of late ordovician ashgill age pole latitude 4degreess longitude 012degreese the remagnetisation was probably spurred by tectonic derived fluids since burial alone is inadequate to explain this remagnetisation event this is the first record of a late ordovician event in scania but it is comparable with the shelveian event in avalonia low grade metamorphism in the north sea basement of ne germany 440 450 ma and sheds new light on the baltica avalonia docking c 2002 elsevier science b v all rights reserved less

exogenic and endogenic breccias a discussion of major problematics abstract pseudotachylitic breccias impact melt rock ultra cataclasites and even ultramylonites may macroscopically be of very similar appearance even detailed optical microscopic work may not suffice to identify the actual type of melt rock studied the difficulties to distinguish different tectonically produced breccias fault rocks and impact breccias for which no uniformly accepted nomenclature exists are examined and the various formational processes friction melting or shock melting at the macro and micro scales are discussed special emphasis is placed on the occurrence of different and multiple breccia types within impact structures where not only impact induced friction melt and impact melt may occur but where tectonically produced fault rocks that are not related to the impact event may further complicate the breccia situation melting on shatter cone surfaces and its likely formation the proposed origin as distal impact breccia of certain diamictites and problems with carbonate breccias and caused by metamorphic overprint on breccias are discussed it is cautioned not too easily to reach generalized conclusions for example with regard to the usage of the a and b type pseudotachylite terminology areas in need of further breccia studies if possible in close collaboration between impact and tectonic researchers are emphasized