relative paleointensity in sediments a pseudo thellier approach we present a method for normalizing sedimentary records for estimating relative paleointensity of the geomagnetic field similar to that successfully used to obtain absolute paleointensity from thermally blocked remanences it has the advantages that it is more effective in removing unwanted viscous remanence thereby improving agreement among various records and that it allows the estimation of the uncertainty in the relative paleointensity calculated

high paleointensities for the canary islands constrain the levant geomagnetic high understanding the behavior of enigmatic geomagnetic traits such as the levant intensity high is currently challenged by a lack of full vector records of regional variations in the geomagnetic field here we apply the recently proposed multi method paleointensity approach to a suite of 19 lavas from the canary islands dating between 4000 bc and 1909 ad our new record reveals high paleointensities vadms 120 zam2 coinciding with and shortly after the peak in geomagnetic intensity in the levant at 1000 bc furthermore our data suggests a westward movement of this geomagnetic phenomenon at a rate of 6 7 12 per century in addition to izzi thellier microwave thellier and the multi specimen method the calibrated pseudo thellier method is an important part of the multi method paleointensity approach the calibration of this relative paleointensity method was derived from a suite of hawaiian lavas it is improved with the results of the canarian cooling units pseudo thellier results from samples with very low curie temperature 150 c however cannot be reliably converted to absolute paleointensity estimates the multi method paleointensity approach yielded a reliable estimate for 60 of the flows sampled an unusually high success rate for a paleointensity study involving lavas

magnetic remanence in the murchison meteorite the murchison meteorite is a carbonaceous chondrite containing a small amount of chondrules various inclusions and matrix with occasional porphyroblasts of olivine and or pyroxene it also contains amino acids that may have served as the necessary components for the origin of life magnetic analyses of murchison identify an ultrasoft magnetic component due to superparamagnetism as a significant part of the magnetic remanence the rest of the remanence may be due to electric discharge in the form of lightning bolts that may have formed the amino acids the level of magnetic remanence does not support this possibility and points to a minimum ambient field of the remanence acquisition we support our observation by showing that normalized mineral magnetic acquisition properties establish a calibration curve suitable for rough paleofield determination when using this approach 1 2 of the natural remanence left in terrestrial rocks with trm and or crm determines the geomagnetic field intensity irrespective of grain size or type of magnetic mineral with the exception of hematite the same method is applied to the murchison meteorite where the measured meteorite remanence determines the paleofield minimum intensity of 200 2000 nt during and or after the formation of the parent body

n paraffins in the sediments and in situ fossils of the lake turkana basin kenya abstract residual hydrocarbons were extracted from a number of vertebrate fossils and their surrounding sediments collected at six sites in the plio pleistocene sediments of paleo lake turkana in northern kenya gas chromatographic separation of these alkane fractions showed three recognizable suites of hydrocarbons a c 15 to c 19 group derived from algae a c 20 to c 30 group with no odd even preference derived from microbial action on soil organics and a c 21 to c 35 group with high odd even preference derived from plant waxes no alkanes identifiable as being derived from the original animal fats were observed the plant wax alkanes and microbial hydrocarbons were nearly ubiquitous in sands silts clays and the fossils the algal hydrocarbons on the other hand were found only in the sands and silts there were no consistent differences between the hydrocarbon content of the fossils and the surrounding sediments there were great local variations in alkane distribution but no patterns were discernible the total hydrocarbon content of these arid region sediments is almost vanishingly small compared to sediments in more temperate climates

source rock distribution model of the periadriatic region the periadriatic area is a mosaic of geological provinces comprised of spatially and temporally similar tectonic sedimentary cycles tectonic evolution progressed from a triassic early jurassic liassic continental rifting stage on the northern edge of the african craton through an early jurassic middle liassic late cretaceous eocene oceanic rifting stage and passive margin formation to a final continental collision and active margin deformation stage in the late cretaceous eocene to holocene this evolution occurred in a transtensional and transpressional framework resulting from the oblique separation and convergence of the african and european plates extensive shallow water carbonate platform deposits covered large parts of the periadriatic region in the late triassic platform breakup and development of a platform to basin carbonate shelf morphology began in the late triassic and extended through the cretaceous on the basis of this paleogeographic evolution the regional geology of the periadriatic region can be expressed in terms of three main upper triassic paleogene sedimentary sequences the platform sequence sequence a the platform to basin sequence sequence b and the basin sequence sequence c these sequences developed during the initial rifting and subsequent passive margin formation tectonic stages three distinct episodes of source bed deposition can be identified middle upper triassic to lower jurassic liassic organic rich oil prone and mature source beds generally are structurally controlled and are closely associated with transtensional intraplatform basins formed in the early continental rifting stage the principal triassic source basins and most of the surface hydrocarbon indications and economically important oil fields of the periadriatic region are associated with sequence b areas the second episode of organic rich rocks deposition includes both shallow and deeper water facies of jurassic cretaceous age thin immature deep water epioceanic organic rich marls and shales are generally bathymetrically controlled these units are related to basin wide anoxic events in the tethys ocean and its submerged continental margin and are associated with sequence b areas middle upper cretaceous shallow water oil prone facies occur in isolated anoxic basins within carbonate platforms these source sequences are generally thicker and are associated with sequence a areas no major hydrocarbon accumulation can be directly attributed to the jurassic cretaceous epioceanic and intraplatform source rock sequences the third episode of source bed deposition characterizes the final active margin deformation stage and is represented by upper tertiary organic rich terrigenous units mostly gas prone these are essentially associated with turbiditic and flysch sequences of foredeep basins and have generated the greater part of the commercial biogenic gases of the periadriatic region

thermoremanence anhysteretic remanence and susceptibility of submicron magnetites nonlinear field dependence and variation with grain size we have measured initial susceptibility 0 and the dependence of anhysteretic remanent magnetization arm and thermoremanent magnetization trm on applied field for seven samples of magnetite with mean grain sizes from 40 to 540 nm trm acquisition is nonlinear in geomagnetically relevant weak fields contrary to the usual assumption made in paleointensity determination over the 40 540 nm range 0 varies with particle shape but only weakly with particle size d and can be used to correct for varying magnetite concentrations in sediment cores arm is strongly size dependent over the same range and is the best parameter for monitoring grain size variations in natural samples arm and trm have similar variations as d 1 for d 1 m suggesting a common source for this pseudo single domain psd dependence on grain size however trm is 10 20 times more intense than arm in grains around 0 2 m in size the trm microstate seems to be a two domain structure whereas the arm microstate may be a vortex structure which has never before been convincingly demonstrated by magnetic measurements independent evidence comes from theoretical fits to trm and arm field dependence data in moderate and strong fields trm in 215 540 nm magnetites is explained by two domain theory but arm is not in smaller grains d 0 1 m a psd theory predicts that trm is carried by single domain sd moments of entire grains but arm resides in moments 1 per grain 20 40 times weaker these remanence levels match those of metastable sd and vortex states respectively we therefore propose that magnetite grains in the 0 1 0 5 m size range can remain in metastable sd or two domain states following acquisition of trm but revert to a vortex ground state when field cycled for example in arm acquisition or alternating field demagnetization

upper cenomanian lower turonian sea level rise and its consequences on the adriatic dinaric carbonate platform the adriatic carbonate platform existed throughout most of the mesozoic as an isolated intraoceanic carbonate platform it is characterized by what has been traditionally labelled a continuous shallow marine carbonate sedimentation without terrigenous influences however global sea level changes left unequivocal imprints in the continuous carbonate record thus proving that the carbonate platform sensitively responded to sea level fluctuations this paper focuses on the relatively short cenomanian turonian drowning event which temporarily submerged the platform below the euphotic zone and which is related here to the well known global cenomanian turonian sea level highstand this drowning episode is characterized by the abrupt disappearance of numerous shallow water benthic invertebrate taxa and by an abundant occurrence of planktonic organisms including calcispheres and primitive planktonic foraminifera near the middle of the turonian the platform regime was re established correlating with the global fall in sea level the situation is different only at the south west margin of the platform where pelagic sedimentation initiated near the end of the cenomanian continues into the santonian and probably marks the adriatic trough the drowning began earlier in the middle cenomanian in those areas nearer to the north east margin of the platform the area of what is today central croatia and then progressed gradually towards the more interior areas of the platform the middle dalmatian islands which were drowned near the end of the cenomanian

the multimethod palaeointensity approach applied to volcanics from terceira full vector geomagnetic data for the past 50 kyr the island of terceira 38 5 n 27 2 w in the azores archipelago boasts a wealth of well dated recent volcanic products it is therefore the ideal location to improve the resolution of the full vector geomagnetic field record for the mid atlantic ocean we investigated 21 sub sites sampled from 10 different cooling units six of these cooling units are from the holocene the other four are approximately coeval with the age of known geomagnetic excursions after successfully determining the palaeodirections from all but one site we applied the multimethod palaeointensity approach to all sites here we used three different palaeointensity methods the izzi thellier protocol the multispecimen technique and the calibrated pseudo thellier method for the holocene sites four robust palaeointensity estimates were obtained they mostly agree with data from the nearby island of sao miguel and data from the iberian peninsula and west africa two older sites dated at 25 7 and 46 3 ka produced low palaeointensities 24 4 and 24 1 t respectively as both the izzi thellier and pseudo thellier methods yielded technically acceptable results for these sites we used them to improve the pseudo thellier calibration relation and establish its applicability to lower palaeointensities sixty per cent of all sampled cooling units ages in our study yielded a technically successful palaeointensity estimate this unusually high success rate is attributed both to our sampling strategy and the implementation of the multimethod approach

response of a carbonate platform to the cenomanian turonian drowning and oae 2 a case study from the adriatic platform dalmatia croatia abstract global perturbations during the cenomanian turonian boundary ctb interval and the oceanic anoxic event 2 oae 2 represent one of the most extensively studied past environmental changes to explore the response of various carbonate platform depositional systems to such major environmental perturbations strata of the intra tethyan adriatic carbonate platform sensu stricto from the island of brac adriatic sea croatia provide excellent exposures and a previously well established upper cretaceous lithostratigraphic framework within this context this study integrated lithostratigraphy biostratigraphy and chemostratigraphy to describe a drowned platform succession underlain and overlain by peritidal carbonates carbon isotope stratigraphy of this succession revealed a shift towards positive 13c values that reached 4 to 5 vpdb and represent the ctb interval excursion plateau we observed variations in thickness of the drowned platform successions and explained them by three superimposed mechanisms 1 diachronous drowning of platform relief 2 intra platform redeposition of parts of the successions by various mass gravity transport processes indicating enhanced instability due to increasing accommodation space related to the late cenomanian platform drowning and synsedimentary tectonics and 3 migration of major carbonate factories during the recovery of shallow platform environments the results indicate that the ctb interval event caused unusual increase in accommodation space on the carbonate platform enabling open marine influence and synsedimentary redeposition however widespread organic rich black shales reported from coeval strata of other regions have not been documented from the platform top successions to date and were probably accumulated in deeper anoxic settings below the rising sea level

global changes in intensity of the earth s magnetic field during the past 800kyr recent advances in palaeomagnetic and dating techniques have led to increasingly precise records of the relative intensity of the earth s past magnetic field at numerous field sites the compilation and analysis of these records can provide important constraints on changes in global magnetic field intensity and therefore on the earth s geodynamo itself a previous compilation for the past 200 kyr integrated 17 marine records into a composite curve1 with the geomagnetic origin of the signal supported by an independent analysis of 10be production made on different cores2 the persistence of long term features in the earth s magnetic intensity or the existence of long term periodic changes cannot however be resolved in this relatively short time span here we present the integration of 33 records of relative palaeointensity3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 into a composite curve spanning the past 800 kyr we find that the intensity of the earth s dipole field has experienced large amplitude variations over this time period with pronounced intensity minima coinciding with known excursions in field direction reflecting the emergence of non dipole components no stable periodicity was found in our composite record and therefore our data set does not support the hypothesis that the earth s orbital parameters have a direct and strong influence on the geodynamo

basalt seawater interaction the plenus cold event enhanced weathering and geochemical change deconstructing oceanic anoxic event 2 cenomanian turonian late cretaceous oceanic anoxic event 2 cenomanian turonian ca 94 ma represents a major palaeoceanographic phenomenon that took place during an interval of extreme global warmth when large amounts of organic matter entered the marine burial record probably triggered by increased availability of nutrients for planktonic biota three sections eastbourne sussex uk raia del pedale campania italy and tarfaya morocco recording this event illustrate the influence on marine geochemistry of mafic volcanic rock seawater interaction anoxia to euxinia and re oxygenation and cooling during the so called plenus cold event the eastbourne section represents the organic lean epicontinental pelagic deposits of the english chalk the raia del pedale section represents a shallow water platform carbonate on the tethyan continental margin also largely devoid of organic matter and the tarfaya core represents an atlantic margin site where cyclically bedded organic rich sediments were well developed correlation between all three sections is readily achieved by biostratigraphy and carbon isotope stratigraphy 13ccarb and 13corg over the oceanic anoxic event 2 interval represented by a characteristic broad positive carbon isotope excursion the stratigraphic range of the plenus cold event defined by the presence in two discrete levels of boreal fauna and an excursion to heavier oxygen isotope values in the english chalk can be identified in raia del pedale and tarfaya by using the carbon isotope curve as a correlative tool similarly a section in southern france allows its co existing osmium isotope excursion to relatively unradiogenic values to be placed in the context of the oceanic anoxic event in all three analysed sections a fall to lower osmium isotope values clearly pre dated the onset of oceanic anoxic event 2 as defined by the initial rise in carbon isotope values allowing the putative magmatic mafic event as a trigger for the oceanic anoxic event an initial drop in sulphur isotope ratios 34scas at eastbourne correlates with the osmium isotope curve suggesting that isotopically light sulphur could have been derived from a mafic igneous source re oxygenation of sediments of all three investigated sections during the plenus cold event is variably illustrated by change in cerium calcium iodine calcium molybedenum calcium and uranium calcium ratios according to the redox behaviour of the elements in question and whether controls on seawater chemistry were local or global in nature changes in molybdenum isotope ratios from tarfaya and portions of the sulphur isotope curve from eastbourne and raia del pedale also indicate the probable presence of more oxygen rich bottom waters during the plenus cold event oxidation by such waters of previously deposited organic rich shales as well as loss of anoxic euxinic sinks is credited with temporarily enriching global seawater in a range of other redox sensitive trace metals for example v cr co ni cu zn and cd during ongoing basalt seawater interaction indicated by persistent relatively non radiogenic osmium isotope seawater values however early diagenetic enrichment of manganese in the english chalk over much of the oceanic anoxic event interval is broadly correlative in time with relatively low osmium isotope values in sections elsewhere a relationship that may be due to the lack of affinity of manganese with carbon rich shales hence allowing relatively elevated concentrations of the element in marine waters to persist during leaching of mafic rocks unlike other redox sensitive species the calcium isotope and lithium isotope ratios from eastbourne and raia del pedale indicate an increase in global weathering during the initial phase of oceanic anoxic event 2 and the shift in strontium isotopes and osmium isotopes to more unradiogenic values during the event suggests that not only construction but also destruction of one or more large igneous provinces was probably a proximal cause of this major palaeoceanographic phenomenon by elevating nutrient levels and planktonic productivity in large tracts of the world ocean globally widespread carbon burial and silicate weathering are both identified as important mechanisms for drawing down atmospheric carbon dioxide that in the absence of overwhelming volcanogenic replenishment of this greenhouse gas during the early phase of oceanic anoxic event 2 caused the plenus cold event

reliable absolute palaeointensities independent of magnetic domain state knowledge of palaeointensity variation is required for determining the full vector variation of the geomagnetic field as a function of geological time this provides essential constraints for numerical geodynamo models to date most palaeointensity determination methods are laborious characterised by rather low success rates and demand substantial processing time the rocks under investigation must obey stringent criteria to yield faithful palaeointensities the magnetic particles must be single domain the natural remanent magnetisation must be a thermoremanent magnetisation and during the successive heating steps in the laboratory no chemical alteration should occur here we describe a new method that allows all magnetic domain states to be processed i e it does not require single domain particles the method makes use of the linearity of partial thermoremanent magnetisation ptrm with the applied laboratory field multiple specimens are used so that every sample is exposed only once to a laboratory field warranting that all samples experienced the same magnetic history through the limited number of thermal steps alteration effects are reduced as well the laboratory ptrm and natural remanent magnetisation nrm of the specimens are oriented parallel to minimise the effects of high temperature tails that affect multidomain minerals the ptrm acquisition temperature is selected below the temperature at which chemical alteration sets in and above the temperature trajectory where secondary viscous nrm components occur the procedure requires a lower number of steps than any other palaeointensity method reducing significantly the total time needed per rock unit we propose to name the new protocol multispecimen parallel differential ptrm method i t provides the correct answer to 5 for artificial samples and natural rocks containing multidomain magnetic particles that were given a laboratory trm of known intensity application to the paricutin september december 1943 lava flow three sites 7 specimens per site yields a weighted mean of 45 9 1 25 t within uncertainty margin of the expected value of 45 0 t

a new three axis vibrating sample magnetometer for continuous high temperature magnetization measurements applications to paleo and archeo intensity determinations we have developed a new three axis vibrating sample magnetometer which allows continuous high temperature magnetization measurements of individual cylindrical 0 75 cm3 samples up to 650 c and the acquisition of thermoremanent magnetization trm in any direction and field intensity up to 200 t we propose a fast less than 2 5 h automated experimental procedure adapted from boyd s nature 319 1986 208 209 modified version of the thellier and thellier ann geophys 15 1959 285 376 method which provides continuous intensity determinations over a large typically 300 c temperature interval for each sample this procedure allows one to take into account both the cooling rate dependence of trm acquisition and anisotropy of trm several examples of analyses of ancient magnetization demonstrate the quality and reliability of the data and illustrate the promising potential of this new instrument in paleo and archeomagnetism

an absolute palaeointensity record from soh1 lava core hawaii using the microwave technique absolute palaeointensity results were obtained from 392 samples 166 of 241 flows from the upper 779 m of the scientific observation hole 1 soh1 basalt core kilauea volcano hawaii using the microwave palaeointensity technique based on k ar dates and a previously published age model this covers the last 45 ka thus giving a high resolution record of geomagnetic intensity in hawaii comparisons with other hawaiian absolute palaeointensity data show similar trend of higher intensity than present day for the last 3 ka and then a general decrease in intensity over the last 45 ka though this study reports consistently lower palaeointensity values direct comparison with previous thellier data from the soh1 core shows some discrepancies between the two methods with the thellier data yielding generally higher palaeointensity estimates than the microwave data in view of these discrepancies between the two methods the introduction of raw palaeointensity data into the public domain is suggested

trm arm and isr of two natural magnetites of md and psd grain size summary trm arm and isr stabilities with respect to alternating fields and high and low temperature treatment are compared for a set of artificial rock specimens the specimens contain grain size fractions of a homogeneous natural magnetite and a natural magnetite showing exsolution lamellae the grain size fractions are in the psd md range and vary between 5 and 250 m for large md grains the coercivity spectra of arm are similar to those of isr but differ from those of trm particularly in the lower part of the spectrum for small 5 m grains the coercivity spectrum of arm is similar to that of trm and both spectra are different from the coercivity spectrum of isr the use of arm instead of trm to determine palaeo intensities is discussed in relation to the results obtained during high and low temperature treatment arm behaves similarly to isr but unlike trm for all grain sizes studied the results of this study are discussed in terms of a remanence composed of psd surface moments and md and psd bulk moments

rudists as gregarious sediment dwellers not reef builders on cretaceous carbonate platforms abstract it has sometimes been claimed that rudist bivalves competitively displaced corals from reef frameworks during the cretaceous this hypothesis combines two assertions 1 that the autecology of rudists was convergent with that of reef building corals and 2 that rudist formations commonly developed as reefs we dispute both assertions and thus reject the hypothesis of competitive displacement we argue instead that mobile sediments rather than frameworks dominated the margins and tops of most of the extensive carbonate platforms of the period and that it was on these non reefal biotopes that the rudists flourished definitions of reefs tend to combine two major elements 1 a robust biogenic framework with accompanying sedimentary and diagenetic components and 2 topographical relief such definitions are clearly rooted in recent coral reefs in which endosymbiotic zooxanthellae permit the extensive growth of colonial coral frameworks in shallow but relatively nutrient poor waters coralline algae and cementation may contribute significantly to the growth of rigid structures and topography is largely the legacy of pleistocene changes in sea level in rudist formations in contrast individual rudist congregations are volumetrically limited relative to sediment they are often loosely constructed and they evidently showed little if any original relief tabular and small lenticular units predominate these differences in structure and palaeoenvironmental situation between rudist and modern coralgal associations reflect the different autecologies of the constituent organisms the clonal growth of corals predisposes them to the development of frameworks projecting above the sediment surface herein termed superstratal growth by contrast the aclonal development of rudists was better suited to the opportunistic occupation of a variety of temporarily available substrata by large numbers of individuals in particular elevator rudists in which the entire commissure exhibited upward growth evidently grew with their shells largely embedded in and supported by the ambient sediment herein termed constratal growth moreover the tolerances and growth responses of rudists to such factors as water turbidity nutrients and current regime were quite different from those of the majority of reef building corals despite repeated assertions in the literature that rudists possessed zooxanthellae only a few species show any evidence for such a symbiosis and other evidence suggests that most lacked them in view of these differences in their preferred biotopes competition between rudists and corals is doubtful even though members of both groups co occur in many areas the relative decline of coral frameworks in the cretaceous was thus probably independently caused

magnetic properties of a freshly fallen ll ordinary chondrite the bensour meteorite abstract a comprehensive rock magnetic magnetic anisotropy and paleomagnetic study has been undertaken in the brecciated ll6 bensour ordinary chondrite a few months only after its fall on earth microscopic observations and electronic microprobe analyses indicate the presence of ni rich taenite tetrataenite and rare co rich kamacite tetrataenite is the main carrier of remanence magnetization and anisotropy measurements were performed on mutually oriented 125 mm 3 sub samples a very strong coherent susceptibility and remanence anisotropy is evidenced and interpreted as due to the large impact responsible for the post metamorphic compaction of this brecciated material and disruption of the parent body we show that the acquisition of remanent magnetization postdates metamorphism on the parent body and predates the entering of the meteorite in earth s atmosphere three components of magnetization could be isolated a soft coherent component is closely related to the anisotropy of the meteorite and is interpreted as a shock remanent magnetization acquired during the same large impact on the parent body two harder components show random directions at a few mm scale this randomness is attributed either to the formation mechanism of tetrataenite or to post metamorphic brecciation all components are likely acquired in very low t to null ambient magnetic field as demonstrated by comparison with demagnetization behavior of isothermal remanent magnetization two other ll6 meteorites kilabo and st mesmin have also been studied for comparison with bensour

toward an optimal geomagnetic field intensity determination technique 1 paleointensity determinations based on double heating techniques in field zero field cooling zero field in field cooling and two in field steps with opposite laboratory fields are generally considered to be functionally interchangeable producing equally reliable paleointensity estimates to investigate this premise we have developed a simple mathematical model we find that both the zero field first and in field first methods have a strong angular dependence on the laboratory field parallel orthogonal and anti parallel while the two in field steps method is independent of the direction of the laboratory produced field contrary to common practice each method yields quite different outcomes if the condition of reciprocity of blocking and unblocking temperatures is not met even with marginal 10 tails of partial thermoremanence our calculations suggest that the zero field first method with the laboratory produced field anti parallel to the natural remanence nrm is the most robust paleointensity determination technique when the intensity of the lab induced field is smaller than ancient field however the zero field first method with the laboratory field parallel to the nrm is the optimum approach when the intensity of the lab induced field is larger than the ancient field by far the best approach however is to alternatethe infield zerofield iz steps with zerofield infield zi steps

toward a robust normalized magnetic paleointensity method applied to meteorites abstract we propose a new paleointensity method based on normalization by isothermal remanent magnetization derivative vs alternating field rem method it provides an estimate of the absolute paleointensity with an uncertainty of about a factor two contrary to methods using normalization by total isothermal remanent magnetization or anhysteretic magnetization it is applicable to multicomponent magnetizations artificial or natural isothermal remanent magnetizations can be recognized and relaxation of natural remanent magnetization can be taken into account it is applicable for magnetizations carried by magnetite feni alloys and pyrrhotite the rem method is of particular interest to estimate paleointensities in meteorites as these materials are often characterized by complex multicomponent magnetization of various origins impact magnetization thermoremanence isothermal remanent magnetization and metastable magnetic minerals not suitable for thellier experiments however like other paleointensity methods the rem method underestimates the true paleointensity for meteorite samples with magnetizations that are heterogeneous on spatial scales below the sampling scale for l ordinary chondrites an upper limit of 1 t is proposed for the paleofield tentative paleofield estimates in the 0 05 0 5 t range are proposed for ll ordinary chondrites which is much lower than previous results the first paleofield estimates for rumuruti chondrites indicate the presence of magnetic fields around 6 t during the last major impact on their parent body aubrites and hed achondrites paleofields of at least 10 t may suggest the existence of a dynamo field during the cooling of their parent body results from martian meteorites are scattered between 1 and 24 t and may represent the crustal magnetic field of the planet after dynamo shutdown carbonaceous chondrites provide contrasting results with possible evidence of strong field mt processes that clearly require additional studies

cretaceous sea surface temperature evolution constraints from tex86 and planktonic foraminiferal oxygen isotopes it is well established that greenhouse conditions prevailed during the cretaceous period 145 66 ma determining the exact nature of the greenhouse gas forcing climatic warming and climate sensitivity remains however an active topic of research quantitative and qualitative geochemical and palaeontological proxies provide valuable observational constraints on cretaceous climate in particular reconstructions of cretaceous sea surface temperatures ssts have been revolutionised firstly by the recognition that clay rich sequences can host exceptionally preserved planktonic foraminifera allowing for reliable oxygen isotope analyses and secondly by the development of the organic palaeothermometer tex86 based on the distribution of marine archaeal membrane lipids here we provide a new compilation and synthesis of available planktonic foraminiferal 18o 18opl and tex86 sst proxy data for almost the entire cretaceous period the compilation uses ssts recalculated from published raw data allowing examination of the sensitivity of each proxy to the calculation method e g choice of calibration and places all data on a common timescale overall the compilation shows many similarities with trends present in individual records of cretaceous climate change for example both sst proxies and benthic foraminiferal 18o records indicate maximum warmth in the cenomanian turonian interval our reconstruction of the evolution of latitudinal temperature gradients low 48 palaeolatitudes reveals temporal changes in the valanginian aptian the low to higher mid latitudinal temperature gradient was weak decreasing from 10 17 c in the valanginian to 3 5 c in the aptian based on tex86 ssts in the cenomanian santonian reconstructed latitudinal temperature contrasts are also small relative to modern 14 c based on low latitude tex86 and 18opl ssts minus higher latitude 18opl ssts compared with 20 c for the modern in the mid campanian to end maastrichtian latitudinal temperature gradients strengthened 19 21 c based on low latitude tex86 and 18opl ssts minus higher latitude 18opl ssts with cooling occurring at low middle and higher palaeolatitude sites implying global surface ocean cooling and or changes in ocean heat transport in the late cretaceous these reconstructed long term trends are resilient regardless of the choice of proxy tex86 or 18opl or calibration this new cretaceous sst synthesis provides an up to date target for modelling studies investigating the mechanics of extreme climates

paleointensity determination using anhysteretic remanence and saturation isothermal remanence 1 determining the strength of ancient planetary magnetic field is pivotal to understanding the evolution of planets and asteroids in the solar system while the thellier type double heating technique provides the most faithful field strength information for rocks carrying a thermoremanent magnetization trm many extraterrestrial rock samples respond unfavorably to heat treatment the present study systematically examined the two well known normalization techniques that avoid any heating by comparing the ratios of trm anhysteretic remanent magnetization arm and trm saturation isothermal remanent magnetization sirm both the ratios of trm arm and trm sirm are dependent on the grain size as well as the volume concentration of magnetite the remanence ratios also were found to increase as the alternating field increased during demagnetization for fine grained magnetite a new calibration relation of 2 60 1 32 for the trm arm and of 3 62 1 28 10 2 for the trm sirm was defined for an external field of 50 t the trm sirm is superior to trm arm because the former showed less dispersion in the grain size dependence the volume concentration dependence and the stability against af demagnetization in addition the standard error of the mean for the trm sirm ratio was smaller than that for the trm arm ratio thus whenever heating is inapplicable the sirm method seems to be a better choice than the arm method however it should be emphasized that the uncertainty of trm arm and trm sirm is still nearly an order of magnitude larger than that of the high fidelity thellier estimation and thus must be limited in use only when samples are irreversibly altered during heating in practice the best approach is to carry out both arm and sirm methods and check whether the two estimations agree within the uncertainties

no evidence for strong fields during the r3 n3 icelandic geomagnetic reversal a previous study of the r3 n3 icelandic reversal which corresponds probably to the matuyama reunion reversal provided relatively large virtual dipole moments when the pole is close to equator to check these former results obtained using the shaw paleointensity method we resampled the very same sections and flows and reanalysed the samples using the thellier method 38 lava units and one baked horizon from 4 sections provide intermediate r3 n3 paleofield directions most of them possibly related to a single eruption display similar directions corresponding to the near equator vgp cluster unfortunately most of the intermediate lava flows are thermally unstable as attested by the irreversibility of the susceptibility versus temperature k t curves which precludes their use for paleointensity purpose the rest of the units provide fairly reversible k t curves and a near magnetite tc due to fe rich titanomagnetite resulting from oxyexsolution at high temperature 25 baked units or lava flows of this kind yield reliable thellier paleointensity data average paleostrengths of 44 7 14 9 t and 32 5 22 9 t were found for the reversed r3 and the normal n3 polarity zones respectively combining these non transitional paleostrengths with other thellier data from over the world indicates that the pliocene dipole moment was close to 8 1022 a m2 the average paleostrength is reduced to 11 3 3 0 t during the r3 n3 transition we find no indication for the strong fields 20 4 to 38 6 t previously obtained by the shaw method thus our results do not confirm the existence of large virtual dipole moments when the pole approaches the equator

palaeoecology of chondrodonta bivalvia from the lower aptian cretaceous apulia carbonate platform gargano promontory southern italy abstract chondrodonta is a cretaceous oyster like bivalve with a predominantly calcitic dorso ventrally elongated and slightly inequivalve shell in the tethyan carbonate platforms this taxon occurs commonly in rudist bearing limestone often preserved with still articulated valves the opportunistic chondrodonta had a cemented and gregarious life habit in the apulia carbonate platform gargano promontory southern italy chondrodonta beds occur within lower aptian lagoonal to platform basin margin deposits the studied chondrodonta concentrations which recorded the early evolutionary phase and spreading of this bivalve are made up of specimens ascribed to chondrodonta glabra stanton in the inner platform the meter thick chondrodonta accumulations were originated by autochthonous bouquet like valve aggregates frequently preserved in living position these aggregates constitute superimposed carpets characterized by only a few generations which were affected by mass mortality and rapid burial processes these mass mortalities were related to repeated environmental lethal fluctuations that occurred at the onset of the early aptian oae 1a the quick fluctuations of the chondrodonta populations are typical of unstable and unpredictable environments characterized by significant changes in trophic resources and hyperthermal and acidification peaks the studied chondrodonta specimens show different shell preservation according to their palaeobathymetric location in the shallow water inner platform specimens the internal aragonite shell layer was rapidly dissolved while in deeper water margin ones it was preserved during the early diagenetic phases this different preservation is interpreted as related to different aragonite saturation state of shallow seawater and tentatively connected to the acidification peak that occurred at the onset of the early aptian oae 1a

thermochemical remanent magnetization in precambrian rocks are we sure the geomagnetic field was weak 1 thellier paleointensity determinations from two dikes of the early proterozoic 2 46 ga matachewan dike swarm canada yield field values of 2 14 0 18 and 9 81 1 65 t corresponding values of virtual axial dipole moment are very low 0 54 0 05 1022 and 2 49 0 42 1022 am2 respectively when compared with the modern field the characteristic remanent magnetization chrm was isolated over a narrow range of high unblocking temperatures 520 580 c detailed rock magnetic analyses indicate that the chrm is carried by nearly stoichiometric pseudo single domain magnetite scanning electron microscopy sem reveals that the magnetite is in the form of fine intergrowths with ilmenite formed by oxyexsolution during cooling the high temperature oxidation defined in the sem images could have continued at temperatures below the curie point of magnetite in this case the chrm would be a thermochemical remanent magnetization tcrm rather than a thermal remanent magnetization trm estimates of the tcrm trm ratio show that the thellier data could underestimate the true field value by a factor of 4 without violating experimental selection criteria this uncertainty in trm fidelity translates into a potential range of field values that spans that defined by the modern field 8 1022 am2 and proposed low precambrian levels 2 1022 am2 therefore understanding further how tcrm is acquired and records the field represents a major challenge if these and many other similar rocks are to be used in thellier studies aimed at defining the strength of the precambrian field

influence of the high arctic igneous province on the cenomanian turonian boundary interval sverdrup basin high canadian arctic abstract emplacement of large igneous provinces lips had a major effect on global climate ocean chemistries as traced in sedimentary records and biotic turnovers the linkage between lips and oceanic anoxic events has been documented with the cenomanian turonian boundary event and oceanic anoxic event 2 oae2 the caribbean lip and high arctic large igneous province halip are regarded as possible triggers the pericratonic arctic sverdrup basin is the partial location of the halip where little is known about sedimentary geochemical and biotic responses to the halip phases sedimentary strata at glacier fiord axel heiberg island exhibit a dynamic cretaceous polar carbon burial history within the lower to middle cenomanian bastion ridge formation and upper cenomanian to turonian part of the kanguk formation we present the first initial 187os 188os osi composition profile for a polar cenomanian turonian boundary interval 100 93 9 ma linked to recently dated magmatic phases of the strand fiord formation part of the halip the carbon isotope record coupled with the osi profile show two events in the upper cenomanian interval marked by positive carbon perturbations and shifts to more non radiogenic osi compositions the earlier short lived event is interpreted as result of weathering of the surrounding strand fiord volcanics causing a local non radiogenic osi signal coinciding transgressive shorelines let to an increase in marine and terrestrially derived organic matter subsequently injection of mantle derived basalts into organic rich sediments is credited with causing the release of methane documented in a distinct negative carbon isotope excursion we speculate that the methane release of the halip was an important contribution for rapid global warming caused by increasing atmospheric co2 levels associated with the oae2 event likewise recognized in the sverdrup basin as climate cooled in the middle and late turonian carbon burial decreased under increasingly oxygenated benthic conditions epifaunal foraminiferal species adapted to low oxygen conditions persisted during the oae2 our cenomanian to turonian multiproxy record of the sverdrup basin distinguishes between local and global signals within a restricted high arctic basin our results demonstrate the interplay between basin tectonism and sea level change increased weathering during transgressive phases seafloor processes such as hydrothermal activity and methane release and biotic response to a complex paleoceanography with future reliable dated frameworks this unique polar record will facilitate correlations to other polar basins and records of lower paleolatitudes

partial anhysteretic remanent magnetization in magnetite 2 reciprocity 1 one necessary condition for successful determination of relative paleomagnetic field intensity using anhysteretic remanent magnetization arm methods is reciprocity a partial arm produced by a steady field h applied over a narrow interval 2 1 of alternating field af must demagnetize over the same interval 2 1 experimentally we find that partial arms of single domain sd and pseudosingle domain psd grains demagnetize mainly between 2 and 1 whereas 50 of partial arms of large psd and multidomain md grains are erased below 1 giving a low field tail in the coercivity distribution natural pumices granites and oceanic basalts violated reciprocity but lake sediments gabbros andesite and red scoria had relatively small low coercivity tails and are better candidates for paleointensity work using total arm to simulate natural remanence we carried out pseudo thellier paleointensity determinations for coarse psd and md grains arm demagnetization outweighed partial arm acquisition at the same af step resulting in convex down curves of arm remaining versus partial arm gained pseudo arai plot pseudo arai plots predicted from experimentally determined distributions of blocking and unblocking fields agreed well with measured pseudo thellier results in particular explaining convex down md curves

paleomagnetic record of martian meteorite alh84001 1 the natural remanent magnetization nrm of the martian meteorite alh84001 is predominantly carried by fine magnetite which is found in association with carbonate the magnetite is in epitaxial and topotactic relation with the carbonate and formed from the carbonate in the major impact event at 4 0 ga the nrm will therefore record this field the local preferential crystallographic and shape alignment of the magnetite defines local easy directions of magnetization may account for the observed inhomogeneity of the nrm on a microscopic scale normalizing the intensity of the nrm by the saturation isothermal remanence irms then gives an estimate for the 4 0 ga martian field one order smaller than the present geomagnetic field such a field is unlikely to be strong enough to generate the high intensity martian magnetic anomalies alh 84001 in its pristine state as an orthopyroxenite is not a plausible source rock for the martian anomalies because its magnetite was not formed until the 4 0 ga event

are arm and trm analogs thellier analysis of arm and pseudo thellier analysis of trm abstract we test the possibility of using the pseudo thellier method as a means of determining absolute paleointensity thellier analysis of anhysteretic remanent magnetization arm and pseudo thellier analysis of thermoremanent magnetization trm have been carried out on a large collection of sized synthetic magnetites and natural rocks in all samples the intensity of trm is larger than that of arm and the ratio r trm arm is strongly grain size dependent the best fit slope b ta from pseudo thellier analysis of trm shows a linear correlation with r the ratio b ta r yielded approximately correct paleointensities although uncertainties are larger than in typical thellier type determinations for single domain and multidomain magnetites alternating field and thermal stabilities of arm and trm are fairly similar however for 0 24 m magnetite arm is both much less intense and less resistant to thermal demagnetization than trm reflecting different domain states for the two remanences and resulting in severely non linear arai plots for thellier analysis of arm

cyanobacteria proliferation in the cenomanian turonian boundary interval of the apennine carbonate platform immediate response to the environmental perturbations associated with oae 2

stratigraphy and paleoenvironments of rudist biostromes in the upper cretaceous turonian upper santonian limestones of southern istria croatia abstract rudists are well preserved in the upper cretaceous limestones of southern istria where they flourished within different shallow water environments during the turonian to upper santonian in order to determine paleoenvironments a vertical succession of the rich rudist assemblages has been investigated and described within sequence stratigraphy framework the turonian to upper santonian sediments of southern istria in the sense of sequence stratigraphy comprise one complete third order sequence and the beginning of the transgressive systems track tst of the next sequence lower turonian pelagic limestones were deposited on a foundered carbonate platform and represent the beginning of the tst limestones of the late tst lowstand systems track lst were deposited on the inner shelf and the early tst of the next sequence was deposited on the outer shelf all the rudists which appeared after the early turonian disappearance and partial extinction were elevators the genera durania and praeradiolites thrived in bouquets which may coalesce to form thickets in inner shelf environments of the late tst lst their growth depended completely durania or partly praeradiolites on net sediment accumulation the environment in which durania and praeradiolites thrived was subtidal and deep enough to be out of reach of emersion within the same depositional environment these genera were later replaced vertically by radiolites individuals with slim cylindrical shells and wide growth lamellae have full contact within the thickets in which their growth depended little if at all on net sedimentation rate also radiolites occupied the shallower parts of the subtidal zone with a commissure rim rising above the sediment surface renewed deepening in the late santonian resulted in the outer shelf environment of the next tst gorjanovicia together with rare vaccinites flourished after the radiolites gorjanovicia differed from radiolites only in possessing more pronounced vertical ribs in their slightly deeper subtidal environment with pelagic influxes gorjanovicia thrived in bouquets loosely packed gorjanovicia gave vaccinites an opportunity to grow among them the environmental setting of the southern istria rudist biostromes and their correlation with other shallow water deposits in the mediterranean region suggests that a sequence stratigraphy approach can be applied to correlate rudist biostratigraphy on a regional or even inter regional scale

geomagnetic intensity and inclination variations at hawaii for the past 98 kyr from core soh 4 big island a new study and a comparison with existing contemporary data abstract reliable thellier thellier paleointensity determinations were obtained from 321 out of 766 examined samples from the upper 200 units 675 m of core soh 4 drilled in the kilauea volcano the main trend of the soh 4 record is a marked decrease from values higher than present in the last 4 kyr to values about 40 smaller from about 20 kyr to the bottom of the sampled interval three main lows coinciding with shallow or negative inclinations observed in the record were identified with an excursion previously documented in hawaii and the mono lake and laschamps events for the last 15 kyr the soh 4 intensities are largely in agreement with the worldwide distribution of volcanic data in the 15 75 kyr interval the general lack of volcanic data makes comparison with the soh 4 data difficult the soh 4 record is similar to a composite record of paleointensity largely based on a recent north atlantic sedimentary paleointensity stack napis 75 the soh 4 record is also generally consistent with a record of geomagnetic field intensity obtained from a study of 36 cl in the grip ice core calculated with the assumption that the production rate of 36 cl is controlled only by the geomagnetic field one pronounced discrepancy between the different records is observed around 50 kyr bp when the sedimentary and cosmogenic based records document high intensities which are not observed in soh 4 these high intensities are also absent in a recent record based on the analyses of sea floor magnetic anomalies the histogram of vadms obtained from soh 4 is different from that obtained from the sedimentary or 36 cl based records and is more skewed than the distribution given by kono and tanaka for the last 2 5 million years

a detailed palaeointensity and inclination record from drill core soh1 on hawaii abstract a new record of absolute palaeointensity was obtained from drill core scientific observation hole 1 soh1 on kilauea volcano hawaii kilauea s high eruption rate resulted in a relatively continuous record and stratigraphic constraints preserved the chronological order three hundred and sixty samples were studied with the thellier thellier technique which gave 195 successful palaeointensity and 271 successful inclination determinations three geomagnetic excursions were observed which exhibited intensity reductions of about 50 initial age control from k ar and ar ar dating only constrained the total age between 20 and 120 ka the final age model was obtained by stretching the soh1 record relative to other hawaiian palaeomagnetic data this gave an age range of 0 45 ka for the flows and identified the excursions as the hilina pali mono lake and laschamp events the soh1 record of the hilina pali event is the most detailed ever incorporating data from around 40 flows this age model suggests that kilauea had a burst of activity at the soh1 site around 20 ka all available data was combined to form a composite record of palaeointensity and inclination on hawaii for 0 45 ka

radiocarbon dating of sediments by accelerator mass spectrometry abstract accelerator mass spectrometry allows the measurement of the abundance of carbon isotopes in much smaller samples 1 mg of carbon in the form of graphite than conventional methods of radiocarbon dating the small sample requirement widens the potential for sediment dating in this study fractions of the sedimentary organic matter for example humic acid lipid macrofossils were isolated and each fraction dated to yield a suite of dates for one sediment sample owing to the complexity of most sedimentary environments a conventional radiocarbon date reflects the input of sediment from different sources with different carbon reservoirs which may combine to alter the date of the event that is required i e the date of sedimentation an estimate of the date of sedimentation may be made by taking specific fractions of the sedimentary organic matter which can be characterized and dated for example the lipid fraction which can be sub divided for analysis to yield information on the relative input of terrestrial and aquatic organic matter results have been obtained for five peat samples the dates of the more water soluble components of the sedimentary organic matter tending to be younger than the lipid samples

orogenic evolution of the external dinarides in the ne adriatic region a model constrained by tectonostratigraphy of upper cretaceous to paleogene carbonates abstract mesozoic to cenozoic evolution of the central part of the adriatic plate external dinarides and adriatic foreland is still a matter of debate this is expressed by opposing paleogeographic models single carbonate platform adriatic or adriatic dinaridic versus two carbonate platforms adriatic and dinaridic separated by the inter platform budva cukali basin estimates of shortening during adria ne subduction that resulted in the development of the dinaric alps differ substantially the single platform model involves minor shortening achieved by folding and faulting along steep reverse faults the two platform model involves significant shortening achieved mainly by thrust stacking which resulted in almost complete underthrusting of the intervening basinal deposits analysis of upper cretaceous to paleogene stratigraphical data from both outcrops and boreholes allows regional correlation and the interpretation of major lithostratigraphic units as a result a few tectonostratigraphic units are recognized the tectonostratigraphy is used as a basis for a new model on the late mesozoic to cenozoic evolution of the region generally adriatic and dinaridic segments acted as major regional crustal entities of adria the upper portions of the sedimentary cover were differentially affected by progressive southwestward verging thin skinned deformations during the paleocene to eocene miocene the adriatic foreland stayed out of the deformations and is characterized predominantly by wrench and salt tectonics the regional tectonic map shows arcuate thrust fronts of the external dinarides they could be a consequence of both differential propagation of early orogenic thin skinned deformations over crustal fragments separated by transversal faults and or differential isostatic movements of the fragments the collision zone of the adriatic and dinaridic segments is characterized by late orogenic oligocene to miocene thick skinned compressional uplift exhumation related gravity gliding and still active escape tectonics wrenching these processes masked primary thin skinned deformations a significant amount of shortening within and between the thin skinned sedimentary covers is proposed therefore the question of the general paleogeography of the region and the original nw extent of the budva cukali basin ne adriatic trough remains open

magnetic hysteresis monitoring of cretaceous submarine basaltic glass during thellier paleointensity experiments evidence for alteration and attendant low field bias on the basis of studies of holocene samples submarine basaltic glass sbg is thought to be an ideal paleointensity recorder because it contains unaltered single domain magnetic inclusions that yield thellier paleointensity data of exceptional quality to be useful as a recorder of the long term geomagnetic field older sbg must retain these optimal properties here we examine this issue through rock magnetic and transmission electron microscope tem analyses of cretaceous sbg recovered at ocean drilling program site 1203 northwestern pacific ocean these sbg samples have very low natural remanent magnetization intensities nrm 2 g and tem analyses indicate a correspondingly low concentration of crystalline inclusions thellier experiments on samples with the strongest nrm intensity 5 10 11 am 2 show a rapid acquisition of thermoremanent magnetization trm with respect to nrm demagnetization taken at face value this behavior implies magnetization in a very weak 17 t ambient field but monitoring of magnetic hysteresis properties during the thellier experiments on subsamples of the sbg samples used for paleointensity determinations indicates systematic variations in values over the same temperature range where the rapid trm acquisition is observed a similar change in properties during heating is observed on monitor sbg specimens using low temperature data with progressive heatings the verwey transition becomes more distinct we suggest that these experimental data record the partial melting and neocrystallization of magnetic grains in sbg during the thermal treatments required by the thellier method resulting in paleointensity values biased to low values we further propose that this process is pronounced in cretaceous and jurassic sbg relative to holocene sbg because devitrification on geologic time scales i e tens of millions of years lowers the transition temperature at which the neocrystallization can commence magnetic hysteresis monitoring may provide a straightforward means of detecting the formation of new magnetic inclusions in sbg during thellier experiments

distinguishing core and flank facies based on shell fabrics in lower jurassic lithiotid shell beds abstract lower jurassic larger bivalves mostly represented by the monospecific lithiotid genera lithiotis cochlearites and lithioperna formed large shell accumulations in the shallow water carbonate tethyan and panthalassa margins a quantitative analysis of lithiotid accumulations from the trento platform northern italy was carried out in order to distinguish the distribution of autochthonous parautochthonous and allochthonous lithiotids in the accumulation core and flanks various representative accumulations are characterized with respect to systematic content shell cover shell density disarticulation shell fragmentation and orientation of individual shells lithioperna shows a high shell cover within the accumulation core while that of cochlearites is variable and lithiotis is rare all three lithiotids occur in high densities in the accumulation flanks as expected autochthonous individuals of all three genera are frequent in the accumulation cores where they are preserved in life position in the flanks most bivalves are parautochthonous except for lithioperna which can grow in life position all bivalves in allochthonous shell beds are highly fragmented and disarticulated the studied traits are potentially useful as proxies for distinguishing core or flank facies when the accumulation does not crop out as a whole

subsidence and sedimentation on jurassic passive continental margin southern alps italy the southern alps of italy preserve a tectonically intact array of jurassic facies that record the evolution of a part of the margin of the apulian plate from its ancestral beginnings in a complex of permian and triassic rifted continental basins through the initial stages of breakup and stepwise foundering of a carbonate platform breakup was accompanied first by the rapid accumulation of thick prisms of carbonate turbidites in newly formed fault troughs then as the new ligurian oceanic basin began to open farther west and as subsidence gradually slowed accumulation of a succession of slowly deposited biogenous pelagic sediments recorded not only the increasing depths of the seafloor but also fluctuations in oceanographic conditions of fertility carbonate dissolutio levels and the strength of bottom currents estimates of the history of seafloor depths based on a simple subsidence law of the form subsidence k age 12 provide a basis for the construction of a set of curves showing the changing depths of significant carbonate dissolution surfaces during the jurassic in this region the rapid 1 km deepening of the compensation depth for calcite during the late jurassic may be due to a change in regional oceanic vertical circulation patterns from upwelling fertile silica rich carbonate dissolving to downwelling less fertile silica poor carbonate preserving

experimental reassessment of the shaw paleointensity method using laboratory induced thermal remanent magnetization 1 artificial thermoremanent magnetization imposed on natural basalt samples was used to check the reliability of shaw s palaeointensity method shaw 1974 kono 1978 rolph and shaw 1985 and to give an indication of the accuracy of paleointensity determinations first thermal remanence was induced in all samples 50 in total in a known field 50 0 1 t this remanence was regarded as the original natural remanent magnetization nrm the samples were divided in to three subsets a b and c and intensity experiments were performed each subset of samples used different thermal remanent magnetization trm acquisition parameters rock magnetic properties on 14 representative subsamples were also measured both before and after the trm acquisition steps to monitor possible magnetochemical alteration it has been demonstrated that intensity estimates by the shaw method give values close to the expected value 50 5 t in all three sets of basalt samples the modified method with rolph and shaw 1985 correction i e using ratios of anhysteretic remanent magnetization given before the trm step arm1 and after arm2 is proved to be a powerful approach to correct the trm capacity changes that result from magnetochemical alteration this is especially so for sample set c where the samples were heated up to 700 c and then were held at this temperature for 40 min during trm acquisition after correction 45 of set c samples gave acceptable results however some samples with strong magnetochemical alteration sometimes invalidated the arm1 arm2 ratio correction and gave wrong intensity estimates monitoring rock magnetic properties is therefore very important when applying the shaw method

preserved ligament in the jurassic bivalve lithiotis adaptive and evolutionary significance an exceptionally well preserved specimen of lithiotis problematica from the lower jurassic of ne italy possesses multiple resilia composed of thin fibres and joining both valves housed in ligamental grooves the resilia were modified to allow small changes in the reciprocal distance of the valves this increased the area in which the extremely thin free valve flexed to allow shell closure and reduced the risk of breakage by fatigue of the valve and or ligament the fact that the valves remained connected by ligament for an extended height of the ligamental area implies that 1 the free valve closed by flexing not by articulating 2 it did not migrate in the ventral direction as often observed in cemented bivalves and 3 it was approximately as long as the attached one

nonheating methods for absolute paleointensity determination comparison and calibration using synthetic and natural magnetite bearing samples nonheating paleointensity methods utilize an anhysteretic remanent magnetization arm or a saturation isothermal remanent magnetization to model the natural thermal remanent magnetization trm to avoid heating induced alteration we report the results of paleointensity experiments using the arm pseudo thellier and ratio of equivalent magnetization rem methods conducted to investigate their relative efficiency in recovering the true paleofield strength and to provide additional estimates of their calibration factors the experiments on synthetic magnetite bearing samples representing single domain sd and pseudo single domain psd magnetic states indicated that the correction factors for the arm based methods depend on the magnetic grain size domain state changing from 6 3 for sd grains to 4 1 for 1 5 m psd grains the pseudo thellier method yielded correct absolute paleointensity values when normalization by the trm arm demagnetization slope was used when applied to samples of lava flows and dikes from the 32 kyr lemptegy volcano france both the arm and pseudo thellier methods produced similar paleointensity estimates 28 0 5 1 t and 26 9 4 7 t respectively consistent with the available thellier data for the 31 33 kyr time interval the correction factors estimated from our synthetic samples for the rem 3000 and for remc 1500 and rem 1500 variants are consistent with the previously published estimates however all rem variants yielded unrealistically high estimates 110 t of the paleofield strength from our natural samples our experimental results support arm as a better proxy of trm and suggest that the arm based methods currently represent the best alternative to heating based absolute paleointensity method

magma emplacement into the lemptegy scoria cone chaine des puys france explored with structural anisotropy of magnetic susceptibility and paleomagnetic data the lemptegy volcano is a small monogenetic scoria cone located in the chaine des puys auvergne france which erupted about 32 000 years ago a first edifice lemptegy 1 formed during a trachybasalt eruption as a group of satellite vents of the puy de gouttes scoria cone a second trachyandesitic edifice lemptegy 2 formed soon after and completely covered lemptegy 1 with an 80 m high breached cone since 1946 the lemptegy volcano has been quarried for scoria and today offers unprecedented three dimensional exposure of the subvolcanic plumbing system to map the internal flow architecture of the plumbing system and to study the subvolcanic deformation of lemptegy 2 structural mapping petrographic observations anisotropy of magnetic susceptibility ams rock magnetic and paleomagnetic data were collected field structural mapping and thin section study of tension gashes riedel shears striations as well as ductile shear zones and bubbles allow the direction and sense of the magma flow to be determined twenty ams sites were established in ten dikes one to four sites in each dike with 504 specimens analyzed and 479 specimens used to infer magma flow patterns structural data the maximum susceptibility axis k 1 and the imbrication of the magnetic foliation k 1 k 2 planes indicate both upward and downward sense of flow as well as flow toward and away from the central vent rock magnetic experiments reveal that a cubic fe ti oxide phase likely low ti titanomagnetite is the principal magnetic phase carrying both the remanence and anisotropy paleomagnetic data from some sites yield statistically distinct at the 95 confidence level remanence directions while at other sites the data are indistinguishable at the 95 confidence level the paleomagnetic results observed steeply tilted scoria layers internal unconformities and faults show that as each dike was emplaced it displaced earlier dikes evidencing subvolcanic deformation the lemptegy 2 volcano shares similarities in terms of inferred eruption style and structures with other scoria cones such as cerro negro nicaragua and thus provides an excellent field laboratory to investigate active scoria cones world wide

geomagnetic intensity variations over the past 780 kyr obtained from near seafloor magnetic anomalies knowledge of past variations in the intensity of the earth s magnetic field provides an important constraint on models of the geodynamo a record of absolute palaeointensity for the past 50 kyr has been compiled from archaeomagnetic and volcanic materials and relative palaeointensities over the past 800 kyr have been obtained from sedimentary sequences but a long term record of geomagnetic intensity should also be carried by the thermoremanence of the oceanic crust here we show that near seafloor magnetic anomalies recorded over the southern east pacific rise are well correlated with independent estimates of geomagnetic intensity during the past 780 kyr moreover the pattern of absolute palaeointensity of seafloor glass samples from the same area agrees with the well documented dipole intensity pattern for the past 50 kyr a comparison of palaeointensities derived from seafloor glass samples with global intensity variations thus allows us to estimate the ages of surficial lava flows in this region the record of geomagnetic intensity preserved in the oceanic crust should provide a higher time resolution record of crustal accretion processes at mid ocean ridges than has previously been obtainable

magnetic properties and paleointensities as function of depth in a hawaiian lava flow the outcome of paleointensity experiments largely depends on the rock magnetic properties of the samples to assess the relation between volcanic emplacement processes and rock magnetic properties we sampled a vertical transect in a 6 m thick inflated lava flow at hawaii emplaced in 588 ad its rock magnetic properties vary as function of distance from the flow top the observations can be correlated to the typical cooling rate profile for such a flow the top and to a lesser extent the bottom parts of the flow cooled faster and reveal a composition of tm60 in which the magnetic remanence is carried by fine grained titanomagnetites relatively rich in titanium with associated low curie and unblocking temperatures the titanomagnetite in the slower cooled central part of the flow is unmixed into the magnetite and ulvospinel end members as evidenced by scanning electron microscope observation the remanence is carried by coarse grained magnetite lamella tm0 with high curie and unblocking temperatures the calibrated pseudo thellier results that can be accepted yield an average paleointensity of 44 1 2 4 t this is in good agreement with the paleointensity results obtained using the thermal izzi thellier technique 41 6 7 4 t and a recently proposed record for hawaii we therefore suggest that the chance of obtaining a reliable paleointensity from a particular cooling unit can be increased by sampling lavas at multiple levels at different distances from the top of the flow combined with careful preliminary testing of the rock magnetic properties

how accurately can nrm sirm determine the ancient planetary magnetic field intensity abstract the present study tested grain size dependence of thermoremanent magnetization trm saturation isothermal remanent magnetization sirm as well as its stability against demagnetization the trm sirm ratio is dependent on the grain size of magnetite suggesting that a strong constraint on grain size characterization is necessary to be used as a paleointensity proxy in planetary magnetism in addition the trm sirm ratio increases as the alternating field increases for fine grained magnetite accuracy of trm sirm was investigated using historic showa lava erupted in 1946 it was observed that the natural remanent magnetization nrm sirm ratio of 0 032 is comparable to the field intensity of 46 80 t however the uncertainty of nrm sirm was an order of magnitude larger than that of the companion thellier estimation therefore the nrm sirm ratio can only provide crude estimations on the absolute planetary magnetic field intensity in practice anisotropy correction is advisable to reduce the scatter of nrm sirm

evolution of the adriatic carbonate platform palaeogeography main events and depositional dynamics abstract the adriatic carbonate platform adcp is one of the largest mesozoic carbonate platforms of the perimediterranean region its deposits comprise a major part of the entire carbonate succession of the croatian karst external or outer dinarides which is very thick in places more than 8000 m and ranges in age from the middle permian or even upper carboniferous to the eocene however only deposits ranging from the top of the lower jurassic toarcian to the top of the cretaceous can be attributed to the adcp defined as an isolated palaeogeographical entity although the entire carbonate succession of the karst dinarides was deposited within carbonate platform environments there were different types of carbonate platforms located in different palaeogeographical settings carboniferous to middle triassic mixed siliciclastic carbonate deposits were accumulated along the gondwanian margin on a spacious epeiric carbonate platform after tectonic activity culminating by regional middle triassic volcanism recorded throughout adria the african promontory a huge isolated carbonate southern tethyan megaplatform abbreviated as stm was formed with the area of the future adcp located in its inner part tectonic disintegration of the megaplatform during the middle to late early jurassic resulted in the establishment of several carbonate platforms including the adriatic apenninic and apulian separated by newly drowned deeper marine areas including the adriatic basin as a connection between the ionian and belluno basins lagonero basin and the area of the slovenian and bosnian troughs the adcp was characterised by predominantly shallow marine deposition although short or long periods of emergence were numerous as a consequence of the interaction of synsedimentary tectonics and eustatic changes also several events of temporary platform drowning were recorded especially in the late cretaceous when synsedimentary tectonics became stronger leading up to the final disintegration of the adcp the thickness of deposits formed during the 125 my of the adcp s existence is variable between 3500 and 5000 m the end of adcp deposition was marked by regional emergence between the cretaceous and the palaeogene deposition during the palaeogene was mainly controlled by intense synsedimentary tectonic deformation of the former platform area some carbonates mostly eocene in age were deposited on irregular ramp type carbonate platforms surrounding newly formed flysch basins and the final uplift of the dinarides reached its maximum in the oligocene miocene the adriatic carbonate platform represents a part although a relatively large and well preserved one of the broader shallow water carbonate platform that extended from ne italy to turkey although its continuity is somewhat debatable in the area near albanian greece boundary this large carbonate body which was deformed mostly in the cenozoic including a significant reduction of its width needs a specific name and the central mediterranean carbonate platform is proposed abbreviated to cmcp although the local names such as adcp for its nw part should be kept to enable easier communication and to facilitate description of local differences in platform evolution

terrestrial and marginal marine record of the mid cretaceous oceanic anoxic event 2 oae 2 high resolution framework carbon isotopes co 2 and sea level change abstract oceanic anoxic event 2 oae2 c 94 5 93 9 ma offers insight into the mechanisms of past climate change linked to organic productivity and carbon sequestration it has been studied extensively but the vast majority of data come from marine records thus providing an incomplete view of past climate dynamics here we integrate new high resolution data and published records on depositional environments the carbon isotope composition of bulk organic carbon 13corg and plant cuticles 13ccut and stomatal index values a proxy for pco2 in well preserved terrestrial through marginal marine archives of the initial phase of oae2 the study area is located on the western margin of the western interior seaway southwestern utah age constraints are based on a new u pb bentonite age and correlation to an orbitally calibrated interval of the bridge creek limestone n alkane abundance suggests predominance of terrestrial contributions to bulk organic carbon for most samples despite similarities between carbon isotope variations and transgressive regressive shoreline movements it is argued that 13corg and 13ccut are not strongly affected by local variables a series of negative 2 carbon isotope excursions is identified and attributed to changes in the size and isotopic value of the atmospheric co2 reservoir the temporal spacing of these anomalies 80 120 kyr is consistent with changes in insolation modulated by orbital eccentricity a systematic phase shifted relationship between the negative carbon isotope excursions and transgressive increments further suggests a link between carbon cycle perturbations and meter scale sea level change on the 100 kyr time scale a conceptual model involving insolation controlled aquifer charge discharge and biomass burial degradation in the monsoonal belt is proposed the framework presented here is available to facilitate further research on the interplay of terrestrial and oceanic carbon reservoirs during oae2

high temperature characteristics of a natural titanomagnetite summary continuous recordings were made of thermal demagnetizations of isr arm and trm induced in artificial rock specimens the artificial rock specimens contained well defined grain size fractions of a natural titanomagnetite which under an optical microscope was homogeneous using a transmission electron microscope it was shown that submicroscopic inclusions exist within the titanomagnetite screening of the remanence of these inclusions by the surrounding titanomagnetite is thought to be responsible for the occurrence of peaks in the continuous thermal decay curves of isr and arm higher peaks observed in the case of trm are thought to be caused by the combined effects of screening and an anti parallel remanence in the titanomagnetite further submicroscopic exsolution processes which occur in the titanomagnetite as a result of repeated heating can be deduced from the development of new peaks from changes in the temperature at which the peak s occur their shape and their relative height the use of stepwise demagnetization techniques on the titanomagnetite yielded erroneous directional results due to the screening in the titanomagnetite the biasing effects due to screening could be avoided by using continuous thermal demagnetization techniques

magnetic paleointensity determination on lunar sample 62235 there have been very few determinations of the ancient lunar magnetic field using the full thellier technique samples studied range in age from 4 0 b y to very young four samples show values less than 0 1 oersteds the fifth sample reported on earlier by collinson et al 1973 has a reported value of 1 3 oe in this paper we have repeated this determination and found essentially the same very high value it remains to be assessed by further sample studies whether this value is anomalous and somehow associated with impact or whether this reflects a high intensity field in early lunar history

possible mechanisms causing failure of thellier palaeointensity experiments in some basalts summary the normally magnetized zone of the jurassic lesotho basalts although providing apparently quite reliable palaeofield directions kosterov perrin 1996 shows anomalous behaviour when studied in vacuum using the thellier palaeointensity method typically the slope of the natural remanent magnetization thermoremanent magnetization nrm trm curves is very steep at intermediate temperatures 200 to 400 460 c in order to elucidate the reasons for such an anomalous behaviour six representative samples from a total of 74 studied using this method were subjected to a variety of analyses these experiments indicate that the magnetic properties are dominated by pseudo single domain psd magnetite grains some 1 mm in size resulting from high temperature oxidation of titanomagnetite laboratory heatings in vacuum up to the curie point do not change significantly the roomtemperature hysteresis characteristics or the initial susceptibility k similarly the k t curves in vacuum are with a single exception rather reproducible since the laboratory trms yield almost ideal nrm trm plots the anomalous nrm trm plot is presumably due to some peculiarity of the natural trm the partial trm ptrm acquisition capacity in the moderate temperature range cooling from 200 to 20 c is generally very strongly reduced after heating to 270 c which indicates that some magnetic alteration has already occurred at these temperatures hysteresis measurements between room temperature and the curie temperature t c show that some small less than 10 per cent but significant irreversible changes in hysteresis characteristics also occur during heating in particular the coercive force h c0 at room temperature is typically reduced after heating at a moderate temperature 175 c but increases after treatments at 475 c and more pronouncedly at 580 c the saturation magnetization j s0 remains unchanged except for a very small decrease less than 5 per cent occurring in some samples after the two latter treatments these changes are most clearly seen on h c t j s t bilogarithmic plots which show that the moderate temperature change in coercivity can extend up to 200 250 c thus hysteresis measurements as a function of temperature over a promising tool for sample pre selection for thellier experiments alternating field demagnetization and cycling of ptrms at liquid nitrogen temperature suggest that the blocking mechanism is largely multidomain like near room temperature but becomes less so as the curie point is approached the main reason for the failure of the thellier experiments is the loss of a fraction of the nrm natural trm at temperatures apparently lower than the blocking temperatures in nature it is suggested that this anomalous behaviour results from the reorganization of the domain structure of the psd grains during heating this transformation which seems to be triggered by the coercivity decrease observed at very moderate temperatures can reduce the nrm intensity without requiring any correlated ptrm acquisition

impact of cretaceous sea level rise and anoxic events on the mesozoic carbonate platform of yugoslavia the adriatic dinaric carbonate platform of yugoslavia was influenced by rapid sea level rise and an oceanic anoxic event during the cenomanian turonian open marine biota such as planktonic foraminifera radiolarians and locally even ammonites associated with and bracketed by successions of typical shallow water carbonates indicate partial drowning of substantial areas of the platform during this time suggestive furthermore that the rate of increase of water depth was locally great enough to outpace carbonate production the presence of carbon rich and fish bearing platy limestones commonly cherty as an associated coeval facies indicates the development of anoxic or euxinic environments and the stromatolitic laminations in such rocks are attributed to the action of bacterial mats it is suggested that an extensive column of deoxygenated water developed in the neighboring marche umbrian adriatic deep water basin and was carried on to the carbonate platform during the cenomanian turonian transgression

rudists and carbonate platforms in the aptian a case study on biotic interactions with ocean chemistry and climate variations in aptian carbonate platform growth and associated turnover among rudists are reviewed and the results synthesized with evidence for climate change to yield an explanatory model extensive platform growth throughout the atlantic tethys low palaeolatitude pacific seamount belt in the earliest aptian was accompanied by prolific rudist diversification especially among the predominantly aragonitic caprinids occupying platform margins it was ubiquitously interrupted in the mid early aptian in tandem with major perturbations of the global carbon cycle that culminated in oceanic anoxic event 1a although the causal linkages remain contentious platform growth terminated along most of the northern tethyan margin and maybe also in the new world meanwhile lithocodium bacinella or similar microbial encrustations became widespread in lower palaeolatitudes recovery of tethyan platforms in the late early aptian was limited to lower palaeolatitudes caprinid rich platform margin facies again prevailed in central and southern tethyan areas but gave way to those dominated by rudists with a thickened calcitic outer shell layer polyconitids and requieniids in marly successions around iberia the end of the early aptian saw the lazarus style disappearance of caprinids and renewed tethyan platform growth in the late aptian was dominated by calcite rich rudists although rudists remained scarce in the new world until the terminal aptian this study postulates that sea water acidification influenced both the mid early aptian platform debacle and the subsequent late early aptian geographical restriction of platform recovery although in contrasting atmospheric regimes at first it was forced by the increasing atmospheric levels of volcanically derived co2 with mitigation in low latitudes from thermal expulsion of aqueous co2 here termed the kettle effect due to greenhouse warming however subsequent cooling due to drawdown of atmospheric co2 by organic carbon burial could have sustained acidification of platform waters in higher latitudes by reducing the protective kettle effect there caprinid susceptibility to such assaults may have been as much due to exposure on their preferred outer platform habitats as to their mineralogy the increased calcite aragonite ratio among rudists through the aptian resulted largely from this taxonomic turnover

micromagnetic coercivity distributions and interactions in chondrules with implications for paleointensities of the early solar system 1 chondrules in chondritic meteorites record the earliest stages of formation of the solar system potentially providing information about the magnitude of early magnetic fields and early physical and chemical conditions using first order reversal curves forcs we map the coercivity distributions and interactions of 32 chondrules from the allende karoonda and bjurbole meteorites distinctly different distributions and interactions exist for the three meteorites the coercivity distributions are lognormal shaped with bjurbole distributions being bimodal or trimodal the highest coercivity mode in the bjurbole chondrules is derived from tetrataenite which interacts strongly with the lower coercivity grains in a manner unlike that seen in terrestrial rocks such strong interactions have the potential to bias paleointensity estimates moreover because a significant portion of the coercivity distributions for most of the chondrules is 10 mt low coercivity magnetic overprints are common therefore paleointensities based on the rem method which rely on ratios of the natural remanent magnetization nrm to the saturation isothermal remanent magnetization irm without magnetic cleaning will probably be biased the paleointensity bias is found to be about an order of magnitude for most chondrules with low coercivity overprints paleointensity estimates based on a method we call remc which uses nrm irm ratios after magnetic cleaning avoid this overprinting bias allende chondrules which are the most pristine and possibly record the paleofield of the early solar system have a mean remc paleointensity of 10 4 mt karoonda and bjurbole chondrules which have experienced some thermal alteration have remc paleointensities of 4 6 and 3 2 mt respectively

paleoecology and proliferation of the bivalve chondrodonta joannae choffat in the upper cenomanian upper cretaceous adriatic carbonate platform of istria croatia abstract chondrodonta joannae choffat is a morphologically variable oyster like bivalve with a predominately calcitic shell an exceptional exposure of c joannae bearing strata of late cenomanian age crops out along the seaside in northern istria croatia and permits a taphonomical and functional analysis in order to define the life habit and growth strategies of this bivalve the c joannae population from the studied succession is characterized by highly elongated large and curved shells reaching about 50 cm in height and 5 cm in length this shell shape is typical of the club like bivalve morphotype which was adapted to soft bottom substrates with high sediment accumulation the shell is slightly inequivalve and characterized by a reduced body cavity a few centimetres high and a dorsal region up to 10 times longer the shell opening mechanism was mostly based on the resilium located between the chondrophores which protrude in the body cavity the abandoned dorsal cavity is filled by a calcite hinge plate the ventral edge of which acted as fulcrum for the valve flexibility in the hinge plate the function of chondrophores changed they acted as a hinge to keep tightly interlocked the valves which considerably emerged above the sediment water interface the individuals were arranged in low shrub type congregations which produced low relief mounds the functional morphology and taphonomic signature suggest that c joannae individuals collected food at a greater distance from the bottom with respect to the co occurring rudists we speculate that the c joannae proliferation could be related to a late cenomanian phase of environmental instability predating the oae2 with fluctuating climatic conditions and ocean fertility

environmental control and dynamics of lower jurassic bivalve build ups in the trento platform southern alps italy abstract bivalve molluscs show a short and peculiar early jurassic evolutionary phase characterized by the lithiotis sensu lato fauna mainly represented by the three monospecific genera lithiotis cochlearites and lithioperna these bivalves with stick like or flattened large shells are mostly restricted to the pliensbachian they have a wide geographical distribution occurring both in tethyan and panthalassian carbonate platforms where considerable biogenic accumulations formed they were common on the trento platform southern alps where they occur in the rotzo formation calcari grigi group this formation was deposited in a tropical lagoon which was closed seawards by oolitic shoals and bars and bordered landwards by marshes the lithiotis s l fauna of the trento platform seems to be restricted to the upper pliensbachian it appeared after a eutrophic phase with recurrent low oxygen and brackish conditions and flourished in meso to oligotrophic waters the stratigraphic and geographic distributions of each genus are compared to the environmental development of the rotzo formation in order to highlight limiting environmental factors and ecological requirements lithioperna occurs throughout the whole formation it is the most eurytopic genus well adapted to dysaerobic habitats and with higher ecomorphic plasticity than the other two genera it frequently occurs in the life position giving rise to densely packed fan like or book like aggregates lithiotis required aerobic and euhaline marine conditions and is common in the middle part of the formation where mesotrophic conditions prevailed this genus is rarely preserved in the theoretical vertical life position probably due to lower shell stability and a less effective attachment modality cochlearites is the most common genus of the rotzo formation this genus inhabited euhaline to slightly hypersaline marine environments occurring in the upper part of the formation prevailing in oligotrophic conditions lithiotis s l fauna gave rise to biogenic accumulations with an elevation of a few decimeters to several meters above the sea bottom and with a lateral extension ranging from ten to several hundred meters therefore these accumulations represent biological build ups which document four developmental phases colonization aggradation progradation and demise the colonization phase is represented by pioneering individuals which were cemented or byssally attached to a bioclastic coarse grained storm layer which constituted the hard substrate for larval attachment the aggradation phase produced the core of the build up and its elevation above the sea bottom the core is mostly represented by individuals which acted as bafflers commonly with an apparently chaotic fabric the lithiotis s s and cochlearites cores are generally mud supported and contain loosely packed to dispersed specimens occasionally preserved in life position the lithiotis s s and cochlearites build ups can be defined as bivalve mounds the cores of the lithioperna build ups are skeletal supported with shells mostly preserved in life position which characterize the bivalve reefs the prograding phase produced lateral additions to the build up flanks of oblique and imbricated articulated individuals the flanks grew centrifugally from the core and represent the most conspicuous part of the build ups ranging from 10 to 20 times the size of the core and occasionally extending over several hundred meters

thermal alteration of the magnetic mineralogy in ferruginous rocks the northampton ironstone contains the paramagnetic minerals siderite and berthierine and a trace of the ferrimagnetic mineral magnetite the magnetic fabric of this sedimentary rock as defined by the anisotropy of magnetic susceptibility is controlled by bedding compaction but is inverse i e the maximum susceptibility axes are normal to the bedding plane this inverse fabric is attributed to the dominating presence of siderite the rocks were incrementally heated to 600 c and the magnetic fabric was measured at room temperature and at near liquid nitrogen temperature after each heating step cooling the samples in liquid nitrogen enhances the paramagnetic contribution to the magnetic fabric after heating the samples above 250 c the room temperature magnetic fabric became normal with the minimum susceptibility axes perpendicular to the bedding plane the low temperature magnetic fabric remains inverse until the samples are heated to about 500 c after heating to higher temperatures a normal fabric was observed at both room temperature and low temperature rock magnetic evidence shows that magnetite is created during the heating the start of mineralogical changes in the rock was detected by electron spin resonance spectroscopy powder x ray diffraction and acquisition of isothermal remanence berthierine starts to break down at approximately 250 c and is totally oxidized by 500 c the creation of magnetite in the heating experiments corresponds with this mineralogical change the change in the room temperature magnetic fabric is associated with the decomposition of berthierine part of which alters to magnetite the new magnetite phase has a normal magnetic fabric which overprints the inverse magnetic fabric of siderite

new stepping stones dugi otok and vis islands in the systematic paleomagnetic study of the adriatic region and their significance in evaluations of existing tectonic models abstract the external dinarides from which several conflicting tectonic models were published are the more tectonized ne margin of autochthonous adria dugi otok and vis islands belong to this margin from the two islands a new paleomagnetic study is presented based on 48 geographically distributed and biostratigraphically controlled cretaceous carbonate sediment localities the results suggest that the two islands certainly moved in co ordination after the mid albian which was the time of resumed sedimentation after a period of emersion although some relative movement could have occurred earlier the new post aptian paleomagnetic results are in perfect agreement with recently published paleomagnetic results from stable adria and from the more northerly adriatic islands this consistency suggests that all these areas moved together from the albian on while the coastal range of the external dinarides seems to have moved independently thus autochthonous adria together with the adriatic islands is established as a crustal block within the central mediterranean region which rotated significantly in ccw sense in post cretaceous times

palaeointensity study of the hawaiian 1960 lava implications for possible causes of erroneously high intensities summary it is known that the hawaiian 1960 lava sometimes yields higher palaeointensities than the igrf 36 2 t in order to clarify the causes we have performed a comprehensive investigation of palaeointensity measurements on 19 cores from the lava according to various rock magnetic analyses they are classified into three groups with degrees of the deuteric oxidation in coe s version of the thellier method a significantly larger mean palaeointensity of 49 0 9 6 t n 17 was observed similar to previous studies these palaeointensities showed a dependence on the oxidation indices which can be explained by thermochemical remanent magnetization tcrm acquisition during the natural cooling stage of the lava although it is generally difficult to distinguish the tcrm from thermoremanent magnetization trm a lowtemperature demagnetization ltd treatment on nrm and trm in the thellier experiment seems to allow us to detect the influence of the tcrm on nrm another possible tool for tcrm detection is the double heating technique dht of the shaw method combined with ltd ltd dht shaw method it gave a better average of 39 4 7 9 t n 9 though the success rate was much lower most of the inappropriate results were screened by a combination of the double heating test the arm correction and the ltd treatment if two outliers are further excluded the average is improved to be 35 7 3 3 t n 7 which agrees well with the expected intensity the results of both methods emphasize the importance of taking and measuring samples from the parts of various oxidation degrees in a lava flow

the motion of adria during the late jurassic and cretaceous new paleomagnetic results from stable istria abstract the motion of adria the largest lithospheric fragment in the central mediterranean region has played an important role in the tectonic development of the surrounding mountain chains and even of distant areas like the eastern alps or the pannonian basin the available paleomagnetic data were insufficient to constrain this motion except in a general way in this paper new paleomagnetic results are presented from one of the stable parts of adria which emerge from the adriatic sea the results were obtained on weakly magnetic platform carbonates of the mud supported type collected from 21 geographically distributed localities the results combined with mean paleomagnetic directions from selected localities from a pioneer study in istria that were chosen using statistical criteria were divided into three age groups tithonian aptian albian cenomanian turonian coniacian the paleomagnetic poles calculated for each of them tithonian aptian n 47 e 275 k 67 95 9 4 n 5 albian cenomanian n 58 e 253 k 145 95 4 3 n 9 turonian coniacian n 63 e 261 k 50 95 7 3 n 9 reveal a moderate shift during the cretataceous which is comparable with that calculated from the african reference poles however the istrian apparent polar wander path is slightly displaced from the african curve as a consequence of about 10 counterclockwise rotation of istria with respect to africa this rotation angle is more that 10 smaller than the difference measured for the mid late eocene between the paleomagnetic direction of platform carbonates from istria and the african reference direction this difference may be the consequence of a small clockwise rotation of istria with respect to africa most probably at the end of cretaceous

a late devensian lateglacial palaeomagnetic record from llyn gwernan north wales comparison with other nw european records summary palaeomagnetic analysis of 222 specimens from a high resolution late devensian lateglacial sedimentary sequence at llyn gwernan north wales has provided the first detailed record of geomagnetic secular variation for the lateglacial period in britain this provides the opportunity to extend the british holocene geomagnetic master curve possibly as far back as 15 000 yr bp the declination log records six well defined oscillations with peak to peak amplitudes of 20 30 the inclinations are shallower than expected for this latitude 52 44 n which are probably due to the magnetic recording process although low geomagnetic inclinations are not ruled out the inclination log defines a number of relatively smooth swings with peak to peak amplitudes of 10 20 no evidence for any geomagnetic excursions such as the gothenburg flip was found the llyn gwernan lateglacial palaeomagnetic record is compared with the published palaeomagnetic records for a number of european sites correlations between records suggest that the ages of the llyn gwernan palaeomagnetic features derived from a series of radiometric radiocarbon measurements are in general compatible with those of the european sites discrepancies between the records are probably due to errors in radiocarbon dating of lateglacial sediments and variability of the palaeomagnetic recording process and do not represent spatially variable geomagnetic field behaviour