oceanic anoxic cycles orbital prelude to the bonarelli level oae 2 abstract the prelude to the second global oceanic anoxic event of the cretaceous oae 2 as recorded in the classic sections of the scaglia bianca formation in the umbria marches region of italy is characterized by an oscillation between black to gray organic rich cherts and white pelagic limestones spectral analysis of these lithologic alternations reveals a robust set of cycles whose periods are remarkably similar to the orbital cycles calculated by laskar et al laskar j robutel p joutel f gastineau m correia a c m levrard b 2004 a long term numerical solution for the insolation quantities of the earth astronomy and astrophysics 428 261 285 bandpass filtering shows that the 140 80 kyr signal approximates the envelope of the 26 16 kyr signal just as expected if these components represent responses to orbital eccentricity and precession matching the presumed eccentricity signal to the theoretical eccentricity of laskar et al yields an age for the base of the bonarelli level onset of oae 2 in italy of 94 21 ma 93 72 ma provides an alternative consistent with radiometric constraints from a correlative section in the western united states given the strong orbital control on the cyclic deposition of the organic rich precursors of oae 2 within the scaglia bianca formation we hypothesize that the timing of oae 2 itself is similarly controlled by astronomical variations indeed the occurrence of oae 2 coincides with a protracted period of unusually low insolation variation owing to simultaneous nodes in all orbital parameters we speculate that other oaes similarly coincided with insolation nodes and dampened seasonality from this perspective some but perhaps not all of the oaes may be periodic events reflecting cycles of oceanic anoxia that predictably punctuated a 50 myr period of cretaceous climate

comparing oxygen isotope records of silurian calcite and phosphate δ18o compositions of brachiopods and conodonts oxygen isotope compositions of silurian calcitic brachiopod shells from gotland are compared with those of phosphatic inarticulate brachiopod shells and conodonts from identical stratigraphic horizons the 18ophosphate values of inarticulate brachiopod shells vary widely 13 0 to 17 5 v smow and are significantly lower than those of coeval conodont samples 17 5 to 19 5 v smow conodont samples from individual beds have homogenous 18ophosphate values with variations close to the analytical precision 0 2 together with a significant correlation of conodont 18ophosphate and articulate brachiopod shell 18ocarbonate values r 0 85 this observation suggests that primary marine oxygen isotope compositions are better preserved in conodont apatite than in inarticulate brachiopod shell apatite however with decreasing 18ocarbonate values the 18ophosphate values of conodonts are higher than expected for theoretical isotopic equilibrium with brachiopod calcite different habitats of conodonts and brachiopods cannot account for the observed offset in 18o because both organisms were thriving on a broad shallow marine carbonate platform whereas 18ophosphate values of silurian conodonts are close to 18ophosphate values of modern and mesozoic tropical biogenic apatites most silurian calcitic brachiopod shells from gotland are depleted in 18o when compared to modern or mesozoic brachiopods we therefore suggest that silurian conodonts from gotland record paleotemperature and 18o of silurian sea water more faithfully than coeval calcitic brachiopod shells

comparative analysis of methods used to define eustatic variations in outcrop late cambrian interbasinal sequence development interbasinal correlation of late cambrian cyclic carbonates from the appalachian and cordilleran passive margins the texas craton and the southern oklahoma aulacogen defines six major third order depositional sequences graphic correlation of biostratigraphically constrained strata was used to establish equivalency of stratigraphic sequences between the individual sections relatively isochronous biomere boundaries were used as time datums for lithostratigraphic correlation although the individual sections are composed of different types of meter scale cycles and component lithofacies that reflect the various environmental settings of the localities the overall upward shallowing character of individual sequences is evident the sequences are late cedaria mid crepicephalus late crepicephalus aphelaspis to earliest elvinia elvinia to early saukia and saukia to the cambrian ordovician boundary interbasinal correlation of stratigraphic sequences permits an evaluation of quantitative techniques for determining accommodation history correlation of fischer plots of cyclic successions from separate basins supports a eustatic control of late cambrian sequence development r2 r3 curves derived from subsidence analysis of the late cambrian sections provide good resolution of the second and third order scales of accommodation change and interbasinal correlations of r2 r3 curves also support eustatic control on sequence development comparing the accomodation curves and subsidence analysis with paleobathymetric trends of late cambrian cyclic strata suggests that themore curves may approximate the form of the eustatic sealevel signal a composite eustatic sealevel curve for late cambrian time in north america was created by qualitatively combining the accommodation curves defined by the different techniques for each of the four localities 129 refs 16 figs 3 tabs less

late paleozoic iberian orocline s and the missing shortening in the core of pangea paleomagnetism from the iberian range supercontinents are usually interpreted to be single and rigid continental plates how and when pangea became a rigid supercontinent is disputed and age estimations vary from 330 to 240 ma the gondwana laurussia collision formed the variscan alleghanian belt the most prominent witness of pangea s amalgamation in iberia this orogen draws an s shape featured by the cantabrian orocline and the central iberian curve the curvature of central iberia is particularly evident in galicia tras os montes and in a change of trend that it draws in the aragonese branch of the iberian range recent research showed that both curvatures are not coeval and that the central iberian curve had to form prior to ca 318 ma i e not a secondary orocline we report paleomagnetic and structural results from paleozoic rocks in the santa cruz syncline aragonese branch of the iberian range that indicate two main vertical axis rotations events 1 a cenozoic alpine clockwise rotation of 20 and 2 a late carboniferous counterclockwise rotation of 70 once the cenozoic rotation is restored the change in structural trend that allegedly evidences the outer arc of the central iberian curve disappears whereas the cenozoic rotation is incompatible with a central iberian curve the late carboniferous rotation is fully compatible with the cantabrian orocline enlarging the area affected by its counterclockwise rotations and the existence of a nonrigid pangea until at least 295 ma

oxfordian magnetostratigraphy in the iberian range the magnetostratigraphy has been established in two sections of middle and late oxfordian age from the iberian range spain the polarity sequences correlate well with the magnetozones in sections at aguilon and tosos juarez et al 1994 a composite magnetostratigraphic sequence has been derived for all the sections in the iberian range it correlates with the handschumacher et al 1988 extension of the geomagnetic polarity time scale and ties the oceanic magnetic anomaly sequence to the oxfordian sedimentary sections

pliensbachian magnetostratigraphy new data from paris basin france sampling of an industrial drill string from the northeastern paris basin montcornet france provides early jurassic magnetostratigraphic data coupled with biochronological control about 375 paleomagnetic samples were obtained from a 145 m thick series of pliensbachian rocks a composite demagnetization thermal up to 300 c and an alternating field up to 80 mt were used to separate the magnetic components a low unblocking temperature component 250 c with an inclination of about 64 is interpreted as a present day field overprint the characteristic remanent component with both normal and reversed antipodal directions was isolated between 5 and 50 mt twenty nine polarity intervals were recognized correlation of these new results from the paris basin with data from the breggia gorge section ticino southern alps switzerland which is generally considered as the reference section for pliensbachian magnetostratigraphy reveals almost identical patterns of magnetic polarity reversals however the correlation implies significant paleontological age discrepancies revised age assignments of biostratigraphic data of breggia as well as an objective evaluation of the uncertainties on zonal boundaries in both breggia and moncornet resolve the initial discrepancies between magnetostratigraphic correlations and biostratigraphic ages hence the sequence of magnetic reversals is significantly strengthened and the age calibration is notably improved for the pliensbachian a stage for which sections combining adequate magnetic signal and biostratigraphic constraints are still very few

tertiary oxygen isotope synthesis sea level history and continental margin erosion tertiary benthic and planktonic foraminiferal oxygen isotope records are correlated to a standard geomagnetic polarity time scale making use of improved chronostratigraphic control and additional oligocene isotope data synchronous changes in both benthic and planktonic 18o values which occurred in the oligocene to miocene 36 5 2 ma are interpreted in part to represent ice growth and decay the inferred ice growth events correlate with erosion on passive continental margins as interpreted from seismic and chronostratigraphic records this association is consistent with a link between oligocene to miocene erosional events and rapid 15 m m y glacioeustatic lowerings of about 50 m high benthic foraminiferal 18o values suggest the presence of continental ice sheets during much of the oligocene to recent 36 0 ma substantially ice free conditions probably existed throughout the paleocene and eocene 66 36 ma the mechanisms and rates of sea level change apparently were different between the early and late tertiary with glacioeustatic changes restricted to the past 36 m y pre oligocene erosion on passive continental margins was caused by eustatic lowerings resulting from global spreading rate changes we apply a model which suggests that large areas of the continental shelves were subaerially exposed during such tectonoeustatic lowstands stimulating slope failure and submarine erosion the different mechanisms and rates of eustatic change may have caused contrasting erosional patterns between the early and late tertiary on passive continental margins this speculation needs to be confirmed by examination of data from several passive margins

evidence of widespread cretaceous remagnetisation in the iberian range and its relation with the rotation of iberia a palaeomagnetic investigation has been carried out at 13 sites of jurassic age in the iberian range northern spain two components of remanent magnetisation have been found at each site a primary high temperature component shows an average counterclockwise rotation with respect to the north of 33 2o clockwise about a vertical axis corresponding to the absolute rotation of the iberian plate since the jurassic a secondary low temperature component shows a systematic declination difference of 16 4o with respect to the primary component this indicates that a rotation of iberia must have occurred between the two acquisition times comparison of the magnetisation directions with previous palaeomagnetic data and with sea floor spreading data constrains the age of the remagnetisation between 95 and 125 ma the remagnetisation may be associated with the extensional phases in the iberian basin in the early cretaceous barremian early albian or late cretaceous cenomanian a principal characteristic of the remagnetisation is its widespread character in the iberian range 1998 elsevier science b v all rights reserved

paleomagnetism and late diagenesis of jurassic carbonates from the jura mountains switzerland and france a crucial fold test for magnetizations measured in bajocian through kimmeridgian limestones from the jura mountain region shows that rare blue gray limestones found in this sequence preserve a prefolding magnetization in contrast tan limestones which predominate in this sequence contain secondary magnetizations acquired after folding in the late miocene the postfolding magnetizations in tan limestones appear to be carried in goethite and because reversed as well as normal polarity directions are present the magnetization in these limestones is probably a post miocene pre brunhes 700 000 yr chemical remanent magnetization crm field relations between tan and blue gray limestones which are present in some cases in the same rock unit for example the hauptrogenstein suggest that the tan limestones may have formed from alteration of blue limestones whereas goethite pseudomorphs after pyrite are found in tan limestones the occurrence of pyrite in the blue limestones supports this model indicating that goethite could have formed from oxidation of pyrite abundant meteoric water probably was available for such an oxidation process during uplift of these strata subsequent to deformation natural remanent magnetization in blue limestones appears to be carried in magnetite the positive fold test for the characteristic magnetization in these rocks is significant at the 99 confidence level k values for 24 site mean directions before and after tilt correction are 9 3 and 43 2 respectively the simplest interpretation for the origin of observed remanence in magnetite in the blue limestones is a primary magnetization of depositional or biogenic origin characteristic directions in these rocks yield a mean paleopole position of 77 7n 148 4e k 26 0 a95 5 9 this pole is in reasonable agreement with one other upper jurassic pole from western europe and with other middle to upper jurassic poles from the atlantic bordering continents after rotation of these continents to a reconstructed configuration for middle to late jurassic time

oxfordian magnetostratigraphy of britain and its correlation to tethyan regions and pacific marine magnetic anomalies a suite of 11 sections through the oxfordian upper jurassic strata in the dorset and yorkshire regions of england and the isle of skye in scotland yielded magnetic polarity patterns directly calibrated to the ammonite biostratigraphy of the boreal and the subboreal faunal provinces the sections include the leading candidate for the global stratotype gssp for the callovian oxfordian stage boundary the mean oxfordian paleomagnetic pole derived from the dorset and yorkshire sections is 71 3 n 172 6 e p 4 2 m 6 1 the integrated magneto biostratigraphic scale is consistent with results from the sub mediterranean faunal province and extends the polarity pattern to the base of the oxfordian after adjusting for the estimated durations of ammonite subzones from cycle stratigraphy the magnetostratigraphy confirms models for marine magnetic anomalies m30 through to m37 including some of the short duration features recorded by deep tow magnetic surveys in the western pacific the callovian oxfordian boundary base of quenstedtoceras mariae zone occurs in a normal polarity zone that is correlated to the youngest part of polarity chron m37n of this extension to the m sequence

new paleomagnetic mesozoic data from the algarve portugal fast rotation of iberia between the hauterivian and the aptian abstract we sampled nine sites of jurassic and cretaceous limestones in the algarve region portugal our study yields a paleopole for the portlandian valanginian 256 58 a95 5 and a paleopole for the aptian albian 232 75 a95 8 these results allow better constraint of the relative rotation of iberia with respect to europe this rotation of 22 14 is a rather fast event occurring during the barremian between 132 and 124 ma confinement of iberia between africa and eurasia would explain the rapid rotation of this microplate the iberian plate was probably attached to europe until 132 ma then detached from europe and acted as an independent plate during the time of fast rotation preceding the oceanic spreading in the bay of biscay

rapid cenozoic glaciation of antarctica induced by declining atmospheric co2 the sudden widespread glaciation of antarctica and the associated shift towards colder temperatures at the eocene oligocene boundary 34 million years ago refs 1 4 is one of the most fundamental reorganizations of global climate known in the geologic record the glaciation of antarctica has hitherto been thought to result from the tectonic opening of southern ocean gateways which enabled the formation of the antarctic circumpolar current and the subsequent thermal isolation of the antarctic continent5 here we simulate the glacial inception and early growth of the east antarctic ice sheet using a general circulation model with coupled components for atmosphere ocean ice sheet and sediment and which incorporates palaeogeography greenhouse gas changing orbital parameters and varying ocean heat transport in our model declining cenozoic co2 first leads to the formation of small highly dynamic ice caps on high antarctic plateaux at a later time a co2 threshold is crossed initiating ice sheet height mass balance feedbacks that cause the ice caps to expand rapidly with large orbital variations eventually coalescing into a continental scale east antarctic ice sheet according to our simulation the opening of southern ocean gateways plays a secondary role in this transition relative to co2 concentration

oxfordian magnetic polarity pattern reply to comment by r e sheridan and k a suydam abstract sheridan and suydam 1 raise several important points which are primarily related to the origin of reported magnetic anomalies within the jurassic magnetic quiet zone of the ocean crust and therefore are not directly relevant to our magnetostratigraphic study of oxfordian sediments 2 we will discuss only two points 1 the consistency of our oxfordian results with other evidence of mixed polarity and 2 the factors complicating the resolution of rapid magnetic reversals in the anomaly record of deep jurassic crust

a paleozoic pangaea paleozoic paleogeographies should be consistent with all available reliable data however comparison of three different devonian paleogeographies that are based largely or wholly on the data of remanent magnetism show them to be inconsistent in many regards when these three paleogeographies are provided with possible ocean surface current circulation patterns and have added to them lithofacies and biogeographic data they also are shown to be inconsistent with such data a pangaeic reconstruction positioned in the southern hemisphere permits the lithofacies and biogeographical data to be reconciled in a plausible manner

stratigraphic and oxygen isotope evidence for my scale glaciation driving eustasy in the early middle devonian greenhouse world article i nfo million year scale 3rd order depositional sequences few 10s to 100 m thick are common in the devonian marine record and are correlated between sedimentary basins and across widely separated continents implying a eustatic origin tectonically driven changes in mid ocean ridge spreading rates lengths are too slow to account for the calculated 3rd order rise fall rates and typical orbital frequencies 20 400 ky are too fast we analyzed oxygen isotopes from conodont apatite to evaluate if early middle devonian 3rd order sea level changes were controlled by paleoclimatically driven ice volume glacio eustasy and seawater temperature change thermo eustasy two successive depositional sequences in the western u s nevada and czech republic prague basin were sampled the 18 o values range from 17 8

paleomagnetic study of the messejana plasencia dyke portugal and spain a lower jurassic paleopole for the iberian plate abstract the only iberian lower jurassic paleomagnetic pole come from the central atlantic magmatic province related messejana plasencia dyke but the age and origin of its remanence have been a matter of discussion with the aim of solving this uncertainty and to go further into a better understanding of its emplacement and other possible tectonic features a systematic paleomagnetic investigation of 40 sites 625 specimens distributed all along the 530 km of the messejana plasencia dyke has been carried out rock magnetic experiments indicate psd low ti titanomagnetite and magnetite as the minerals carrying the nrm the samples were mostly thermally demagnetized most sites exhibit a characteristic remanent component of normal polarity with the exception of two sites where samples with reversed polarities have been observed the paleomagnetic pole derived from a total of 35 valid sites is representative of the whole structure of the dyke and statistically well defined with values of pla 70 4 n plo 237 6 e k 47 9 and a 95 3 5 paleomagnetic data indicates that i there is no evidence of a cretaceous remagnetization in the dyke as it was suggested ii most of the dyke had a brief emplacement time furthermore two dyke intrusion events separated in time from it by at least 10 000 y have been detected iii the high grouping of the vgps directions suggests no important tectonic perturbations of the whole structure of the dyke since its intrusion time iv the pole derived from this study is a good quality lower jurassic paleopole for the iberian plate and v the messejana plasencia dyke paleopole for the iberian plate is also in agreement with quality selected european and north american lower jurassic paleopoles and the magnetic anomalies data sets that are available for rotate them to iberia

unraveling multiple thermotectonic events accommodated by crustal scale faults in northern iberia spain insights from k ar dating of clay gouges

remagnetization of lower cretaceous limestones from the southern pyrenees and relation to the iberian plate geodynamic evolution paleomagnetic study 34 sites of thick cretaceous 5000 m marine carbonate strata from the organya basin ob in the southern pyrenees reveals a uniformly normal polarity characteristic remanence with varying declination d berriasian barremian d 295 o aptian albian d 348 o upper cretaceous d 354 o that resides in magnetite and predates late cretaceous tertiary folding the lack of reverse polarity magnetizations in the berriasian barremian series together with their distinct hysteresis properties that are typical of remagnetized carbonates elsewhere are taken as evidence for a secondary overprint in the lower part of the succession a hypothesized age of remagnetization near the barremian aptian boundary fits with a major tectosedimentary event in the basin that changed deposition from platform to basinal conditions and increased subsidence during the aptian the angular difference 53 o between declination from the remagnetized strata and the mean for aptian albian strata indicates that a counterclockwise rotation occurred between the two acquisition times part of this rotation is interpreted to be local and due to slip variation along strike of a normal fault that bounded the basin and tilted the pre aptian series this cretaceous extensive phase is framed in the rift evolution of the northern margin of the iberian plate the inferred remagnetization age within the ob falls within the range of previously inferred widespread cretaceous remagnetization events affecting the iberian plate in the ob remagnetization is speculated to have taken place through chemical burial diagenetic origin rather than simple thermoviscous resetting

pre cretaceous tectonic evolution of the pacific plate and extension of the geomagnetic polarity reversal time scale with implications for the origin of the jurassic quiet zone abstract linear magnetic anomalies resulting from seafloor spreading were mapped in the vicinity of the magnetic bight in the western pacific ocean new aeromagnetic data allowed the magnetic bight to be more accurately mapped from m21 to m28 and enabled the identification of low amplitude magnetic lineations in the jurassic quiet zone these lineations were formed by magnetic field reversals prior to m29 a revised jurassic geomagnetic polarity reversal time scale was constructed with nineteen reversals older than m29 numbered m30 m38 these reversals extend the record of geomagnetic polarity back in time by approximately 8 ma and are important constraints on the origin of the quiet zone in particular they imply that the jurassic was not a period of constant normal polarity an explanation offered by some authors further they cast doubt on a model of systematically decreasing geomagnetic field strength with increasing age during this period the early history of the northern pacific plate and pacific farallon izanagi p f i triple junction was traced by mapped magnetic isochrons the pacific plate seems to have evolved from a small plate that formed near the phoenix farallon izanagi triple junction about 180 188 m y ago at approximately 17 n 160 e in present coordinates until m21 time the evolution of the northern pacific plate was relatively simple and the p f i triple junction migrated north northwest with respect to the pacific

geomagnetic polarity in the early cretaceous and jurassic knowledge of the polarity history of the earth s magnetic field during the mesozoic stems primarily from oceanic m sequence magnetic anomalies certain of these anomalies have been biostratigraphically dated from sediments immediately overlying basaltic basement at deep sea drilling project d s d p sites within the m sequence the biostratigraphic control is such that these age estimates are generally imprecise and moreover the sediment ages represent only minimum ages for the basaltic basement itself magnetostratigraphy in sedimentary land sections provides improved age estimates for magnetozones which can then be correlated with m sequence anomalies magnetostratigraphy provides not only enhanced dating of the ocean floor and resolution of the behaviour of the geomagnetic field during the cretaceous and jurassic oceanic quiet zones but also a world wide correlation tool for sedimentary stratigraphy the middle cretaceous is characterized by a long period of normal polarity extending from the early aptian to the early campanian reversed magnetozones corresponding to oceanic anomalies m 0 m 1 and m 3 have been palaeontologically dated as early aptian middle barremian and early barremian respectively magnetozones corresponding to oceanic anomalies m 5 to m 15 are hauterivian to valanginian in age but have not been individually associated with stage boundaries mainly due to poor biostratigraphic control in italian pelagic limestone sections of this age however magnetozones corresponding to oceanic anomalies m 16 to m 22 have been individually correlated to lower berriasian and tithonian palaeontological zones and extrapolation of this correlation gives an age for anomaly m 25 close to the oxfordian kimmeridgian boundary the jurassic 9quiet zone in the oceans is recognized in land sections as an extended period of predominantly normal polarity and although poor biostratigraphic control in this interval limits our knowledge of its duration we consider that it extended through the oxfordian and callovian stages the bathonian and older jurassic stages are characterized by mixed polarity a precise correspondence of magnetozones to ammonite zonations and stage boundaries is only available for the aalenian to pliensbachian interval where the frequency of reversal was apparently very high

magnetostratigraphy and biostratigraphy of callovian oxfordian limestones from the trento plateau monti lessini northern italy abstract callovian oxfordian ammonitico rosso limestones from the trento plateau carry a characteristic remanent magnetization indicating frequent geomagnetic polarity reversals which can be correlated to callovian oxfordian ammonite zones the characteristic magnetization component has low coercivity and blocking temperatures below 600 c suggesting that magnetite is the carrier the age of the magnetization is not constrained by field tests although sedimentological evidence for early lithification and the close stratigraphic juxtaposition of normal and reversed component directions tend to indicate that acquisition of the magnetization occurred close to the sediment water interface stratigraphic gaps and the condensed nature of the sections inhibit the correlation of polarity reversals between sections the data suggest a reversed polarity bias for the oxfordian and a normal polarity bias for the callovian

oxfordian magnetostratigraphy of the aguilon and tosos sections iberian range spain and evidence of a pre oligocene overprint abstract a composite magnetic polarity sequence has been constructed for the middle and late oxfordian late jurassic from four overlapping sections situated in both limbs of an anticline two stable magnetisation components could be isolated in every sample analyzed both components pass the fold test a low temperature secondary component with dec 340 9 and inc 44 9 95 1 7 of pre oligocene age showing always normal polarity and a high temperature primary component with dec 324 1 and inc 40 6 95 2 9 the latter shows both normal and reversed polarities and provides the geomagnetic record for the late jurassic the magnetostratigraphy of the four overlapping sections has given consistent results and indicates that a high frequency of reversals characterises the pattern of the geomagnetic field during the middle to upper oxfordian the corresponding oxfordian paleopole is p lat 251 2 p long 55 9 95 3 1

palaeogeographic evolution of the pieniny klippen basin using stratigraphic and palaeomagnetic data from the veliky kamenets section carpathians ukraine abstract a 40 m thick carbonate succession of the bajocian to berriasian age from the veliky kamenets quarry novoselica area pieniny klippen belt ukraine resembles both the czorsztyn and niedzica successions of the pieniny klippen belt traditionally considered ridge slope related deposits a total of 176 individually oriented cores collected from the bottom to the top of the sequence with sampling density dependent on inferred sedimentation rates show multicomponent remanent magnetization with magnetite as a main magnetic carrier thermal demagnetization revealed two main components of natural remanent magnetization nrm a low blocking temperature component s of normal polarity is considered of posttectonic probably thermoviscous origin due to overheating by neogene volcanics a stable high blocking temperature nrm component p shows dual polarity distribution and is considered primary it was possible to recognize 23 polarity zones that have been correlated with a biostratigraphic scale since two significant sedimentary gaps occur at 422 and 860 cm the main hiatus ms from the base the latter comprising the middle callovian early oxfordian time span 6 8 ma an obtained pattern of magnetic reversals presented in this study cannot be considered complete a palaeolatitude of 41 5 is calculated for the mid jurassic part below ms similar to that expected for the european craton at the kamenets locality the mid oxfordian limestone directly overlying the ms has palaeolatitudes around 28 6 this implies a relatively fast opening of the oceanic domain to the north from the kamenets block this conclusion combined with similarity of the kamenets sequence to ridge related sediments of the pieniny klippen belt makes it possible to speculate on the existence of the kamenets ridge a new term a structure of uncertain although possible structural links to the czorsztyn ridge palaeomagnetic declinations suggest 100 counterclockwise rotation of the whole section before the neogene

cretaceous slab break off in the pyrenees iberian plate kinematics in paleomagnetic and mantle reference frames the pyrenees at the iberia europe collision zone contain sediments showing albian cenomanian high temperature metamorphism and coeval alkaline magmatic rocks stemming from different views on jurassic cretaceous iberian microplate kinematics two schools of thought exist on the trigger of this thermal pulse one invoking hyperextension of the iberian and eurasian margins the other suggesting slab break off competing scenarios for mesozoic iberian motion compatible with pyrenean geology comprise 1 transtensional eastward motion of iberia versus eurasia or 2 strike slip motion followed by orthogonal extension both favoring hyperextension related heating and 3 scissor style opening of the bay of biscay coupled with subduction in the pyrenean realm favoring the slab break off hypothesis we test these kinematic scenarios for iberia against a newly compiled paleomagnetic dataset and conclude that the scissor type scenario is the only one consistent with a well defined 35 counterclockwise rotation of iberia during the early aptian we proceed to show that when taking absolute plate motions into account aptian oceanic subduction in the pyrenees followed by late aptian early albian slab break off should leave a slab remnant in the present day mid mantle below nw africa mantle tomography shows the reggane anomaly that matches the predicted position and dimension of such a slab remnant between 1900 and 1500 km depth below southern algeria mantle tomography is therefore consistent with the scissor type opening of the bay of biscay coupled with subduction in the pyrenean realm slab break off may thus explain high temperature metamorphism and alkaline magmatism during the albian cenomanian in the pyrenees whereas hyperextension that exhumed pyrenean mantle bodies occurred much earlier in the jurassic

oxygen isotope variations in phosphate of biogenic apatites i fish bone apatite rechecking the rules of the game abstract the major advantage of the oxygen in phosphate isotope paleothermometry is that it is a system which records temperatures with great sensitivity while bone and teeth building organisms are alive and the record is nearly perfectly preserved after death fish from seven water bodies of different temperatures 3 23 c and different 18 o values 16 to 3 of the water were analysed the 18 o values of the analysed po 4 vary from 6 to 25 the system passed the following tests a the temperatures deduced from isotopic analyses of the sequence of fish from lake baikal are in good agreement with the temperatures measured in the thermally stratified lake b the isotopic composition of fish bone phosphate is not influenced by the isotopic composition of the phosphate which is fed to the fish but only by temperature and water composition isotopic analysis of fossil fish in combination with analysis of mammal bones should be a useful tool in deciphering continental paleoclimates

analysis of anisotropy of magnetic susceptibility in iron oolitic beds a potential tool for paleocurrent identification a combined sedimentological shape preferred orientation and anisotropy of magnetic susceptibility ams analysis has been performed at the arroyofrio bed callovian oxfordian boundary level in the locality of moneva iberian range ne spain the arroyofrio bed is a widespread iron ooid limestone interval forming a condensed sequence the present study has focused on the analysis of the potential presence of a preferred ooid orientation at the arroyofrio bed the obtained data show that ooids were originally ellipsoidal and had an imbricate disposition with respect to the bedding lamination surface the main ooid orientation within the bedding plane shows a nne ssw trend results of ams analyses show a magnetic foliation parallel or slightly imbricated with respect to bedding and magnetic lineation parallel to the main ooid orientation magnetic mineralogy of studied samples shows that ams is mainly controlled by magnetite with minor contributions of hematite and paramagnetic minerals that can reach contributions of 35 the analyzed ooids show axial ratios between 1 4 and 2 8 intrinsic anisotropy while the anisotropy of their distribution shows lower anisotropies e g rs 1 15 or very low values of the anisotropic magnetic parameters e g p 1 01 sedimentary texture matrix features bioturbation and fossil content influenced both ooid main orientation and the magnetic fabric magnetic lineation and main orientation of long ooid axes are transverse to the inferred coastline in the studied area and parallel to the expected paleocurrent direction with respect to the ejulve maestrazgo paleogeographic high the direct correlation between ams magnetic lineation and the ooid analysis permits to demonstrate that the paleocurrent imprint can be recorded by means of ams despite the highly ferromagnetic context fabric and at coarse deposits obtained results support the interest and reliability of ams to unravel paleocurrent imprints for paleogeographic reconstructions

visions of ice sheets in a greenhouse world abstract backstripped eustatic estimates from new jersey and the russian platform show large 25 m and rapid 18 o record highlights the enigma this was the warmest interval of the past 200 my yet it was bracketed by two inferred eustatic falls of 25 m that were associated with two large 0 75 deep sea 18 o increases 92 93 ma mid turonian and 96 ma mid cenomanian we reconcile records of warm high latitudes with glacioeustasy by proposing that late cretaceous early eocene ice sheets generally reached maximum volumes of 8 12 10 6 km 3 20 30 m glacioeustatic equivalent but did not reach the antarctic coast hence coastal antarctica hence deep water remained relatively warm even though there were significant changes in sea level as the result of glaciation unlike the oligocene and younger icehouse world these ice sheets only existed during short intervals of peak milankovitch insolation leaving antarctica ice free during much of the greenhouse late cretaceous to middle eocene these results highlight the need to re evaluate the paradigm that polar ice sheets did not exist during times of warm high latitude climates

a long marine history of carbon cycle modulation by orbital climatic changes pacing of the marine carbon cycle by orbital forcing during the pliocene and pleistocene ice ages past 2 5 million years myr is well known as older deep sea sediment records are being studied at greater temporal resolution it is becoming clear that similar fluctuations in the marine carbon system have occurred throughout the late mesozoic and tertiary despite the absence of large continental ice sheets over much of this time variations in both the organic and the calcium carbonate components of the marine carbon system seem to have varied cyclically in response to climate forcing and carbon and carbonate time series appear to accurately characterize the frequency spectrum of ancient climatic change for the past 35 myr much of the variance in carbonate content carries the polar signal of obliquity 41 000 years 41 kyr forcing over the past 125 myr there is evidence from marine sediments of the continued role of precessional 21 kyr climatic cycles repeat patterns of sedimentation at about 100 400 and 2 400 kyr the modulation periods of precession persistently enter into marine carbon cycle records as well these patterns suggest a nonlinear response of climate and or the sedimentation of organic carbon and carbonates to precessional orbital perturbations nonlinear responses of the carbon system may help to amplify relatively weak orbital insolation anomalies into more significant climatic perturbations through positive feedback effects nonlinearities in the carbon cycle may have transformed orbital climatic cycles into long wavelength features on time scales comparable to the residence times of carbon and nutrient elements in the ocean

oxfordian magnetostratigraphy of poland and its correlation to sub mediterranean ammonite zones and marine magnetic anomalies abstract a nearly continuous magnetostratigraphic polarity pattern was compiled from several ammonite zoned carbonate successions of southern poland and from a composite magnetostratigraphy from the iberian range of spain the array of sections spans the middle two thirds of the oxfordian within the sub mediterranean province cordatum through bifurcatus ammonite zones the average paleopole calculated from eight of these polish sections is at 78 5 n 184 9 e p 2 6 m 3 5 the sub mediterranean polarity pattern is consistent with an independent polarity pattern derived from the boreal realm sections of the british isles and improves the inter correlation between these faunal realms cycle stratigraphy published for these ammonite subzones from southern france enabled temporal scaling of the polarity pattern thereby facilitating correlation to marine magnetic anomalies m28 through m33 as modeled from deep tow magnetometer surveys in the western pacific the bases of the middle and upper oxfordian substages as defined in the sub mediterranean zonation in poland correspond approximately to chrons m33 and m29 of that pacific m sequence model

a reply to the comment on assessing discrepancies between previous plate kinematic models of mesozoic iberia and their constraints by barnett moore et al we welcome the comments of van hinsbergen et al 2017 on the recent efforts of barnett moore et al 2016 specifically van hinsbergen et al 2017 raise concerns about two of the major conclusions made by barnett moore et al 2016 firstly barnett moore et al 2016 choose to negate the cretaceous iberian paleomagnetic database as a viable plate kinematic constraint on the plate motions of mesozoic iberia this conclusion criticized by van hinsbergen et al 2017 was based on citing the previous efforts of neres et al 2012 2013 which exposed several shortcomings elaborated on below within this dataset secondly van hinsbergen et al 2017 criticize barnett moore et al 2016 for dismissing mantle tomographic interpretations in support of a preserved cretaceous pyrenean subducted slab beneath northern africa below we have addressed each of these major criticisms from van hinsbergen et al 2017 in a two section layout similar to their comment above

the rotation of iberia during the aptian and the opening of the bay of biscay abstract the cretaceous rotation of the iberian plate in a geodynamical active setting between africa and europe is contemporaneous with the opening of the northern atlantic ocean and provides fundamental temporal and kinematical constraints on the evolution of the bay of biscay and the pyrenees here we report new paleomagnetic data from 50 sites 1109 drilled cores from marine sediments of the cretaceous organya basin in the southern pyrenees to constrain the timing and magnitude of the rotation of iberia berriasian to barremian directions in exclusively limestone lithology are remagnetised in agreement with previous organya basin studies the aptian to cenomanian marls and limestones in the organya basin however provide primary magnetisations asserted by rock magnetic experiments and positive fold tests our results constrain the rotation of iberia to be finished just before the albian paleomagnetic data cannot well constrain the onset of the rotation but sea floor anomaly studies restrict the onset of the rotation to anomaly m0 or the barremian aptian boundary this implies that the entire rotation of iberia happened in one single phase and is confined to the aptian this is in contrast to earlier studies that suggested a two phase rotation of iberia but we argue that the large errors in published ages are not in disagreement with our results in summary we constrain the 35 rotation of iberia to the aptian period which implies a rotation rate of 2 7 5 1 myr depending on the controversial duration of the aptian

new paleomagnetic results from cretaceous sediments near lisboa portugal and implications for the rotation of iberia abstract paleomagnetic study of outer platform sediments of late jurassic early cretaceous age from portugal lisboa area leads to characteristic remanent magnetization directions for the hauterivian barremian d 317 i 58 and the aptian d 344 i 47 the absolute rotation of iberia between 125 and 110 ma is consequently of about 27 in an anticlockwise sense a later rotation of about 14 follows the first one in the same sense from 110 ma the total absolute rotation of iberia from the hauterivian age determined by paleomagnetism is thus about 41 the comparison of declinations measured with paleodeclinations calculated in lisboa from the eurasian and african poles of similar age indicates that the main phase of relative rotation of iberia with respect to eurasia occurs during the first stage of relative motion i e hauterivian to aptian the tectonic history of the bay of biscay is in good agreement with these two stages of rotation the total relative rotation with respect to europe is 34 this value is consistent with results previously established by van der voo 2 3 25 but we have established that the main phase of rotation 30 occurs in the hauterivian aptian interval the movement of iberia is clearly linked to the movement of africa in direction and age but the amount of rotation of iberia during the early cretaceous is much larger and implies that iberia was not a real part of the african plate

paleomagnetism and potassium argon age of the messejana dike portugal and spain angular limitation to the rotation of the iberian peninsula since the middle jurassic abstract a paleomagnetic and potassium argon dating investigation has been carried out on a 530 km long dike system which transects the western iberian peninsula in a northeasterly direction the k ar age determinations were made on mineral separates exclusively they range between 160 and 200 ma and the authors suppose that this reflects the actual time interval of the intrusion in accord with previous results the paleomagnetic pole derived from 12 sites regularly distributed along the dike 71 n 236 e coincides well with other mesozoic paleomagnetic poles from the western africa a contemporaneous pole from stable europe is tentatively deduced from african and north american late triassic early jurassic poles using different reconstruction models around the north atlantic ocean the divergence between this pole and the iberian pole corresponds to the result obtained for permian poles

oxygen isotope variations in phosphate of biogenic apatites iii conodonts abstract the method for measurement of the isotopic composition of oxygen in phosphates has been improved and adapted for analysis of small quantities of apatite down to 10 mg this extension enables one to analyze hand picked conodont samples with an analytical reproducibility better than 0 5 1 46 samples of conodonts ranging from the ordovician to the pennsylvanian of north america were analysed some insoluble phosphatic residues ichthyoliths and inarticulate brachiopods of the same time range were also measured the range of the 18o values of the analysed conodonts is between 15 and 19 it shows a general trend of decreasing d18o with increasing age from an average value of about 19 in the pennsylvanian to 17 in the ordovician this trend parallels that previously detected in marine phosphorites for the time range between the devonian and pennsylvanian our data are in agreement with independent paleoclimatic information specifically we detect maximum18o enrichment at the end of the pennsylvanian and minimum enrichment at the end of the devonian the difference between these two extremes is equivalent to about 10 c from about 40 to 30 c assuming constant isotopic composition of ocean water the success of oxygen isotopic analysis of conodonts raises the possibility of their use in paleozoic paleo oceanography in a similar way to foraminifera in the mesozoic cenozoic

long periodic variations in the earth s obliquity and their relation to third order eustatic cycles and late neogene glaciations abstract evolutive spectra of four high resolution climatic proxy records reveal that the spectral power in the obliquity frequency band increases during five well defined intervals in the last 5 3 million years these intervals correspond to periods of high amplitude variations in the tilt obliquity of the earth s axis connected with a 1 2 myr cycle and to sea level lowstands of third order eustatic cycles in the haq et al 1987 curve this implies that the development of major plio pleistocene glaciations proceeded episodically and that third order cycles are glacio eustatically controlled in at least two of these intervals sinistrally coiled neogloboquadrinids entered the mediterranean at times of glacial periods one interval starts around 2 8 ma and is characterized by the first occurrence of n atlantica s another interval begins at the plio pleistocene boundary around 1 8 ma and is characterized by the common occurrence of sinistrally coiled n pachyderma also during the late miocene third order cycles correlate well with the 1 2 myr cycle of obliquity a significant drop in the third order eustatic curve starting at the tortonian messinian boundary for instance coincides with a period of high amplitude variations in the obliquity time series connected with the 1 2 myr cycle

reconciling cretaceous paleomagnetic and marine magnetic data for iberia new iberian paleomagnetic poles 1 the cretaceous paleogeography and the kinematic evolution of the iberian plate are poorly constrained especially problematic is to reconcile iberian paleomagnetic data with paleomagnetic data of the neighboring plates and with euler poles derived from seafloor magnetic anomalies the first limitation arises from the cretaceous normal polarity superchron where paleogeographic reconstruction using marine magnetic anomalies is handicapped the second arises from the paucity of reliable paleomagnetic poles with satisfactory statistical criteria and age in order to address these shortcomings and provide new high quality paleomagnetic poles for iberia we conducted a detailed rock magnetic and paleomagnetic study of two cretaceous magmatic sills the paco de ilhas pi and foz da fonte ff sills from the lusitanian basin portugal recently dated at about 88 and 94 ma respectively our results show that the magnetic mineralogy of the sills is primary i e acquired during magma cooling and essentially represented by titanomagnetite the corresponding paleomagnetic poles match the synthetic apwp from the african plate at 80 and 100 ma on the basis of a rigorous selection of iberian cretaceous poles we then calculated mean paleomagnetic poles for different time intervals and found that iberian paleomagnetic data fit well the global apwp between 70 and 120 ma but move far away from the apwp at pre rift times our approach shows that new and better constrained paleomagnetic poles can aide in solving part of the contradiction between iberian and african apwps

downhole magnetostratigraphy in sediments comparison with the paleomagnetism of a core the magnetostratigraphy of weakly magnetized sediments is determined for the first time from direct downhole measurements experimental results were obtained in both scientific and oil exploration drillholes penetrating jurassic sediments of the paris basin france the magnetic polarity of the remanence is deduced from the total magnetic induction combined with the magnetic susceptibility the magnetic induction is measured in depth by a proton precession magnetometer with overhauser effect designed by the laboratoire d electonique de technologie et instrumentation commissariat a i energie atomique this method gives a continuous record with an accuracy of 0 1 nt and an excellent stability in order to cancel out the transient component of the earth s magnetic field the magnetic induction is computed as the difference between the induction measured in the borehole and that obtained at a surface reference point located near the drillhole the dipole dipole susceptibility probe gives a continuous record with an accuracy of a few 10 6 the four total magnetic induction logs recorded in oil exploration holes show a tight correlation although distant from up to 80 km this technique is therefore excellent for precise stratigraphic correlation data processing allows us to isolate the component of induction due to remanent magnetization and to find the magnetic polarity a sequence of magnetic polarity is proposed for kimmeridgian and oxfordian stages the variation of the sedimentation rate is analyzed with a very high resolution in time and compared with the mean sedimentation rate deduced from a lithologic log cores were collected in the lowermost part of two holes the correlation between the magnetostratigraphy deduced from paleomagnetic measurements performed on 240 standard plugs and that obtained by logging is good a study of the components of magnetization found in the core has shown that the remagnetization occurred mainly during the coring operation itself or during the storage of the core consequently downhole magnetostratigraphy proves to be reliable besides providing the advantage of a continuous investigation performed over a large volume of rock scrutinized in situ

magnetostratigraphy of early middle toarcian expanded sections from the iberian range central spain abstract the magnetostratigraphy of the lower middle toarcian has been established in two well dated stratigraphically expanded sections the sierra palomera and the arino sections located in the iberian range in central eastern spain two magnetisation components could be isolated by thermal cleaning a secondary syntectonic component of always normal polarity unblocking at intermediate temperatures up to 450 c 475 c a component and a high temperature unblocking component up to 575 c b component the b component passes fold and reversal tests and is considered the characteristic remanent magnetisation of primary origin the first toarcian palaeomagnetic pole for iberia has been obtained plat 77 4 plon 241 3 e dm 5 4 dp 6 0 five pairs of normal and reversed polarity zones were calibrated to regional ammonite subzones the pattern can be calibrated to other toarcian magnetostratigraphic studies but provides a more detailed biostratigraphic framework a refined magnetic polarity time scale is proposed for the lower middle toarcian

seismic induced pore water pressure records from the mammoth lakes california earthquake sequence of 25 to 27 may 1980 abstract eight records of seismic induced pore water pressure and corresponding acceleration records were gathered from aftershocks of the 25 to 27 may 1980 mammoth lakes california earthquake sequence the records were obtained from lakeshore sediments at convict lake that had undergone liquefaction and subsequent lateral spreading failure the pore pressure records showed several similarities to corresponding strong motion acceleration records the pore pressure traces show clear p and s wave phases and are in phase with corresponding p wave components of the acceleration records s wave components of pore pressure records appear most similar in waveform to one or the other of the corresponding horizontal acceleration components although the p wave portions of pore pressure are in phase with their acceleration counterparts the amplitudes are not related by a strictly proportional factor s wave portions of the porepressure records show a phase lag compared to the s wave of the respective acceleration trace in most cases the frequency of the pore pressure s wave components are also about 5 hz lower in frequency than the acceleration s waves

late cretaceous chronology of large rapid sea level changes glacioeustasy during the greenhouse world we provide a record of global sea level eustatic variations of the late cretaceous 99 65 ma greenhouse world ocean drilling program leg 174ax provided a record of 11 14 upper cretaceous sequences in the new jersey coastal plain that were dated by in tegrating sr isotopic stratigraphy and biostratigraphy backstripping yielded a late cre taceous eustatic estimate for these sequences taking into account sediment loading com paction paleowater depth and basin subsidence we show that late cretaceous sea level changes were large 25 m and rapid k1 m y suggesting a glacioeustatic control three large d 18 o increases are linked to sequence boundaries others lack sufficient d 18 o data consistent with a glacioeustatic cause and with the development of small 10 6 km 3 ephemeral ice sheets in antarctica our sequence boundaries correlate with sea level falls recorded by exxon production research and sections from northwest europe and russia indicating a global cause although the exxon record differs from backstripped estimates in amplitude and shape

global correlation of cenomanian upper cretaceous sequences evidence for milankovitch control on sea level we have investigated the sequence stratigraphy of two widely separated marine cenomanian successions in southeast india and northwest europe and used high resolution ammonite biostratigraphy to demonstrate that sea level changes are globally synchronous and therefore must be eustatically controlled sequence scale sea level changes in the cenomanian were driven by the long eccentricity cycle 400 k y in the milankovitch band we hypothesize that during pre quaternary time the third order sequences of vail and haq are essentially a sediment response to sea level changes driven by the 400 k y cycle construction of a relative sea level curve for the marginal marine succession in india demonstrates that the short term sea level changes are rapid 10 100 m m y and have a magnitude of 2 20 m glacioeustasy is a possible but unproven driving mechanism

jurassic early cretaceous intermediate virtual geomagnetic poles and pangaean subduction zones abstract the objective of this paper is to show that the distribution of jurassic early cretaceous intermediate virtual geomagnetic poles vgps seems to be conditioned by pangaean subducted slabs palaeomagnetic data from between 200ma and 125ma were compiled from reliable studies and their vgps repositioned in their jurassic early cretaceous geographic location considering a zero longitude motion of africa over the last 200m y and the corresponding palaeomagnetic poles from each sequence those repositioned vgps lying between latitudes of 60 were considered to be intermediate to avoid bias as a function of simple sampling numbers for those sequences with more data each vgp was weighted by love s methodology a colour scale map shadow scale map in printed issue of density of the weighted intermediate vgps was obtained and compared with the pangaean subduction zones there is a good visual correlation between the distribution of these vgps and the location of the subduction zones during the jurassic suggesting that there is a relationship between the jurassic early cretaceous geomagnetic reversals and the plate tectonic setting at that time minima of intermediate vgps correlate well with the absence of vgps predicted with a tomographic model and the intermediate vgp distribution is also well correlated with zones of faster seismic wave propagation in the lower mantle just above of the core mantle boundary which suggests that the jurassic geomagnetic polarity transitions could have been controlled by a structure of the core mantle boundary similar to that at the present time we suspect that the subducted lithospheric slabs refrigerated the deepest mantle causing more heat than average flowing out from the core and controlling the geometry of the jurassic early cretaceous polarity transitions the earth s lithospheric plate motion history could have played a controlling role in the geometry of the geomagnetic reversals

magnetostratigraphic correlation of the oxfordian kimmeridgian boundary a magnetic polarity pattern for boreal and sub boreal ammonite zones of the upper oxfordian to lower kimmeridgian was established and confirmed in four british sections including the proposed global boundary stratotype section and point gssp on the isle of skye scotland to define the base of the international kimmeridgian stage a coeval pattern for sub mediterranean ammonite zones was compiled from seven sections in poland one german section and multi section composites from france and spain the mean paleopole for the european craton excluding spain at the oxfordian kimmeridgian boundary is 74 2 n 181 3 e 95 3 8 the common magnetic polarity scale enables inter correlation of ammonite subzones among these three faunal provinces and to the marine magnetic anomaly m sequence the proposed gssp at the base of the pictonia baylei zone is near the base of an extended interval dominated by reversed polarity which is interpreted to be chron m26r this gssp level projects to the lower to middle part of the epipeltoceras bimammatum subzone which is the middle subzone of this e bimammatum zone in the sub mediterranean standard zonation in contrast the traditional placement of the oxfordian kimmeridgian boundary in that sub mediterranean standard zonation base of sutneria platynota zone is at the base of chron m25r or nearly 1 million years younger