post depositional remanent magnetization lock in for marine sediments deduced from 10 be and paleomagnetic records through the matuyama brunhes boundary abstract geomagnetic field intensity records from marine sediments have contributed to improved understanding of variations in the earth s magnetic field and have helped to establish age models for marine sediments however lock in of the geomagnetic signal below the sediment water interface in marine sediments through acquisition of a post depositional remanent magnetization pdrm adds uncertainty to synchronization of marine sedimentary records although quantitative models enable assessment of delays in remanence acquisition associated with pdrm processes the nature of the filter function and the pdrm lock in zone thickness remain topics of debate we performed both forward numerical simulations and inverse parameter estimation to assess the best fit filter function and pdrm lock in zone thickness in marine sediments based on a comparison of 10be flux and relative paleointensity records our simulations reveal that the rate of pdrm lock in increases in the middle of the lock in zone and that a gaussian function with a 17 cm lock in zone thickness provides a good approximation to the pdrm lock in within the studied core with this function pdrm lock in is delayed but with relatively little distortion of the geomagnetic signal our results also imply that a pdrm is not simply locked due to progressive marine sediment consolidation and dewatering and that the arbitrary functions linear cubic and exponential that are often used to model pdrm lock in starting from the base of the surface mixed layer cannot explain fully the observed paleomagnetic signal

the upper and lower thvera sedimentary geomagnetic reversal records from southern sicily detailed paleomagnetic records of the upper and lower thvera polarity transitions have been determined from pliocenc marine marls in southern sicily the dominant magnetic mineral is fine grained magnetite the two transitions have vgp paths following a great circle passing south america and the west coast of north america there are strong indications that the vgp paths result from smoothing of the non antipodal stable directions before and after the transitions the upper thvera transitional record is preceded by two excursions and followed by a third one the first excursion is a sedimentary artefact caused by post depositional migration of magnetic minerals and the third one by is caused by weathering of the sediment the upper thvera transition from sicily is compared with the record from calabria about 250 km away the two records show similarities as well as differences both transitions have identical vgp paths but in calabria the transition is recorded lower in the sediment the first and third excursions have different characters and the second one is not present apparently the registration of transitions of the earth s magnetic field in sediments is strongly influenced by smoothing and diagenetic processes after deposition

magnetism of loess palaeosol sequences recent developments abstract investigation of the global loess record primarily as a palaeoclimatic archive continues unabated one important aspect of this research effort is the determination of the magnetic properties of the loess itself and of the palaeosols developed within it in earlier work these have provided a record of major long term past climatic changes however recent studies are now revealing sub milankovitch signals with teleconnections from the chinese loess plateau clp to the greenland and antarctic ice caps as well as to climate related events in sediments recovered from the north atlantic these high resolution profiles cover to the last 130 000 years however progress is also being made in extending the record down below the loess sensu stricto of the clp into the so called red clay so that the aeolian record can now be carried back beyond 7 ma bp several authors have attempted to obtain quantitative estimates of palaeoprecipitation by comparing magnetic susceptibility of palaeosols with values for modern soils although the broad picture is qualitatively clear wetter interglacials dryer glacials the actual quantitative values provided by the various techniques differ significantly in the classic chinese sites palaeosols are always magnetically enhanced due to in situ pedogenic processes however evidence is now emerging to indicate that this is not the only magnetoclimatological model in cases such as siberia where wind vigour dominates over pedogenesis the opposite pattern is found with magnetic susceptibility minima in palaeosols this also occurs in situations where the sediments are water logged for significant amounts of time leading to gleying and concomitant loss of magnetic minerals the use of magnetic remanence as a geomagnetic polarity clock requires caution early interpretations were acceptable for establishing broad chronological control however recent scrutiny suggests that remanence lock in may be delayed by as much as 20 000 years furthermore synthetic magnetostratigraphies modelled on the basis of realistic sediment characteristics indicate that there are limits to the amount of geomagnetic detail likely to be resolved this seems to be the case for the blake event which manifests itself in a very variable way at different sites in the clp

late cretaceous sea level changes in tunisia a multi disciplinary approach a multi disciplinary study of sea level and climate proxies including bulk rock and clay mineral compositions carbon isotopes total organic carbon toc sr ca ratios and macro and microfaunal associations reveals seven major sea level regressions in the southwestern tethys during the last 10 million years of the cretaceous late campanian c 74 2 ma 73 4 72 5 ma and 72 2 71 7 ma early maastrichtian 70 7 70 3 ma 69 6 69 3 ma and 68 9 68 3 ma and late maastrichtian 65 45 65 3 ma low sea levels are generally associated with increased terrigenous influx low kaolinite chlorite mica ratios high toc and high sr ca ratios whereas high sea levels are generally associated with the reverse conditions these sea level changes may be interpreted as eustatic as suggested by the global recognition of at least four of the seven major regressions identified 74 2 ma 70 7 70 3 ma 68 9 68 3 ma and 65 45 65 3 ma climatic changes inferred from clay mineral contents correlate with sea level changes warm or humid climates accompany high sea levels and cooler or arid climates generally accompany low sea levels

a paleomagnetic and rock magnetic study of the manicouagan impact structure implications for crater formation and geodynamo effects we report rock magnetic and paleomagnetic data from the similar to 214ma manicouagan canada impact crater based on 25 widely distributed sites of impact melt and basement rocks collected at the surface as well as from boreholes drilled to depths 1 5km titanomagnetite and titanohematite carry the magnetic remanence in impact melts above 320m elevation and in most basement rocks impact melts below 320m contain solely titanomagnetite magnetic susceptibility and saturation magnetization proxies for titanomagnetite concentration increase more than tenfold toward the base of the thickest impact melt that underwent fractional crystallization the titanomagnetite enriched zone partially contributes to a 2000nt magnetic anomaly in the crater s center stepwise demagnetization reveals a single normal polarity magnetization component in all samples regardless of the magnetic phases present coeval lock in remanence times for titanomagnetite and titanohematite indicate that the titanohematite formed 570 degrees c during oxi exsolution the average paleomagnetic direction and intensity coincide well with 214ma reference values we find no evidence for an aberration of the geomagnetic field over the several thousands of years it took to cool a 481m thick portion of the impact melt body hence the energy released by the manicouagan impact that created one of the 10 largest known craters on earth provoked no measurable disturbance of the geodynamo magnetic anisotropy of clast free impact melts define magnetic lineation directions that are in places radially oriented with respect to the crater s center centrifugal flow of the melt within the evolving transient crater probably generated the fabric

unusual seawater composition of the late cretaceous tethys imprinted in glauconite of narmada basin central indiaunusual seawater composition of the late cretaceous tethysu bansal et al a detailed investigation of a glauconite bed within the late cretaceous bryozoan limestone formation of the bagh group in central india as well as the study of existing records reveals the existence of a glauconitic sea along the margins of the palaeo tethys ocean during the late cretaceous epoch the authigenic green mineral formed abundantly on shallow seafloors unlike in its modern deep sea counterpart we present an integrated petrographical geochemical and mineralogical investigation of the glauconite within late cretaceous transgressive deposits to highlight its unique geochemistry with moderate fe 2 o 3 and high al 2 o 3 sio 2 mgo as well as k 2 o contents x ray diffractional parameters identify the evolved to high evolved nature of the glauconite while mossbauer spectroscopic study reveals the dominance of fe 3 compared to fe 2 in the atomic structure the rare earth elements ree pattern of glauconite reveals moderate light ree heavy ree lree hree fractionation and weak negative eu anomaly the ce anomaly of the glauconite indicates a sub oxic diagenetic condition we propose that late cretaceous glauconites formed within a shallow marine depositional setting across the tethyan belt because of enhanced supply of k si al fe mg cations through continental weathering under the extant greenhouse climate

magnetostratigraphy of chinese loess paleosol sequences abstract as one of the longest and most continuously deposited terrestrial sedimentary archives in the world chinese loess paleosol sequences record paleoclimatic and paleomagnetic variations at a range of time scales magnetostratigraphic studies provide a first order chronological framework for chinese loess sequences in this review we highlight recent developments in loess magnetostratigraphy including pedostratigraphy based on magnetic susceptibility variations we highlight progress in understanding the mechanisms by which the natural remanent magnetization nrm is acquired and discuss in detail the fidelity of paleomagnetic recording in loess records including the recording of magnetic polarity reversals excursions and relative paleointensity variations finally we discuss future prospects for studies of loess nrm

the age and duration of the matuyama brunhes transition from new k ar data from la palma canary islands and revisited 40ar 39ar ages abstract paleomagnetic investigations conducted on lava sequences from la palma canary islands yielded several independent records of the matuyama brunhes transition mbt seven k ar ages of flows sampled across the mbt suggest a duration between 0 and 11 kyr and provide a weighted mean age of 786 3 ka analytical uncertainty only for the transition this value is significantly older than the previously admitted age of 779 2 ka derived from volcanic or sedimentary sequences when the 1 uncertainty on the calibration standard used in the present study is considered our age for the transition recorded at la palma becomes 786 8 ka we have recalculated the 40ar 39ar determinations from the previous studies using recent revisited ages for 40ar 39ar standards this yields a global dataset of 23 k ar and 40ar 39ar determinations our best estimate for the mbt age derived from this compilation is 789 2 ka analytical error or 789 8 ka total error within this 8 kyr uncertainty which could be considered as a minimum estimate this age remains compatible with recent determinations made by the astronomical time scale however the present study suggests that better control of the lock in depth as well as better quantification of uncertainties involved in the tuning of 18o records to orbital forcing models are needed to improve further the astronomical polarity time scale derived from sedimentary records in addition absolute dating by k ar and 40ar 39ar will gain in accuracy when uncertainty determinations on standards will be significantly improved

palaeomagnetic records of the brunhes matuyama polarity transition from odp leg 124 celebes and sulu seas summary palaeomagnetic records of the brunhes matuyama geomagnetic polarity transition were obtained from deep sea sediments of odp leg 124 in the celebes and sulu seas advanced piston core apc samples with high magnetization intensities 2 200 ma m1 and high sedimentation rates 8 4 10 cm kyr1 were recovered from this cruise rock magnetic measurements revealed the carrier of the remanence to be nearly pure magnetite in the pseudo single domain range pass through measurements at intervals of 5 mm on apc cores across the brunhes matuyama polarity transition for holes 767b 769a and 769b were deconvolved with the magnetometer sensor response using the abic minimizing method discrete samples were also taken from the polarity transition zones and subjected to either thermal or alternating field stepwise demagnetization the results were generally consistent with the pass through data after the deconvolution results from the three holes are in good agreement particularly those from the two holes 100 m apart at site 769 the transitional vgp paths from these two holes show two small loops near new zealand before the equator is crossed the vgps continue to swing eastwards to the north atlantic and then move to the northeastern margin of the pacific ocean the positions of the vgp loops obtained from site 769 are dierent from the vgp clusters obtained from both the known volcanic records and the sediment records at the boso peninsula and the north atlantic sites with high sedimentation rates such a dierence may imply the predominance of the non dipole field during the transition relatively stable mid high northern latitude vgps are recognized on all three cores just after the reversal lasting about 4000 years the plot of relative intensity versus vgp latitude for the sediment records from the north atlantic dsdp hole 609b shows a remarkable similarity with our records similar patterns were also obtained for the plot of the palaeointensity versus vgp latitude for the la palma volcanic lava records these results may suggest the existence of a metastable state of the geodynamo producing a zonal component just after the brunhes matuyama boundary which may have played a role in the change of the field intensity

evidence for an increase in cosmogenic 10be during a geomagnetic reversal reversals in the geomagnetic field which occur every few hundred thousand years represent a dramatic change in the earth s environment although there is no satisfactory theory for such reversals it is generally accepted that the dipole field intensity decreases to 20 of its normal value for a few thousand years during the change in direction1 because the galactic and solar cosmic rays which impinge on the earth s atmosphere are charged a significant fraction about half of them are deflected by the geomagnetic field2 at the time of a reversal this magnetic shielding is greatly reduced and it has been suggested that the increased flux of high energy particles could have effects on evolutionary3 or climatic4 processes for example the statistically significant coincidence in levels of some marine faunal extinctions and reversal boundaries in ocean sediments5 could be caused directly or indirectly by the decreased geomagnetic intensity during the reversal we report here evidence in marine sediments for an increase in cosmogenic 10be production in the earth s atmosphere during the brunhes matuyama reversal 730 000 yr ago in addition to confirming an increase in cosmogenic isotope production the results provide information on the magnitude and duration of the geomagnetic intensity decrease during such an event and the depth at which rmanent magnetism is acquired in marine sediments

biogeochemical remanent magnetization in pelagic sediments of the western equatorial pacific ocean paleomagnetic data from pelagic sediments are an important source of information on the history of the geomagnetic field however fundamental uncertainties about how these sediments acquire their magnetizations remain here we address whether biogenic magnetite formed at depth within the sediments can contribute to remanent magnetizations in sediments of the western equatorial pacific ocean odp site 805 biogenic magnetite found near the fe redox boundary carries a natural remanent magnetization because the production of biogenic magnetite is tied to the geochemical zonation of the sediments we call this magnetization a biogeochemical remanence these data indicate that some pelagic sediments can continue to acquire remanence significantly after the post depositional lock in of detrital magnetic grains

orbital time scale intra platform basin correlation carbon isotope stratigraphy and sea level history of the cenomanian turonian eastern levant platform jordan two cenomanian turonian boundary ctbe sections kb3 and gm3 of the karak silla intra platform basin of the eastern levant carbonate platform jordan are correlated based on high resolution calcimetry kb3 contains black shales with over 7 wt total organic carbon toc gm3 was deposited at shallower water depth and reveals four conspicuous gypsum beds used for sea level reconstruction spectral analysis of carbonate content and toc reveals forcing mainly by the 100 ka cycle of earth s orbit eccentricity whole rock stable carbon isotope data show a conspicuous positive d13c excursion representing the oceanic anoxic event 2 oae2 the carbon isotope records of kb3 and gm3 correspond well with the cycles in the dc record of the global stratotype gssp at pueblo usa the gssp orbital timescale thus can be applied to the jordan record furthermore all stable isotope events defined in the english chalk reference record are recognized in jordan our orbital model for the jordan sequence stratigraphical framework reveals approximately 1 2 0 2 ma duration of a third order sequence proposed to represent one cycle of the long obliquity 1 2 ma this longterm period is superimposed on three fourth order fluctuations of 400 ka length long eccentricity fourth order sea level fluctuations each of which comprises four carbonate cycles 100 ka eccentricity fifth order sea level fluctuations demise of the levant platform occurred during the phase of decreasing dc values after oae2 in the interval between the cenomanian turonian c t boundary and the end of the early turonian the levant carbonate platform deposits of central jordan represent a textbook like shallow marine platform setting subdivided into intra platform basins during cenomanian turonian c t times kuss et al 2003 the morphological structuring by these basins induced lithologically highly variable successions especially during black shale deposition that preferably occurred in deeper subbasins a correlation of these different successions is possible by means of high resolution calcimetry and stable carbon isotope stratigraphy in this paper we present such a correlation that enables the study of three research aspects a linking different palaeoenvironments over the c t boundary interval b refining the sequence stratigraphic model by constructing an orbital time scale c correlating the successions to the global record exemplified for the well dated c t boundary interval in order to eliminate ambiguities in the local stratigraphy furthermore our data support the global picture and estimates of duration of the c t boundary interval that includes the global oceanic anoxic event 2 oae2 the duration of oae2 has been the matter of many studies in recent years resulting in a range of values from 320 to 960 ka obradovitch 1993 sageman et al 2006 partly caused by considering different intervals an orbital timescale for the pueblo stratotype section was given by sageman et al 2006 providing a precise time measure for the period investigated in our study in addition a comprehensive study of stable carbon isotope records in europe was given by jarvis et al 2006 providing a detailed set of isotope events suitable for global correlation recently an orbital model was also presented for the wunstorf germany section voigt et al 2008 this record correlates well with the present results and can be used to support the new hypothesis put forward in the present paper regarding the orbital trigger of third order sequences

depositional remanent magnetization toward an improved theoretical and experimental foundation the first theoretical predictions for the behavior of magnetic particles in water were that sedimentary magnetizations would be fully aligned with the ambient field yet redeposition experiments showed a strong and quasi linear dependence on the external field this empirically observed linearity has served as the fundamental assumption of sedimentary paleointensity studies for decades we present redeposition experiments which suggest instead that the relationship between depositional remanence drm and applied field may frequently be curved for magnetic fields in the range of the earth s numerical simulations using a flocculation model can explain the redeposition data and suggest that drm will be significantly non linear when the flocs are small several microns there is a strong dependence of floc size on salinity particularly in low salinity environments floc size has a profound influence on the efficiency of drm hence low salinity environment may give results with poor reproducibility the size of the floc in which magnetic particles are embedded is not accounted for in current methods of normalization yet is the most important parameter on the bright side however it now seems possible to quantitatively explain paleointensity in sedimentary systems opening the door to absolute paleointensity estimates from sediments whose key parameters of floc size distribution and settling times can be constrained

post depositional remanent magnetization lock in depth in precisely dated varved sediments assessed by archaeomagnetic field models accurate and precise chronologies are needed to evaluate the existence and effect of a post depositional remanent magnetization lock in process on sedimentary palaeomagnetic records here we present lock in modelling results of two palaeomagnetic records from varved lake sediments lakes kalksjon and gyltigesjon in sweden by using model predictions based on archaeomagnetic data we used the c 14 wiggle match dating technique to improve the precision of the kalksjon varve chronology in the period between 3000 and 2000 cal bp which is characterized by pronounced palaeomagnetic secular variation this method allowed us to infer an age model with uncertainties of 20 years 95 4 probability range furthermore we compared the palaeomagnetic record of kalksjon to gyltigesjon which has a corresponding 14c wiggle matched chronology the ages of palaeomagnetic features derived from the wiggle matched varve chronologies are older than those predicted by the archaeomagnetic models lock in modelling was performed with different filter functions to explain the temporal offset and the amplitude of the lake sediment palaeomagnetic data the analyses suggest that a linear lock in function with lock in depths the depth below which no more natural magnetic remanence is acquired that range between 30 and 80 cm in kalksjon and 50 and 160 cm in gyltigesjon are most appropriate to explain the data these relatively deep lock in depths in sediments without a bioturbated mixed zone can be attributed to the relatively high organic contents and low density of the lake sediments which contribute to a thick unconsolidated upper zone of the sediment sequence in which re alignment of magnetic particles can take place c 2014 elsevier b v all rights reserved

regionally consistent western north america paleomagnetic directions from 15 to 35 ka assessing chronology and uncertainty with paleosecular variation psv stratigraphy abstract new paleomagnetic secular variation psv data from fish lake utah usa along with previously published regional records allow us to build an independently dated western north america psv stack wnam17 from about 35 to 15 ka that quantifies dating and paleomagnetic uncertainties in february 2014 we recovered a composite 11 m long sediment record from fish lake utah that retrieved glacially influenced and post glacial sediments computed tomography ct scans and magnetic susceptibility were used to build a precise depth scale while radiocarbon dating of terrestrial macrofossils and tephrostratigraphy provide tight age control glacially influenced sediments have well defined characteristic remanent magnetizations with all maximum angular deviation values

geomagnetic secular variation as recorded in british lake sediments and its application to archaeomagnetic studies abstract lake sediments can play an important role in understanding and reconstructing temporal characteristics of the geomagnetic field as they potentially offer near continuous high resolution archives of magnetic information extending throughout the holocene to date lake sediment geomagnetic data has typically been excluded from british archaeomagnetic secular variation curves svc due to uncertainties with the acquisition of magnetisation by lake sediments this paper presents the argument that with regards to british datasets the real problem lies with poor chronological control and sets out to illustrate that with british archaeomagnetic data some progress has been made the results indicate that it is not currently possible to resolve secular variation on a time scale of 100 years from published british lake sediment data but more success has been made with data from archaeological sediments this level of detail has been considered necessary for the incorporation of lake sediment data into the british archaeomagnetic dataset as the ability to resolve short term geomagnetic changes is critical for the integration of any dataset into the british svc as the latter is predominantly employed to date archaeological architecture and artefacts requires that it has the ability to resolve changes over timescales relevant to human lifetimes using currently available data this retrospective critique confirms that in archaeological sediments depositional and thermoremanent magnetisation can record the same direction over the same time interval

late cretaceous upwelling system along the southern tethys margin israel interrelationship between productivity bottom water environments and organic matter preservation organic rich upper cretaceous sequences in israel were deposited in an extensive highly productive upwelling linked system which prevailed along the southern tethys margin and lasted for 19 m y santonian to late maastrichtian an understanding of the spatial and temporal characteristics of this system was gained through detailed paleontological and geochemical analyses of subsurface sequences in two basins in israel representing an outer shefela and an inner zin facies belt the nature of the upwelling system and its effect on the sedimentary record is related to two basic environmental parameters namely paleoproductivity intensity and oxygen levels at the bottom the assessment of these parameters and their interrelationship has been performed through the development of paleontological foraminiferal criteria which are independent of the organic matter content following the establishment of these criteria it is concluded that the productivity reached its maximum intensity during the late campanian which was also the time of most notable differentiation between the center of the upwelling system in the inner belt and the less intense conditions in the outer basin this distribution is expressed in varied lithology organic rich carbonates phosphorites and siliceous rocks at the core of upwelling and a uniform lithology organic rich carbonates at the margin of this system the uniform lithology of the maastrichtian in both basins composed of organic rich carbonates is ascribed to a gradual weakening of productivity the bottom conditions in the inner belt during the late campanian the time of maximum surface productivity were near anoxic changing to more aerated dysaerobic conditions during the early maastrichtian in the outer belt a more aerated bottom dysaerobic prevailed throughout the late campanian to late maastrichtian the elevated organic matter content in both basins reflects the overall environment of high productivity its actual variations however seem to be unrelated to changes in surface productivity and bottom oxygen levels

reconstruction of the last deglaciation deconvolved records of δ18o profiles micropaleontological variations and accelerator mass spectrometric14c dating bioturbation acts as a low pass filter in displacing and reducing the amplitudes of stratigraphic signals this often leads to a loss of high frequency events in the stratigraphic record in addition when considering an isotopic signal 18o 14c measured in stratigraphic carriers such as foraminifera bioturbation and carrier abundance changes can create artifacts which may be falsely interpreted as leads or lags in the paleoclimatic record

the cretaceous paleogene boundary in jordan abstract the cretaceous paleogene k pg boundary in jordan is marked by a major depositional hiatus that differs in magnitude from place to place due to variable structural movements of the syrian arc fold belt that resulted in irregularity of jordan levant depositional basin after the deposition of maastrichtian succession to elucidate the nature of this hiatus fieldwork was carried out at a number of locations including lithofacies and stratigraphic analysis and a multi proxy study of microplanktonic biostratigraphy calcareous nannofossilis and planktonic formaminifera however the duration of this hiatus extended over latest maastrichtian and early danian stages this is based on the absence of the planktonic foraminifera pseudoguembelina hariaensis cf3 pseudoguembelina palpebra cf2 plummerita hantkeninoides cf1 guembelitria cretacea p0 parvularugoglobigerina eugubina p zones and parasubbotina pseudobulloides p1a subzones and the coeval calcareous nannofossils nephrolithus frequens and markalius inversus zones we estimate that in the paleo lows areas an unexpected 3 96 ma hiatus is present conversely in swell areas the duration of the hiatus represents the entire danian selandian interval and revealed an unexpected 10 33 ma hiatus especially in the central part of jordan subsequently a marked transgression took place over the whole of jordan which resulted in the prevalence of deep water conditions zones p4 or equivalent np7 8 this caused the deposition of a retrogradational parasequence set of middle shelf pelagic marl and chalk during a rapid relative rise of sea level a correlative hiatus and time gap have also been reported in different parts of the arabian and african plates indicating that jordan was influenced by regional tectonics that combined with the latest maastrichtian sea level fall resulted in a long term sub marine hiatus and or non deposition of sediments a combination of sea level changes and tectonic uplift are the likely cause for such a long gap in the sediment record in the region

upper cretaceous sequence stratigraphy of the galala plateaux western side of the gulf of suez egypt abstract based on the study of lithology biostratigraphy and analysis of facies this study deduces the occurrence of nine third order upper cretaceous cenomanian maastrichtian depositional sequences which are bounded by eleven sequence boundaries of geographic extent in the galala plateaux situated along the western side of the gulf of suez egypt some of the recorded sequence boundaries e g cenomanian turonian turonian coniacian intra santonian and campanian maastrichtian sequence boundaries are not yet confirmed to eustatic sea level changes fourteen main mixed carbonate siliciclastic facies associations were recognized on a lateral transition between inner to outer ramp settings with apparent subsidence towards the south the tectonic position of the galala plateaux played an important role in the profound complexity of facies changes and the configuration of depositional sequences representing variable time gaps

the upper kaena sedimentary geomagnetic reversal record from southern sicily a detailed paleomagnetic and rock magnetic record of the upper kaena polarity reversal was determined from late pliocene marine marls in southern sicily two separate characteristic magnetization components were distinguished a low temperature lt component between 200 and 50 c and a high temperature ht component between 500 and 580 610 c the two components record the reversal in a slightly different way but both were acquired in an early stage following deposition most probably by authigenic biogenic formation of magnetic minerals the actual r n reversal via e and horizontal inclinations seems to take 3 3 kyr and is followed by a stable normal interval 3 3 kyr and subsequently by a significant excursion 50 60 in declination 3 6 kyr relative intensities were lower during a time span of 5 6 kyr and show a minimum of 10 of the nontransitional values but during the excursion no intensity changes are apparent the vgps of the ht component are confined to a longitude between india and australia those of the lt component oscillate between this same longitude and one passing over north and south america we conclude that most if riot all observed features are largely determined by the remanence acquisition process which is complicated by authigenic formation of magnetic minerals and cyclically fluctuating paleoredox conditions this has not only resulted in considerable smoothing but also in delayed nrm acquisition in specific sedimentary intervals we believe that the observed excursion is a sedimentary artifact and not related to geomagnetic field behavior during transitions we emphasize that many reported geomagnetic features may in fact be due to the sedimentary remanence acquisition process

astronomical calibration of the matuyama brunhes boundary consequences for magnetic remanence acquisition in marine carbonates and the asian loess sequences we have compiled 19 records from marine carbonate cores in which the matuyama brunhes boundary mbb has been reasonably well constrained within the astronomically forced stratigraphic framework using oxygen isotopes by correlation of the 18o data to a timescale based on astronomical forcing we estimate astronomical ages for each of the mbb horizons in all but one record the mbb occurs within stage 19 most magnetostratigraphic sections in asian loess place the mbb within a loess interval since loess deposition is presumed to be associated with glacial intervals loess horizons should correspond to even numbered oxygen isotope stages a glacial age for the mbb is at odds with the results presented here which firmly place the mbb within interglacial stage 19 inconsistency among the many loess sections and between the loess and the marine records suggests that the magnetic interpretation of loess sections may be more complicated than hitherto supposed the mean of the stage 19 age estimates for the mbb is 777 9 1 8 n 18 inclusion of the single stage 20 age results in a mean of 778 8 2 5 n 19 the astronomical age estimate of the mbb compares favorably with an unweighted mean of 778 2 3 5 n 10 from a compilation of 40ar 39ar results of transitional lava flows combining the two independent data sets yields a grand mean of 778 0 1 7 n 28 the new compilation shows virtually no trend in placement of the mbb within isotope stage 19 as a function of sediment accumulation rate we interpret this to mean that the average depth of remanence acquisition is within a few centimeters of the sediment water interface separating the cores into two geographic regions an indo pacific caribbean ipc group and an atlantic group results in a significant difference in the position of the mid point of the reversal with respect to the astronomical time scale the data presented here suggest a difference of several thousand years between the two regions this observation could be caused by systematic differences between the two regions in sedimentation rate within the interval of interest systematic differences in remanence acquisition or by genuine differences in the timing of the directional changes between the two regions

detrital remanent magnetization viscosity theory of the lock in zone post depositional remanent magnetization pdrm becomes permanent within a lock in zone whose apparent time delay depth and time span thickness are related to the characteristic time constants of compaction and magnetic grain rotation two simple models of the pdrm lock in zone are described using yaskawa s idea of effective sedimentary viscosity and mooney s empirical relation for the viscosity of a concentrated suspension of spheres the impulse response of the lock in zone determines the fidelity of the paleomagnetic recording

longitudinal confinement of geomagnetic reversal paths as a possible sedimentary artefact the positions of the virtual geomagnetic pole vgp during a large number of reversals of the earth s magnetic field seem to show a remarkable confinement to longitudes over the americas or to antipodal longitudes1 2 although it has been argued that this confinement is statistically insufficiently constrained3 it has also been pointed out4 that the same bands of longitude appear in other geophysical observations such as the pattern of fluid motion in the outer core and regions of higher seismic velocities in the lower mantle suggesting a causal relationship here we show that longitudinal confinement of vgps can arise from the smoothing of non antipodal stable directions just before and after a geomagnetic reversal because of the filtering effect of the remanence acquisition process in sediments the origin of this non antipodality is still uncertain and must remain speculative until more reversal records become available that include sufficiently long pre and post transitional intervals

avalanches at the core mantle boundary 1 the partial collapse of topographic structure at the core mantle boundary cmb in avalanches slumps or turbidity flows would cause sudden temperature changes in both the upper core and the lower mantle although such collapses are hypothetical it is interesting to investigate the potential consequences downwelling from such events could disrupt core convection cells and trigger geomagnetic excursions and reversals buoyant sediment from the freezing of the inner core is hypothesized to rebuild the avalanched structures large avalanches could trigger mantle plumes oblique extraterrestrial impacts impart high shear to the cmb and can trigger one or more simultaneous avalanches yielding observed coincidences between craters tektite fields and reversals a triggered avalanche can explain the coincidence between the formation of the largest known volcanic province the ontong java plateau the start of the 35 myr cretaceous geomagnetic quiet period and reported coincidences between large flood basalts and extinctions

40ar 39ar age constraints for the jaramillo normal subchron and the matuyama brunhes geomagnetic boundary our mid pleistocene 4oar 39ar age recalibration of the geomagnetic polarity timescale is nearly in accord with the oxygen isotope climate record calibration of the astronomical timescale proposed by johnson 1982 and shackleton et al 1990 4oar 39ar ages of a normally magnetized rhyolite dome in the valles caldera northern mexico yielded a weighted mean age of 1 004 0 019 ma a k ar age of 0 909 0 019 ma for this rock by doell and dalrymple 1966 was the linchpin for the recognition and calibration of the jaramillo normal subchron jns other 4oar 39ar ages from the vailes caldera and 4oar 39ar ages of ivory coast tektites indicate that the jns began at about 1 11 ma and ended before 0 92 ma probably near 0 97 ma the matuyama brunhes boundary occurred between 0 79 ma and 0 76 ma on the basis of 4oar 39ar sanidine ages from 1 three reversely magnetized rhyolite domes of the valles caldera 0 793 0 018 ma 0 794 0 007 ma and 0 812 0 023 ma and pumice 0 789 0 006 ma from the reversely magnetized oldest toba tuff of sumatra and 2 pumice 0 764 0 005 ma and 0 757 0 009 ma from the lower and upper units of the normally magnetized bishop tuff the age of the boundary may be close to 0 77 ma as deduced from rates of sedimentation in ancient lake bonneville utah increasingly aware that the polarity of earth s magnetic field has changed repeatedly through geologic time and isotopic dating of these polarity reversals resulted in a geomagnetic polarity time scale gpts for the late cenozoic this combined paleomagnetic and isotopic research played a pivotal role in confirming plate tectonic theory glen 19821 which revolutionized the earth sciences continual refinement of isotopic ages which define the gpts has increased the usefulness of geomagnetic polarity reversals as marker hori zons in many types of geologic studies we present 4oar 39ar data and ages for some key volcanic units that support changes in the isotopic age chronology of the gpts using volcanic rocks erupted near the time of the geologically youngest two geomagnetic polarity reversals figure 1 the older of the two reversals originally called by doell and dalrymple 1966 the jaramillo event is now named the jaramillo normal subchron jns it is recorded in middle pleistocene rocks as a brief episode of normal polar ity within the late matuyama chron the younger of the two called the matuyama brunhes boundary mbb is regis tered in middle pleistocene rocks worldwide and consists of

misleading positions of geomagnetic reversal boundaries in eurasian loess and implications for correlation between continental and marine sedimentary sequences abstract the matuyama brunhes boundary mbb where the earth s magnetic field changed to its present orientation is one of the most frequently used time markers in continental quaternary stratigraphy although magnetic signals have been successfully recovered from loess deposits and an apparently coherent magnetostratigraphy seems to be in place a close examination of the published loess records from northern mid latitudes reveals significant uncertainty and variability for the position of the mbb in asia and part of central europe the mbb has been found in loess a glacial deposit this is in contrast to the well established palaeomagnetic records in deep sea sediments where the mbb is located in the interglacial oxygen isotope stage 19 this discrepancy has caused serious confusion in stratigraphic correlation between loess and marine sequences here we examine the causes of the discrepancy between the two sedimentary environments in their records of the mbb our approach includes a comparison of the mbb in loess and other continental records and an evaluation of the stratigraphic significance of the microtektites found around the mbb based on the occurrence of the mbb in an interglacial stage in lake and continental margin sequences and the correlative stratigraphic positions of the microtektites in marine sediments and loess we demonstrate that the measured positions of the mbb in loess are erroneous and misleading and its true occurrence was during the time of formation of the palaeosol corresponding to oxygen isotope stage 19 the most plausible cause for the apparent offset i e the mbb being found in the underlying loess instead is that the acquisition of remanent magnetisation in loess occurs at a certain depth substantially below the land surface the degree of such displacement is dependent on the lithology and structure of the deposits formed prior to the reversal and the time delay is estimated to be in the order of 103 104 years we show that other geomagnetic boundaries such as those of jaramillo and cobb mountain in loess have been similarly displaced though to a varying extent we suggest that the remanence acquisition in loess is closely related to the post depositional evolution in the structure of loessic materials which is in part influenced by regional climate conditions our conclusions on the displaced remanence acquisition have implications for loess chronology magnetostratigraphy as well as the geomagnetic interpretation of detailed magnetic signatures from loess

ivory coast microtektite strewn field description and relation to the jaramillo geomagnetic event abstract during the present study the ivory coast microtektite layer was found in cores from five equatorial atlantic sites bringing the total number of ivory coast microtektite bearing cores to eleven the strewn field appears to be restricted to between 9 n and 12 s latitude there is a general increase in the concentration of microtektites towards the bosumtwi crater which is generally thought to be the source of the ivory coast tektites the relationship between the onset of the jaramillo subchron and the ivory coast microtektite layer has been investigated in six cores a plot of the difference in depth between the base of the jaramillo subchron and the microtektite layer versus sediment accumulation rate was used to determine the average post depositional remanent magnetization pdrm acquisition depth and the age difference between the onset of the jaramillo subchron and the deposition of the microtektites assuming that the pdrm acquisition depth does not vary with sediment accumulation rate we find that the average pdrm acquisition depth is 7 cm and that the microtektites were deposited approximately 8 ky after the onset of the jaramillo subchron this indicates that the impact responsible for the ivory coast tektites and microtektites could not be causally related to the geomagnetic reversal at the base of the jaramillo subchron

geomagnetic reversals from impacts on the earth the impact of a large extraterrestrial object on the earth can produce a geomagnetic reversal through the following mechanism dust from the impact crater and soot from fires trigger a climate change and the beginning of a little ice age the redistribution of water near the equator to ice at high latitudes alters the rotation rate of the crust and mantle of the earth if the sea level change is sufficiently large 10 meters and rapid in a few hundred years then the velocity shear in the liquid core disrupts the convective cells that drive the dynamo the new convective cells that subsequently form distort and tangle the previous field reducing the dipole component near to zero while increasing the energy in multipole components eventually a dipole is rebuilt by dynamo action and the event is seen either as a geomagnetic reversal or as an excursion sudden climate changes from other causes such as volcanic eruptions could also trigger reversals this mechanism may not be the sole cause of geomagnetic reversals but it can account for the rapid drop of the dipole component preceding a reversal the predominance of multipole components during a transition the associations of microtektites temperature drops and extinctions with reversals and the possible correlation between peaks in the geomagnetic reversal rate and the times of mass extinctions the model may also account for the long term changes in the average rate of reversals we make several testable predictions

the maximum likelihood dating of magnetostratigraphic sections summary in general stratigraphic sections are dated by biostratigraphy and magnetic polarity stratigraphy mps is subsequently used to improve the dating of specific section horizons or to correlate these horizons in different sections of similar age this paper shows however that the identification of a record of a sufficient number of geomagnetic polarity reversals against a reference scale often does not require any complementary information the deposition and possible subsequent erosion of the section is herein regarded as a stochastic process whose discrete time increments are independent and normally distributed this model enables the expression of the time dependence of the magnetic record of section increments in terms of probability to date samples bracketing the geomagnetic polarity reversal horizons their levels are combined with various sequences of successive polarity reversals drawn from the reference scale each particular combination gives rise to specific constraints on the unknown ages of the primary remanent magnetization of samples the problem is solved by the constrained maximization of the likelihood function with respect to these ages and parameters of the model and by subsequent maximization of this function over the set of possible combinations a statistical test of the significance of this solution is given the application of this algorithm to various published magnetostratigraphic sections that included nine or more polarity reversals gave satisfactory results this possible self sufficiency makes mps less dependent on other dating techniques

an estimate of late pleistocene geomagnetic intensity variation from sulu sea sediments abstract sediments from site 769 of the ocean drilling program s leg 124 provide a record of geomagnetic intensity variation over the past 110 ky using continous shipboard measurements exclusively i estimate the variation in the geomagnetic field strength by employing low field magnetic susceptibility as a normalization parameter for the measured remanence intensity by calibrating the resultant relative paleointensity record against previously available holocene age estimates of absolute paleointensity i derive an estimate of virtual dipole moment since 110 ka the record obtained from these sulu sea sediments is strikingly like that previously obtained from sediments of a similar age in the mediterranean basin with distinct intervals of low intensity near 15 20 40 and 65 70 ka the sulu sediments also indicate a low intensity feature near 108 ka important differences in paleointensity estimates obtained from these different regions for the interval between 30 and 20 ka suggest that a relatively large non dipolar component of the geomagnetic field might have been present at that time

reply to the comment on 40ar 39ar dating of the tephra layer in the pliocene seneze maar lacustrine sequence french massif central constraint on the age of the reunion matuyama transition and implications on paleoenvironmental archives

paleoclimate record for northwind ridge western arctic ocean core nwr 5 from northwind ridge in the western arctic ocean contains a climatic record that extends back for over 1 million years dark brown beds with abundant planktonic foraminifers represent interglacial conditions whereas glacial and transitional conditions are represented by lithologies barren or nearly barren of planktonic foraminifers we conclude that seven and possibly all nine interglacials of the brunhes magnetic chronozone the last 780 000 years are represented in nwr 5 for about the last 800 000 years the western arctic ocean apparently had a permanent thick ice cover and was unable to support significant populations of planktonic foraminifers except during major interglacials when seasonally open and high productivity surface waters occurred at least along the basin margins our results support previous interpretations that climate variations in the arctic are in phase with glacial interglacial cycles observed in other proxy records of the brunhes

maastrichtian climate productivity and faunal turnovers in planktic foraminifera in south atlantic dsdp sites 525a and 21 abstract stratigraphic faunal and isotopic analyses of the maastrichtian at dsdp sites 525a and 21 in the south atlantic reveal a planktic foraminiferal fauna characterized by two major events an early late maastrichtian diversification and end maastrichtian mass extinction both events are accompanied by major changes in climate and productivity the diversification event which occurred in two steps between 70 5 and 69 1 ma increased species richness by a total of 43 and coincided with the onset of major cooling in surface and bottom waters and increased surface productivity the onset of the terminal decline in maastrichtian species richness began at 67 5 ma and the first significant decline in surface productivity occurred at 66 2 ma coincident maximum cooling to 13 c in surface waters and the reduction of the surface to deep temperature gradient to less than 5 c major climatic and moderate productivity changes mark the mass extinction and the last 500 kyr of the maastrichtian between 200 and 400 kyr before the k t boundary surface and deep waters warmed rapidly by 3 4 c and cooled again during the last 100 kyr of the maastrichtian surface productivity decreased only moderately across the k t boundary species richness began to decline during the late maastrichtian cooling and by k t boundary time the mass extinction had claimed 66 of the species viewed within the context of maastrichtian climate and productivity changes the k t mass extinction could have resulted from extreme environmental stress even without the addition of an extraterrestrial impact

diagenetic evolution of the eocene ramp carbonates a paradigm from the nile valley egypt petrographical and geochemical attributes abstract carbonate rocks of east nile valley in egypt have been investigated as a paradigm for revealing the diagenetic evolution of the eocene ramp carbonates the integration of petrographical elemental geochemical and stable isotopic data revealed that the studied carbonates have been influenced by a sequence of diagenetic processes which are included in three diagenetic episodes i e eogenesis mesogenesis and telogenesis and are related to four diagenetic environments i e marine phreatic meteoric phreatic burial and uplifting environments the paragenetic sequence of the studied carbonates commences with the eodiagenetic episode which includes the marine and meteoric phreatic diagenetic environments the marine phreatic diagenetic environment comprises micritization glauconitization pyritization marine cementation fibrous calcite and syntaxial overgrowth rim cements early dolomitization formation of fine crystalline matrix replacive dolomites and early stages of mechanical compaction before significant burial the meteoric phreatic diagenetic environment includes the neomorphism dissolution meteoric cementation earlier phases of sparry calcite cements and precipitation of megaquartz in the void spaces of the peritidal carbonates during the mesogenesis episode the studied carbonates were exposed to burial diagenesis the shallow burial diagenesis resulted in the creation of point tangenetial contacts between the allochemical constituents and the precipitation of a medium coarse crystalline dolomite cement filling the dissolved fossils and dissolution pores the deep burial diagenetic processes embody the chemical compaction condensed fitted interpeneteration and pressure dissolution fabrics fracturing and burial cementation the telodiagenesis represents the last episode in the diagenetic history of the studied carbonates it witnessed the fracturing meteoric vadose cementation and hematitization processes

recognizing magnetostratigraphy in overprinted and altered marine sediments challenges and solutions from iodp site u1437 core disturbance drilling overprints post depositional acquisition of remanence authigenic growth of magnetic iron sulfides and alteration all contribute challenges to recognizing the primary magnetostratigraphy in marine sediments we address these issues in a sequence of tuffaceous muds and volcaniclastics at international ocean discovery program site u1437 and produce the longest continuous magnetic polarity stratigraphy in the history of scientific ocean drilling remanence measurements were filtered to remove intervals affected by fluidization plastic sediment disturbance and core biscuiting drilling overprints are concentrated in the disturbed annulus surrounding intact core material bioturbation was limited to a vertical extent of at most 15 cm changes in sediment color stiffness and magnetic hysteresis all suggest that remanence was locked in within a few meters of the sediment water interface we did not observe any systematic offset between magnetostratigraphic and biostratigraphic datums authigenic growth of greigite in response to both initial sulfate reduction in the upper 50 m of the sediment column and to deeper resupply of sulfate has led to magnetic overprinting anomalous polarity artefacts extending 5 m and occurring within about 20 m below a real polarity transition appear to be due to a chemical remanence acquired by greigite produced during early diagenesis diagenetic magnetic mineral alteration resulted in the progressive loss of fine grained magnetite which enhanced susceptibility to drilling and post drilling overprints and increased the resistance of these overprints to removal by conventional demagnetization we recovered the magnetostratigraphic record from many samples with resistant overprints through low temperature demagnetization through the verwey transition this article is protected by copyright all rights reserved

dolomite occurrence evolution and economically important associations abstract dolomite is not a simple mineral it can form as a primary precipitate a diagenetic replacement or as a hydrothermal metamorphic phase all that it requires is permeability a mechanism that facilitates fluid flow and a sufficient supply of magnesium dolomite can form in lakes on or beneath the shallow seafloor in zones of brine reflux and in early to late burial settings it may form from seawater from continental waters from the mixing of basinal brines the mixing of hypersaline brine with seawater or the mixing of seawater with meteoric water or via the cooling of basinal brines bacterial metabolism may aid the process of precipitation in settings where sulfate reducing species flourish and microbial action may control primary precipitation in some hypersaline anoxic lake settings dolomite is a metastable mineral early formed crystals can be replaced by later more stable phases with such replacements repeated a number of times during burial and metamorphism each new phase is formed by the partial or complete dissolution of an earlier dolomite this continual re equilibration during burial detracts from the ability of trace elements to indicate depositional conditions and resets the oxygen isotope signature of the dolomite at progressively higher temperatures because subsurface dolomite evolves via dissolution and reprecipitation a bed of dolomite can retain or create porosity and permeability to much greater burial depths and into higher temperature realms than a limestone counterpart dolomitization also creates new crystals with new rhomb growth following the dissolution of less stable precursors repetition of this process without complete pore cementation can generate intercrystalline porosity a number of times in the rock s burial history intercrystalline porosity is a highly interconnected style of porosity that gives dolomite reservoirs their good fluid storage capacity and efficient drainage the fact that many dolomite reservoirs formed via brine reflux means that they sit beneath an evaporite seal in both platform and basinwide evaporite settings the same association of evaporites sulfate source and entrained hydrocarbons means that burial conditions are also suitable for thermochemical sulfate reduction and the precipitation of base metals this tends to occur at higher temperatures 60 c 80 c and so the resulting dolomites tend to be ferroan and consist of saddle shaped crystals

correlation of widespread tephra deposits based on paleomagnetic directions link between a volcanic field and sedimentary sequences in japan abstract magnetic measurements were made of the yabakei and the imaichi pyroclastic flow deposits of the late matuyama chron in central kyushu and their correlative co ignimbrite ashes the pink and the azuki tephra deposits in the kinki district and the ku6c and the o7 tephra deposits in boso peninsula site mean magnetic directions of the imaichi deposit are all of reversed polarity with declinations deflected slightly to the east these directions are consistent with those of the azuki and the ku6c ashes magnetizations of the yabakei the pink and the o7 ashes are also consistent with one another all are characterized by shallow inclinations about 30 of normal polarity with slightly westerly declinations the identical paleomagnetic directions of these widespread tephra confirm correlations that have been proposed mainly on the basis of glass and mineral chemistry and provide a tephrochronological linkage between the source volcanic area and the lacustrine or marine sequences over distances of at least 1000 km this linkage allows us to correlate the oxygen isotope record of the kazusa group in boso peninsula with the alternating marine non marine lithology of the osaka group in the kinki district radiometric dates from the yabakei and the imaichi pyroclastic flow deposits are concordant with the astronomically calibrated geomagnetic polarity time scale

tektites and climate only four tektite strewn fields have been produced during the past 40 m y even though at least 60 impact craters have been produced during the same period in continental lithologies having tektite like compositions the apparent reason for this discrepancy is that the ejecta from most crater forming impacts was not completely melted laboratory and modeling studies show that projectiles as different as anorthosite and metal densities from 2 8 to 8 g cm 3 produce similar amounts of melt and this conclusion probably holds for comet like densities near 1 5 g cm 3 our interpretation of the limited evidence indicates that the influence of projectile trajectory and velocity on melting efficiency is minor the key factor affecting melt production seems to be the nature of the target particularly its porosity the fraction of projectile kinetic energy converted to heat may be an order of magnitude higher in a highly porous target than in a void free target the grain size and water content of the target are also important the ideal target is a porous fine grained sediment such as loess particularly if it is also dry we suggest that the rate of impact production of fully molten crater ejecta is proportional to the fraction of the continental surface having thick 10 m blankets of dry loess and that tektites are mainly produced during cold dry climate periods when such deposits are an order of magnitude more common than at present this model is best tested at the australasian site since detailed climate records cannot be obtained for the czechoslovakian and north american sites and have not yet been obtained for the ivory coast site the fossil o isotopic records in cores containing the australasian microtektites show that these were deposited during a period of cold climate near glacial stage 20 2 the chemical homogeneity and the high 10be contents of australasian tektites are well explained by melting a loess target

continuous record of geomagnetic field intensity between 4 7 and 2 7 ma from downhole measurements abstract a continuous record of the geomagnetic field intensity from 4 7 to 2 7 ma has been obtained together with a precise magnetostratigraphy from downhole magnetic measurements at site 884 of odp leg 145 in the north pacific the record confirms the saw tooth pattern of geomagnetic field intensity proposed by valet et meynadier 10 reversals are characterized by a steep intensity decrease followed by a quick regeneration over each polarity interval rapid variations are superimposed over a progressive decrease in the mean intensity we find that the duration of each polarity interval is inversely proportional to the mean rate of decrease in the field intensity over this period and thus this duration seems to be pre determined

are hydrodynamic shape effects important when modelling the formation of depositional remanent magnetization recent conceptual models have attributed the weak depositional remanent magnetizations observed in natural sediments to flocculation processes in the water column magnetic particles included into flocs have not only to rotate themselves into alignment with the geomagnetic field but also the larger particles to which they are attached making remanence acquisition an inefficient process alignment is hindered further when the magnetization vectors of the particles in any given floc partially cancel reducing the overall magnetic torque existing numerical simulations of flocculation effects on depositional remanence formation have been limited to spherical bodies with translational and rotational motion acting independently of each other in the case of non spherical flocs the translational and rotational motion are coupled and such bodies will describe a complex trajectory through the water column calculations will be presented that show the torque exerted on a non spherical floc by the surrounding water can be orders of magnitude greater than the magnetic torque non spherical flocs will therefore align less efficiently with the geomagnetic field and hydrodynamic effects may play an important role in controlling the magnitude of sedimentary remanence

sequence architecture and carbonate platform configuration late cenomanian santonian sinai egypt relative sea level changes on the mixed carbonate siliciclastic platform of sinai are manifested in shifts of distinct facies belts deep water facies highenergy subtidal shallow subtidal lagoon shallow shoreface siliciclastics supratidal and are interpreted in terms of sequence stratigraphy eight sedimentary sequences are recognized for the upper cenomanian to santonian their correlation along a north south transect reveals distinct changes in lithofacies and progradation retrogradation patterns within the individual systems tracts the number and stratigraphy of the sequence boundaries of sinai correlate well with those from adjacent areas patterns of increased subsidence are documented for the central sinai basin since the late cenomanian by increased thickness of the stratal packages post cesin 7 hst post tusin 1 lst and hst post tusin 2 lst and are balanced by varying accumulation rates based on new sedimentological and biostratigraphic data large scale palaeogeographic maps and cross sections show the 1 temporal and spatial evolution of the central sinai basin e g its latest cenomanian initial formation lower turonian deep water facies middle turonian to coniacian synsedimentary subsidence 2 drowning of the cenomanian platform coinciding with the latest cenomanian to early turonian relative sea level rise 3 re establishment of the platform in middle late turonian times and 4 a coniacian basin and swell morphology

orbital tuning of geomagnetic polarity time scales milankovitch climate cyclicity and magnetic polarity stratigraphy are being successfully combined as a powerful geochronometer in the astronomical polarity timescale apts the apts for 0 5 23 ma has been rapidly accepted as the denitive chronology for the pliocene and pleistocene against which even high precision radiometric dating is now calibrated extensions of astronomical calibration to the late miocene 5 23 ma to ca 10 ma in mediterranean and pacic marine sections agree to within about a 100 ka eccentricity which amounts to an uncertainty of only ca 1 of the age orbital eccentricity periods are thought to remain stable over very long times and thus provide the possibility of precise relative age control in the preneogene an apts for example has been developed in a thick lacustrine section of late triassic age ca 202 233 ma on the basis of the 404 ka orbital eccentricity cycle modulating the expression of the precession climate cyclicity finally there has been renewed speculation about an obliquity modulated precessional geodynamo based on periodicities in relative palaeointensity data from ocean drilling program sediment cores

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

post depositional remanent magnetization lock in and the location of the matuyama brunhes geomagnetic reversal boundary in marine and chinese loess sequences article i nfo pdrm lock in loess paleosol bioturbation disturbs detrital magnetic particles after deposition so accurate recording of the ancient geomagnetic field in bioturbated sediments is widely attributed to acquisition of a post depositional remanent magnetization pdrm whereby the geomagnetic field exerts a torque on a magnetic particle and aligns it with the field after the final mixing event experienced by the particle the relationship between the matuyama brunhes boundary mbb and oxygen isotope age tie points in marine sediments has been widely used to determine the depth at which the paleomagnetic signal is locked in however such analyses can be badly affected by age discrepancies among different paleoclimatic proxies and by varying isotopic compositions of seawater in different locations and from the presence of different water masses at different depths at the same location it is therefore necessary to separately compare paleomagnetic data with respect to either benthic or planktonic foraminiferal oxygen isotope records for sites from the same water mass to avoid inadvertently introducing age differences to the analysis when the global data set is subjected to such a rigorous analysis few reliable data remain for the mbb using two complementary approaches we estimate that the mbb is on average shifted 20 cm below its true position in marine sediments this offset is the sum of the thickness of the bioturbated surface mixed layer which is possibly dominant and the pdrm lock in depth there is also controversy concerning observed differences in the position of the mbb relative to paleoclimatic proxies in marine sediments and chinese loess deposits for the chinese loess quartz grain size is insensitive to pedogenic alteration and is a useful parameter for determining the true position of the mbb with respect to paleoclimatic boundaries we conclude that the mbb occurs late in marine oxygen isotope stage 19 and in the upper part of chinese paleosol unit s8 rather than at the mid or lower part of loess unit l8 our results require adjustment of the generally accepted positions for the mbb and resolve a longstanding chronological conundrum for marine and chinese loess sequences

cenomanian turonian transition in a shallow water sequence of the sinai egypt environmental and depositional changes across the late cenomanian oceanic anoxic event oae2 in the sinai egypt are examined based on biostratigraphy mineralogy 13c values and phosphorus analyses comparison with the pueblo colorado stratotype section reveals the whadi el ghaib section as stratigraphically complete across the late cenomanian early turonian foraminifera are dominated by high stress planktic and benthic assemblages characterized by low diversity low oxygen and low salinity tolerant species which mark shallow water oceanic dysoxic conditions during oae2 oyster biostromes suggest deposition occurred in less than 50 m depths in low oxygen brackish and nutrient rich waters their demise prior to the peak 13c excursion is likely due to a rising sea level characteristic oae2 anoxic conditions reached this coastal region only at the end of the 13c plateau in deeper waters near the end of the cenomanian increased phosphorus accumulations before and after the 13c excursion suggest higher oxic conditions and increased detrital input bulk rock and clay mineralogy indicate humid climate conditions increased continental runoff and a rising sea up to the first 13c peak above this interval a dryer and seasonally well contrasted climate with intermittently dry conditions prevailed these results reveal the globally synchronous 13c shift but delayed effects of oae2 dependent on water depth

depth of post depositional remanence acquisition in deep sea sediments a case study of the brunhes matuyama reversal and oxygen isotopic stage 19 1 although post depositional magnetization pdrm in deep sea sediments appears to be acquired during the earliest stages of sediment compaction the natural variability of the pdrm lock in depth in deep sea sediments is poorly understood and as yet unquantified here we consider variations in the relative stratigraphic positions of oxygen isotopic interglacial stage 19 1 and the brunhes matuyama b m chronozone reversal for eight deep sea sediment cores results from a similar study of the displacement between a widespread microtektite layer and the b m boundary are also included 1 the pdrm lock in depth and the temporal relationships between the b m and stage 19 1 datums can be determined from the offsets between the paleomagnetic and the isotopic and microtektite stratigraphies for cores with sedimentation rates greater than 1 cm kyr a the depth offset between the paleomagnetic and isotopic datums is a linear function of sedimentation rate a simple model r 2 0 77 demonstrates that 1 pdrm acquisition occurs 16 cm below the sediment surface and 2 the b m reversal occurs 6 kyr 4 2 kyr after the stage 19 1 datum and the stage 19 1 datum occurs 9 kyr 4 3 kyr after the deposition of the australasian microtektite strewnfield this example argues against simple geophysical models linking geomagnetic field reversals to climate change or impact events the b m boundary is anomalously deep 30 50 cm in very low accumulation rate sediments 1 cm kyr 1 and this may reflect the unusual physical properties of these sediments a review of the geotechnical literature suggests that very low accumulation rate sediments have sufficient time to develop enhanced interparticle rigidity structural strength which inhibits early compaction and hence pdrm acquisition

magnetic paleointensity stratigraphy and high resolution quaternary geochronology successes and future challenges abstract magnetic paleointensity stratigraphy is used to detect variations in the strength of earth s ancient magnetic field paleointensity studies have demonstrated that a dominantly dipolar geomagnetic signal can be recorded in a globally coherent manner in different types of sediments and in non sedimentary archives including ice core records and marine magnetic anomaly profiles the dominantly dipolar nature of geomagnetic paleointensity variations provides a global geophysical signal that has come to be widely used to date quaternary sediments despite the many successful applications of paleointensity assisted chronology the mechanisms by which sediments become magnetized remain poorly understood and there is no satisfactory theoretical foundation for paleointensity estimation in this paper we outline past successes of sedimentary paleointensity analysis as well as remaining challenges that need to be addressed to place such work on a more secure theoretical and empirical foundation we illustrate how common concepts for explaining sedimentary remanence acquisition can give rise to centennial to millennial offsets between paleomagnetic and other signals which is a key limitation for using paleointensity signals for geochronology our approach is intended to help non specialists to better understand the legitimate uses and limitations of paleointensity stratigraphy while pointing to outstanding problems that require concerted specialist efforts to resolve

australasian microtektites in the south china sea and the west philippine sea implications for age size and location of the impact crater abstract microtektites from two deep sea cores in the south china sea and the west philippine sea are identified as belonging to the australasian tektite strewn field based on the morphology chronostratigraphic occurrence and geographical location of these microtektites the higher concentrations of microtektites 1000 cm2 in the marginal seas of the western pacific with the peak concentration in the south china sea support the hypothesis of a large impact crater in indochina these two new occurrences lead to a more precise dating of the impact event at 793 ka whereas the size of the australasian source crater on the indochina peninsula is estimated to be 90 1 16 km introduction the australasian strewn field covering at least one tenth of the earth s surface is the largest and the youngest 0 77 0 02 ma izett and obradovich 1992 of the four known tektite strewn fields microtektites belonging to the australasian strewn field have been found in more than 40 deep sea cores throughout much of the indian ocean the western equatorial pacific ocean and the sulu celebes and philippine seas glass

shelf architectures of an isolated late cretaceous carbonate platform margin galala mountains eastern desert egypt abstract an asymmetrical carbonate platform margin to basin transect has been investigated in the upper campanian maastrichtian succession of the galala mountains northern egypt identification of systems tracts and their lateral correlation was possible in slope sections only whereas the monotonous chalk marl alternations of the basinal sections could not be subdivided with respect to sequence stratigraphic terminology the platform asymmetry is expressed by varying large scale depositional architectures exhibiting a rimmed platform with a sigmoidal slope curvature in south easterly dip sections and a ramp with a linear slope curvature in south westerly dip sections the rimmed platform is subdivided into a gentle upper slope and a steep lower slope the platform formed as a result of the initial topography that was controlled by the tectonic uplift of the northern galala wadi araba syrian arc structure the calculated angles of the steep lower slope of the rimmed part range from 5 to 8 whereas the ramp part has an angle of less than 0 1

latitudinal dependency of geomagnetic polarity transition durations palaeomagnetic records of the matuyama brunhes polarity transition were obtained from seven low sedimentation rate deep sea cores from the pacific ocean the cores were taken near the 180 meridian and provide a latitudinal transect of transition records extending from 45 3 n to 33 4 s examination of these records suggests that low sedimentation rate cores may not be capable of recording the fine details of transitional field behaviour but there are indications that these cores may in fact provide accurate records of the more general features of the reversal most notable of these features is that the duration of the transition is dependent on the site latitude with durations at mid latitudes being more than a factor of 2 longer than at equatorial latitudes

millennial scale instability in the geomagnetic field prior to the matuyama brunhes reversal changes in the earth s magnetic field have global significance that reach from the outer core extending out to the uppermost atmosphere paleomagnetic records derived from sedimentary and volcanic sequences provide important insights into the geodynamo processes that govern the largest geomagnetic changes polarity reversals but dating uncertainties have hindered progress in this understanding here we report a paleomagnetic record from multiple lava flows on tahiti that bracket the matuyama brunhes m b polarity reversal 771 thousand years ago our high precision 40 ar 39 ar ages constrain several rapid and short lived changes in field orientation up to 33 000 years prior to the m b reversal these changes are similar to ones identified in other less well dated lava flows in maui chile and la palma that occurred during an extended period of reduced field strength recorded in sediments we use a simple stochastic model to show that these rapid polarity changes are highly attenuated in sediment records with low sedimentation rates this prolonged 33 000 year period of reduced field strength and increased geomagnetic instability supports models that show frequent centennial to millennial scale polarity changes in the presence of a strongly weakened dipole field

asynchronous records of brunhes matuyama reversal in marine sediments and chinese loess review and discussion abstract geomagnetic polarity reversals are generally considered to occur synchronously around the world and are commonly used as time markers to correlate events between different sediment archives they also play an indispensable role for understanding the mechanisms which generate the earth s geomagnetic field nevertheless in the case of the most recent reversal the brunhes matuyama b m reversal 780 ka comparison of paleomagnetic studies in chinese loess paleosol sequences versus marine cores reveal a marked discrepancy in timing of this event this timing offset has led to uncertainties in correlating the chinese loess paleosol sequences with other global climate records this paper briefly reviews the history of study on the b m reversal both in marine and chinese loess sediments and reviews several contentious explanations of the aforementioned b m boundary offset finally the most recent progress of paleogeomagnetic field variation studies using cosmogenic 10 be in chinese loess is introduced with the purpose of suggesting a potential way to address this b m boundary timing offset issue

magnetic properties of pelagic marine carbonates abstract pelagic carbonates are deposited far from continents usually at water depths of 3000 6000 m at rates below 10 cm kyr and are a globally important sediment type recent advances with recognition of widespread preservation of biogenic magnetite the inorganic remains of magnetotactic bacteria have fundamentally changed our understanding of the magnetic properties of pelagic carbonates we review evidence for the magnetic minerals typically preserved in pelagic carbonates the effects of magnetic mineral diagenesis on paleomagnetic and environmental magnetic records of pelagic carbonates and what magnetic properties can tell us about the open ocean environments in which pelagic carbonates are deposited we also discuss briefly late diagenetic remagnetisations recorded by some carbonates despite recent advances in our knowledge of these phenomena much remains undiscovered we are only at early stages of understanding how biogenic magnetite gives rise to paleomagnetic signals in sediments and whether it carries a poorly understood biogeochemical remanent magnetisation recently developed techniques have potential for testing how different magnetotactic bacterial species which produce different magnetite morphologies respond to changing nutrient and oxygenation conditions future work needs to test whether it is possible to develop proxies for ancient nutrient conditions from well calibrated modern magnetotactic bacterial occurrences a tantalizing link between giant magnetofossils and paleogene hyperthermal events needs to be tested much remains to be learned about the relationship between climate and the organisms that biomineralised these large and novel magnetite morphologies rather than being a well worn subject that has been studied for over 60 years the magnetic properties of pelagic carbonates hold many secrets that await discovery

can remanence anisotropy detect paleomagnetic inclination shallowing due to compaction a case study using cretaceous deep sea limestones we studied 35 cretaceous limestone specimens from five pacific plate deep sea drilling project sites inclination in of the natural remanence is on average 17 shallower than the average 44 expected paleofield inclination i anhysteretic remanence arm applied identically to various axes was found to be weakest armmin perpendicular to bedding and strongest armmax parallel to bedding the average armmin armmax of 0 87 as well as the inclination shallowing of 17 likely originated from sediment compaction rotating the long axes of magnetite grains toward the bedding plane this origin is theoretically and experimentally consistent with the average fractional compaction of 0 6 experienced by our sediments estimated from their porosity a compaction origin is also supported by the significant correlation found between tan in tan i and armmin armmax the correlation line s slope of 2 3 0 7 agrees with theory taking into account our observation that arm given perpendicular to the long axes of magnetite grains has on average 0 37 times the intensity of arm given axially these results suggest that compaction induced inclination shallowing may be detected in a suite of fine grained magnetite bearing sediments by looking for a correlation between tan in and armmin armmax having shown that arm anisotropy is foliated in the bedding plane this correlation line s prediction of in when armmin armmax 1 should estimate i corrected for inclination shallowing

a quantitative comparison of two paleomagnetic records of the cobb mountain subchron from north atlantic deep sea sediments we present a new paleomagnetic record of the cobb mountain subchron obtained from deep sea sediments cored at ocean drilling program site 647 in the southern labrador sea the details of the transitional field behavior documented by this record appear to be very similar to those recorded in a previously published record of this subchron obtained at deep sea drilling project dsdp site 609 in the north atlantic clement and kent 1987 we used a quantitative correlation technique martinson et al 1982 to establish statistically the degree of similarity between these two records and thereby constrain the spatial variability in these transitional fields the error in the alignments is reduced significantly by aligning records of virtual geomagnetic pole positions rather than directions indicating that these records document such large scale changes in the fields that we can not distinguish them from dipolar changes given the proximity of these two sites these replicate records of the cobb mountain subchron provide evidence that deep sea sediments are capable of providing high resolution records of geomagnetic field behavior a reexamination of the sequence of polarity transitions recorded at dsdp site 609 in light of these results suggests the presence of two preferred transitional field configurations the field appears to change from one configuration to the other for several reversals and then back to the original configuration suggesting that a geographical influence on the reversal process persists through this sequence the variability in these reversal records provides insights into the response of the geodynamo to this geographical influence

santa ana winds of southern california their climatology extremes and behavior spanning six and a half decades santa ana winds saws are an integral feature of the regional climate of southern california northern baja california region but their climate scale behavior is poorly understood in the present work we identify saws in mesoscale dynamical downscaling of a global reanalysis from 1948 to 2012 model winds are validated with anemometer observations saws exhibit an organized pattern with strongest easterly winds on westward facing downwind slopes and muted magnitudes at sea and over desert lowlands we construct hourly local and regional saw indices and analyze elements of their behavior on daily annual and multidecadal timescales saws occurrences peak in winter but some of the strongest winds have occurred in fall finally we observe that saw intensity is influenced by prominent large scale low frequency modes of climate variability rooted in the tropical and north pacific ocean atmosphere system

cenomanian turonian carbonate platform deposits in west central jordan we studied upper albian to turonian shallow marine shelf deposits ajlun group of west central jordan along a nne ssw running transect the carbonate dominated succession includes few siliciclastic intercalations claystones and shales and can be subdivided into five formations the naur fuheis and hummar formations of upper albian to upper cenomanian age represent shallow subtidal to supratidal platform environments the uppermost cenomanian to middle turonian shueib formation includes deeper water deposits of the inner mid shelf and locally toc rich black shales shallow marine platform environments once again dominate the wadi as sir formation middle upper turonian a new multibiostratigraphic framework is based on ammonites mainly of the middle cenomanian rhotomagense zone to the middle turonian woollgari zone and calcareous nannofossils biozones cc 9 cc 11 supplemented by benthic and planktonic foraminifers and ostracods it forms the base of a sequence stratigraphic subdivision containing eight sedimentary sequences s1 s8 which are separated by four cenomanian sequence boundaries cejo1 cejo4 and three turonian sequence boundaries tujo1 tujo3 this scheme allows the correlation of the platform succession from distal to proximal shelf areas in contrast to previous correlations using lithologic units furthermore comparisons between the platform successions and sequence patterns of west central jordan and those from neighbouring areas allow to differentiate local regional and global controlling factors of platform development within the study area

the influence of high latitude flux lobes on the holocene paleomagnetic record of iodp site u1305 and the northern north atlantic 1 paleomagnetic analysis and radiocarbon dating of an expanded holocene deep sea sediment sequence recovered by integrated ocean drilling program iodp expedition 303 from labrador sea site u1305 lat 57 28 5 n long 48 31 8 w water depth 3459 m provides insights into mechanisms that drive both paleomagnetic secular variation psv and magnetization acquisition in deep sea sediments seventeen radiocarbon dates on planktonic foraminifera define postglacial ca 8 ka sedimentation rates as ranging from 35 to 90 cm kyr alternating field af demagnetization of u channel samples show that these homogeneous sediments preserve a strong stable and consistently well defined component magnetization normalized remanence records pass reliability criteria for relative paleointensity rpi estimates assuming that the age of magnetization is most accurately defined by well dated psv records with the highest sedimentation rates allows us to estimate and correct for temporal offsets at site u1305 interpreted to result from postdepositional remanence acquisition at a depth of 20 cm comparisons indicate that the northern north atlantic psv and rpi records are more consistent with european than north american records and the evolution of virtual geomagnetic poles vgp are temporally and longitudinally similar to global reconstructions though with much larger latitudinal variation the largest deviations from a geocentric axial dipole gad are observed during times of the highest intensities in contrast to the usual assumption these observations are consistent with the idea that psv in the north atlantic and elsewhere during the holocene results from temporal oscillations of high latitude flux concentrations at a few recurrent locations

a paleomagnetic and geochemical record of the upper cochiti reversal and two subsequent precessional cycles from southern sicily italy abstract a detailed paleomagnetic and geochemical study of the upper cochiti n r reversal recorded in marine marls on southern sicily shows two consecutive and very rapid transitions r n and n r that coincide with distinct lithological boundaries a fe migration model is presented in which magnetite is formed under different diagenetic conditions during sulphate reduction originally formed primary magnetite is preserved this primary magnetite has recorded the pre transitional normal polarity after burial migration of ferrous iron occurs and subsequent oxidation produces secondary magnetite which records the post transitional reversed polarity and produces the two apparent transitions in addition low temperature lt and high temperature ht components record the reversal in a slightly different way the ht component being acquired with a delay it is probable that both components reside in magnetite but have a different origin and grain size distribution giving different blocking temperature spectra the actual upper cochiti reversal occurs at a level with an estimated astronomically calibrated age of 4 165 ma

apparent timing and duration of the matuyama brunhes geomagnetic reversal in chinese loess the matuyama brunhes mb geomagnetic reversal in chinese loess has been studied extensively as an important boundary for land ocean stratigraphic and paleoclimatic correlations however the apparent timing and duration of the mb boundary remain controversial in chinese loess deposits due to its inconsistent stratigraphic position and the uncertain chronologies here we synthesized high resolution paleomagnetic records from four loess sequences in the central chinese loess plateau and synchronized the loess paleosol chronology by matching the grain size variations to orbitally tuned grain size time series the synthesized paleomagnetic results reveal consistent features of the mb transition in chinese loess including the stratigraphic position l 8 s 8 transition timing 808 826 ka duration 14 16 ka and rapid directional oscillations compared with the mb transition in marine records 770 775 ka the timing of the mb transition is relatively older and longer in chinese loess due to a complex interplay between different remanence acquisition mechanisms which occurred during the course of postdepositional physical and chemical processes

can rogue waves be predicted using characteristic wave parameters rogue waves are ocean surface waves larger than the surrounding sea that can pose a danger to ships and offshore structures they are often deemed unpredictable without complex measurement of the wave field and computationally intensive calculation which is infeasible in most applications consequently there a need for fast predictors here we collate quality control and analyse the largest dataset of single point field measurements from surface following wave buoys to search for predictors of rogue wave occurrence we find that analysis of the sea state parameters in bulk yields no predictors as the subset of seas containing rogue waves sits within the set of seas without however spectral bandwidth parameters of rogue seas display different probability distributions to normal seas but these parameters are rarely provided in wave forecasts when location is accounted for trends can be identified in the occurrence of rogue waves as a function of the average seas state characteristics at that location these trends follow a power law relationship with the characteristic sea state parameters mean significant wave height and mean zero up crossing wave period we find that frequency of occurrence of rogue waves and their generating mechanism is not spatially uniform and each location is likely to have its own unique sensitivities which increase in the coastal seas we conclude that forecastable predictors of rogue wave occurrence will need to be location specific and reflective of their generation mechanism therefore given location and a sufficiently long historical record of sea state characteristics the likelihood of occurrence can be obtained for mariners and offshore operators

cenomanian turonian stable isotope signatures and depositional sequences in northeast egypt and central jordan abstract lithostratigraphic biostratigraphic and microfacies studies of two cenomanian turonian shallow marine siliciclastic carbonate successions at gebel ekma plateau southwestern sinai egypt and wadi karak section central jordan are calibrated with 13c profiles to reveal relative sea level changes within a sequence stratigraphic framework the study provides significantly enhanced stratigraphic resolution and key sections for regional correlation lithofacies are dominated by well developed peritidal to subtidal facies associations indicating deposition in a rimmed carbonate shelf setting biostratigraphic analysis indicates the presence of 6 ammonite zones 3 calcareous nannofossil zones and 3 planktonic foraminiferal zones within the cenomanian to turonian succession six third order depositional sequences bounded by correlatable sequence boundaries can be traced across the african arabian platform comparison with 13c records in deeper water pelagic sequences help to improve the resolution of the boundaries of each depositional sequence recognition of time gaps at the sequence boundaries on the platform recorded in different parts of african arabian platform is attributed to local tectonic activity associated with the change from passive to active margins which are overprinted by the global eustatic signature

a geomagnetic paleointensity record of 0 6 to 3 2 ma from sediments in the western equatorial pacific and remanent magnetization lock in depth

benthic foraminiferal response to relative sea level changes in the maastrichtian danian succession at the dakhla oasis western desert egypt the maastrichtian danian benthic foraminiferal diversity and assemblages through sequence stratigraphy were studied at dakhla oasis egypt benthic foraminifera numbers bfn high flux species and characteristic benthic foraminiferal species and genera distribution are also incorporated to assess palaeobathymetry palaeoenvironment and palaeoproductivity all these proxies are then taken together to construct a sea level curve and interpreted in terms of regional tectonics climate and eustasy data suggest a remarkably highly equitable benthic environment deposited in a brackish littoral and or marsh setting with moderate to low oxygen conditions and reduced salinity oligotrophic possibly due to increased precipitation and terrestrial runoff the interrupted dominance of calcareous forms and high organic flux species suggests occasional marine incursions and high palaeoproductivity due to local upwelling the inferred sea level curve replicates the global eustatic curve and suggests that the curve is more influenced by the prevailing climate and global eustasy rather than by regional tectonics the post cretaceous palaeogene boundary displays improvement in the environment in terms of diversity and number of species and specimens with a marked reduction in the abundance of high organic flux species during early paleocene danian time indicating a shift from a more mesotrophic open marine environment to much reduced oligotrophic conditions

millennial to submillennial scale features of the matuyama brunhes geomagnetic polarity transition from osaka bay southwestern japan 1 a high resolution magnetic record of the matuyama brunhes mb reversal transition was obtained from homogeneous marine clay in a 1700 m core from osaka bay the transition stretches over a core length of 6 4 m and yields four short reversal episodes two predate the main mb boundary mbb and two postdate it we made diatom analyses of sediments to estimate relative sea level changes and constructed an age model by correlation with the astronomically calibrated marine oxygen isotope curve the age model shows the short reversal episodes with durations of 1 kyr occurred at 4 5 kyr intervals within stage 19 and the mbb occurred about 5 kyr after the sea level highstand corresponding to isotopic event 19 3 it also shows the paleointensity minimum of 15 20 of the postreversal mean occurred at about 6 kyr before the mbb and another minimum at about 1 kyr after four virtual reverse to normal polarity boundaries found in this study suggest different ages for the mbb could be observed in lava flow studies some millennial to submillennial scale transition features found in this study are compatible with the previous numerical simulations of geomagnetic field reversal

archeomagnetic secular variation from korea implication for the occurrence of global archeomagnetic jerks abstract an archeomagnetic paleosecular variation psv was first defined in korea using baked materials collected from 26 kilns or hearths with ages ranging from 1100 bc to ad 1790 variations of geomagnetic declination and inclination from the korean peninsula are distinctively different from the prediction of a global model cals3k 3 or cals7k 2 for the past 3500 yr in particular a distinctive offset in magnitude and phase is noticeable between the observations and predictions at 745 bc ad 300 and ad 1400 1700 a bi plot of magnetic declination versus inclination displays three cusps at the corresponding time intervals these time intervals are nearly identical to or at least overlap with three of the four potential archeomagnetic jerks suggested by gallet et al 2003 from the european archeomagnetic data a comparison of the psv curves for neighboring countries regions revealed that european archeomagnetic jerks at 800 bc ad 200 ad 800 and ad 1400 were all preserved in east asia suggesting that the archeomagnetic jerks were global or at least northern hemispheric features

local and synoptic mechanisms causing southern california s santa ana winds the atmospheric conditions that lead to strong offshore surface winds in southern california commonly referred to as santa ana winds are investigated using the north american regional reanalysis and a 12 year 6 km resolution regional climate simulation of southern california we first construct an index to characterize santa ana events based on offshore wind strength this index is then used to identify the average synoptic conditions associated with santa ana events a high pressure anomaly over the great basin this pressure anomaly causes offshore geostrophic winds roughly perpendicular to the region s mountain ranges which in turn cause surface flow as the offshore momentum is transferred to the surface we find however that there are large variations in the synoptic conditions during santa ana conditions and that there are many days with strong offshore flow and weak synoptic forcing this is due to local thermodynamic forcing that also causes strong offshore surface flow a large temperature gradient between the cold desert surface and the warm ocean air at the same altitude creates an offshore pressure gradient at that altitude in turn causing katabatic like offshore flow in a thin layer near the surface we quantify the contribution of synoptic and local thermodynamic mechanisms using a bivariate linear regression model and find that unless synoptic conditions force strongly onshore winds the local thermodynamic forcing is the primary control on santa ana variability

the relationship between 10be and geomagnetic field strength records in central north atlantic sediments during the last 80 ka abstract a profile of leached 10 be 9 be has been measured in an 80 ka sediment core from the northeast atlantic ocean this profile shows a significant inverse correlation with the palaeomagnetic intensity profile inferred from nrm arm measurements in the same core particularly between 40 and 50 ka where a rapid decrease in field intensity is accompanied by a rapid increase in 10 be 9 be the extent to which this increase in 10 be 9 be at 40 ka is associated with a 10 be peak seen in polar ice cores at about the same time remains speculative