monsoonal and fertility controls on recent marginal sea and continental shelf coccolith assemblages from the western pacific and northern indian oceans gephyrocapsa oceanica is often overwhelmingly dominant in coccolith assemblages found in monsoonal regions including the marginal seas of the western pacific and the more open seas and continental shelf of the northern indian ocean the dominance of g oceanica is thought to reflect its preference for elevated nutrient levels and a tolerance of lithogenic particles emiliania huxleyi is subordinate in assemblages deposited in monsoonal regions coccolith assemblages with dominant e huxleyi are restricted to marginal seas with lagoonal anti estuarine circulation e g red sea and open seas and continental shelves with strong oceanic influences but no monsoonal effects e g southern great barrier reef coral sea and great australian bight

the mediterranean sea a miniature ocean for climatic and environmental studies and a key for the climatic functioning of the north atlantic the mediterranean sea provides a case study not only for dense water formation and climatic functioning at a basin scale but also as a body of water evolving in response to the effects of environmental changes through marine circulation marine signatures of changes may be used to provide estimates of the evolution of the external driving forces of climate and environment that is to say to provide a coupling between marine sciences and climatic and socio economic studies different examples may be given i nutrients and trace metal changes in the western mediterranean permit quantification of external changes at a basin scale ii sapropels organic rich layers sedimented in anoxic conditions provide records for the last 2 million years of interactions between marine circulation climate and biology iii temperature and salinity changes that have taken place since the 1960s in response to changes in heat and water budgets across the sea surface sapropel studies and ongoing changes in temperature and salinity also require that the mediterranean functioning be considered in relation to global climate and to the atlantic ocean as well as taking into account the changing role of salty mediterranean waters in the atlantic ocean these factors highlight a dual role for the mediterranean sea which acts as a miniature ocean for physical chemical or climatic and environmental studies and also as a key factor in understanding global ocean circulation in which past changes have taken place

paleoenvironmental changes at the lower pleistocene montalbano jonico section southern italy global versus regional signals abstract integrated high resolution data from calcareous plankton assemblages foraminifera and nannofossils together with geochemical and mineralogical investigations have been collected at the on land montalbano jonico section southern italy in order to reconstruct the paleoenvironmental changes through marine isotope stages mis 23 37 time series analysis on globigerina bulloides and cassidulina carinata 18o records and on selected calcareous plankton proxies mainly revealed the occurrence of precession and obliquity forcing the deposition of sapropel layers which are interbedded in the montalbano jonico section was driven by water column stratification insolation cycle i 104 and enhanced sea surface water productivity insolation cycle i 112 i 102 and i 86 different paleoenvironmental conditions mark the sedimentary evolution of the section from 1240 to 1082 ka mis 37 mis 32 high percentage abundances of warm and oligotrophic planktonic foraminifera and calcareous nannofossil taxa indicate the establishment of oligotrophic and stratified surface water conditions a key paleoenvironmental change occurred during mis 31 from about 1080 to 1065 ka which was a very warm interglacial characterized by an increase of tropical subtropical globigerinoides ruber group and globigerinoides trilobus and low salinity braarudosphaera bigelowii sea surface water taxa during this interval more humid climate conditions coupled with changes in local paleomorphology may have triggered a higher and unusual freshwater input and the creation of a new entry point for sediment supply into the basin from a different drainage area from about 1065 to 1010 ka mis 30 mis 29 a cool and dry climate prevailed in the circum mediterranean area during a time of precession maxima this favored lowered sea surface temperatures and an increase of polar water neogloboquadrina pachyderma left coiling there are also indications of a reduction of the terrigenous input from the new source area from 1010 ka upward mis 28 mis 23 the higher abundances of globigerina bulloides turborotalita quinqueloba and calciosolenia spp indicate enhanced productivity conditions probably related to high turbidity of sea surface waters triggered by a more conspicuous sediment input from land analysis of the long term trends in the multiproxy patterns suggests that the major paleoenvironmental changes occurred as a consequence of the combined effect of orbitally controlled global climate and regional processes

sea surface water variability during the mid brunhes inferred from calcareous plankton in the western mediterranean odp site 975 abstract planktonic foraminifera and calcareous nannoplankton were analyzed in core ocean drilling program site 975 located in the western mediterranean in order to study their response to environmental changes across the mid brunhes interval and specifically through marine isotope stage mis 15 and 8 ca 650 230 ka multivariate analysis of assemblage composition revealed that the calcareous plankton dynamics were mainly driven by surface water temperatures both on glacial interglacial and stadial interstadial time scales throughout the studied interval foraminiferal and nannoplankton assemblages responded to environmental forcing in concert except during mis 15 when multiple environmental factors appear to have been superimposed on the otherwise dominating effect of temperature variability sea surface temperature sst has been estimated from planktonic foraminiferal assemblages using the artificial neural networks method pointing out relevant seasonal variations through the record our reconstructions reveal that calcareous plankton assemblages also responded to other environmental factors than temperature including modification in surface water stratification nutrient availability and detrital input specifically a more stable stratified water column seems to have accompanied the interval through mis 15 13 on the other hand across the mid brunhes interval from mis 12 onwards the enhanced glacial strength affected both planktonic foraminifera and calcareous nannofossils planktonic foraminifera indicate that mixed and productive surface waters developed during glacials and stadials accompanied by episodes of increased detrital input as suggested by calcareous nannoplankton assemblages enhanced food availability was likely driven by wind induced upwelling and or by continental coastal input during dry conditions persisting in the mediterranean region and over north africa finally spectral and wavelet analyses of calcareous plankton time series allowed to identify the pattern of periodic response of the plankton at milankovitch cycles and in some cases at millennial variability the dominant 100 kyr periodicity recorded in surface water temperature proxies clearly reflects a major response of the planktonic community to the global glacial interglacial climate pattern high frequency variation 5 8 11 13 ky of surface water temperature proxies and of selected taxa abundance highlights the occurrence of millennial scale instability superimposed on the paleoenvironmental modifications occurring through the mid brunhes interval climate transition this framework accounts for the occurrence of different surface water dynamics across the mid brunhes interval and is in favor of the hypothesis that the millennial scale surface water temperature variations are modulated by the harmonics of the precession forcing

the sapropel record of the eastern mediterranean sea results of ocean drilling program leg 160 research on sediments recovered during ocean drilling leg 160 has concentrated on two issues the first concerned the stratigraphy of sapropel formation the second was oriented to clarify specific processes that explain sapropel origin progress has been made in the construction of stratigraphic composites out of sedimentary sequences from individual holes at each of the palaeoceanographic sites on the composites initial work has resulted in the establishment of high resolution and intermediate resolution stratigraphies for three sites 963 964 967 correlation of sedimentary cycles to astronomical insolation cycles extends the stratigraphies to sites 969 and 966 the sapropel occurrences in the marine and land sequences over the entire eastern mediterranean are correlated with the resolution that can be obtained from isotope studies groups of sapropels occurred simultaneously over the entire basin in detail however the temporal and facies patterns of sapropel sequences differ between individual sites and depositional basins the differences may be related to effects of water depth diagenesis and post depositional tectonic attenuation of sequences studies on the geochemistry and facies of sapropels agree that anoxic conditions favoured preservation of organic matter in sapropels caused the enrichment of trace metals associated with sapropels and helped to preserve primary sedimentary structures besides all evidence is consistent with elevated fluxes of organic matter and associated elements during sapropel events

revision of the early middle pleistocene calcareous nannofossil biochronology 1 75 0 85 ma the extant nannofossil biostratigraphic and biochronologic framework for the early middle pleistocene time interval has been tested through the micropaleontological analysis of globally distributed high quality low to mid latitude deep sea successions the quantitative temporal distribution patterns of relative abundances of selected taxa were reconstructed in critical intervals and the following biohorizons were defined first occurrence of medium sized gephyrocapsa spp last occurrence of calcidiscus macintyrei first occurrence of large gephyrocapsa spp last occurrence of large gephyrocapsa spp first occurrence of reticulofenestra asanoi re entrance of medium sized gephyrocapsa spp and last occurrence of reticulofenestra asanoi the detailed patterns of abundance change at these biohorizons were used to generate a detailed biostratigraphy and the biostratigraphic data were transformed into a precise biochronology by means of correlation to isotope stratigraphies and astronomical timescales the degree of isochrony or diachrony of the biohorizons was evaluated biohorizons and are isochronous occurring close to marine isotope stages mis 55 and mis 22 respectively and and are slightly diachronous on the order of 30 40 kyr whereas biohorizons and are confirmed as diachronous on the order of 100 80 and 60 kyr respectively some of the events are clearly controlled by environmental conditions e g the last occurrence of r asanoi related to significant environmental changes associated with the first large amplitude glaciation of the late quaternary mis 22

chronology of the lower middle pleistocene succession of the south western part of the crotone basin calabria southern italy biostratigraphy based on calcareous nannofossils integrated by magnetostratigraphic geochronological and isotopic data allowed establishing a precise chronological framework for the pleistocene

rock magnetism and palaeomagnetism of the montalbano jonico section italy evidence for late diagenetic growth of greigite and implications for magnetostratigraphy summary the montalbano jonico mj section cropping out in southern italy represents a potential candidate to define the lower middle pleistocene boundary and it has been proposed as a suitable global stratotype section and point gssp of the ionian stage middle pleistocene the mj section is the only continuous benthic and planktonic 18o on land reference in the mediterranean area for the mid pleistocene transition spanning an interval between about 1240 and 645 ka combined biostratigraphy and sapropel chronology tephra stratigraphy and complete high resolution benthic and planktonic foraminiferal stable oxygen isotope records already provide a firm chronostratigraphic framework for the mj section however magnetostratigraphy was still required to precisely locate the brunhes matuyama transition and to mark the gssp for the ionian stage we carried out a palaeomagnetic study of a subsection ideale section of the mj composite section sampling 61 oriented cores from 56 stratigraphic levels spread over a ca 80 m thick stratigraphic interval that correlates to the oxygen isotopic stage 19 and should therefore include the brunhes matuyama reversal the palaeomagnetic data indicate a stable and almost single component natural remanent magnetization nrm a characteristic remanent magnetization chrm was clearly identified by stepwise demagnetization of the nrm the chrm declination values vary around 0 and the chrm inclination around the expected value 59 for a geocentric axial dipole field at the sampling locality this result indicates that the section has been remagnetized during the brunhes chron a preliminary study of 27 additional not azimuthally oriented hand samples collected at various levels from other parts of the mj composite section indicates that all the samples are of normal polarity and demonstrates that the remagnetization is widespread across the whole exposed stratigraphic sequence a series of specific rock magnetic techniques were then applied to investigate the nature of the main magnetic carrier in the study sediments and they suggest that the main magnetic mineral in the mj section is the iron sulphide greigite fe3s4 scanning electron microscope observations and elemental microanalysis reveal that greigite occurs both as individual euhedral crystals and in iron sulphides aggregates filling voids in the clay matrix therefore we infer that the remagnetization of the section is due to the late diagenetic growth of greigite under reducing conditions most likely resulting in the almost complete dissolution of the original magnetic minerals iron sulphide formation in the mj section can be linked to migration of mineralized fluids our inferred timing of the remagnetization associated with greigite growth represents the longest remanence acquisition delay documented in greigite bearing clays of the italian peninsula so far

diagenetic sources of stable remanence in remagnetized paleozoic cratonic carbonates a rock magnetic study hysteresis measurements lowrie fuller tests cisowski tests and low temperature demagnetization experiments on samples of the knox dolomite trenton limestone and onondaga limestone indicate that the remanence in these remagnetized carbonate units resides principally in single domain magnetite in contrast to previous interpretations volumetrically however a significant fraction of the magnetite is coarser grained as previous scanning electron microscopic work on magnetic extracts has shown these conclusions are based mainly on the characteristic wasp waisted shape of the hysteresis loops and on the anomalously high ratios of remanent coercivity to bulk coercivity both of which clearly indicate a bimodal distribution of coercivities grain sizes the magnetization is controlled mainly by cubic magnetocrystalline anisotropy consistent with the spheroidal particles commonly observed in extracts hysteresis trends show that especially the finest particles lack shape anisotropy in view of these conclusions the two components of natural remanence in these rocks are interpreted as 1 a late paleozoic kiaman chemical remanence carried by single domain diagenetic magnetite and 2 a cenozoic thermoviscous overprint residing principally in coarser pseudosingle domain and multidomain magnetite also of late paleozoic diagenetic origin

the evolution of pleistocene climate a time series approach abstract in the later part of the pleistocene variations in global ice volume have been dominated by an approximate 100 000 year cycle analysis of 2 myr long oxygen isotope record from an equatorial pacific core indicates that this is true only for the last 900 000 years prior to this time the amplitude of the 100 000 year cycle is much reduced as is the variance of all oscillations with periods greater than 60 000 years based on results of time series analysis of this 2 myr long record the pleistocene glacial cycles can be divided into three sections 1 the late pleistocene 0 900 kyr b p where the variations in the isotope record are dominated by the 100 000 year cycle 2 the middle pleistocene 900 1450 kyr b p in which low frequency components are not as important as in the later period of the pleistocene and 3 the early pleistocene late pliocene 1450 2000 kyr b p where general reductions of importance at all frequencies is seen as compared to the later intervals recent modeling efforts which describe variations in global ice volume show that the dominant low frequency component observed in the late pleistocene can result from different time constants for the rate of glacial growth and decay in response to variations in the earth s orbital parameters it is hypothesized that during the early pleistocene the rate of growth and decay of glaciers were more similar and that continental erosion by successive glacial advances lowered the land surface in areas of ice cap formation to below sea level when the ice caps became marine based more rapid decay of the ice became possible

orbital variations in planktonic foraminifera assemblages from the ionian sea during the middle pleistocene transition abstract the middle pleistocene transition 1 2 0 7 ma is the most recent re organization of the global climate system which includes variations in the frequency and amplitude of glacial interglacial cycles increased ice sheet volume sea surface temperature cooling and a significant drop in the co 2 atmospheric levels here we present high resolution planktonic foraminifera data mean sampling resolution of about 780 years from core lc10 recovered in the ionian sea eastern mediterranean between 1 2 and 0 9 ma selected taxa among them g ruber t quinqueloba and g bulloides show significant periodicities that can be associated to orbital cycles mainly precession and obliquity the planktonic foraminifera based paleoclimatic curve exhibits a cooling linear trend that can be associated to similar phenomena observed in the north atlantic on the other hand we refer to the influence of the north african monsoon the occurrence of two peaks of the low salinity tolerant species g quadrilobatus that fall in coincidence of sapropel layers finally we discuss the distribution pattern of n pachyderma sinistral coiling with peaks up to about 20 between mis 30 and 28 and compare it to middle late quaternary records of the sicily channel and western mediterranean

distribution of recent nannofossils beneath the benguela system southwest african continental margin abstract one hundred and forty eight surface samples recovered from the southwest african continental margin 35 17 s have been examined for their nannofossil content coccolith abundance is high in sediments from the deep water areas but declines toward the coast under the main areas of upwelling five distinct bathymetric oceanographic assemblages can be characterized by their nannofossil content coastal upwelling orange bank intermediate southern deep water and northern deep water angola current these distinctions are based on the distribution of eight ecologically significant taxa in order of decreasing abundance they are gephyrocapsa oceanica helicopontosphaera kamptneri cyclococcolithina leptopora coccolithus pelagicus syracosphaera div sp thoracosphaera div sp rhabdosphaera div sp and umbilicosphaera sibogae sea surface temperature and salinity variations which correlate with the extent and intensity of the main upwelling cells are thought to be the most important controls on coccolith distribution although nutrient availability and reduction of surface water transparency may be of local importance the exclusion of three stratigraphical index species for the quaternary emiliania huxleyi gephyrocapsa caribbeanica and g ericsonii from the quantitative analysis will permit the future application of these results to paleoceanographic reconstructions of the benguela system in pleistocene core sections

plate reconstruction of the bay of biscay a plate reconstruction of the bay of biscay to a predrift stage is proposed on the basis of 1 an aptian albian tectonic pattern of the basque cantabrian region in northern spain which suggests major left lateral strike slip movements and 2 a continental margin that matches predrift stages plate reconstruction results from the juxtaposition of the two continental margins of the bay of biscay so that the eastern north spanish margin lies laterally adjacent to the southwest french margin landes plateau and the western north spanish margin borders the eastern part of the meriadzek terrace in the armorican margin the restoration obtained is supported by both the implied amount of clockwise rotation of iberia 37 very close to the 35 suggested by paleomagnetism and the positive matching of north south oriented transform structures from the south biscay margin with northeast southwest oriented transform structures from the north biscay margin

a pleistocene warming event at 1 ma in prydz bay east antarctica evidence from odp site 1165 abstract bio and magnetostratigraphic age data and nannofossil assemblage analysis from odp site 1165 evidence an anomalous warming event of the surface waters in and around prydz bay during the early pleistocene approximately 1 ma this results from an increase in the abundance of nannofossils at site 1165 that occurred at 1 ma detailed high resolution sampling permits a new bio magnetostratigraphic interpretation for odp site 1165 a decrease in 18o values at sites 1165 and 1167 also occurs at this time supporting the presence of warming conditions in the prydz bay area a return to colder surface waters indicated by the absence or rare occurrence of nannofossils in the upper cores from site 1165 suggests that more stable glacial conditions existed in the prydz bay basin for the last 900 ka the biogenic carbonate sequence identified at site 1167 is similar to the carbonate shales recovered from the cape roberts project 1 both have been dated at about 1 ma supporting the idea that a significant surface waters warming occurred during the pleistocene these data and the presence of calcareous nannofossils from locations around the antarctic continent also suggest that the warming event was not limited to the analysed basin but it extended around the east antarctic continent these new evidence call for a re evaluation of the notion that the east antarctic ice sheet has experienced stable conditions similar to today since the late neogene

vegetation and climate across the early middle pleistocene transition at montalbano jonico southern italy abstract pollen analysis of the montalbano jonico marine succession mjs southern italy provides a continuous vegetational record between 858 ka and 745 13 ka which includes marine isotope stage mis 19 now considered the closest orbital analogue to the holocene a comparison between paleoclimate proxies and global signals of past climate change allows the pollen record to be interpreted in terms of major environmental and climate modifications through mis 21 18 at the orbital and sub orbital scale this is also central to understanding migration patterns of the genus homo interglacials are expressed by the dominance of a mesophilic vegetation typical of a warm temperate and relatively humid climate deciduous quercus dominated fully temperate arboreal forest already devoid of subtropical taxa wooded steppes to steppes expanded during glacials when cold and dry conditions prevailed at mjs the main expansion of temperate forest dominated by broad leaved trees correlates to mis 19 3 whereas the expansion of steppe vegetation during drier conditions marks mis 19 2 directly above the volcaniclastic layer v4 dated at 773 9 1 3 ka more intensively arid conditions developed during mis 20 and mis 18 the pollen temperature index reaches its minimum in uppermost mis 20 in agreement with a significant cold and arid climate phase of wide significance in the north hemisphere as documented by prominent peaks in north atlantic ice rafted debris ird and mediterranean aeolian dust records on the other hand artemisia a significant component of steppes shows its maximum expansion during earlier phases of mis 18 millennial to sub millenial scale climate variability is evidenced by two abrupt short term pollen events within mis 19 3 which show a dominant increase of the cosmopolitan herbaceous component at around 783 54 ka and 774 84 ka respectively the vegetational and inferred climate changes for mis 19 offer two possibilities 1 to investigate the interglacial climate variability and discuss the linkage between climate and changes in geomagnetic field intensity close to the matuyama brunhes paleomagnetic boundary mbb and 2 to help evaluate the role of the mbb in defining the middle pleistocene global boundary stratotype section and point gssp with respect to point 2 a comparison of data at mjs with the pollen record at the nearby and coeval valle di manche section is relevant and evidences the complex response of vegetation to climate events possibly under the effects of both astronomical and local factors

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

a review of calcareous nannofossil astrobiochronology encompassing the past 25 million years this paper presents a review of astrobiochronological calibration of recent to late oligocene calcareous nannofossil datum events biohorizons included in the paper are those of the widely used standard nannofossil zonations of martini e 1971 standard tertiary and quaternary calcareous nannoplankton zonation in farinacci a ed proceedings of the second international conference on planktonic microfossils roma rome ed tecnosci vol 2 pp 739 785 and okada h and bukry d 1980 supplementary modification and introduction of code numbers to the low latitude coccolith biostratigraphy zonation bukry 1973 1975 marine micropaleontology 51 321 325 as well as supplementary biohorizons proposed in the literature the biohorizons have been selected on the basis of the unambiguous taxonomy of the index taxa and their biostratigraphic usefulness we emphasise the application of rigorous methodology in nannofossil studies which permits an evaluation of biohorizons in terms of reliability and calibrates their potential correlatability astrochronological age estimates rely on the geologic timescale developed by the ics in 2004 with some new calibrations included we provide an overview of the relative position of biohorizons versus the astronomically calibrated ages of magnetic reversals and reference isotope stratigraphies surprisingly there are still few high resolution quantitative biostratigraphic studies of astrochronologically tuned sections in spite of the central role of such studies in addressing fundamental problems such as the tempo and mode of plankton evolution

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

calcareous nannofossil bioevents and environmental control on temporal and spatial patterns at the early middle pleistocene quantitative distributions of calcareous nannofossils are analysed in the early middle pleistocene at the small gephyrocapsa and pseudoemiliania lacunosa zone transition in deep sea cores from the mediterranean sea and north atlantic ocean ocean drilling program odp sites 977 964 and 967 deep sea drilling project dsdp site 607 the temporal and spatial mode of occurrence of medium sized gephyrocapsids and reticulofenestrids has been examined to refine biostratigraphic constraints and evaluate possible relationships of stratigraphic patterns to environmental changes during a period of global climatic deterioration the timing of bioevents has been calibrated using high resolution sampling and correlation to the y 18 o record in chronologically well constrained sections newly identified events and ecostratigraphical signals enhance the stratigraphic resolution at the early middle pleistocene the first occurrence fo of intermediate morphotypes between pseudoemiliania and reticulofenestra reticulofenestra sp is proposed as a reliable event within marine isotope stage mis 35 or at the mis 35 34 transition the distribution of reticulofenestra asanoi is characterized by rare and scattered occurrences in its lowest range but the first common occurrence fco is consistently identified at mis 32 or 32 31 the last common occurrence lco of the species is a distinctive event at mis 23 in the studied interval gephyrocapsa omega dominates among medium sized gephyrocapsa the fo of g omega and contemporaneous re entry of medium sized gephyrocapsids at the lower middle pleistocene transition are diachronous between the atlantic ocean and mediterranean sea and from the western to eastern mediterranean in the mediterranean the lo of g omega falls at mis 15 insolation cycle 54 and is isochronous among the sites abundance fluctuations of g omega show notable relations to early middle pleistocene climate changes they considerably increase in abundance at the interglacial stages suggesting warm water preferences gephyrocapsa omega temporarily disappears during the glacial mis 22 and mis 20 above mis 20 an impoverishment in g omega and in the total abundance of medium sized gephyrocapsids occurs a decrease in abundance of g omega is observed between the western site 977 and the easternmost site 967 in the mediterranean sea as a possible response to high salinity and or low nutrient content possible environmental influences on the distribution of r asanoi and of reticulofenestra sp are discussed d 2004 elsevier b v all rights reserved

quantitative analysis of quaternary nannoplankton in the subtropical northwestern pacific ocean abstract time progressive changes of nannoflora and biometry of coccoliths for the last 1 3 m y were investigated for a piston core recovered from the west mariana ridge the species compositions were quantitatively investigated under an electron microscope and six assemblages assemblages a through f were identified significant changes in relative abundances of various types of genus gephyrocapsa are the main cause for the stratigraphic change of the flora a dominant occurrence of gephyrocapsa protohuxleyi var a which can be identified only under an electron microscope was observed for the first time in a thin sequence which corresponds to the lowest part of the brunhes epoch 0 75 0 62 ma because of this characteristic occurrence assemblage d was further subdivided into three subassemblages the dominant occurrence of small gephyrocapsa which is well known in the small gephyrocapsa zone of the equatorial pacific ocean was not observed but the almost complete absence of medium to large gephyrocapsa during approximately 200k years of the middle pleistocene was confirmed a stratigraphically restricted occurrence of a large form of reticulogenestra was also confirmed by the biostratigraphic study under a light microscope and the last and first occurrences of the largest form reticulofenestra sp a 6 5 m were identified at 0 81 and 0 98 ma respectively in addition to these four events precise ages for another five well known evolutionary events were also calibrated these ages are generally in good agreement with previously reported ages from other world oceans and diachronism was not evident for most of these evolutionary events

evaluation of the astronomically calibrated time scale for the late pliocene and earliest pleistocene an astronomically calibrated time scale was recently established hilgen 1991a b for the pliocene and earliest pleistocene based on the correlation of dominantly precession controlled sedimentary cycles sapropels and caco3 cycles in mediterranean deep sea sections to astronomical solution ber90 berger and loutre 1991 this time scale which differed substantially from the conventional time scales then widely used is essentially confirmed by a new generation of radiometric dates using the ar 40 ar 39 laser fusion technique to evaluate this time scale we here extract both precession and obliquity related components from late pliocene earliest pleistocene climatic proxy records in the mediterranean and determine coherencies and phase time lags between these components and the respective orbital variations this work is found to support the new time scale because significant coherencies are found between the astronomically related components in our proxy records and the orbital variations not only at the main period of precession but also at the main period of obliquity and because of the eccentricity modulation of precession in the low frequency eccentricity bands of the spectrum but the calculated time lag between obliquity and 41 kyr components in the climatic proxy records shows a significant increase of 5 6 1 kyr with respect to the late pleistocene if the phase relation with precession is kept constant this increase can be explained by a change in the climate response time to obliquity or to precession by a small uncertainty in the astronomical solution or by a combination of these factors

paleoceanography of the mid pleistocene the fossil record of the pleistocene calcareous nannoplankton indicates that during the mid pleistocene 0 93 1 25 my occurred an episode of overwhelming dominance of smallgephyrocapsa during this episode normally abundant large size specimens of this genus mainlygephyrocapsa oceanica were virtually excluded from the phytoplankton of tropical and subtropical oceans the best modern analog of this dominantly smallgephyrocapsa assemblage is the subpolaremiliania huxleyi assemblage which implies that nutrient content was significantly greater and water temperature was lower in the photic water column of the tropical oceans than they are today increased equatorial upwelling in the oceans on a scale much greater than today may explain the above pattern to achieve such broad equatorial upwelling there must be a source and a drive for cold dense water the arctic ocean which was probably seasonally free of ice during this interval of the mid pleistocene is capable of providing the requisite source as well as a drive for the inferred equatorial upwelling the energy balance of a predominantly ice free arctic ocean requires an approximately three to seven fold increase of hydrospheric heat transport from the north atlantic to the arctic ocean which dictates a corresponding or even greater increase in the volume of warm water entering the arctic ocean at the surface and cold dense water exiting at depth to the north atlantic such enhanced dense water formation in the arctic ocean could drive the intensified equatorial upwelling implied by the smallgephyrocapsa dominance interval if the above scenario is correct then the climate of the earth s northern hemisphere during the mid pleistocene may have been very different from the younger pleistocene climate one manifestation of this difference may be the mid pleistocene shift in climatic cycle periodicity from 40 ky to 100 ky another important aspect is that the enhanced greenhouse effect expected during the next century because of an increase of atmospheric co2 is thought to lead directly to melting of the arctic ocean ice cover and of the greenland ice sheet thus the greenhouse arctic ocean and its attendant ocean circulation would resemble the inferred mid pleistocene conditions

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

calcareous nannofossil changes during the mid pleistocene revolution paleoecologic and paleoceanographic evidence from north atlantic site 980 981 abstract new quantitative data on calcareous nannofossil assemblages through 583 1138 thousand years ago kyr have been acquired in high sample resolution 2 3 ky at northern atlantic odp ocean drilling program site 980 981 assemblage composition reflects a temperate paleobioprovince suggesting significant influx of warm north atlantic current at the site location during the mid pleistocene transition between marine isotope stage mis 35 and 15 three intervals have been described based on changes in nannofossil composition and abundance fluctuations of taxa reticulofenestrids are abundant just in the first interval mis 35 22 which is also characterised by the absence of gephyrocapsa 4 m and c pelagicus s l the latter occurring in upper mis 24 only the second interval corresponds to the expanded warm mis 21 that is accompanied by high carbonate content absence of both nannofossil reworking and ice rafted debris ird higher abundance of c leptoporus 5 8 m and h carteri and absence of c pelagicus s l and medium gephyrocapsids the third interval mis 20 15 records the occurrence of c pelagicus s l and medium gephyrocapsa generally higher abundance and higher amplitude fluctuations of helicoliths and absence of reticulofenestrids the major changes in nannofossil assemblages seem to be the result of combined paleoenvironmental factors related to sea surface water features temperature and nutrient availability sea ice cover and possibly to deep and intermediate water production of both northern and southern hemisphere origin during glacial and interglacial phases complex inter relationships between environmental parameters and evolutionary ecological factors are inferred to explain the patterns of coccolithus pelagicus subspecies whose distribution and abundance fluctuations are compared with the available patterns of turborotalia quinqueloba and neogloboquadrina pachyderma left coiled at site 980 and with the c pelagicus subspecies patterns from north atlantic dsdp deep sea drilling project site 607 and south atlantic odp site 1090 data collected provide additional information on stratigraphic distribution of selected taxa the first occurrence fo of gephyrocapsa omega is confirmed as a diachronous event even in the atlantic ocean while the first and last common occurrence fco lco of r asanoi appear as diachronous and synchronous events respectively on a global scale

the lower to middle pleistocene valle di manche section calabria southern italy state of the art and current advances the valle di manche vdm section represents one of the best documented on land marine records of the early to middle e m pleistocene transition available to date accordingly the vdm succession is among the few appropriate candidates to host the gssp of the middle pleistocene ionian stage in particular the vdm section uniquely documents the matuyama brunhes magnetic reversal mid mis 19 which is agreed to be the main criterion for defining the chronostratigraphic position of the base of the middle pleistocene the section also yields a wide range of chronological paleoclimatic and stratigraphic data sets that allow long distance correlation with both marine and terrestrial reference records notably the stratigraphy across the mis 19 interglacial is greatly expanded permitting a precise and detailed investigation of this critical interval the section is also easy to reach and fortunately the exposure is destined to persist therefore the section fulfills the essential requirements to host the gssp for the ionian stage and middle pleistocene subseries we suggest that the gssp be placed at the base of the pitagora ash a prominent bed that occurs in mid mis 19 close to the matuyama brunhes magnetic reversal here we present and discuss scientific information gathered in the past two decades and give a preliminary account of the work to which we are presently committed that aims at improving our knowledge on the vdm section

conical folds and apparent rotations in paleomagnetism a case study in the southern pyrenees abstract the so called apparent rotation was defined as the angular deviation between a local paleomagnetic direction after the standard bedding correction and their corresponding paleomagnetic reference j geophys res 85 1980 3659 in this paper we make a theoretical exploration on this concept and we conclude that depending on the number sequence orientation and magnitude of the deformation axes that have affected to the rock volume the apparent rotation may be the addition of a vertical axis rotation plus a spurious rotation the later is an error whose origin is the inappropriate application of the bedding correction during the restoration which does not fit the reverse sequence of deformations then apparent rot s l spurious rot vertical axis rot conical folds are complex geometries that cannot be restored by using the bedding correction however appearance of apparent and spurious rotations has not been studied even though the presence of this kind of folds is very common in fold and thrust belts in this paper we show a way to restore these structures and its associated paleomagnetic data by means of forward modelling on a stereographic projection the modelling has to be based on a good characterization of the geometry fold axis orientation and understanding of the kinematics of the fold general modelling has also allowed us to predict the apparent rotation in conical synclines its magnitude depends on the semiapical angle and on the degree of development of the fold the sense of the rotation clockwise or counter clockwise will depend on the sense of rotation the fold axis the western external sierras provide an excellent case study of apparent rotations due to the presence of a conical fold in the footwall ebro foreland basin of the south pyrenean sole thrust in addition a vertical axis clockwise rotation up to 47 32 in average has been detected in the hagingwall an apparent rotation up to 28 20 in average is observed in the footwall of the structure when a simple bedding correction is used this deviation does not fit with the expected ebro basin direction reference and is caused by the effect of the riglos conical syncline developed by the flexure of the foot wall ramp of the south pyrenean sole thrust the forward modelling carried out considering the geometry and kinematics non significant rotations in the autochthonous foot wall of this structure predicts very well the paleomagnetic observations in the field geographic coordinates with angular departures of only 5 in average the only application of the bedding correction would introduce errors spurious rotations up to 21 12 in average related to the conical geometry that would not allow the differentiation of these distinct structural units

remagnetizations as a tool to analyze the tectonic history of inverted sedimentary basins a case study from the basque cantabrian basin north spain 1 in this work we use syntectonic remagnetization data to determine the synrift geometry of inverted basins this methodology analyzes remagnetization directions in order to obtain the tilting of beds at the moment of the acquisition of the overprint filtering the subsequent compressional deformation we collected samples from jurassic and lower cretaceous limestones and red beds cabuerniga and pas groups in the cabuerniga basin one of the most important mesozoic basins developed near the iberia europe mesozoic plate boundary in northern spain that later inverted during the uplift of the pyrenees these deposits represent the synrift sequence linked to a widespread extensional stage in the iberian basins during the mesozoic all sampled rocks show a normal polarity remagnetization fold and conglomerate tests indicate that remagnetization postdates the main extensional stage of basin formation late jurassic barremian and was acquired before the subsequent compressional deformation the analysis of these overprinted directions allows the basin geometry of the studied area to be restored at the moment of acquisition of the remagnetization this approach represents a powerful tool to study basinal evolution and uplift of sedimentary basins to be tested in other inverted basins with syn extensional related secondary overprints

southern ocean pleistocene calcareous nannofossil events calibration with isotope and geomagnetic stratigraphies abstract several cores recovered from the northern belt of the southern ocean were analysed to study the pleistocene calcareous nannofossil records calcareous nannofossil events previously described in medium and low latitudes were identified and calibrated with the oxygen isotope and geomagnetic time scales although sedimentation rates hiatuses and degree of calcareous nannofossil preservation sometimes prevent the identification and or accurate calibration of some of these events a useful stratigraphic framework was obtained the possibility of using these calibrated events from high to low latitudes facilitates correlations and should facilitate isotope event identification in a region with low temperature where calcareous plankton stratigraphies are in general restricted in general pleistocene southern high latitude calcareous nannofossil events show synchronism with those observed in warm and temperate surficial waters small discrepancies in the assigned ages are sometimes related to low sampling resolution due to low sedimentation rates the first occurrence fo of emiliania huxleyi and the last occurrence lo of pseudoemiliania lacunosa are observed in marine isotope stages mis 8 and 12 respectively a reversal in abundance between gephyrocapsa muellerae and e huxleyi is observed close to the mis 4 5 boundary mis 6 is characterised by an increase in g muellerae and mis 7 features a dramatic decrease in the proportion of gephyrocapsa caribbeanica this latter species began to increase its proportions from the mis 13 14 boundary to mis13 showing diachronism between the different sites the lo of reticulofenestra asanoi is observed at mis 22 confirming this event as a global synchronous reference datum by contrast the fo of r asanoi occurs at mis 35 and is diachronous with the existing data from other oceanic regions a re entry of medium sized gephyrocapsa 3 5 m maximum diameters can be identified in some cores close to mis 25 although the low abundance of this taxon prevents an accurate calibration it may be concluded that this event is diachronous as compared with the existing low latitude data the lo of large morphotypes of gephyrocapsa is well correlated with mis 37 showing synchronism with other oceanic regions whereas the fo of this species is not well calibrated due to the absence of age control points

a high resolution record of the last deglaciation in the sicily channel based on foraminifera and calcareous nannofossil quantitative distribution abstract relative abundance fluctuations in planktic foraminiferal and calcareous nannofossil assemblages are reported on the basis of a high resolution study of odp leg 160 hole 963d drilled in the sicily strait near capo rossello southern sicily with its 8 m of undisturbed sediments the core covers the interval from 1 5 to 23 kyr allowing a 50 100 yr sampling resolution all the short warm and cold events and sub events recorded in this time interval in the grip greenland ice core and at several mediterranean sites were recognized on this basis a total number of nine ecozones based on planktic foraminifera and seven ecozones based on calcareous nannofossils were identified a short interval of climatic amelioration identified above the base of the holocene precedes the segment contemporaneous with the deposition of sapropel s1 which has no lithological expression in the local sedimentary record this segment has been subdivided into the two warm s1a and s1b phases separated by a cold intermediate event a gradual climatic deterioration is recorded above the top of the interval correlated with sapropel s1 it is interrupted by short cold spells tentatively correlated with similar short duration cold events reported for this interval in the recent literature

coccolithophores in surface sediments of the arabian sea in relation to environmental gradients in surface waters abstract one hundred surface sediment samples of the arabian sea indian ocean were investigated and relative abundances of coccoliths were compared to mean annual gradients of temperature salinity chlorophyll po4 and mixed layer depth total coccolith concentrations ranged from 42 106 g sediment in coastal areas to more than 19 000 106 g sediment in oceanic regions the general distribution does not seem to be dependent on coccolithophore productivity in surface waters alone but also on the diluting input of terrigenous material a total of 27 taxa were identified the main species dominating the assemblages were gephyrocapsa oceanica emiliania huxleyi and florisphaera profunda with a combined average abundance of more than 70 several species and species groups reflect with their distribution the environmental parameters of the overlying water masses and may be successfully used to improve palaeoclimatic reconstructions e g a f profunda exhibits a high similarity or even positive correlation to the mean annual mixed layer depth b calciosolenids can be described as coastal or shelf species while temperature and salinity gradients do not seem to be crucial for coccolithophores in this region the mean mixed layer depth as well as the po4 concentration representative for total nutrient availability may control in part the coccolithophore assemblages according to the results of a cluster analysis and the distribution pattern of all species it was possible to differentiate three main coccolithophore assemblages a g oceanica dominated assemblage mainly occurs in the northern part of the study area and can be described as high nutrient assemblage the second assemblage dominated by f profunda may be typical for oligotrophic and stable conditions in open ocean waters a third assemblage with high amounts of coastal species characterises coastal conditions on the shelves

changes in calcareous nannofossil assemblages during the mid pleistocene revolution the distribution of calcareous nannofossils are quantitatively analysed in high resolution deep sea core samples from north atlantic dsdp site 607 and eastern mediterranean odp site 967 between marine oxygen isotope stage mis 35 and 15 in order to observe the response of calcareous nannofossils to the mid pleistocene revolution mpr nannofossil abundance patterns show major variations through mis 25 22 and distinct higher amplitude changes from mis 21 upward sometime clearly correlatable to glacial interglacial cycles high amplitude short term fluctuations of small placoliths and f profunda characterize the interval through mis 24 to 22 21 suggesting strong instability in nutricline dynamics and surface water productivity principal component analysis and shannon weaver indices diversity and dominance highlight significant shifts mainly related to variations in the characteristics of surface waters in both sites a minimum in diversity is recorded at mis 22 21 corresponding to a maximum in the dominance of reticulofenestra spp at site 607 and of pseudoemiliania lacunosa at site 967 above mis 21 the increase in abundance of various taxa c leptoporus umbilicosphaera spp syracosphaera spp rhabdosphaera spp oolithotus spp and a general increase in diversity are related to a distinct trend toward more stable and oligotrophic surface waters in contrast to the higher productivity and less stratified surface waters of the early pleistocene in addition power spectral analysis was performed on calcareous nannofossil abundances shannon index diversity values and factor 1 of principal component analysis these show significant peaks in the obliquity 41 kyr and eccentricity 100 kyr frequency bands indicating that the quasi periodic oscillations in the climate proxy data are controlled by these orbital parameters a relationship between changes in abundance of calcareous nannofossils and production of glacial north atlantic deep water is inferred

paleoenvironmental changes during sapropel 19 i cycle 90 deposition evidences from geochemical mineralogical and micropaleontological proxies in the mid pleistocene montalbano jonico land section southern italy an integrated micropaleontological geochemical and mineralogical study has been performed across the mid pleistocene sapropel 19 i cycle 90 from the montalbano jonico land section southern italy to reconstruct the paleoenvironmental conditions at time of its formation the sapropel interval is characterized by two oxygen depletion phases phase a and c interrupted by a temporary re oxygenation interval phase b the beginning and the end of sapropel deposition are dated at 957 0 81 kyr and 950 0 86 kyr respectively the duration of the interruption is estimated to 0 350 0 32 kyr the multiproxy approach highlights that deposition of sapropel 19 reflects a period of enhanced freshwater runoff induced by a wetter climate as a consequence of a more efficient fluvial erosion a higher terrigenous input mostly ascribable to a southern apennines source and an increased turbidity of surface waters accompanied most of sapropel deposition biotic and abiotic proxies document that different paleoenvironmental conditions occur through phases a c the beginning of phase a is characterized by warm on land paleoclimate as well as warm and oligotrophic surface water conditions during the upper part of phase a temperature starts decreasing and surface waters appear more productive this change probably represents the prelude to cooler and drier conditions characterizing phase b which displays a river supply reduction and an eolian input increase sahara dust during phase c the restored depleted oxygen environment at the bottom sediments is clearly coupled with the re establishment of humid conditions and increased river supply at the same time enhanced mixing of water column a cooler paleoclimate and increased productivity of surface waters are recorded the latter likely favored by the enhanced mixing of water column and also increased delivery of land derived nutrients the end of phase c is marked by a restored normal run off enhanced productivity in surface waters and low oxygen conditions at the bottom sediments persist slightly above phase c the overall results suggest that the onset of sapropel deposition is related to water stratification that caused low oxygen exchanges with the sea bottom although enhanced productivity characterizes most of the sapropel deposition it was not the primary factor triggering sapropel deposition

theory and application of the day plot mrs ms versus hcr hc 2 application to data for rocks sediments and soils 1 new theoretical curves relating the hysteresis parameters mrs ms and hcr hc for single domain sd superparamagnetic sp pseudo single domain psd and multidomain md grains and their mixtures are applied to published data for natural materials the day plot of mrs ms versus hcr hc has been used to crudely classify samples into box like sd psd and md or sometimes incorrectly md sp regions with arbitrary boundaries new type curves for md psd sd md and sd sp grains and mixtures permit more subtle and precise modeling the predicted md trend and its junction with the psd trend are observed in two data sets for magnetite spherules from carbonate rocks and for temperature varying hysteresis results spanning the verwey transition the latter data are the basis of a suggested new method for pinpointing the psd md threshold size selected data for pottery clays soils and paleosols generally follow sd md type curves and indicate intermediate size psd magnetite with narrow to broad size distributions a lake sediment section with known grain size progression tracks in the predicted sense along the sd md trend selected data for glaciomarine and pelagic sediments are also generally compatible with sd md trends examples of remagnetized carbonate rocks submarine basaltic glasses and glassy rims of pillow basalts all follow predicted sp sd or sp psd mixing curves with a large range in volume fraction of sp grains 0 75 but a narrow range of sp particle sizes 10 2 nm larger sp grains spanning the range to sd size 25 30 nm are absent for unknown reasons oceanic dolerites gabbros and serpentinized peridotites in some cases fall in a novel region of the day plot parallel to but below magnetite sd md mixing curves

integrated stratigraphy and astronomical tuning of lower middle pleistocene montalbano jonico section southern italy abstract astronomical calibration of the lower middle pleistocene montalbano jonico section located in the lucania basin southern italy is presented previous papers widely discussed the integrated stratigraphy calcareous nannofossils sapropel stratigraphy benthic and planktonic oxygen stable isotopes and the paleoenvironmental features of this section and its potential suitability for the selection of the middle pleistocene global stratotype section and point gssp in this study new planktonic 18 o data additional biostratigraphical constraints and new tephrochronology on volcaniclastic layers occurring within the studied record are reported the new chronostratigraphic framework provides a robust base for correlation of the oxygen isotope stratigraphy for the montalbano jonico section with the glacial and interglacial fluctuations of the oceanic and mediterranean 18 o reference deep sea records specifically the lower part of the montalbano jonico section interval a provides correlation of the planktonic and benthic 18 o cycles to marine isotope stage mis 36 to mis 23 interval a includes a distinct peak of left coiled neogloboquadrinids the globoratalia crassaformis influx the first occurrence of gephyrocapsa omega and the first common occurrence and last common occurrence of reticulofenestra asanoi these stratigraphical constraints support the tuning of five sapropel layers included in this part of the section to insolation cycles i 112 i 104 i 102 i 90 and i 86 the upper part of the section interval b which includes the temporary disappearance td2 of g omega and tephra layer v5 ar ar age dated at 719 5 12 6 ka is consistent with identification of mis 22 to mis 16 in the planktonic 18 o pattern the 18 o time series of the whole section was reconstructed using the midpoints of individual sapropels and their correlative precession minima visual comparison of the 18 o pattern with the record available at the mediterranean odp site 975 and in the upper part of the section the ar ar age of tephra v5 the developed astronomical tuning revealed that the montalbano jonico section covers an interval from 1240 ka to 645 ka a significant change in sedimentation rate occurs between intervals a 0 53 m ky and interval b 0 91 m ky at about 870 ka and is consistent with a sea level drop from a bathyal to a circalittoral environment bioevents recognised in the montalbano jonico section have been dated according to the astronomical calibration and age assignments of tephra v1 v4 and v6 v9 are also proposed the montalbano jonico section fills the gap between the top of the vrica section and the base of the ionian informal middle pleistocene stage and represents a mediterranean reference section for the mid pleistocene transition

a new kinematic model for iberia further palaeomagnetic and isotopic age evidence abstract palaeomagnetic results and k ar age data from the algarve igneous province have uncovered three ancient relative field components it is inferred that the principal magnetization of the monchique complex with a mean direction of d 42 i 181 95 4 5 was acquired at around the time of the pluton s emplacement some 72 2 ma ago a second magmatic pulse affected the region at 68 2 ma leaving behind a relative field component of d 42 i 341 95 1 7 furthermore an overprinted magnetization characterized by shallow inclination and somewhat smeared northwesterly southeasterly declination most likely originates from the lower tertiary the new palaeomagnetic data are seen in conjunction with previously published upper cretaceous results from the sintra and sines intrusive complexes the resulting database gives entirely new perspectives for evaluating the plate tectonic history of the peninsula in upper cretaceous lower tertiary time a two phase rotation of the iberian micro plate an anticlockwise one of 40 followed by a clockwise one of 70 is clearly in evidence the net clockwise rotation provided a major impetus for the compressive deformation in the pyrenees and the bay of biscay and led to extensive remagnetization of older rock formations in the northern regions of iberia previous palaeomagnetic conclusions in favour of a single anticlockwise rotation of 35 supposed to be directly connected with the formation of the bay of biscay appear to be artefacts which stem from an incorrectly adopted palaeomagnetic reference frame

coccolithophores in the equatorial atlantic ocean response to seasonal and late quaternary surface water variability abstract the present study was initiated to ascertain the significance of coccolithophores as a proxy for paleoceanographic and paleoproductivity studies in the equatorial atlantic data from a range of different samples from the plankton surface sediments as well as sediment cores are shown and compared with each other in general the living coccolithophores in the surface and subsurface waters show considerable variation in cell numbers and distribution patterns cell densities reached a maximum of up to 300 103 coccospheres l in the upwelling area of the equatorial atlantic here emiliania huxleyi is the dominant species with relatively high cell numbers whereas umbellosphaera irregularis and umbellosphaera tenuis are characteristic for oligotrophic surface waters although they are observed in high relative abundances these species only occur in low absolute numbers the lower photic zone is dominated by high abundances and considerable cell numbers of florisphaera profunda the geographical distribution pattern of coccoliths in surface sediments reflects the conditions of the overlying surface water masses however abundances of the oligotrophic species umbellosphaera irregularis and umbellosphaera tenuis are strongly diminished causing an increase in relative abundance of the lower photic zone taxa florisphaera profunda and gladiolithus flabellatus during the past 140 000 years the surface water circulation of the equatorial atlantic has changed drastically as can be seen from changes in the coccolithophore species composition absolute coccolith numbers as well as coccolith accumulation rates significant increases in coccolith numbers and accumulation rates is observed in the southern equatorial atlantic during the last glacial interval oxygen isotope stages 2 4 which we attribute to enhanced upwelling intensities and advection of cool nutrient rich waters at this site in the western equatorial atlantic we observe an opposite trend with decreasing numbers of coccoliths during glacial periods which probably is caused by a deepening of the thermocline

in situ sediment temperature measurements and geochemical porewater data suggest highly dynamic fluid flow at isis mud volcano eastern mediterranean sea isis mud volcano is located on the upper slope of the nile deep sea fan and has been described as the surface expression of a deep seated gas chimney loncke l gaullier v mascle j vendeville b 2002 shallow structure of the nile deep sea fan interactions between structural heritage and salt tectonics consequences on sedimentary dispersal in ciesm ed turbidite systems and deep sea fans of the mediterranean and the black seas ciesm workshop series vol 17 monaco detailed geothermal and geochemical investigations of isis mv have been carried out during the nautinil 2003 and mimes 2004 cruises within the framework of the euro margins mediflux project sediment temperatures of more than 40 c at 10 m below the seafloor at the center of the mud volcano indicate an exceptionally high level of activity rapidly decreasing temperature gradients away from the center support the hypothesis of a dominantly axisymmetric functioning of isis mv the microbathymetry along dive tracks of the submersible nautile reveals the presence of terraces and shows that the temperature gradients at shallow sediment depth follow the morphology at the center porewater profiles are characterized by a rapid decrease of chlorinity within the uppermost meter of the sediments whereas the chlorinity of cores taken at short distances away is equal to bottom water values applying simple analytical models to the data provides evidence of recent mud volcano activity but no straightforward explanation of the observed anomalies which points to a transient regime of variable fluid flow possibly accompanied by episodic mud eruptions numerical modeling suggests that rapid cooling of the sediment column and downward progression of the sharp decrease in porewater chlorinity observed between the two cruises is related to episodic infiltration of bottom seawater into the mud

paleoenvironmental and climatostratigraphic insights for marine isotope stage 19 pleistocene at the montalbano jonico succession south italy abstract quantitative analyses on pollen and ostracods were performed on the montalbano jonico succession mjs through marine isotope stages mis 18 21 in order to acquire details of paleoenvironmental changes and climate pattern during mis 19 which includes the matuyama brunhes paleomagnetic boundary mbb while the mjs does not record the mbb which is the main criterion for defining the early middle pleistocene boundary it is a candidate global boundary stratotype section and point gssp for the ionian stage and middle pleistocene subseries because of its excellent exposure continuous deposition and astronomically tuned record between mis 37 and mis 16 the new 40ar 39ar age of 773 9 1 3 ka for volcaniclastic layer v4 allows the age model for the succession to be refined ostracod assemblages show significant paleodepth fluctuations at the glacial interglacial scale in agreement with the pollen distality index pinus vs caryophyllaceae amaranthaceae and ephedra which also suggests higher values during mis 19 pollen analysis provides supplementary paleoclimate data that are valuable to reconstruct temperature variation during the identified phases a major expansion of steppic vegetation at 790 ka in the uppermost mis 20 correlates with a significant cold and arid northern hemisphere climate phase as documented by a concurrent peak both in north atlantic ice rafted debris and mediterranean dust records climate conditions recorded in mis 19 3 were similar to those of the present interglacial whereas a dry climate phase marks mis 19 2 at 771 84 ka slightly above the v4 layer millennial scale climate variability occurred during mis 19 as evidenced by two abrupt short term moderately dry pollen events at 783 5 ka and 774 8 ka that could be related to a period of reduced geomagnetic field intensity through the mbb transition additional environmental chronological events accompanied this stratigraphic interval i the volcaniclastic layers v3 and v4 radiometrically dated at 801 2 19 5 ka and 773 9 1 3 ka respectively ii the co occurrence of maximum flooding and thermal maximum in agreement with the previously recorded co occurrence of the neopycnodonte community and tropical subtropical mesopelagic teleostean bonapartia pedaliota close to the increase of quercus and iii the maximum depth md between 777 3 and 773 25 ka as recorded by outer shelf upper slope macroinvertebrate fauna close to the highest value of pollen distality index in mis 19 results enhance the understanding of orbital suborbital paleoenvironmental change during the mid pleistocene and particularly of the climate pattern during mis 19 and across the mbb

geomorphology and tectonics of uplifted coasts new chronostratigraphical constraints for the quaternary evolution of tyrrhenian north calabria southern italy abstract the tyrrhenian coastal sector of north calabria stretching between torre s nicola and the lao river belongs to the inner extensional sector of the neogene apennines thrust belt it is characterised by a stair of quaternary marine and fluvial terraces representing the geomorphic response to the interaction between the quaternary sea level fluctuations and the regional trend of tectonic uplift experienced by the margins of the tyrrhenian back arc basin since the last century several authors studied the north calabria coasts where the flight of terraces preserves significant marine and continental successions and proposed several paleo geomorphological and tectonic reconstructions in this paper we present a new stratigraphic and morphostructural setting of the north calabria coasts based on both chronostratigraphical constraints obtained from marine deposits and detailed geomorphological analysis a ten order stair of marine terraces stepping between 240 and 0 m a s l was recognized and time constrained by the age of the fornaci s nicola marine succession which was ascribed by integrated paleoecological biostratigraphical and paleomagentic analyses to the early middle pleistocene mis 19 15 in particular the 240 200 and 160 m a s l high strandlines were ascribed to the early pleistocene and the ones between 100 and 15 m a s l to the middle pleistocene the total amount of the vertical motion experienced by the studied area was estimated and evaluation of the average rates of uplift for the middle and late pleistocene times were also given considering the elevation a s l of the oldest terraces a tectonic uplift of at least 240 m was calculated for the north calabria coasts since the early pleistocene times 100 m of which gained from the beginning of the middle pleistocene on the other hand the 8 m high late pleistocene strandlines display a negligible vertical displacement affecting the area during the last 130 ka the entire staircase of terraces preserves a record of slowing down in the rate of uplift which attained an average value of 0 15 mm year during the middle pleistocene

evidence of a cretaceous remagnetization in the cameros basin north spain implications for basin geometry abstract the paleomagnetic results obtained in 23 sites from red beds of the northern border of the inverted cameros basin northern iberian peninsula prove a cretaceous widespread remagnetization paleomagnetic and rock magnetic analyses indicate that the natural remanent magnetization nrm is dominated by a stable and always normal polarity component carried by haematite two conglomerate test and five fold test indicate that this component is a syn tectonic overprint dated between albian and santonian times most probably albian contemporary with a low grade metamorphism remagnetization was acquired before compressional deformation and post dates the main extensional stage of basin formation berriasian albian incremental fold tests provide best clustering solutions showing dispersed results and far from the expected direction an alternative procedure to obtain fold test solution was applied considering asymmetric limb rotation mean directions obtained from these asymmetric solutions are consistent with the expected direction and yield a statistical value for significant grouping at the 95 confidence level in all fold tests performed this reconstruction allows to determine the tilting of beds at the moment of acquisition of magnetization these original dips were used to reconstruct the original geometry of the northern basin border later modified during the tertiary inversion stage this extensional geometry can be characterised as a large scale syn sedimentary normal fault drag with a minor roll over anticline the procedure developed in this paper should be tested in other inverted basins that also have undergone burial remagnetizations

the valle di manche section calabria southern italy a high resolution record of the early middle pleistocene transition mis 21 mis 19 in the central mediterranean abstract the on land marine valle di manche section crotone basin calabria southern italy one of the candidates to host the gssp of the middle pleistocene ionian stage preserves a manifold record of independent chronological paleoclimatic and stratigraphic proxies that permit a straightforward correlation with marine and terrestrial reference records at the global scale in particular the section holds an excellent record of the matuyama brunhes magnetic reversal which occurs in the midst of marine isotope stage mis 19 we report on a complete revision of the section that improves dramatically the available dataset especially in the stratigraphic interval straddling the lower middle pleistocene boundary our benthic 18o record provides evidence that the matuyama brunhes transition the stratigraphic position of which is marked by a prominent tephra the pitagora ash occurred during full mis 19 in agreement with many records worldwide we obtained an age of 786 9 5 ka for the matuyama brunhes magnetic reversal and pinpointed the paleomagnetic transition of to a 3 cm thick interval indicating that the event was very fast since the section fulfills all the requirements to host the gssp of the ionian stage we propose that the boundary should be placed at the base of the pitagora ash ca 12 5 cm below the midpoint of the matuyama brunhes reversal

a paleoecological and paleobiogeographic evaluation of helicosphaera inversa gartner theodoridis and the diachrony of its first occurrence abstract the distribution pattern of helicosphaera inversa gartner theodoridis is examined from a mid latitude north atlantic core md01 2446 and two mediterranean cores ocean drilling program odp site 975 and core kc01b through marine isotope stage mis 13 to 9 the earliest rare occurrences are observed from the uppermost part of mis 12 while common and continuous abundances characterize mis 11 the paleoenvironmental framework of the study cores suggests that the taxon thrived in warm surface waters correlation with new data from planktonic foraminifera also suggests that h inversa may have only flourished within a limited salinity range comparison with previous findings highlights major diachrony in the fo of the taxon between low and mid latitude records it first occurred at lower latitude in the pacific as early as 0 8 ma while in the mid latitude north atlantic regions it is not recorded before 0 51 ma the distribution of the taxon in the north atlantic ocean also apparently varies in relation with surface water masses and hydrographic fronts the results suggest that the fo of h inversa is ecologically controlled and needs to be used with caution in worldwide stratigraphic correlation nevertheless the distribution of the species within the mediterranean basin can produce an invaluable ecostratigraphical signal

extant calcareous nannoplankton in the australian sector of the southern ocean austral summers 1994 and 1995 abstract living calcareous nannoplankton in the region between australia and antarctica are distributed in five assemblages associated with distinct physico chemical properties of surface and subsurface water masses temperature and salinity ranges for living assemblages were 2 15 7 c and 33 7 35 56 respectively with maximum cell densities for austral summer 1994 found at 9 63 c and 34 44 and for austral summer 1995 at 12 8 c and 35 17 nutrients phosphate silicate and nitrate increase poleward and vertically from surface to depth abundance and diversity of calcareous nannoplankton decrease in a poleward direction with major shifts located across both the subtropical and the subantarctic fronts higher cell densities were found below 50 m equatorward of the subtropical front and above 50 m poleward of this front poleward of the antarctic divergence coccolithophores are absent from all samples three different morphotypes of emiliania huxleyi were identified one of which has a distribution associated with the subtropical front of the subordinate species syracosphaera spp calciosolenia murrayi and umbellosphaera tenuis dominate equatorward of the subtropical front with syracosphaera spp and calcidiscus leptoporus dominant poleward of this front a peculiar community of weakly calcified species is recorded for the first time outside the weddell sea

syntectonic remagnetization in the southern methow block resolving large displacements in the southern canadian cordillera 1 the upper cretaceous ventura member of the goat wall unit in the southern methow block of southern british columbia and northern washington state holds a syntectonic magnetization eight new sites from manning park in british columbia give a mean direction of d 27 5 i 60 1 k 304 7 95 3 2 after optimal partial tilt correction of five groups of bedded sites from farther south in the basin reported by bazard et al 1990 four have a syntectonic remanence with a direction similar to what we observe the exception is one group which has optimal concentration of remanence directions on 100 untilting and an abherent direction which must be rejected combining the accepted sites the optimal differential syntilting direction is d 11 8 i 61 5 k 39 3 95 3 4 n 47 giving a mean pole of 79 8 n 359 2 e k 19 5 and a95 4 8 the age of the remagnetization is constrained to be between 88 and 80 ma compared to cratonic north america this result indicates that the southern methow block was displaced from the south by 1800 500 km meaning it lay south of the sierra nevada subduction zone but well north of other paleomagnetically constrained cretaceous rock units from the insular superterrane including correlative strata of the mount tatlow area in the northern methow block among several possibilities to reconcile this discrepancy the most plausible has the whole methow block translated coherently but with the southern methow block strata remagnetized during transit

floral and solution patterns of coccoliths in surface sediments of the north pacific coccolith assemblages from core top samples of the north pacific seafloor follow the distribution of surface water masses gephyrocapsa caribbeanica umbellosphaera tenuis and coccolithus pelagicus are the most important identifiers of surface water mass different multivariate statistical techniques group shallow samples in somewhat different spatial patterns factor analysis condenses the information contained in sixteen ies percentages to four new variables that can be interpreted as species assemblages by canonical correlation analysis these assemblages can in turn be related to the environment the first canonical correlation indicates that factor 2 the g caribbeanica assemblage is represented in samples underlying cooler surface water a second possible correlation describes a direct relationship between factor 3 the umbilicosphaera sibogae assemblage and the remaining environmental variable surface water salinity factor 1 the g oceanica assemblage and factor 4 the emiliania huxleyi assemblage are not as closely related to the selected environmental measures of temperature salinity dissolved oxygen and inorganic phosphate phosphorus as are factor 2 and factor 3 because samples were coded according to their overlying water mass group separations produced by discriminant analysis are easily interpreted in terms of the environment overlap of group assignments occurs for samples from the south china sea and extreme western pacific even partially dissolved samples retain the signature of surface water mass group assignment for those samples is generally reliable with the exception of samples from the central water mass where almost half of the shallow and half of the deep samples show strongest affinities with one of the other three water masses selective solution therefore only partially obscures the record of floral provinciality partial dissolution of coccolith assemblages does not proceed according to one systematic rank order the sequence of species removal is variable from region to region the more abundant species tend to consistently appear at an extreme of the ranking for example umbilicosphaera sibogae is among the least resistant and c leptoporus and g oceanica are among the most resistant species maximum depths of coccolith lysocline and compensation depth occur generally in the central part of the basin and shoal towards its margins as previously observed for planktonic foraminifera

the warm interglacial marine isotope stage 31 evidences from the calcareous nannofossil assemblages at site 1090 southern ocean article i nfo calcareous nannofossil assemblages have been investigated at ocean drilling program odp site 1090 located in the modern subantarctic zone through the pleistocene marine isotope stages mis 34 29 between 1150 and 1000 ka a previously developed age model and new biostratigraphic constraints provide a reliable chronological framework for the studied section and allow correlation with other records two relevant biostratigraphic events have been identified the first common occurrence of reticulofenestra asanoi distinctly correlated to mis 31 32 the re entry of medium gephyrocapsa at mis 29 unexpectedly similar to what was observed at low latitude sites the composition of the calcareous nannofossil assemblage permits identification of three intervals i iii intervals i and iii correlated to mis 34 32 and mis 30 29 respectively are identified as characteristic of water masses located south of the subtropical front and reflecting the southern border of subantarctic zone at the transition with the polar front zone this evidence is consistent with the hypothesis of a northward shift of the frontal system in the early pleistocene with respect to the present position and therefore a northernmost location of the subantarctic front during interval ii which is correlated to mis 31 calcareous nannofossil assemblages display the most significant change characterized by a distinct increase of syra cosphaera spp and helicosphaera carteri lasting about 20 ky an integrated analysis of calcareous nannofossil abundances and few mineralogical proxies suggests that during interval ii site 1090 experienced the influence of subtropical waters possibly related to a southward migration of the subtropical front coupled with an expansion of the warmer agulhas current at the core location this pronounced warming event is associated to a minimum in the austral summer insolation the present results provide a broader framework on the mid pleistocene dynamic of the ocean frontal system in the atlantic sector of the southern ocean as well as additional evidence on the variability of the indian atlantic ocean exchange