new findings of bronze age homogenites in the ionian sea geodynamic implications for the mediterranean abstract holocene homogenites similar in character and stratigraphic position to those previously recorded in the ionian basin and related to the gigantic tsunami originating from santorini bronze age eruption are described from a core transect crossing the deformation front of the mediterranean ridge east of victor hensen seahill investigations on grain sizes and carbonate content carried out on three cores from three different areas of the ionian basin encompassing the bronze age homogenite revealed important similarities and some differences the most obvious difference concerns the carbonate content which is minimum at the base of the unit in a core close to the messina abyssal plain whereas it is maximum in cores from the western mediterranean and calabrian ridges characterized by the typical cobblestone topography a terrigenous versus pelagic nature of the components is documented and a distal versus local provenance is inferred homogenites are critically compared with unifites a type of re sediment recently described from the eastern mediterranean comparison includes in particular a source and sediment transport and b triggering mechanism a substantial difference exists between the sedimentation patterns of the ionian and levantine basins seaward of the calabrian and hellenic arcs in the latest quaternary and the difference contains a clear geodynamic message sedimentation rates increase from the late pleistocene to the holocene in the ionian basin whereas they decrease in the levantine basin the glacio eustatic signal is well expressed in the levantine basin where the source areas are situated consistently in the south or on a passive type aseismic continental margin north african margin in the ionian basin on the contrary the glacioeustatic signal is totally obscured by the strong tectonic signal from the active northern continental margin of the mediterranean

the rise and demise of podozamites in east asia an extinct conifer life style abstract in the late triassic early jurassic forests dominated by podozamites an apparently deciduous shoot dropping conifer with broad multi veined leaves were extensive in what were the mid latitudes of eastern asia podozamites was the only conifer in many forests of this region and at times appeared to have formed an almost mono specific vegetation podozamites appears to have been little effected through the triassic jurassic transition but responded to climate changes later in the jurassic the chinese region progressively dried through the middle jurassic and aridity had developed in some areas by the late jurassic early cretaceous the centre of distribution of podozamites shifted north to the siberian region where conditions remained wet there it typically coexisted with conifers having a diverse range of smaller leaf morphologies by the late albian angiosperms had arrived in the siberian area and risen to dominance some time after this event podozamites became extinct this is significant as it represents the permanent extinction of a unique lifestyle a deciduous broad leaved and multi veined conifer the broad history of podozamites raises some interesting issues 1 the existence of a large dominantly deciduous vegetation at mid latitudes in the late triassic early jurassic is little discussed 2 it is unexpected that as broad leaved angiosperms took over amongst the conifers it was the broad leaved multi veined podozamites that became extinct this is the morphology that might have been expected to compete with the apparently more shade forming angiosperms instead it was the smaller leaved and single veined conifers that remained to coexist with the angiosperms

holocene earthquake records from the cascadia subduction zone and northern san andreas fault based on precise dating of offshore turbidites abstract we present preliminary evidence for a 10 000 year earthquake record from two major fault systems based on sediment cores collected along the continental margins of western north america new stratigraphic evidence from cascadia demonstrates that 13 earthquakes ruptured the entire margin from vancouver island to at least the california border since the eruption of the mazama ash 7700 years ago the 13 events above this prominent stratigraphic marker have an average repeat time of 600 years and the youngest event 300 years ago coincides with the coastal record we also extend the record of past earthquakes to the base of the holocene at least 9800 years ago during which 18 events correlate along the same region the sequence of holocene events in cascadia appears to contain a repeating pattern of events a tantalizing first look at what may be the long term behavior of a major fault system the northern california margin cores show a cyclic record of turbidite beds that may represent holoce

sedimentological record of tsunamis on shallow shelf areas the case of the 1969 ad and 1755 ad tsunamis on the portuguese shelf off lisbon one of the aims of the sedport project esf euromargins eurocores program was to investigate the depositional features on the shelf and upper slope of the portuguese margin tagus system during the holocene to fulfill the objectives two shallow box cores and two sedimentary sequences were studied po287 26b and the spliced sequence of sites d13902 po287 26g recovered on the portuguese continental shelf ssw off the tagus river mouth and the box po287 28b and gravity core geob8903 collected towards the w of the river mouth magnetic susceptibility grain size and xrf fe data as well as 210 pb and ams 14 c dating of these sedimentary sequences have allowed the identification of an instantaneous deposit at about 20 cm in the box cores downcore we could establish a hiatus corresponding to 355 yr of sedimentation at both sites a 39 cm instantaneous deposit of coarse material including carbonate broken shells on the ssw site and a 1 5 m instantaneous deposit of fine material on the w site both hiatus and instantaneous deposits are considered to be of tsunamigenic origin the box cores deposit has an estimated age of 1969 ad and it is attributed to the 1969 earthquake caused tsunami the hiatus and deposits found downcore are due to the age limits encountered believed to represent the tsunami related to the 1755 lisbon major earthquake these data further indicate a sediment deposit similar in type and thickness on both ssw and w sites in 1969 while the 1755 ad record indicates a higher energy backwash along the ssw and a preferential deposition of fine suspended matter towards the w c 2007 elsevier b v all rights reserved

the effects of the november 1 1755 lisbon earthquake in morocco abstract the lisbon earthquake of november 1 1755 the effects of which have been described at length in the iberian peninsula was likewise strongly felt in morocco especially on the atlantic coast which was laid waste not only through the direct agency of seismic waves but also through that of a formidable tsunami the study of these effects in morocco based on a critical analysis of european and arab sources entailing whenever possible a consultation of the original sources has lead to the hypothesis that two distinct destructive earthquakes would have followed the main shock of november 1 one on november 18 1755 was probably an aftershock of the november 1 event and originated in the gorringe bank the other on november 27 1755 was located in the meknes area and is supposed to have destroyed that town the values of intensities interpreted from the observations of the november 1 event have been compared with the values derived from the attenuation laws obtained from the recent earthquake of february 28 1969 originating at the same source the moroccan isoseismals of which are well established extrapolated isoseismals for the effects of the november 1 1755 event in morocco as derived from this study are then assigned

an ams radiocarbon method to determine the emplacement time of recent deep sea turbidites abstract this paper reports the evaluation of a novel method based on accelerator mass spectrometer ams radiocarbon dating of planktonic foraminifera to evaluate the times of emplacement of recent deep sea turbidites it assumes that the standing stock of relatively large 150 m planktonic foraminifera in the bioturbated surface mixed layer of box cores represents an integration of the flux from the water column since the turbidite was emplaced and exploits the potential of the ams method to analyse the resultant small samples which can be readily separated the method is evaluated by application to three atlantic turbidites which form the present day sediment surfaces on the horseshoe madeira and tagus abyssal plains the time of emplacement of madeira abyssal plain turbidite is estimated at 1120 730 and 870 years before present each 120 140 years in three different cores the resultant weighted mean emplacement time 930 76 years before present is somewhat older than previous estimates by geochemical methods the times of emplacement for the horseshoe 240 and 140 years before present each 120 years and tagus 300 120 years before present abyssal plains are both consistent with initiation by the lisbon earthquake of 1755

chronology of palaeoclimatic change at the end of the last glaciation analysis of sediments recorded in a piston core located east of southern north island new zealand gives a detailed record of climate change at the end of the last glacial accumulation rates1 of both detrital quartz and biological carbonate and biogenic silica components of the sediment are much higher during glacial than post glacial time and they all show a synchronous rapid decline at 14 700 yr bp we attribute this to a decline in intensity of the strong glacial westerly winds in the new zealand region as the polar winds contracted to their present latitudes2 6 the greatest rate of quartz accumulation occurs between 16 200 and 14 700 yr bp and is not matched by any change in carbonate or silica accumulation we believe this reflects accelerated fluvial transport of detritus out of the mountain ranges and consequently increased aeolian dust transport before the decline of the polar westerlies

neogene through quaternary tectonic reactivation of sw iberian passive margin southwest portugal the gulf of cadiz and morocco are under the potential threat of natural hazards linked to seismicity and tsunami generation we report the results of two multi channel seismic mcs surveys carried out in 1992 and 1998 along the continental margin and oceanic crust of sw iberia this mcs data set shows the evidence of the compressional deformation which involves both the continental and the oceanic crust of the study area the area of deformation extends from the southern border of the tagus abyssal plain to the seine abyssal plain encompassing the continental margin of sw portugal most of the structures observed are probably related to a mid miocene phase of africa europe plate convergence in this paper we discuss the recent advances on the identification of the tectonic structures that are still active and that may generate great earthquakes and tsunamis the tectonic structures identified are located respectively at the guadalquivir bank along the eastern border of the horseshoe abyssal plain and along the southern continental slope of sw portugal

a thick holocene homogenite from the ionian abyssal plain eastern mediterranean abstract a homogenite layer thicker than 12 m holocene in age occurs in the ionian abyssal plain the graded sandy base is 1 3 m thick most of the layer is structureless and homogeneous in grain size and mineral composition the most remarkable components are siltsized grains composed of aragonite needles they are interpreted as skeleton fragments of the green alga halimeda sp the homogenite covers an area of at least 1100 km 2 and assuming a minimum thickness of 10 m comprises a volume of 11 km 3 the source of the material of the homogenite is a matter of speculation very likely it has been remobilized from different areas around the ionian abyssal plain as triggering event a tsunami generated by the collapse of the santorini caldera about 3500 yrs b p is assumed

abyssal ne atlantic benthic foraminifera during the last 15 kyr relation to variations in seasonality of productivity abstract benthic foraminiferal faunas 63 m and stable isotopes from the last 15 kyr were studied in bengal programme high resolution temporal and spatial study of the benthic biology and geochemistry of a north eastern atlantic abyssal locality kasten core 13078 16 from the porcupine abyssal plain ne atlantic 48 49 91 n 16 29 94 w water depth 4844 m changes occurred in the accumulation rates species composition diversity and stable isotopes during the last 15 kyr today the area is strongly influenced by seasonal inputs of phytodetritus following the spring blooms in surface water primary productivity variations in the relative abundance of the two most abundant species epistominella exigua and alabaminella weddellensis which today show significant increases in abundance with the presence of phytodetritus on the sea floor are interpreted as resulting from changes in the seasonality of productivity seasonal productivity was higher during the holocene than during the last deglaciation and younger dryas probably coinciding with the retreat of the polar front to higher latitudes this hypothesis is consistent with simultaneous decreases in the percentage of the polar planktic foraminifera neogloboquadrina pachyderma s and increases in the percentage of globigerina bulloides a warmer water planktic foraminifera indicative of phytoplankton blooms and enhanced productivity the relative abundance of the phytodetritus species e exigua and a weddellensis covary between 14 7 and 8 1 kyr but not between 7 8 and 1 2 kyr major decreases in the numbers per gram and accumulation rates of planktic and benthic foraminifera occurred at 12 8 5 kyr and at 4 kyr which correspond to decreases in the sediment coarse fraction and published data on inorganic carbon contents suggesting that dissolution may have increased at these times relationships between benthic foraminiferal faunas and benthic stable isotope records suggest no simple relationship between faunal abundances and test isotope chemistry for example the abundances of phytodetritus species do not show strong correlations with either the 13c values of e exigua or the 13c e exigua p wuellerstorfi record which have previously been suggested as indicative of seasonality of productivity

mixing sedimentation rates and age dating for sediment cores abstract analytic solutions to the advection diffusion equation useful as a guide for the interpretation of mixing sedimentation rate and age dating effects in sediment cores have been derived various simplified mixing models appropriate to 14 c and 210 pb measurements have been considered the emphasis has been on a discussion of the various interrelations and dependencies among the mixing coefficient sedimentation rate and radioactive decay constant parameters in determining the 14 c and 210 pb concentrations as a function of depth porosity variations within the sediment column are also considered and the transformed advection diffusion equation including porosity effects is derived

holocene earthquake record offshore portugal sw iberia testing turbidite paleoseismology in a slow convergence margin the sw margin of the iberian peninsula hosts the present day boundary between the eurasian and african plates convergence 4 5 mm yr is accommodated through a wide deformation zone characterized by moderate magnitude seismic activity this zone has also been the source of the most important seismic events in western europe such as the 1755 lisbon earthquake and tsunami and 1969 horseshoe earthquake despite efforts to identify active seismogenic structures in the gulf of cadiz in the last ten years little is known about its paleoseismic history the turbidite paleoseismology approach was applied for the first time in a low rate convergent margin to determine the recurrence interval of large earthquake events that occurred in sw iberia during the holocene four sediment cores collected at strategically located sites offshore portugal i e tagus abyssal plain infante don henrique basin and horseshoe abyssal plain reveal that these deep sea basins preserve a record of episodic deposition of turbidites in the sw iberian margin excluding special climatic events earthquakes are the most likely triggering mechanism for synchronous widely spaced distributed turbidites during the holocene when the sea level was relatively stable age correlation together with textural mineralogical physical properties and geochemical signatures of the new cores complemented by pre existing multicores and gravity cores reveals a total of 7 widespread turbidite events for the holocene precise dating of the most recent turbidite event e1 based on

comparative behavior of authigenic re u and mo during reoxidation and subsequent long term burial in marine sediments the trace element re is enriched in mildly reducing suboxic sediments close to or slightly later in the redox sequence than u and before reduction of mo in more reducing sulfidic sediments this work investigates the behavior of authigenic re during oxidation and long term burial in the sediments of several turbidites from the madeira abyssal plain exposure to bottom water o2 clearly remobilizes authigenic re as found in previous work but reimmobilization occurs in reducing sediments below the oxidation front over a depth range of 0 5 3 m the large spread of the re burndown peak must be kinetically controlled perhaps influenced by the corg content once reimmobilized however the authigenic re signal remains immobile for at least 3 4 myr authigenic u in contrast consistently forms peaks 0 5 m broad whereas authigenic mo is lost on oxidation and does not appear to be refixed unless authigenic pyrite is formed these results imply that any paleoenvironmental significance of authigenic re will be compromised in low sedimentation rate environments 10 cm kyr where there is significant exposure of authigenic re to bottom water o2 however authigenic re records from rapidly accumulating continental margin sediments with much less exposure to bottom water o2 still offer considerable potential as high fidelity recorders of past reducing conditions

tsunami induced sediment transport in the abyssal mediterranean sea an unusual stratigraphic unit nicknamed homogenite fills topographic lows in the complex ridge and trough bathymetry at two survey sites on the western mediterranean ridge and the calabrian ridge on near bottom 4 khz seismic reflection profiles this unit us an acoustically transparent near surface flat lying layer whereas in cores it is a homogeneous gray marl as much as 7 m thick grain size decreases upcore within the unit implying that it was deposited in a single event controlled by gravitational settling the stratigraphic position of the homogenite relative to a firmly dated sapropel bed suggests emplacement between 4400 and 3100 yr b p the source of the homogenite is inferred to be the nearby basin walls farther east two other sites with similar rugged topography lack homogenite entirely a triggering mechanism is required which is capable of initiating massive sediment transport simultaneously in many separate basins at the western two survey sites but which is not effective at the eastern sites a large archeologically recorded earthquake of the correct age is considered and rejected because its epicenter is closer to the nonhomogenite bearing sites than to the sites where this sediment type was observed and because several other earthquakes of comparable magnitude have since been recorded in the area whereas the homogenite is unique the 3 500 yr b p collapse of the caldera of the volcano of santorini caused a huge tsunami which is recorded archeologically and geologically around the eastern mediterranean because of refraction of the tsunami by the bathymetry and because the caldera collapsed in its southwest corner a disproportionate amount of tsunami energy was directed toward the western area where homogenite is observed in contrast the homogenite free sites were relatively sheltered an order of magnitude calculation shows that the near bottom oscillating currents accompanying the santorini tsunami were at or above the threshold erosion velocity at the homogenite bearing sites in addition the near bottom pressure pulse under the tsunami at the homogenite bearing sites was sufficient to cause liquefaction of sediments neither mechanism was adequate to cause sediment transport or slope failure at the homogenite free sites

particle mixing rates in sediments of the eastern equatorial pacific evidence from 210pb 239 240pu and 137cs distributions at manop sites abstract particle mixing rates db calculated from excess 210pb gradients in sediments of the east equatorial pacific range from 0 04 to 0 5 cm2 y with variation of a factor of 3 4 at a single site diffusion of the 236ra daughter 222rn may affect 210pb distributions under conditions of slow mixing and low 210pb flux to the seafloor as shown by a siliceous ooze clay core which contained the fallout radionuclides 239 240pu and 137cs but no excess 210pb relative to 226ra there is no clear relationship between 210pbderived mixing rates and sediment type accumulation rate or organic carbon flux to the sediments comparison of 210pb mixing rates with those calculated from 239 240pu and 137cs distributions reveals better agreement for a pulse input of the fallout radionuclides db 0 03 0 4 cm2 y than for continuous input at a constant rate db 0 1 1 6 cm2 y although the pu and 137cs data are better fit by the latter model the agreement may be fortuitous because 239 240pu and 137cs appear significantly deeper than 210pb in at least one core tracer separation could be caused by particle size selective mixing by the benthic fauna or by chemical mobilization if the fallout radionuclides are scavenged from surface waters by large organic rich particles such as fecal pellets their release and migration may result from decomposition of the carrier in surface sediments either a relatively unreactive form of pu e g oxidized pu has been released by this process or a one dimensional model is inadequate to explain its observed penetration into the sediments activity ratios of 239 240 pu 137 cs in the sediments decrease with increasing north latitude and the trend reflects higher fluxes of 239 240pu near the weapons test site at christmas island 2 n the 239 240 pu 137 cs ratios and fluxes to the sediment assuming constant input at the siliceous ooze red clay site are consistent with published sediment trap data from a nearby site thus if fallout radionuclide fluxes to the sea floor were higher in the past both 239 240pu and 137cs have been released from sinking particles

palaeoenvironment and ecology of the middle cretaceous grebenka flora of northeastern asia the grebenka flora from the main exposure of the albian cenomanian krivorechenskaya formation in northeastern russia represents a range of plant communities from pioneer to mature forest that grew close to the mid cretaceous north pole 72degreesn the diversity of this flora is dominated by angiosperms followed by conifers ferns and other plant groups the age is constrained by ar 40 ar 39 analyses of associated volcaniclastics similar to 96 5 ma coupled with biostratigraphic correlation of the plant bearing non marine beds with marine units of the krivorechenskaya formation and the overlying dugovskaya formation limited palaeosol development and pronounced episodic floodplain aggradation indicate that the 100 m thick plant bearing volcaniclastic floodplain succession was deposited rapidly resulting in excellent trapping and preservation of the plant communities but dilution of the palynoflora analysis of the megaflora 100 foliage taxa plus woods and fructifications provides a snapshot of the mid cretaceous climate and offers reliable quantitative climatic signals of conditions near the mid cretaceous north pole multivariate analysis of leaf physiognomy climate leaf analysis multivariate program on the whole flora suggests that the plants experienced a mean annual temperature of 13 0 1 8degreesc and a cold month mean temperature of 5 5 3 3degreesc however analyses of individual florules yield slightly different results that help constrain the uncertainties inherent in such an approach these and other foliar physiognomic data are compared across the arctic less

mesozoic ecosystems climate and biotas this issue of palaeogeography palaeoclimatology palaeoecology is devoted to papers on mesozoic ecosystems and is an outcome of the international geoscience program igcp 632 igcp is a joint opera

biological pumping upwards of the coarse fraction of deep sea sediments abstract in a restricted part of an area intensively sampled by box coring approximately 50 samples from a 2 4 km rectangle a stiff muddy glacial gravel till is encountered at a depth of 30 40 cm x radiographs of the upper 15 to 20 cm of the cores reveal gravel in overlying foraminiferal mud only from the area where there is the deeper till layer the localization strongly suggests that the material in the top of the cores has its source in the deeper layer i postulate that burrowing organisms move gravel upward by pushing aside the particles that are too large to be eaten because the strength of the enclosing mud decreases upwards the gravel particles move preferentially upward the upward decrease in shear strength of he sediment is rapid at an interface occurring 4 cm below the surface on average thus hydrostatic pressures of 20 to 200 g cm2 exerted by vermiform burrowing animals act within an environment of asymmetrical sediment property permitting an asymmetrical response to the uniformly directed body pressure this asymmetrical response a pumping mechanism affecting material that does not pass through the gut is contrasted with the mixing of finer sediments that are eaten and excreted documented by many other workers dimensional arguments suggest the flux of material is related to the ratio of biological mixing rate to sedimentation rate the mechanism is also applicable to maintenance of mn nodules and their nuclei at the surface if macrofossils have behaved like gravel some s ell beds may have been generated and some stratigraphic anomalies caused by this means

on the behavior of boundary undercurrents near canyons a simple finite froude number quasi geostrophic frictionless model is developed to study the response of a boundary undercurrent such as the california undercurrent to variations in the underlying topography despite its baroclinic nature the flow tends to follow contours of total depth although this pattern of response is not fully achieved over deep narrow canyons the flow separates from the bottom another simple model containing stratification and frictional effects predicts upwelling to occur in the underlying water within the canyon

cheirolepidiacean foliage and pollen from cretaceous high latitudes of southeastern australia cheirolepidiaceae leaves and pollen are recorded from valanginian albian strata of southeastern australia that were deposited at high latitudes under cool moist climates in contrast to the semi arid or coastal habitats preferred by many northern gondwanan and laurasian representatives of this group leaves of this family are characterized by thick cuticles and cyclocytic stomata with randomly oriented apertures arranged in scattered or longitudinal rows or bands stomata are deeply sunken and surrounded by four to six subsidiary cells that bear one or two ranks of prominent overarching papillae which may constrict the mouth of the pit three new taxa otwayia denticulata tosolini cheirolepidiaceae cuticle sp a and sp b are distinguished based on cuticular features adding to several previously documented cheirolepid conifers in the early cretaceous of eastern australia cheirolepidiaceae foliage is preserved predominantly in fluvial floodbasin settings and is interpreted to be derived from small trees occupying disturbed or low nutrient sites the foliage is associated with classopollis corollina pollen and roots characterized by prominent mycorrhizal nodules a cenomanian classopollis type recognised from bathurst island northern australia is recorded for the first time from the early cretaceous eumeralla formation otway basin classopollis locally is rare in valanginian barremian strata of boola boola gippsland but constitutes up to 14 of the palynomorph assemblage in albian strata this indicates that the family was locally abundant in cool southern high latitude climates of the mesozoic contrary to previous reports of its rarity in this region

mid cretaceous floras and climate of the russian high arctic novosibirsk islands northern yakutiya abstract two mid cretaceous floras collected in terrigenous and volcaniclastic deposits of the novosibirsk islands in the russian high arctic were studied these floras are the most poleward mid cretaceous floras known and existed at palaeolatitudes up to 82 85 n these represent our best insight into polar conditions at one of the warmest intervals in earth history an albian flora from the balyktakh formation of the kotel nyi island comprises 40 species of ferns bennettites cycadophytes ginkgoaleans czekanowskialeans conifers and gymnosperms incertae sedis this flora is most similar to the albian buor kemuss flora widespread in the arctic siberia and alaska and to a lesser extent to the aptian silyap flora of siberia a turonian flora from the derevyannye gory formation on the novaya sibir island includes approximately 50 taxa of ferns ginkgoaleans conifers and angiosperms this flora exhibits plants common for the early cretaceous as well as taxa typical for cenomanian senonian which implies that the age of the plant bearing deposits is likely to be turonian the cretaceous climate has often been described as warm with a higher degree of equability than today with the near polar regions in particular being much warmer than today our estimates using clamp and a new global gridded climate calibration demonstrate that for the turonian novaya sibir flora plant physiognomy reflects a humid climate with warm summers and mild frost free winters the mean annual temperature is estimated to have been 9 2 2 2 c the warm month mean temperature 17 2 2 8 c the cold month mean temperature 1 1 3 8 c and the mean growing season precipitation 537 392 mm these temperature parameters indicate that within 900 km of the turonian north pole the climate was similar to that of modern temperate or even warm temperate zones but must have differed considerably in having pronounced high latitude sunlight seasonality the ecology of the late cretaceous arctic plants reflects their adaptation to this climate synchronous shedding of foliage deciduousness was by far the most common strategy and retention of leaves year round evergreenness was also viable for a small number of taxa large deciduous leaves typical for the cretaceous arctic dicots probably reflect the combination of a warm and humid climate with high latitude light regime long days in summer and predominance of relatively weak and mostly diffuse sunlight the large range of leaf size in a given plant species of arctic angiosperms was most probably linked to the seasonal character of annual shoot development

destruction of atlantis by a great earthquake and tsunami a geological analysis of the spartel bank hypothesis numerous geographical similarities exist between plato s descriptions of atlantis and a paleoisland spartel in the western straits of gibraltar the dialogues recount a catastrophic event that submerged the island ca 11 6 ka in a single day and night due to violent earthquakes and floods this sudden destruction is consistent with a great earthquake m 8 5 and tsunami as in the gulf of cadiz region in 1755 when tsunami run up heights reached 10 m great earthquakes m 8 9 and tsunamis occur in the gulf of cadiz with a repeat time of 1 5 2 k y according to the sedimentary record an unusually thick turbidite dated as ca 12 ka may coincide with the destructive event in plato s account the detailed morphology of spartel paleoisland as determined from recently acquired high resolution bathymetric data is reported here the viability of human habitation on this paleoisland ca 11 6 ka is discussed on the basis of a new bathymetric map

influence of sea level and basin physiography on emplacement of the late pleistocene herodotus basin megaturbidite se mediterranean sea radiocarbon 14c dates from pelagic intervals above a megaturbidite in the herodotus basin give direct evidence of emplacement at the beginning of the last glacial period approximately 27 125 calendar years before present as sea level lowered rapidly and entered a low stand phase the herodotus basin megaturbidite is a basinwide deposit that forms a recognisable acoustically transparent layer on 3 5 khz high resolution seismic profiles and covers an area of approximately 40 000 km2 it thins from about 20 m in thickness proximally to some 10 m distally over a basin length in excess of 400 km the total volume is estimated at around 400 km3 which is significantly more than the volume of sediment that could have been displaced from its most likely source area the funnel shaped marginal embayment of the gulf of salum to the west of the nile cone the additional material may have been derived in part from synchronous failures on other parts of the libyan egyptian shelf and slope but most is believed to have come from large scale erosion at the base of the very large volume turbidity current that was generated from the original slide detailed sedimentary analyses of cores recovered from the megaturbidite show its distinctive characteristics graded sand silt mud and bioturbated mud units poorly developed structures proximally becoming more distinct and ordered distally variation in grain size and structures that suggest either flow separation reflection around topographic highs and or an inherently unstable flow and a mixed source bioclastic terrigenous composition these features together with its size and lateral extent would make any similar megabed an excellent marker horizon in basin analysis a combination of factors was responsible for triggering the initial slide debris flow event that evolved downslope into this mega turbidity current these include lowered sea level that destabilised the outer shelf upper slope sediments tectonic oversteepening of the margin relatively high rates of sedimentation and seismic activity

bioturbation into a recently emplaced deep sea turbidite surface as revealed by210pbexcess 230thexcess and planktonic foraminifera distributions abstract this study concerns the surface of a single distal turbidite emplaced on the madeira abyssal plain a few hundred years ago the vertical and horizontal homogeneity of the unit and the low pelagic sediment accumulation rate enable a ready identification of the post emplacement signals of near surface bioturbation data have been gathered to define 210 pb excess 230 th excess and pelagic foraminifera profiles with depth these are used as constant input flux tracers and treated by models conventionally used to determine bioturbation parameters the mixed layer depths 7 11 cm bioturbation coefficients 0 08 0 18 cm 2 y 1 and inventory data 10 23 dpm cm 2 derived from the 210 pb excess data in five out of six cores are similar to those previously observed elsewhere with the same model in the deep sea under steady state sediment accumulation conditions although the mixed layer depths are similar for all three tracers the 210 pb excess bioturbation intensities are larger by a factor of 3 than those estimated from 230 th excess profiles and about an order of magnitude larger than those from the foraminifera profiles it is suggested that the conventional 210 pb excess model and those for other short lived tracers probably over estimate the intensity of biomixing of foraminifera for palaeontological and related geochemical purposes

seismoturbidites a new group of resedimented deposits abstract turbidite beds of exceptionally large volume and areal extent occur in both modern and ancient deep water basins these beds which may reach individual volumes in excess of 100 km3 are apparently the product of catastrophic gravity flows triggered by earthquakes along the margins of highly mobile basins most commonly elongate flysch troughs turbidite beds produced by these catastrophic events are generally characterized by very distinctive geometry internal structures and composition and are termed herein seismoturbidites characteristically these sediments lack time persistent features of deep sea fans such as channels and lobes seismoturbidites may occur as scattered intercalations diluted within otherwise normal turbidite sequences thus forming generally excellent markers for basin wide correlations or as closely spaced repetitive units comprising the bulk of the sedimentary fill of certain flysch basins in both cases they may offer a tremendously useful tool for a better understanding of the distribution of paleoseismic zones in time and space

origin sedimentary processes and depositional evolution of the agadir turbidite system central eastern atlantic the oligocene to recent agadir turbidite system occurs in the agadir basin abutting against the continental margin off south morocco central eastern atlantic this system is part of the submarine drainage system linking back to the anti and high atlas mountains through the agadir canyon and its sedimentary evolution is shown to comprise lateral shifts of canyon channel overbank and lobe deposits governed by local topography draped palaeorelief seamounts and a contourite ridge and channel avulsions in addition the turbidite system shows an overall retrogradational stacking migrating about 60 km upslope this probably reflects a decrease in gradient on the continental margin gradual basin filling and or a progressive decrease in energy and load of the sediment gravity flows that fed the system the latter change in sediment flux could result from the interplay between the progressive denudation of the source areas together with the climatic change which led to the present arid desertic conditions in the hinterland the seismic features observed with new ultra high resolution seismic tools allow the recognition of the present day sedimentary activity within the agadir turbidite system and this is related among other factors to the active seismicity of the area

late quaternary turbidite input into the east mediterranean basin new radiocarbon constraints on climate and sea level control the late pleistocene holocene 0 30 ka bp allochthonous sedimentation in the herodotus basin of the eastern mediterranean has been controlled in part by a combination of regional climatic change and eustatic sea level fluctuation a new series of radiocarbon dates made on planktonic foraminifers and pteropod shells taken from the pelagic and hemipelagic intervals between individual turbidite units has given bracketing dates for each major turbidity current event that deposited sand and mud on the herodotus basin plain two partly independent cycles are evident climate induced cycles have lead to an alternation of periods of turbidites sourced from the nile delta fan system with those from the north african shelf and anatolian rise these correlate with pluvial and inter pluvial climatic periods recognized in the nile hinterland sea level cycles have tended to focus turbidite emplacement from whatever source at periods of sea level fall within the latest wisconsin and sea level rise from the wisconsin holocene period in addition to the herodotus basin megaturbidite hbm described previously six other beds with volumes in excess of 25 km3 and wide lateral extent across the basin can be termed megaturbidites there is no simple sea level or climate control on the timing of these events so we must conclude that triggering and emplacement of megaturbidites is independent and variable

particle mixing rates in deep sea sediments determined from excess 210pb and 32si profiles particle mixing rates have been determined for 5 south atlantic antarctic and 3 equatorial pacific deep sea cores using excess 210 pb and 32 si measurements radionuclide profiles from these siliceous calcareous and clay rich sediments have been evaluated using a steady state vertical advection diffusion model in antarctic siliceous sediments 210 pb mixing coefficients 0 04 0 16 cm 2 y are in reasonable agreement with the 32 si mixing coefficient 0 2 or 0 4 cm 2 y depending on 32 si half life in an equatorial pacific sediment core however the 210 pb mixing coefficient 0 22 cm 2 y is 3 7 times greater than the 32 si mixing coefficient 0 03 or 0 07 cm 2 y the difference in 210 pb and 32 si mixing rates in the pacific sediments results from 1 non steady state mixing and differences in characteristic time and depth scales of the two radionuclides 2 preferential mixing of fine grained clay particles containing most of the 210 pb activity relative to coarser particles large radiolaria containing the 32 si activity or 3 the supply of 222 rn from the bottom of manganese nodules which increases the measured excess 210 pb activity relative to 226 ra at depth and artificially increases the 210 pb mixing coefficient based on 32 si data and pore water silica profiles dissolution of biogenic silica in the sediment column appears to have a minor effect on the 32 si profile in the mixed layer deep sea particle mixing rates reported in this study and the literature do not correlate with sediment type sediment accumulation rate or surface productivity based on differences in mixing rate among three antarctic cores collected within 50 km of each other local variability in the intensity of deep sea mixing appears to be as important as regional differences in sediment properties

increased fire activity at the triassic jurassic boundary in greenland due to climate driven floral change an episode of climate warming 200 myr ago was associated with catastrophic environmental changes experimental and palaeontological data suggest that a climate driven shift to more flammable leaf shapes contributed to increased fire activity in east greenland at this time one of the largest mass extinctions of the past 600 million years myr occurred 200 myr ago at the triassic jurassic boundary the major floral and faunal turnovers1 have been linked to a marked increase in atmospheric carbon dioxide levels2 probably resulting from massive volcanism in the central atlantic magmatic province3 4 future climate change predictions suggest that fire activity may increase5 in part because higher global temperatures are thought to increase storminess6 7 here we use palaeontological reconstructions of the fossil flora from east greenland to assess forest flammability along with records of fossil charcoal preserved in the rocks to show that fire activity increased markedly across the triassic jurassic boundary we find a fivefold increase in the abundance of fossil charcoal in the earliest jurassic which we attribute to a climate driven shift from a prevalence of broad leaved taxa to a predominantly narrow leaved assemblage our fire calorimetry experiments show that narrow leaf morphologies are more flammable than broad leaved morphologies we suggest that the warming associated with increased atmospheric carbon dioxide levels favoured a dominance of narrow leaved plants which coupled with more frequent lightening strikes led to an increase in fire activity at the triassic jurassic boundary

preliminary analysis of climate indicator plant distribution in the early cretaceous of china abstract we review the distribution of early cretaceous megafossil plants from china the distribution patterns of ginkgoales acanthopteris nilssonia podozamites gleichenites frenelopsids otozamites zamites zamiophyllum ptilophyllum and weichselia are illustrated on maps the early cretaceous flora of china has been divided into two floristic provinces the northern type tetori type or siberia canadian flora flourished under a warm temperate and humid climate while the southern type ryoseki type or euro sinian flora flourished under a tropical subtropical and rather arid climate although most researchers agree with the estimations of climate mentioned above the locations of the boundary between these two floristic provinces and their mixed zone are still controversial distribution maps from the present study show that each taxon has a different distribution area this means that the boundary positions advocated previously are not supported by the present study these results indicate that an objective methodology is needed for further study to solve this problem we compiled a database of the early cretaceous flora and its components in east asia which includes all the taxa described in the referenced publications

climatic control of turbidite deposition on the madeira abyssal plain studies of sedimentation in the southwestern part of the madeira abyssal plain have revealed sequences of turbidites correlatable over thousands of square kilometres turbidites are sediments transported by turbidity currents and represent rapidly accumulated sedimentary units1 in this case in the distal part of the flow they are very fine grained and homogeneous occasionally with silty bases individual turbidites are separated by thin pelagic units which alternate from oozes to pelagic clays a stratigraphy for these pelagic units has been produced from combining coccolith distributions and lithological changes which enables comparison to cores containing only pelagic sediments from outside the turbidite province these comparisons show that turbidity currents cause no significant erosion in the area the major turbidites occur between lithological alternations which reflect global climate changes associated with glaciations and related eustatic sea level fluctuations turbidites have been linked with eustacy on previous occasions but only with low stands of sea level2 3 our work shows that turbidites are more likely to occur during regressions and transgressions rather than in the quiet periods between

jurassic dextral and cretaceous sinistral movements along the hida marginal belt abstract the hida marginal belt hmb which consists of various kinds of fault bound blocks is located between the continental massif of the hida belt and the mesozoic accretionary complex of the mino belt in central japan detailed field investigation reveals that the hmb had grown through the two different movements i e jurassic dextral and cretaceous sinistral movements the jurassic dextral ductile shear zones run in the southern marginal part of the hida belt and the northern part of the hmb whereas the cretaceous sinistral cataclastic shear zones occur in the southern part of the hmb and the northern marginal part of the mino belt geologic map and field evidence seem to suggest that the jurassic dextral movement form the fault bound blocks of the hmb to form the basic structure of the hida marginal belt i e formation of the proto hmb following the dextral movement the sinistral one restructured the proto hmb to complete the present feature of the hida marginal belt the cretaceous sinistral movement might result in the sinistral collision between the proto hmb and the mino belt

peat forming materials and evolution of swamp sequences case analysis of a jurassic inland coal basin in china abstract a case analysis was conducted in the yima coal mine which is located in a jurassic inland basin located in the henan province of central china using data from palynological ecology plant residues coal petrography and some geochemical characteristics the plant community during this coal forming period and the precursors of the coal forming peat were determined the peat forming paleoenvironment and evolutionary sequences within the swamp were reconstructed according to the differences in the spore pollen complex of the coals in the yima mine seven kinds of palynofacies each characterized by predominant species occured within the relative beds seven different types of ecological characteristics are indicated the different stages are represented by the corresponding floral facies six diagnostic properties of the coal facies were determined by studying the petrographic characteristics of each coal and seven different kinds of ancient peat forming swamp paleoenvironments are indicated by the coal facies a genetic model of formation development and evolutionary sequences of the coal forming swamp in the jurassic of central china is proposed

early cretaceous changes of vegetation and environment in east asia abstract early cretaceous floras of the razdolnensky suifun and partizansky suchan basins currently located close to each other in south primorye differ significantly the pre albian flora assemblages of the razdolnensky basin are similar to those of northeastern china whereas the pre albian assemblages of the partizansky basin are close to the rioseki complex of the outer japan tectonic reconstructions using these data have showed that the voznesenka terrane underlying cretaceous sediments of the razdolnensky basin as well as the terranes of inner japan were displaced northwards along faults of the tan lu system for more than 5 by latitude the sergeevka terrane forming the basement of early cretaceous sediments of the partizansky basin as well as the terranes of outer japan were displaced in the same direction for a much larger distance about 15 by latitude the major movements occurred in the earliest albian as is suggested by the same albian flora assemblages in the two basins

oxygen isotopes of east asian dinosaurs reveal exceptionally cold early cretaceous climates early cretaceous vertebrate assemblages from east asia and particularly the jehol biota of northeastern china flourished during a period of highly debated climatic history while the unique characters of these continental faunas have been the subject of various speculations about their biogeographic history little attention has been paid to their possible climatic causes here we address this question using the oxygen isotope composition of apatite phosphate from various reptile remains recovered from china thailand and japan values indicate that cold terrestrial climates prevailed at least in this part of asia during the barremian early albian interval estimated mean air temperatures of about 10 4 c at midlatitudes 42 n correspond to present day cool temperate climatic conditions such low temperatures are in agreement with previous reports of cold marine temperatures during this part of the early cretaceous as well as with the widespread occurrence of the temperate fossil wood genus xenoxylon and the absence of thermophilic reptiles such as crocodilians in northeastern china the unique character of the jehol biota is thus not only the result of its evolutionary and biogeographical history but is also due to rather cold local climatic conditions linked to the paleolatitudinal position of northeastern china and global icehouse climates that prevailed during this part of the early cretaceous

textural and dispersal patterns of thick mud turbidites from the madeira abyssal plain abstract the madeira abyssal plain is the site of a thick sequence of thick pleistocene turbidites that are almost entirely of material less than 63 m in grain size the major turbidites are 1 to 5 m in maximum thickness concentrating on three turbidites cored at 24 locations detailed patterns of thickness and vertical and lateral grain size changes reveal flow paths on the plain in general the bases of the units are of graded silt showing thick and thin planar lamination and occasionally ripple cross lamination a new idealised sequence of changes in size and structures with distance along the flow path is developed closer to source the beds comprise a graded structured silty base overlain by structureless mud which may also be graded down current the silty base becomes thinner with less apparent structure and the upper homogeneous part becomes thicker and more uniform in an overall thickening trend at the distal end uniform beds up to 5 m in thickness are found in one turbidite the modal size structure shows some silt modes which are hydrodynamically sorted and change size vertically and spatially while one particular mode is constant in size due to a particular species of coccolith the turbidites originated from slumps on the northwest african continental margin and from the vicinity of madeira and the canaries some of which exceeded 100 km3 in volume

increased marine sediment suspension and fluxes following an earthquake earthquakes are commonly cited as one possible triggering mechanism for turbidity flows dense sediment water plumes that can transport large volumes of sediment great distances down slope in both marine and lacustrine settings1 2 3 4 5 6 heezen and ewing1 were the first to make such a suggestion attributing breaks in a sea floor telephone cable in the north atlantic ocean to turbidity flows generated by the 1929 grand banks earthquake anumber of workers have consequently used sedimentary turbidite records to reconstruct the earthquake histories of various regions2 7 8 here we present direct observations of a seismically induced turbidity flow measurements of light scattering and sediment fluxes in the cariaco basin indicate that the earthquake that occurred along the coast of northern venezuela on 9 july 1997 resulted in considerable downslope displacement of sediments probably 105 tonnes into the deep part of the basin in such a seismically active region this mechanism of sediment transport may be responsible for a significant component of the long term sediment accumulation in the basin furthermore this process may result in the sequestration in deep sea sediments of large amounts of carbon initially deposited at shallow depths

calculating erosion by deep sea turbidity currents during initiation and flow turbidity currents transport massive amounts of sediment from continental margins to the deep sea individual flows can catastrophically remove and redeposit as turbidites many hundreds of cubic kilometres of material1 2 with the larger events reaching the bottom of the continental slope to form the abyssal plains3 here we show that the age range of sediments in individual turbidites can be used directly to estimate both the thickness of failed sediment in the source region even when its exact location is unknown and the extent to which the turbidity current caused erosion of the sea bed our method involves the comparison of the abundance ratios of microfossil coccolith species in turbidites with those in the ocean margin sediments of the source region analysis of a recently emplaced turbidite on the madeira abyssal plain shows that it contains a mixture of sediments with an age range of about 200 000 years equivalent to the failure of a block of sediment about 15 m deep radiocarbon dating and coccolith ratios show that the turbidite contains only about 12 of recent near surface sediment indicating that this turbidity current caused surprisingly little erosion en route

recent sediment transport and deposition in the lisbon setubal and cascais submarine canyons portuguese continental margin abstract recent sediment transport and deposition in the lisbon setubal and cascais submarine canyons portuguese continental margin were investigated on the basis of water column profiles of suspended particulate matter records of near bottom currents and settling fluxes of particulate matter obtained with benthic landers and analysis of surface sediments the results show that fine grained predominantly lithogenic sediment derived from adjacent shelf areas accumulates in the upper reaches of the canyons sediment deposited further down in the middle and lower reaches of the canyons is essentially similar to the hemipelagic sediment found on the adjacent continental slope indicating that down canyon transport of sediment from the upper to the lower canyon is limited tidal currents measured at various depths in the lisbon setubal canyon appear sufficiently strong to resuspend and transport sediment but net up canyon flow of the bottom water may retain shelf derived lithogenic sediment in the upper canyon sediment gravity flows which in the nearby nazare canyon are an effective mechanism for down canyon sediment transport appear rare in the lisbon setubal canyon and probably also in the cascais canyon turbidity current events recorded in the sedimentary record of the canyons may correspond to seismic events of 1969 and 1755 ad

mobility of authigenic rhenium silver and selenium during postdepositional oxidation in marine sediments sedimentary records of redox sensitive trace elements hold significant potential as indicators of paleoceanographic environmental conditions records of re can reveal the intensity of past reducing conditions in sediments at the time of deposition whereas records of ag may record the magnitude of past diatom fluxes to the seafloor confidence in paleoenvironmental reconstruction from records of either metal however requires it to have experienced negligible redistribution since deposition this study examines diagenetic rearrangements of re and ag that occur in response to exposure to bottom water o2 in environments of low sedimentation rate including madeira abyssal plain turbidites and eastern mediterranean basin sapropels authigenic re was remobilized quantitatively by oxidation but poorly retained by the underlying sediments all records are consistent with previous work demonstrating that only a limited reimmobilization of re occurs preferentially in corg rich reducing sediments silver was also mobilized quantitatively by oxidation but it was subsequently immobilized more efficiently in all cases as sharp peaks immediately into anoxic conditions below active oxidation fronts and these peaks remain immobile in anoxic conditions during long term burial comparison of ag s and se records from various cores suggests that ag is likely to have been immobilized as a selenide a mechanism previously proposed for hg in similar situations mercone et al 1999 coexisting narrow peaks of ag and hg with se offer a means of assessing whether oxidative burndown has ever occurred at the top of corg and sulfide rich sedimentary units although these results suggest that caution must be used when inferring paleoenvironmental information from records of ag and re in cores with low sediment accumulation rates 5 cm ka 1 they should not affect the promise that authigenic ag and re records hold for paleoenvironmental reconstruction in sediments with higher accumulation rates and where anoxic conditions have been maintained continuously

low sea level emplacement of a very large late pleistocene megaturbidite in the western mediterranean sea large volume turbidites termed megaturbidites or megabeds result from catastrophic slope failures and the associated downslope transport of enormous quantities of sediment from continental margins to the deep sea such large sediment failures can generate tsunamis and in terrains underlain by gas hydrates clathrates may be associated with the release of substantial amounts of the greenhouse gas methane it has been proposed that the megaturbidite events may be triggered by seismic activity or may result from gas hydrate release itself caused by a lowering of hydrostatic pressure on clathrates as a result of low sea level previous conclusions on the significance of sea level change however have been conditional because of the lack of absolute times of turbidite emplacement here we use accelerator mass spectrometry radiocarbon dating in five widely spaced cores to constrain the date of emplacement of a large volume 500 km3 bed in the balearic basin of the western mediterranean this turbidite is exceptional in its magnitude and represents the main sedimentation event in the balearic basin over the past 100 kyr our data provide an estimate of 22 000 calendar years before present for emplacement of the megabed a time when sea level stood at its lowest level during the last glacial maximum the coincidence of these dates is consistent with emplacement due to clathrate destabilization caused by low sea level although other triggering mechanisms such as seismic shock cannot be ruled out