eemian cooling in the norwegian sea and north atlantic ocean preceding continental ice sheet growth changing conditions in the north atlantic region may drive global climate changes1 2 according to previous reconstructions of the last interglacial the eemian north atlantic sea surface tempera tures ssts were similar to present day values3 in the norwegian sea even warmer conditions appeared as a single pulse of short duration4 5 whereas the greenland ice record suggests that the warm interglacial air temperatures were interrupted by several cold periods6 here we use faunal and stable isotope analyses of foraminifera in two sediment cores from the north atlantic ocean and norwegian sea to reconstruct high resolution records of sst and sea surface salinity sss during the eemian interglacial our results which differ significantly from the greenland record6 show a sharp decrease in sst and sss of the norwegian sea associated with a more moderate cooling and freshening of the north atlantic at the middle of isotope substage 5e several millennia before the beginning of continental ice sheet growth changes in the norweg ian sea surface conditions appear to have represented an important climate change affecting global atmospheric and thermohaline circulations

holocene trends in 18o in land snail shells from the negev desert and their implications for changes in rainfall source areas abstract the 18o value of the carbonate of land snail shells is related to the 18o content of precipitation which in turn relates to the source region and trajectory of the rain bearing air masses analyses of 18o of the shell carbonate of 76 radiocarbon dated holocene samples of the land snail trochoidea seetzeni from the northern negev desert in southern israel were carried out and the results were compared to modern snails from the same region early holocene 18o values are similar to modern but during the period centered around 6500 6000 yr b p a depletion of some 2 below modern is observed a change in the atmospheric circulation pattern for this period is thus indicated most likely an increase in the frequency of storm systems reaching the region from north eastern africa by 3500 yr b p 18o values had reached modern levels and indicate a stable pattern of atmospheric circulation since that time

oxygen isotope studies of achondrites abstract oxygen isotope abundances provide a powerful tool for recognizing genetic relationships among meteorites among the differentiated achondrites three isotopic groups are recognized l snc mars 2 earth and moon and 3 hed howardites eucrites diogenites the hed group also contains the mesosiderites main group pallasites and silicates from iiiab irons the angrites may be marginally resolvable from the hed group within each of these groups internal geologic processes give rise to isotopic variations along a slope 1 2 fractionation line as is well known for terrestrial materials variations of 17o from one planet to another are inherited from the inhomogeneities in the solar nebula as illustrated by the isotopic compositions of chondrites and their constituents among the undifferentiated achondrites five isotopic groups are found 1 aubrites 2 winonaites and iab iiicd irons 3 brachinites 4 acapulcoites and lodranites and 5 ureilites the isotopic compositions of aubrites coincide with the earth and moon and also with the enstatite chondrites these bodies apparently were derived from a common reservoir the isotopic composition of which was established at the chondrule scale by nebular processes isotopic similarities between chondrites and achondrites are seen only for the following instances 1 enstatite chondrites and aubrites 2 h chondrites and he irons and 3 l or ll chondrites and iva irons the isotopic data also support the following genetic associations 1 winonaites and iab iiicd irons 2 acapulcoites and lodranites and 3 ureilites and dark inclusions of c3 chondrites an attempt to reconcile the whole planet isotopic compositions of earth mars and the eucrite parent body with mixing models of their chemical compositions failed it is not possible to satisfy both the chemical and isotopic compositions of the terrestrial planets using known primitive solar system components

inferred glacio eustatic control for high frequency depositional sequences of the plio pleistocene kazusa group a forearc basin fill in boso peninsula japan abstract the plio pleistocene forearc basin fill of the kazusa group as much as 3000 m thick is represented by a series of marine environments ranging from deep sea basin plain to shallow sea it developed during about 2 4 to 0 45 ma and is well exposed in the boso peninsula japan chronostratigraphic resolution of the kazusa group is partly within about 0 05 m y based on the combination of fission track dating of volcanic ash layers and bio and magneto stratigraphy many volcanic ash layers are intercalated in the kazusa group and provide distinct chronostratigraphic surfaces within the heterogeneous lithologies detailed outcrop studies on depositional facies discontinuities and lateral terminations of volcanic ash layers allow high resolution sequence stratigraphic interpretation of the kazusa group seventeen depositional sequences were identified in the kazusa group each depositional sequence was tentatively correlated with the stable oxygen isotope sea level index integrated with the age framework of the kazusa group this correlation indicates that frequencies of the depositional sequences can be estimated to be in the range of 0 2 0 02 m y and are within fourth and fifth order stratigraphic cyclicities depositional sequences constitute third order transgressive and highstand sequence sets and the kazusa group is interpreted to represent a third order composite sequence with a duration of about 1 95 m y development of the third order composite sequence was also controlled by an overall rise and fall of glacio eustatic sea levels overprinted by tectonic events related to fluctuations in oceanic plate motion which occurred at about 2 6 ma and 0 5 ma respectively

high resolution proxy record of the environmental response to climatic variations during transition mis3 mis2 and mis2 in central europe the loess paleosol sequence of katymar brickyard hungary abstract according to the findings of a complex radiocarbon dated sedimentological geochemical anthracological phytolite malacological study implemented on an open 1036 cm wind blown sand loess sandy loess and fossil soils profile of western part of brickyard at katymar village in hungary increased boreal mixed leaved forest steppe and temperate grassland cover characterized the interstadials in the se great hungarian plain during the terminal phase of mis3 stage and mis2 stage these interstadials correlate well with the dansgaard oeschger do interstadials 8 7 6 5 4 3 2 and the post lgm warm interval do1 seen in the greenland ice core oxygen isotope records intervening cold phases on the other hand their start correlating with heinrich event 1 2 3 4 and the lgm these data overall confirm that millennial scale climate variability during mis3 and mis2 stages had profound effect on the terrestrial ecosystems in the continental interior of se europe leading to periodic mixed leaved boreal forest steppe within mosaic structure expansions in the interstadias and cold steppe taiga and tundra like spots mosaic and mixed vegetation expansion in the stadial phases 1400 1500 year long drier interstadial and humid extended vegetation covered stadial periods interchanged at katymar sequence therefore the vegetation and fauna development was different from the atlantic and central european schemes and inferred an independent local and regional south carpathian basin trend

primary igneous carbon in ureilites petrological implications the ureilite meteorites are carbonaceous olivine pyroxene achondrites they typically contain up to 4 wt carbon carbonaceous matrix as graphite diamond and lonsdaleite shock degradation has effectively obliterated primary textures in the carbonaceous matrix of previously described ureilites a factor that has hampered efforts to explain the origin of this material in contrast the antarctic ureilite alha78019 displays perfectly preserved primary textures in the carbonaceous matrix characterized by euhedral graphite blades intergrown with fe ni metal and sulfide diamonds are absent this petrographic feature suggests that most graphite in ureilites originated by crystallization from a c rich metallic phase assuming that fo2 is controlled by c co co2 reactions the compositions of silicates and metals in ureilites imply a two stage redox history the noble gases and rare earths of ureilites are discussed in light of this model

climate variations in europe over the past 140 kyr deduced from rock magnetism rapid shifts in climate during the last glacial are now well documented particularly from the oxygen isotope records of the two greenland ice cores grip1 2 and gisp23 in the grip record1 2 these climate events are also seen during the preceding eemian interglacial which may be an analogue for the future climate warmed by the greenhouse effect but these shifts are not found in the eemian section of the gisp2 core3 casting doubt on whether the rapid shifts in the grip oxygen isotope record really do represent a climate signal here we present magnetic susceptibility pollen and organic carbon records from maar lake deposits in the massif central france these data provide an independent record of past climate and we find that they correlate well with the ice core records during the last glacial during the eemian two rapid cooling events seen in our record also correlate with those seen in the grip ice core supporting the idea that rapid climate change did occur in the eemian interglacial and demonstrating that it extended to continental europe

feldspathic clast populations in polymict ureilites stalking the missing basalts from the ureilite parent body abstract polymict ureilites dag 164 165 dag 319 dag 665 and eet 83309 are regolith breccias composed mainly of monomict ureilite like material but containing 2 vol of feldspathic components we characterized 171 feldspathic clasts in these meteorites in terms of texture mineralogy and mineral compositions based on this characterization we identified three populations of clasts each of which appears to represent a common igneous generally basaltic lithology and whose mafic minerals show a normal igneous fractionation trend of near constant fe mn ratio over a range of fe mg ratios that extend to much higher values than those in monomict ureilites the melts represented by these populations are unlikely to be impact melts because the ubiquitous presence of carbon in polymict ureilites the regolith of the ureilite parent body implies that impact melts would have crystallized under conditions of carbon redox control and therefore have highly magnesian mafic mineral compositions with constant mn mg ratio therefore these melts appear to be indigenous products of igneous differentiation on the ureilite parent body upb complementary to the olivine pigeonite residues represented by the majority of monomict ureilites the most abundant population is characterized by albitic plagioclase in association with pyroxenes phosphates ilmenite silica and incompatible element enriched glass model calculations suggest that it formed by extensive fractional crystallization of the earliest melt s of precursor materials from which the most magnesian shallowest olivine pigeonite ureilites formed a less abundant population characterized by labradoritic plagioclase may have formed from melts complementary to more ferroan olivine pigeonite ureilites and derived from deeper in the upb the third population characterized by the presence of olivine and augite could only have formed from melts produced at greater depths in the upb than the olivine pigeonite ureilites many other feldspathic clasts cannot be positively associated with any of these three populations because their mafic mineral compositions exhibit carbon redox control however they may be products of early crystallization of basaltic melts produced on the upb before carbon was exhausted by reduction partial melting on the ureilite parent body was a fractional or incremental process melts were produced early in upb history and most likely extracted rapidly thus preserving primitive chemical and oxygen isotopic signatures in the residues

high frequency depositional sequences of the upper part of the kazusa group a middle pleistocene forearc basin fill in boso peninsula japan abstract a middle pleistocene forearc basin fill of the upper part of the kazusa group is represented by slope to shelf sediments and is well exposed in the boso peninsula of japan the slope to shelf sediments are a northeasterly prograded clastic wedge as much as 700 m in maximum thickness and include many volcanic ash layers mapping of volcanic ash layers together with the interpretation of depositional facies permits identification of stratal terminations and spatial and temporal variations of depositional environments this allows sequence stratigraphic analysis of the slope to shelf sediments of the upper part of the kazusa group six depositional sequences were identified in the upper part of the kazusa group by correlating each depositional sequence with the stable oxygen isotope sea level index integrated with the age framework for the upper part of the kazusa group ca 0 72 0 45 ma periodicity of the depositional sequences of the upper part of the kazusa group can be estimated at about 20 000 to 90 000 years the high frequency depositional sequences are interpreted to be a result of interaction between high sedimentation rate in the forearc basin and high rate of glacio eustatic sea level changes during the middle pleistocene

british late glacial and holocene climatic history reconstructed from land snail assemblages gations have enabled refinement of the stratigraphic scheme as shells of land snails occur in quantity throughout the sequence preece 1998 they provide a detailed mollusk succession from the beginning of the late glacial until the present day the late glacial assemblages are dominated by species of open country and marsh but shadeintolerant species are replaced by a succession of woodland species during the early part of the holocene following forest clearances during the neolithic and bronze age 5000 3000 yr b p these closed forest communities show a reversion to grassland assemblages with only minor indications of scrub fig 2 a detailed chronology for this succession is provided by a series of

explosive volcanism and the graphite oxygen fugacity buffer on the parent asteroid s of the ureilite meteorites the 39 ureilite meteorites are in many respects primitive objects they are highly carbonaceous averaging 3 0 wt c mostly as graphite yet their consistently coarse grained textures and plagioclase depleted compositions imply that they are igneous despite diverse mafic silicate mg mg fe and pyroxene olivine ratios plagioclase is totally absent among 35 monomict unbrecciated ureilites even among 4 polymict brecciated ureilites the average al concentration is only 0 28 0 04 wt we suggest that the ureilites are residues from partial melting of graphite rich source materials which formed sufficiently deep in a relatively large low f o2 asteroid or more likely asteroids for graphite to be stable even at magmatic t the al rich basaltic magmas that ascended from the residues were nearly quantitatively lost from the asteroid during pyroclastic eruptions graphite entrained in the ascending magmas was oxidized by an extremely pressure sensitive reaction into cox the expansion of which into the vacuous environment of the asteroid engendered pyroclastic exit velocities greatly in excess of the asteroid s escape velocity carbon would oxidize long before the attainment of magmatic temperatures in small asteroids but we infer that basalt dissipative explosive volcanism was common on all c rich asteroids that were roughly 100 200 km in radius and heated to widespread deep melting and most unmetamorphosed chondritic meteorites are c rich based on the ureilites consistently modest depletions of light rare earth elements siderophile elements and feni metal we infer that the melt fraction was removed mostly by equilibrium batch partial melting late stage ureilite evolution involved an abrupt increase in the cooling rate implying a drop in environmental temperature and a slight amount of graphite oxidation implying a drop in pressure the simplest model to account for this non sequitur and for the conversion of some of the graphite into diamonds is catastrophic impact disruption of the primary asteroid the remarkably efficient removal of the final traces of melt from the ureilites is difficult to explain by any model but possibly was caused by thermal migration along steep thermal gradients engendered after the catastrophic disruption

non uniform across shelf variations in thickness grain size and frequency of turbidites in a transgressive outer shelf the middle pleistocene kakinokidai formation boso peninsula japan abstract across shelf variations in thickness grain size and frequency of sandstone beds in a transgressive outer shelf succession were investigated from the middle pleistocene ca 0 7 ma kakinokidai formation on the boso peninsula japan the transgressive deposits are generally muddy and contain slumps and slump scars the intercalated sandstone beds are interpreted to have been formed from turbidity currents as a response to erosion and resuspension of sandridge complex deposits in the southwestern upslope area during storm events mapping of volcanic ash beds and a transgressive surface in the base of the formation permits detailed bed by bed correlation of the outer shelf sandstone beds although overall thickness grain size and frequency of sandstone beds decrease in the downslope direction some sandstone beds locally thin out and coarsen in association with slump scars in the surrounding muddy deposits these sandstone beds subsequently thicken and fine and finally thin out in the farther downslope area in addition to the local thinning of sandstone beds the frequency of sandstone beds first decreases and then increases in the farther offshore direction from this evidence we concluded that these non uniform patterns of across outer shelf variations in thickness grain size and frequency of sandstone beds were caused by the local increases in flow speeds and subsequent expansion and reduced speeds of turbidity currents along with a local increase in the seafloor gradient that was induced by the development of slump scars in the transgressive outer shelf floor these physiographic features in the outer shelf are interpreted not to have permitted monotonous downslope thinning and fining of sandstone beds compared with the bed shape models of depletive turbidity currents and with the proximality trend of shelf sandstones from modern and ancient highstand stage shelf systems

thermal evolution and physics of melt extraction on the ureilite parent body we develop a physical model of the thermal history of the ureilite parent body upb that numerically tracks the history of its heating hydration dehydration partial melting and smelting as a function of its formation time and the initial values of its composition formation temperature and water ice content petrologic and chemical data from the main group non polymict ureilite meteorites which sample the interior of the upb between depths corresponding to pressures in the range 3 10 mpa are used to constrain the model we find that to achieve the 30 melting inferred for ureilites from all sampled depths the upb must have had a radius between 80 and 130 km and must have accreted about 0 55 ma after cai formation melting began in the body at 1 ma after cai and the time at which 30 melting was reached varied with depth in the asteroid but was always between 4 5 and 5 8 ma after cai the total rate at which melt was produced in the upb varied from more than 100 m 3 s 1 in the very early stages of melting at 1 ma after cai to 5m 3 s 1 between 2 and 3 ma after cai decreasing to extremely small values as the end of melting was approached beyond 5 ma although the initial period of high melt

origin of mass independent oxygen isotope variation among ureilites clues from chondrites and primitive achondrites ureilite meteorites are abundant carbon rich primitive achondrites made of coarse grained equilibrated olivine and pyroxene usually pigeonite they probably sample the baked heterogeneous melt depleted mantle of a large once chondritic parent body that was broken up catastrophically while still young and hot heterogeneity in the parent body is inferred from a considerable slope 1 variation from one meteorite to another in oxygen isotopes 2 5 17o 0 2 which correlates with both molar feo mgo range 0 03 0 35 and molar feo mno range 3 57 i e 17o correlates with the redox state no consensus has yet emerged on the cause of these correlated trends one view favors their inheritance via silicates from hot nebular preaccretion processes another invokes smelting reduction of feo by c in the hot parent body here guided mainly by similar trends among equilibrated ordinary and r chondrites studies of their unequilibrated counterparts and work on other primitive achondrites we propose a new model for ureilites in which the parent body accreted nebular ice with high 17o mg rich silicates with low 17o and varying amounts of metallic iron water from the thawing ice then oxidized the metal yielding secondary feo bearing minerals with high 17o that with metamorphism became incorporated into the ureilite silicates feo mgo feo mno and 17o correlate because they rose in unison by amounts that varied spatially depending on the local amount of metal that was oxidized we suggest that the parent body was so large radius 100 km that smelting was inhibited and that carbon played a passive role in ureilite evolution although ureilites are regarded as complicated meteorites we believe our analysis explains their mass independent oxygen isotope trend and related feo variation through well understood processes and enlightens our understanding of the evolution of early planetesimals from cold wet bodies to hot dry ones

wave modified turbidites combined flow shoreline and shelf deposits cambrian antarctica sandstone tempestite beds in the starshot formation cen tral transantarctic mountains were deposited in a range of shoreline to shelf environments detailed sedimentological analysis indicates that these beds were largely deposited by wave modified turbidity currents these currents are types of combined flows in which storm generated waves overprint flows driven by excess weight forces the interpreta tion of the tempestites of the starshot formation as wave dominated turbidites rests on multiple criteria first the beds are generally well graded and contain bouma like sequences like many turbidites the soles display abundant well developed flutes they also contain thick divisions of climbing ripple lamination the lamination however is dominated by convex up and sigmoidal foresets which are geometries identical to those produced experimentally in current dominated com bined flows in clear water finally paleocurrent data support a tur bidity current component of flow asymmetric folds in abundant con volute bedding reflect liquefaction and gravity driven movement and hence their orientations indicate the downslope direction at the time of deposition the vergence direction of these folds parallels paleocur rent readings of flute marks combined flow ripples and a number of other current generated features in the starshot event beds indicating that the flows were driven down slope by gravity the wave component of flow in these beds is indicated by the presence of small to large scale hummocky cross stratification and rare small two dimensional ripples wave modified turbidity currents differ from deep sea turbidity cur rents in that they may not be autosuspending and some proportion of the turbulence that maintains these flows comes from storm waves such currents are formed in modern shoreline environments by a com bination of storm waves and downwelling sediment laden currents they may also be formed as a result of oceanic floods events in which intense sediment laden fluvial discharge creates a hyperpycnal flow event beds in the starshot formation may have formed from such a mechanism oceanic floods are formed in rivers of small to medium size in areas of high relief commonly on active margins the starshot formation and the coeval douglas conglomerate are clastic units that formed in response to uplift associated with active tectonism sedi mentological and stratigraphic data suggest that coarse alluvial fans formed directly adjacent to a marine basin the geomorphic conditions were therefore likely conducive to rapid fluvial discharge events asso ciated with storms the abundance of current dominated combined flow ripples at the tops of many starshot beds indicates that excess weight forces were dominant throughout deposition of many of these beds

femgmn relations of ureilite olivines and pyroxenes and the genesis of ureilites abstract the fe mn fe mg relations of published microprobe analyses of ureilite olivine cores suggest that feo reduction in the magmatic stage was important in the genesis of some of these meteorites consideration of mg mn and fe mn partitioning between olivine and pigeonite cores shows that these two phases are not in equilibrium the data are consistent with combined fractional crystallization and feo reduction being the major processes of ureilite genesis few if any of the analyzed ureilites are consistent with a partial melting residue model

evidence of across shelf transport of fine grained sediments turbidite filled shelf channels in the campanian aberdeen member book cliffs utah usa the shore normal transport of fine grained sediments by shelf turbidity currents has been the focus of intense debate over the last 20 years many have argued that turbidity currents are unlikely to be a major depositional agent on the shelf however sedimentological architectural stratigraphic and palaeogeographic data from the campanian aberdeen member book cliffs eastern utah suggests otherwise and clearly demonstrates that storm generated and river flood generated underflows can transport a significant volume of fine grained sediments across the shelf these across shelf flowing turbidity currents cut large subaqueous channel complexes up to 7 m deep tens of kilometres basinward of their time equivalent shoreface the shelf channels were filled with organic rich siltstones mudstones and very fine to fine grained bouma like sandstone beds including wave modified turbidites hyperpycnites and classical turbidites deposition was above storm wave base palaeocurrent data reveal an overwhelmingly dominant across shelf east south east offshore directed transport trend tectonic activity and or concomitant palaeogeographic reorganization of the basin may favour the generation of these turbidite rich shelf deposits by altering the relative balance of wave versus fluvial energy increased erosion and sediment supply rates because of tectonic uplift of the hinterland may have increased the probability of fluvial dominance along the coastline and hence the possibility of submarine channelization in front of the river mouths additionally the coastline may have become more sheltered from direct wave energy thus allowing the fluvial processes to dominate seasonal increases in rainfall and storm activity may also favour the generation of across shelf underflows on wave dominated shorelines isolated shelf channels and lobes are most likely to be found down dip of fluvial feeder systems in relatively high sediment supply settings these features are also most likely to occur in systems tracts that straddle a sequence boundary especially those which are tectonically generated as these would enhance the potential for altering basin morphology and hence the balance of fluvial and wave energy isolated shelf channels are recognized in older and younger strata in the book cliffs region implying that wave supported gravity flows were a recurrent phenomena in the campanian of utah it is probable that isolated shelf bodies are preserved in other stratigraphic intervals in the cretaceous western interior of north america and other basins worldwide and are currently being overlooked or misidentified shoreface to shelf facies models should be revised to incorporate turbidite rich shelf deposits in some shelf settings

bypass zone tempestite facies model and proximality trends for an ancient muddy shoreline and shelf member 2 of the late precambrian to lower cambrian chapel island formation of southeast newfoundland was primarily deposited in storm influenced nearshore and shelf environments along a fine grained coastline deposition took place within or adjacent to a deltaic system that supplied abundant silts and clays thin bedded graded sandstone beds hummocky cross stratified beds and a variety of very thin conglomerate units contain evidence for deposition by storm currents sedimentological and stratigraphic evidence is used to reconstruct the relative paleobathymetric position of the three major facies in member 2 the gutter cast facies is a shallow subtidal deposit characterized by very thin sandstone laminae and abundant pot and gutter casts the siltstone dominated facies contains more laterally extensive thin bedded sandstones and fewer erosional features and was deposited in the inner shelf the sandstone dominated facies consists of thin to medium graded and hummocky cross stratified sandstone beds deposited in a more distal shelf setting but above storm wave base the facies model and set of proximality trends developed for member 2 deposits may be applicable to other storm influenced fine grained shorelines in this model the shallow subtidal is a zone of throughput with high velocity sediment laden flows eroding deep narrow scours gutter casts and depositing very little sand outside of these scours as the storm generated flows move into deeper water they decelerate resulting in less erosion of the sea floor and depositing thicker and more continuous sand beds siltstone dominated facies further from shore bed thickness reaches a maximum sandstone dominated facies and hummocky crossstratification is abundant even more distally bed thickness decreases again represented by thinly laminated siltstones of the overlying member 3 analysis of sedimentary structures and paleocurrent data suggests deposition by storm currents that transported sediment nearly perpendicular to shore

sand suspension and transport on the middelkerke bank southern north sea by storms and tidal currents abstract estimates have been made of the suspended sand transport at two sites on the middelkerke bank in the southern north sea from suspended sand profiles and current meter measurements over a period of approximately 40 days sand resuspension was mainly due to waves while transport was dominated by a few hours when large waves coincided with peak flood currents soulsby s relationships for the stress under combined currents and waves were found to be poor predictors for the observed near bed concentrations the mean stress m predicting 45 of the variance while the maximum stress max predicted just 15 and overestimate the effects of the waves when the influence of the stress due to the waves is reduced the variance explained increases to 67 the sand transport rate on the steep slope of the bank was 10 times that of the southern end and was up slope at 25 to the bank axis in the direction of the major axis of the tidal ellipse the transport on the steep slope was mainly in the size range 100 140 m which did not occur in any significant proportion in samples of the sea bed at that site but was advected from deeper water to the southeast excluding this finer component the transport rates of coarser sand 200 m at the two sites were similar over the 40 day period the up slope transport during storms suggests that waves play an important part in the bank maintenance and are not simply the mechanism which prevents the continual growth of the sand bank due to asymmetrical transport by the tidal currents alone the transport rates are consistent with a time scale of 10 2 10 3 years for the formation of the middelkerke bank

climate instability during the last interglacial period recorded in the grip ice core isotope and chemical analyses of the grip ice core from summit central greenland reveal that climate in greenland during the last interglacial period was characterized by a series of severe cold periods which began extremely rapidly and lasted from decades to centuries as the last interglacial seems to have been slightly warmer than the present one its unstable climate raises questions about the effects of future global warming

abrupt change in slope causes variation in the deposit thickness of concentrated particle driven density currents abstract abrupt changes in slope occur frequently in some marine environments laterally confined laboratory experiments show that when dense surge like particulate flows travel over abrupt slope reductions their deposits may have an asymmetric bell shaped thickening near the break of slope this thickening is herein called a slope break deposit and is related to the change in kinetic energy of the flow slope break deposits are particularly pronounced under relatively high velocity flows in our experiments these are flows with high particle concentrations c 5 10 by volume silicon carbide moving down slopes steeper than 3 the experiments were designed such that currents generated by a lock exchange mechanism flowed down a slope variable slope angle onto a flat surface the bodies of the flows became thicker and slower just downstream of the slope break because the flow body slows very rapidly particles are dumped forming the slope break deposit the peak in sediment thickness of the slope break deposit is downstream of the break in slope because falling particles continue to move forward in the flow during settling the slope break deposits may be several tens of percent thicker than deposits from an equivalent flow in which no change in slope occurred the parameters of the slope break deposit correlate with slope angle change

early stages of core segregation recorded by fe isotopes in an asteroidal mantle ureilites displays 56 fe values higher than average chondrite 29 segregation of fe sulfide melts explains the high 56 fe values in ureilites 30 formation of a core can begin at very low degrees of melting through the circulation of a fe s melt 31 through a silicate mantle 32 33 earth and planetary science letters in press 11 3 15 34 2 35 abstract 36 37 ureilite meteorites are achondrites that are debris of the mantle of a now disrupted 38 differentiated asteroid rich in carbon they provide a unique opportunity to study the differentiation 39 processes of such a body we analyzed the iron isotopic compositions of 30 samples from the ureilite 40 parent body upb including 29 unbrecciated ureilites and one ureilitic trachyandesite alm a 41 which is at present the sole large crustal sample of the upb the 56 fe of the whole rocks fall within a 42 restricted range from 0 01 to 0 11 with an average of 0 056 0 008 which is significantly 43 higher than that of chondrites we show that this difference can be ascribed to the segregation of s 44 rich metallic melts at low degrees of melting at a temperature close to the fe fes eutectic and 45 certainly before the onset of the melting of the silicates 1100 c in agreement with the marked s 46 depletions and the siderophile element abundances of the ureilites these results point to an efficient 47 segregation of s rich metallic melts during the differentiation of small terrestrial bodies 48 49

earthquake induced sediment failures on a 0 25 slope klamath river delta california on november 8 1980 a major earthquake magnitude 6 5 to 7 2 occurred 60 km off the coast of northern california a survey of the area using high resolution seismic reflection and side scan sonar equipment revealed the presence of extensive sediment failure and flows in a zone about 1 km wide and 20 km long that trends parallel to the shelf on the very gently sloping c and a prominent 1 to 2 m high seaward facing toe scarp on the outer margin of the terrace this toe scarp is sinuous appears to be nearly continuous for a distance of 20 km and closely parallels the 60 m isobath evidence indicates that the toe scarp is the terminus of lateral spreads and lobes of sediment flows side scan sonar records show evidence of gas vents and small 10 3 0 5 m high pressure ridges formed seaward of and parallel to the sediment flow scarp indicators of liquefaction sand boils and collapse craters are present on the sediment flow terrace extensive sediment failure occurred on a sea floor slope of less than 0 25 and we can unequivocally pinpoint the cause as an earthquake of known location magnitude and time

tectonic versus climatic control on the evolution of a loess paleosol sequence at beremend hungary an integrated approach based on paleoecological clay mineralogical and geochemical data the role of two major factors climate and tectonism in controlling loess paleosol evolution has been evaluated in the present study based on a multi proxy dataset comprising mollusc bulk and clay mineralogical and geochemical data a recent trend has been to use chemical indices such as the chemical index of alteration cia for paleoclimate reconstructions in loess paleosol sequences spanning several hundreds of thousands of years but without any tectonic interpretation possible effects of geodynamic factors on physical erosion chemical weathering and consequently weathering proxies are discussed clearly the relative rates of physical erosion and chemical weathering in a sedimentary environment could be significantly influenced by geodynamic factors and governed not just by climate intensifying tectonic uplift gives rise to enhanced physical erosion leading to increased supply of fresh mineral surfaces having less time to react with weathering agents in theory this process may point towards decreasing chemical weathering in a sequence without any real changes of climate in the studied loess paleosol sequence at beremend hungary a trend of decreasing chemical weathering has been observed which can be explained by a global climate deterioration and accelerating uplift in and around the sedimentary basin increasing dust sedimentation could theoretically also contribute to this process as a result of increasing aridification and wind strength reflecting climate change in weathering records following a non linear amplification the findings refer to the fact that the impact of tectonism should also be taken into consideration in tracing past chemical weathering trends on timescales of hundreds of thousands or millions of years this is because tectonic effects may impose on the cia signal and distort it suggesting a potential bias in reconstructing paleoclimate change based only on this proxy from certain loess sequences associated with young orogenic belts

quantifying velocity and turbulence structure in depositing sustained turbidity currents across breaks in slope two dimensional experiments investigating sediment transport and turbulence structure in sustained turbidity currents that cross breaks in slope are presented as analogue illustrations for natural flows the results suggest that in natural flows turbulence generation at slope breaks may account for increased sand transport into basins and that the formation of a hydraulic jump may not be necessary to explain features such as the occurrence of submarine plunge pools and the deposition of coarser grained beds in the bottomsets of gilbert type fan deltas experimental flows were generated on 0 3 6 and 9 slopes of equal length which terminated abruptly on a horizontal bed two component velocities were measured on the slope at the slope break and downstream of the slope break flows were depositional and non uniform visibly slowing and thickening with distance downstream one dimensional continuous wavelet transforms of velocity time series were used to produce time period variance maps peaks in variance were tested against a background red noise spectrum at the 95 level a significant period banding occurs in the cross wavelet transform at the slope break attributed to increased formation of coherent flow structures kelvin helmholtz billows variance becomes distributed at progressively longer periods and the shape of the bed normal velocity spectral energy distribution changes with distance downstream this is attributed to a shift towards larger turbulent structures caused by wake stretching mean velocity reynolds shear stress and turbulent kinetic energy profiles illustrate the mean distribution of turbulence through the currents a turbulent kinetic energy transfer balance shows that flow non uniformity arises through the transfer of mean streamwise slowing to mean bed normal motion through the action of reynolds normal stresses net turbulence production through the action of normal stresses is achieved on steeper slopes as turbulence dissipation due to mean bed normal motion is limited at the slope break an imbalance between the production and dissipation of turbulence occurs because of the contrasting nature of the wall and free shear boundaries at the bottom and top of the flows respectively a rapid reduction in mean streamwise velocity predominately affects the base of the flows and steeper proximal slope flows have to slow more at the break in slope the increased turbulent kinetic energy limited bed normal motion and strong mixing imposed by steep proximal slopes means rapid slowing enhances turbulence production at the break in slope by focusing energy into coherent flow structures at a characteristic period thus mean streamwise slowing is transferred into turbulence production at the slope break that causes increased transport of sediment and a decrease in deposit mass downstream of the slope break the internal effects of flow non uniformity therefore can be separated from the external influence of the slope break

fractional melting and smelting on the ureilite parent body we investigate petrologic and physical aspects of melt extraction on the parent asteroid of the ureilite meteorites upb we first develop a petrologic model for simultaneous melting and smelting reduction of feo by c at various depths for a model starting composition determined from petrologic constraints to have been cv like except for elevated ca al 2 5 ci we determine 1 degree of melting 2 the evolution of mg 3 production of co co2 gas and 4 the evolution of mineralogy in the residue as a function of temperature and pressure we then use these relationships to examine implications of fractional vs batch melt extraction in the shallowest source regions 30 bars melting and smelting begin simultaneously at 1050 c so that mg and the abundance of low ca pyroxene initially pigeonite ultimately pigeonite orthopyroxene begin to increase immediately however in the deepest source regions 100 bars smelting does not begin until 1200 c so that mg begins to increase and low ca pyroxene pigeonite appears only after 21 melting the final residues in these two cases obtained just after the demise of augite match the end members of the ureilite mg range 94 76 in pyroxene abundance and type in all source regions production of co co2 by smelting varies over the course of melting the onset of smelting results in a burst of gas production and very high incremental gas melt ratios up to 2 5 by mass after a few s melting however these values drastically decline to 0 05 in the final increments physical modelling based on these relationships indicates that melts would begin to migrate upwards after only 1 2 melting and thereafter would migrate continuously fractionally and rapidly reaching the surface in a year in a network of veins dikes all melts produced during the smelting stage in each source region have gas contents sufficient to cause them to erupt explosively and be lost however since in all but the shallowest source regions part of the melting sequence occurs without smelting fractional melting implies that a significant fraction of upb melts may have erupted more placidly to form a thin crust 3 3 km thick for a 100 km radius body our calculations suggest that melt extraction was so rapid that equilibrium trace element partitioning may not have been attained we present a model for disequilibrium fractional melting in which ree partitioning is limited by diffusion on the upb and demonstrate that it produces a good match to the ureilite data the disequilibrium model may also apply to trace siderophile elements and might help explain the overabundance of these elements in ureilites relative to predictions from the smelting model our results suggest that melt extraction on the upb was a rapid fractional process which can explain the preservation of a primitive oxygen isotopic signature on the upb

53mn 53cr and 26al 26mg ages of a feldspathic lithology in polymict ureilites abstract we report 53 mn 53 cr and 26 al 26 mg isotopic data obtained by in situ sims analysis for feldspathic clasts in polymict ureilites dag 319 and dag 165 the analyzed clasts belong to the albitic lithology the most abundant population of indigenous feldspathic materials in polymict ureilites and are highly fractionated igneous assemblages of albitic plagioclase fe rich pyroxenes phosphates ilmenite silica and fe mn k p ti enriched glass glass in dag 165 clast 19 has extremely high and variable 55 mn 52 cr ratios 500 58 000 and shows correlated 53 cr excesses up to 1500 clearly indicating the presence of live 53 mn at the time of formation the slope of the well correlated isochron defined by glass and pyroxenes from this clast corresponds to 53 mn 55 mn 2 84 0 10 10 6 2 data for less 55 mn 52 cr enriched glasses from dag 319 clast b1 as well as phosphates from several other clasts are consistent with this isochron the 53 mn 55 mn ratio obtained from the isochron implies that these clasts are 0 70 0 18 ma younger than the d orbigny angrite corresponding to the absolute age of 4563 72 0 22 ma plagioclase in dag 319 clast b1 has a fairly constant 27 al 24 mg ratio of 900 and shows resolvable 26 mg excesses of 2 the slope of the isochron defined by pyroxene and plagioclase in this clast is 3 0 1 1 10 7 2 corresponding to a time difference of 5 4 0 3 0 5 ma after cai assuming the canonical initial 26 al 27 al ratio of 5 10 5 and an age 0 5 0 3 0 5 ma younger than d orbigny its absolute age relative to d orbigny is 4563 9 0 4 0 5 ma in agreement with the 53 mn 53 cr age from clast 19 these data provide the first high precision age date 5 4 ma after cai for ureilites giving a minimum estimate for the age of differentiation of their parent asteroid interpretation of this age for the thermal and physical history of that asteroid depends on a number of currently unknown or model dependent parameters including its size bulk composition and oxidation state and the petrologic relationship between the feldspathic clasts and main group ureilites

a note on the preservation of offshore tsunami deposits abstract in this contribution we explore the preservation potential of offshore tsunami deposits the application of linear wave theory and flat bottom conditions allows a simplified representation of the physical environment in such an environment it is possible to compute the boundary water depth below which the influence of storm waves on tsunami deposits is negligible the majority of the tsunami deposits described in the literature were deposited onshore where the tsunami wave is transformed into bores and rollers these deposits differ from tsunami sediments of the deeper shelf where the water sediment interaction corresponds more to wave influences we define the boundary depth db as the depth below which tsunami deposits cannot be reworked due to storm waves this is based on the assumption that the wave base coincides with the seabed if the wave base is below the bed a reworking of bed sediments occurs if it is above no energy is transferred to the bottom as an example we use tide gauge records at pointe de la rue seychelles and ca 50 km offshore from brisbane australia at a water depth of 70 m to derive the major wave parameters of the sumatra tsunami and a category 1 cyclone that occurred from 4 6 march 2004 in brisbane the brisbane storm wave reached the maximum wave height of 14 3 m wave periods varied between 6 s and 14 s and the computed maximum wavelength was 237 m the largest height of the sumatra tsunami was 3 01 m periods of between 24 min and 61 min were computed for the time between two subsequent peaks the combination of our hydrodynamic considerations with information from a simplified hjulstrom sundborg diagram implies that the most powerful storm and tsunami waves produce conditions near and at the sea bed that allow the transport of sediment grains from decimeters to meters in diameter that means a sandy tsunami deposit in the area of the brisbane tide gauge would be reworked by storm waves assuming the highest wave amplitude during the 2004 march storm at brisbane as such a boundary wave the water depth below which preservation of tsunami deposits is most likely is greater than 65 m

the climate in western europe during the last glacial interglacial cycle derived from pollen and insect remains using the pollen sequence of la grande pile xx france we review problems with the application of transfer functions in paleoclimatic reconstructions one of them is to find modern analogues for the herbaceous vegetation of the cold periods we propose a method to distinguish between steppes and tundra vegetations for which the moderns are only partial analogues of the glacial periods another method to solve these problems is based on constraining by insect remains the two methods provide coherent reconstructions the results are also compared with other paleodata there is a good correlation with the six cold heinrich events between 70 and 15 ka b p a cooling event during the eemian period marked by high percentages of taxas at about 125 ka b p needs still to be correlated with high resolution ocean and ice cores

ch4 and δ18o of o2 records from antarctic and greenland ice a clue for stratigraphic disturbance in the bottom part of the greenland ice core project and the greenland ice sheet project 2 ice cores the suggestion of climatic instability during the last interglacial period eem based on the bottom 10 of the greenland ice core project grip isotopic profile has been questioned because the bottom record from the neighboring greenland ice sheet project 2 gisp2 core 28 km away is strikingly different over the same interval and because records of the 18o of atmospheric o2 from both cores showed unexpected rapid fluctuations here we present detailed methane records from the vostok antarctica grip and gisp2 cores over the relevant intervals the grip and gisp2 data show rapid and large changes in methane concentration which are correlative with variations of the 18o of the ice while the vostok record shows no such variations this discrepancy reinforces the suggestion that the bottom sections of the greenland records are disturbed by combining the methane data with measurements of 18o of o2 in the same samples we attempt to constrain the nature of the stratigraphic disturbance and the age of the analyzed ice samples our results suggest that ice layers from part of the last interglacial period exist in the lower section of both ice cores and that some of the apparent climate instabilities in the grip core would be the result of a mixture of ice from the last interglacial with ice from the beginning of the last glaciation or from the penultimate glaciation

numerical simulation of turbidity current flow and sedimentation ii results and geological applications a process based forward computer model of turbidity current flow and sedimentation termed the tcfs model has been developed to trace the downslope evolution of individual turbidity flows details of the model itself have been presented in a preceding paper we here outline a series of tests of the tgfs model the sensitivity tests of the tcfs model to general geological controls reveal the quantitative relationship between these controls and the behaviour of turbidity flows and the geometry and textural features of the resulting turbidites experimental turbidity currents on relatively steep slopes accelerate more rapidly and reach higher velocities than those on gentle slopes flows with larger initial volumes have higher initial velocities travel further downslope and form beds of greater thickness and downslope extent than smaller flows experimental high concentration flows with suspended sediment concentrations of 25 accelerate more rapidly and reach higher downslope velocities than dilute flows with 5 suspended sediment the higher velocities and enhanced hindered settling effects of the high concentration flows lead to much greater transport distances and reduced vertical and lateral sediment size grading in the resulting turbidites beds formed by experimental high concentration flows are massive or show coarse tail grading whereas beds formed by low concentration flows show distribution grading experimental flows fed by coarse sediment sources tend to deposit the bulk of their suspended sediment loads on the proximal slope resulting in more rapid flow deceleration and sedimentation than flows fed by silt rich fine grained sediment sources turbidites formed by coarse sediment flows tend to have a wedge shaped geometry with low downslope extent and high surface relief whereas turbidites formed by fine sediment flows tend to have a tabular geometry with greater downslope extent and lower surface relief a specific geological test of the tcfs model is based on studies of modern turbidity currents in bute inlet british columbia canada with the input initial and boundary conditions estimated from bute inlet the model predicts the downslope velocity evolution of turbidity currents comparable to those of modern and ancient turbidity flows measured in bute inlet model calculated vertical and downslope grain size properties of turbidites are similar to those exhibited by surface and cored bute inlet turbidites model flows tend to decelerate more rapidly than some stronger turbidity currents in the bute inlet system and model beds tend to decrease in grain size downslope more rapidly than observed bottom sediments this is probably because the tcfs model flows lacked clay which is abundant in bute inlet they do not fully simulate turbulent mixing of suspended sediments and they better represent the unsteady depositional stage of turbidity currents than the preceding stage of more or less steady flow conditions these tests demonstrate that the tcfs model provides a semi quantitative method to study the growth patterns of submarine turbidite systems it can serve as a predictive tool for analysing the facies architecture of ancient turbidite systems through simulating multi depositional events by improving its erosion function and the compatibility between its numerical components

early petrologic processes on the ureilite parent body we present a petrographic and petrologic analysis of 21 olivine pigeonite ureilites along with new experimental results on melt compositions predicted to be in equilibrium with ureilite compositions we conclude that these ureilites are the residues of a partial melting smelting event textural evidence preserved in olivine and pigeonite record the extent of primary smelting in pigeonite cores we observe fine trains of iron metal inclusions that formed by the reduction of olivine to pigeonite and metal during primary smelting olivine cores lack metal inclusions but the outer grain boundaries are variably reduced by a late stage reduction event the modal proportion of pigeonite and percentage of olivine affected by late stage reduction are inversely related and provide an estimation of the degree of primary smelting during ureilite petrogenesis in our sample suite this correlation holds for 16 of the 21 samples examined olivine pigeonite liquid phase equilibrium constraints are used to obtain temperature estimates for the ureilite samples examined inferred smelting temperatures range from 1150 c to just over 1300 c and span the range of estimates published for ureilites containing two or more pyroxenes temperature is also positively correlated with modal percent pigeonite smelting temperature is inversely correlated with smelting depth the hottest olivine pigeonite ureilites coming from the shallowest depth in the ureilite parent body the highest temperature samples also have oxygen isotopic signatures that fall toward the refractory inclusion rich end of the carbonaceous chondrite anhydrous mineral ccam slope 1 mixing line these temperature depth variations in the ureilite parent body could have been created by a heterogeneous distribution of heat producing elements which would indicate that isotopic heterogeneities existed in the material from which the ureilite parent body was assembled

eemian climatic and hydrographical instability on a marine shelf in northern denmark abstract benthic foraminifera and stable isotope data from the last interglaciation eemian substage 5e from a borehole at skagen denmark provide evidence for major environmental and hydrographic changes during this period during the first millennium of the eemian water masses covering northern denmark became gradually warmer temperate conditions prevailed during most of the interglaciation but these were interrupted by two periods with decreased water temperatures the first cooling event s 1 was not very distinct at skagen but the second event s 2 seen in both the foraminiferal and oxygen isotope record represents a large shift to subarctic conditions carbon isotopes indicate a change in ocean circulation during both events no comparable climate variations are seen within the holocene record at the site the final cooling of the water masses associated with the substage 5e 5d boundary occurred within a few hundred years these last interglacial climatic changes were probably caused by variations in strength and or position of the north atlantic drift possibly as a result of varying vigor of the atlantic conveyor in addition minor variations in the fossil assemblages also indicate fluctuations in the inflow of atlantic water to the skagerrak kattegat area during the warm intervals of substage 5e

inner shelf to lower shoreface hummocky sandstone bodies with evidence for geostrophic influenced combined flow lower cretaceous west greenland abstract hummocky sandstone bodies were deposited on the margin of an early cretaceous rift basin in an overall progradational inner shelf to lower shoreface unit excellent outcrops of this unit permitted a detailed study of sedimentary structures and paleocurrents in relation to sandstone geometries the sandstone bodies are lensoid and 0 5 4 m thick with lateral extensions from a few meters to more than 30 m laterally they pinch into thin sandstone sheets that continue for at least 130 m along the entire outcrop or swell within a distance of 20 30 m to form another sandstone lens the lower boundaries are sharp with local erosional relief up to 1 m hummocky cross stratification wave ripple cross lamination and low angle cross stratification are closely interbedded within the sandstone aminated mudstone beds 10 60 cm thick separate the sandstone bodies and are generally continuous over the entire length of the outcrop sedimentary structures in the sandstone bodies were produced by high energy wave generated oscillatory currents and unidirectional geostrophic currents vertical stratification successions from individual storm events reflect deposition during both increasing storm current velocity succeeded by waning storm deposits and more typically waning storm facies successions deposition of the unusual vertical successions was probably controlled by an episodically high sediment supply the local presence of the hummocky sandstone bodies on a regional scale was controlled by a paleogeographic setting where the bathymetric contours locally caused geostrophic cu rents to decelerate

deposits from wave influenced turbidity currents pennsylvanian minturn formation colorado u s a turbidity currents generated nearshore have been suggested to be the source of some sandy marine event beds but in most cases the evidence is circumstantial such flows must commonly travel through a field of oscillatory flow caused by wind generated waves little is known however about the interactions between waves and turbidity currents we explore these interactions through detailed process oriented sedimentological analysis of sandstone event beds from the pennsylvanian minturn formation in north central colorado u s a the minturn formation exhibits a complex stratigraphic architecture of fan delta deposits that developed in association with high topographic relief in a tectonically active setting an 20 35 m thick unconformity bounded unit of prodelta deposits consists of dark green shale and turbidite like sandstone beds with tool marks produced by abundant plant debris some of the sandstone event beds most abundant at distal localities contain reverse to normal grading and sequences of sedimentary structures that indicate deposition from waxing to waning flows in contrast proximal deposits in some cases less than a kilometer away contain abundant beds with evidence for deposition by wave dominated combined flows including large scale hummocky cross stratification we interpret the majority of these event beds as a record of deposition from hyperpycnal flows i e turbidity currents generated directly from highly concentrated river plumes which accelerated and decelerated in response to a rising and falling flood discharge additional support for this interpretation includes the following 1 a variety of sole marks including flute and gutter casts as well as tool marks made by relatively large up to tens of centimeters across woody debris i e groove prod and chevron marks 2 consistent unimodal orientation of sole marks and abundant ripple cross stratification which indicate strong downslope directed flow 3 a well documented sedimentological framework for the formation of fan delta deposits adjacent to nearby highlands and 4 plant fossils typical of middle to high elevation habitats that are abundant in the turbidite beds but absent in underlying and overlying shoreline and marginal marine deposits which have a separate floral assemblage differences in grain sizes vertical stratification sequences and bed thicknesses between outcrops are interpreted to result from the spatial distribution of wave effects the time history of hyperpycnal flows and the interaction of these processes the latter varied both spatially and temporally and produced a wide range of bed types which are incorporated into a new conceptual model for storm influenced hyperpycnal flows

origin of ureilites inferred from a sims oxygen isotopic and trace element study of clasts in the dar al gani 319 polymict ureilite secondary ion mass spectrometer sims oxygen isotope analyses were performed on 24 clasts representing 9 clast types in the dar al gani dag 319 polymict ureilite with precisions better than 1 olivine rich clasts with typical ureilitic textures and mineral compositions have oxygen isotopic compositions that are identical to those of the monomict ureilites and plot along the ccam carbonaceous chondrite anhydrous mineral line other igneous clasts including plagioclase bearing clasts also plot along the ccam line indicating that they were derived from the ureilite parent body upb thus we suggest that some of the plagioclase bearing clasts in the polymict ureilites represent the missing basaltic component produced by partial melting on the upb trace element concentrations mg k sc ti v cr mn fe co ni cu rb sr and ba in ureilitic plagioclase and glass from 13 clasts were obtained by using the sims high mass resolution method the trace element contents of the plagioclase generally show monotonic variations with anorthite content mol that are consistent with partial melting and fractional crystallization incompatible trace element concentrations k ti and ba are low and variable for plagioclase with an 40 indicating that the parental magmas for some clasts were derived from a depleted source we performed partial melt modeling for ci and cm precursor compositions and compared the results to the observed trace element k ba and sr abundances in the plagioclase our results indicate that 1 the upb evolved from a alkali rich carbonaceous chondritic precursor 2 parent melts of porphyritic clasts could have formed by 5 20 equilibrium partial melting and subsequent fractional crystallization and 3 parent melts of the incompatible trace element depleted clasts could be derived from fractional melting where low degree 10 partial melts were repeatedly extracted from their solid sources thus both the oxygen isotopic and trace element compositions of the plagioclase bearing clasts in dag 319 suggest that the upb underwent localized low degree partial melting events the partial melts could have been repeatedly extracted from the precursor resulting in the formation of the olivine pigeonite monomict ureilites as the final residue

fe mg fe mn relations of meteorites and primary heterogeneity of primitive achondrite parent bodies abstract we examine fe mg mn relations of meteorites as represented on plots of molar fe mg ratio vs molar fe mn ratio and use them to consider whether it is meaningful to classify achondrites as primitive or evolved first we demonstrate that fe mg fe mn plots can be used to identify some of the major processes that have affected meteorite parent bodies during both the nebular condensation and accretion and the planetary igneous stages of their evolution examination of compositions of chondrites on this diagram reveals distinct patterns that result from three nebular processes 1 volatility controlled mn mg fractionation 2 metal silicate fractionation under highly reducing conditions and 3 subsequent oxidation leading to variations in feo mgo ratio ordinary chondrites ocs show a characteristic pattern that records all three of these processes and suggests that the latter two are coupled examination of the compositions of achondrites on this diagram shows that all of those that have been classified as primitive lodranites acapulcoites winonaites iab silicate inclusions brachinites and ureilites are easily distinguished from those that have been classified as evolved sncs heds and lunar basalts the mn mg ratios of the former are chondritic while those of the latter are superchondritic hence they plot in two graphically distinct regions of the fe mg fe mn diagram a simple melting calculation reveals that this distinction results principally because the former are residues and the latter are melts or cumulate products of melts rather than because the latter are more evolved additionally however some of the groups classified as primitive achondrites show fe mg fe mn patterns similar to that of ocs constant but distinct mno mgo ratios over large ranges of feo mgo ratio we argue that these trends reflect primary heterogeneity resulting from the same nebular processes as those that affected ocs and therefore preserve evidence that more of the materials that accreted to form planetesimals experienced these processes than is apparent from known chondrites this evidence is preserved principally because these meteorites are residues in contrast groups commonly classified as evolved achondrites show fe mg fe mn patterns that reflect only igneous processing and any evidence for primary heterogeneity of their parent bodies has been obliterated again this is principally because these meteorites represent melts rather than beause they are more evolved usage of the terms primitive and evolved to describe achondrites should be clearly defined

origin and evolution of the ureilite parent magmas multi stage igneous activity on a large parent body analyses of olivine and pigeonite cores interpreted as cumulate crystals in eight low shock ureilites show well defined correlations between fe x where x is one of the minor elements mn cr ca al ti p or ni and fe mg ratios for the lithophile minor elements these trends are linear with positive slope and pass through or near the origin indicating various degrees of feo reduction of the parent magmas the trends shown by p and ni are consistent with this interpretation and additionally require equilibrium crystallization of 20 27 mole metal graphite was most likely the reducing agent which implies that the ureilites equilibrated at different pressures because the graphite fo2 buffer is pressure dependent there is no evidence for fractionation of olivine or pryroxene in any of these trends the ca ti and al trends show significant scatter indicating that there must have been multiple parent magmas with very similar mg mn and mgcr ratios but different mgal mgca and mgti ratios cao al2o3 ratios vary by a factor of 3 among the eight magmas and are superchondritic 14 32 molar similar to lunar mare basalts we propose the following model for generation and crystallization of ureilite parent magmas upm chondritic material undergoes 10 25 partial melting leaving a plagioclase depleted residue the magma or magmas form a differentiated crust on the ureilite parent body upb with mafic cumulates and plagioclase cumulates spatially separated later remelting 10 of the mafic cumulates produced the upm siderophile elements indicate that the source region of the upm had not experienced segregation of metal such as would occur during core formation in the source region the pressure must have been at least 0 5 1 kb because only at pressures this high does the graphite buffer allow iron oxide to be the stable phase relative to metallic iron the graphite bearing upm were emplaced at various levels in the crust where they were reduced to various extents dependent on depth ureilites are early olivine pigeonite cumulates from these magmas compositions of interstitial low ca pyroxenes indicate that the trapped interstitial liquids from which they crystallized had lower mnmg crmg camg almg and namg ratios than the upm and indicate an abrupt change in liquid composition coincident with impact excavation of ureilites this interstitial material may be derived by mixing a shock melt of nearby olivine pigeonite cumulates with residual primary liquid our model predicts that the upb had a differentiated crust did not have a core and was at least 235 km in radius the lack of a ureilite like body among spectrally analyzed asteroids suggests that either the spectral signature of the upb is not that of ureilites themselves perhaps of carbon free feldspathic material instead that the upb is not intact or that ureilites did not originate in the asteroid belt

effects of ambient currents and waves on gravity driven sediment transport on continental shelves abstract observations from several shelf environments show that down slope gravity driven transport may constitute an important mode of suspended sediment dispersal across shelves and highlight the influence of ambient waves and currents on gravity induced sediment flux the phenomena discussed here involve high concentrations of suspended sediment mixed with seawater and thus differ in genesis from hyperpycnal plumes released directly from sediment laden rivers the field sites examined are the gulf of bohai off the mouth of the yellow river huanghe the northern california shelf off the mouth of the eel river and the louisiana shelf west of the mouths of the mississippi river off the yellow river rapid down slope transport over distances of a few km occurred when frictional resistance induced by strong along shelf currents was temporarily relaxed more prolonged down slope motion over longer distances occurred following floods of the eel river when wave and current agitation provided turbulence to sustain gravity driven transport of fluid mud on the louisiana inner shelf the down slope gravity force was much weaker but observations suggest that thin gravity flows may still have occurred in the presence of waves a simple analytical theory is developed that incorporates the influence of ambient shelf currents on gravity driven transport of suspended sediment this theory is quantitatively consistent with the observations from the three sites if the supply of easily suspended sediment is less than the capacity of ambient currents including waves to carry sediment then intense turbulence limits gravity induced sediment transport by increasing the drag at the base of the flow when ambient currents abruptly cease rapid down slope transport can then occur over short distances until the sediment settles such flows do not remain intensely turbulent because the slope of the continental shelf is too gentle to induce shear instability within the gravity flow the maximum sustained rate of gravity induced sediment transport occurs when ambient currents are strong but the supply of easily suspended sediment exceeds the resuspension capacity of the ambient currents feedback then leads to values of the gradient richardson number ri within the flow that are near the critical value of 1 4 this partially damps bottom drag but still allows the generation of sufficient turbulence to maintain sediment in suspension observations also indicate systematic relationships among ri the supply of easily suspended sediment and the bottom drag coefficient acting on the gravity flow

climatic interpretation of terrestrial malacofaunas of the last interglacial in southeastern france abstract the sequence of the ruisseau de l amourette in the french alps covering the isotope stages 5e 5d 5c and part of 5a and 6 was studied for terrestrial mollusks correspondence analysis of the mollusk assemblages permits reconstruction of temperature and moisture trends using knowledge of the modern ecology of the recognized species the classic environmental succession of the last interglacial early glacial wurmian is recognized the eemian sub stage 5e suggests warm and moist conditions it is followed by the cold melisey i sub stage 5d showing moisture variation from dry in the lower part to moist in the upper part the mollusk equivalent of st germain i and ii also indicates warm and moist conditions the melisey ii stadial sub stage 5b is missing but may be reflected by the deposition of barren gravel layers all these environmental oscillations agree with the fluctuations described in the literature however stage 5e indicates a particular trend as the mollusks recorded two well individual cool events which seem to correspond to variations identified in various west european continental records however as no particular cold indicator species were identified these events cannot be related to strong climatic fluctuations as emphasized in the early studies of the greenland grip ice core or in north atlantic and western european records

estimation of the depositional time by comparison of foreset lamina cross stratification angles and ocean current fluctuations the pleistocene ichijiku formation kazusa group abstract the formation time of cross beds was estimated by comparing fluctuations of foreset angle of cross stratification of paleo kuroshio current deposits within the pleistocene ichijiku formation japan with variations in flow velocity in the present day kuroshio current foreset lamina angles were measured from a continuous 14 m long bed and angles of cross stratification were determined using fourier analysis the periodicities of kuroshio current velocity fluctuations were also subjected to the same fourier analysis comparison between the periodicities of foreset lamina angle and kuroshio velocity revealed that the two are related with interval ratios of the peaks in periodicity of 1 1 8 3 2 4 2 and 1 1 9 3 2 4 4 respectively these two ratios are almost identical it is calculated that 4 0 7 3 12 8 and 17 0 foreset lamina were formed in 12 4 24 0 39 4 55 9 h

trace element analysis of ureilites new constraints on their petrogenesis abstract six ureilites alha77257 alha81101 alh82130 pca82506 kenna and novo urei were analyzed using neutron activation analysis for ca sc cr mn fe co ni zn ga ree w re os ir and au we examined bulk samples as well as acid treated samples in the bulk samples the refractory siderophiles concentrations range from approximately 0 1 to 1 0 times ci chondrites while the volatile siderophiles range from about 0 07 to 0 3 times ci chondrites rare earth elements rees in ureilites are quite depleted and display light and heavy rare earth enrichments the antarctic meteorites display either much less pronounced v shaped patterns or no enrichment in the light rare earths at all in terms of the new trace element results ureilites do not fall into the coherent groups that other workers have defined by chemical or petrographic characteristics trace elements do provide additional constraints on the models for the petrogenesis of ureilites in particular the siderophile element abundances call for simplified models of chemical processing rather than the complex multistage processing called for in silicate fractionation models ree concentrations on the other hand imply multistage processing to produce the ureilites none of the ureilite petrogenesis models extant account for the trace element data these new data and the considerations of them with respect to the proposed ureilite petrogenesis models indicate that the direction of modelling should be toward contemplation of mixtures and how the components we observe in ureilites behave under such conditions

origin of ureilite meteorites and implications for planetary accretion although ureilites have been considered bizarre meteorites our analysis of their properties suggests that they formed by simple well known processes we conclude that 1 ureilites are the sole rock type in a major fraction of their parent body 2 they are partial melt residues and not cumulates 3 removal of 90 of the al in the basalts would largely stop radioactive heating if 26al was the heat source ensuring that large volumes of ureilite like material were generated 4 they formed in a large chondritic body that had a heterogeneous o isotopic composition 5 slow diffusion of o in solid and molten silicates ensured that partial melting did not homogenize the o isotopes of the residues 6 the puzzling absence of the basaltic melts that accompanied ureilite formation probably results from ejection into space by explosive volcanism together these conclusions provide a simple plausible origin for ureilites that accounts for most of their properties ureilites are residues from the partial melting of isotopically heterogeneous chondritic material we suggest that other meteorite parent bodies and planetesimals may have experienced similar histories and that ureilites provide important constraints on the accretionary and igneous histories of planets and asteroids

primary magmatic carbon in ureilites evidence from cohenite bearing metallic spherules metallic spherules containing cohenite fe ni metal sulfides and rare phosphorus bearing minerals occur as inclusions within olivine and pigeonite grains in five low shock ureilites the bulk compositions mineralogy and textures of these spherules indicate that they represent fe ni c s alloys that existed as droplets of immiscible metallic liquid in the magma s from which ureilites crystallized at magmatic temperatures these alloys were carbon saturated and probably coexisted with graphite in the magma this is consistent with the occurrence of graphite crystals as inclusions in olivine in some ureilites and supports the view that graphite in ureilites was a primary magmatic component graphite could have been a residue from the solid source materials that melted to produce the ureilite parent magma s or could have crystallized from the magma s the metallic liquids separated into immiscible fe c liquids and fe s liquids after they were trapped within silicates the fe c liquids contained 4 5 wt c and 3 7 wt ni cohenite was the liquidus phase and started to crystallize at 1200 1225 c forming euhedral and subhedral crystals at the eutectic 1175 c iron containing 7 9 ni and 1 8 c crystallized along with cohenite at lower temperatures the iron exsolved cohenite and possibly iron

breaching in fine sands and the generation of sustained turbidity currents in submarine canyons natural moderately loosely packed sands can only erode from the surface of the bed after an increase in pore volume because of this shear dilatancy negative pore pressures are generated in the bed in cases of low permeability these negative pressures are released relatively slowly which retards the maximum rate of erosion this effect is incorporated in a new analytically derived pick up function that can explain the observation of gradual retrogressive failure of very steep subaqueous slopes sometimes more than 5 m high in fine non cohesive sands this process termed breaching in the field of sediment dredging may produce large failures in sand bars or river banks the analytical function that describes the breaching process in fine sand is incorporated in a one dimensional steady state numerical model of turbidity currents describing the spatial development of flow this model is applied to simulate a large flushing event in scripps submarine canyon pacific coast of california breach retrogradation and the successive evolution in time of the resulting turbidity current in the canyon are predicted in a sequence of discrete steps predicted velocities are compared with values measured during a flushing event implications for the interpretation of deep water massive sands are discussed

west european terrestrial molluscs assemblages of isotopic stage 11 middle pleistocene climatic implications rousseau d d puiss6gur j j and lecolle f 1992 west european terrestrial molluscs assemblages of isotopic stage ii middle pleistocene climatic implications palaeogeogr palaeoclimatol palaeoecol 92 15 29 tufil deposits in the seine and the avelasse valleys have yielded numerous molluscs assemblages belonging to the lyrodiscus biome these malacofaunas primilarily indicative of forest which developed under a warm climate have no present day counterpart the biostratigraphical study of several localities based on new investigations at vernon seine valley and arrest avelasse valley and a reexamination of the faunas from st pierre les eibeuf suggests the allocation of a holsleinian age this is supported by u th dates for vernon and the stratigraphy of the loess sequence of st pierre les elbeuf similar assemblages yielded by tufas of the same age in england and germany indicate that the lyrodiscus biome was widespread the warm climate recorded by the molluscs of the tufa deposits is in agreement with pollen and marine analyses for the isotopic stage 11 362 423 kyr b p in this way the lyrodiscus biome appears as an interesting marker for the continental quaternary in western europe if the occurrence of these particular molluscan assemblages is due to climate refuges from the declined tertiary biota from which i e r lyrodiscu s could have emigrated also needed to exist

confirmation of an interglacial age for the condat tufa dordogne france from biostratigraphic and isotopic data the condat tufa is a localised deposit reaching 8 2m in thickness composed of freshwater carbonates deposited in a complex series of environments which include marsh spring and stream facies five radiocarbon determinations had previously been obtained from different stratigraphic levels within the tufa and had given a consistent series ranging from 12320 175 bp to 31050 1500bp although the youngest two dates from near the surface of the tufa had been rejected as being anomalously young the older dates were regarded as indicating tufa formation during the last cold stage biostratigraphic analyses of the molluscan and ostracod faunas presented here demonstrate that the tufa formed under fully temperate conditions throughout the occurrence of certain snails that are either locally extinct e g belgrandia marginata or unknown living in western france e g daudebardia brevipes together with the geomorphological setting suggest that the tufa is of interglacial age new radiocarbon determinations of the condat tufa all proved to be 33 ka bp and support this conclusion

late pleistocene climate record in the eustis loess section nebraska based on land snail assemblages and magnetic susceptibility abstract based on multivariate analysis of mollusk assemblages and magnetic susceptibility of the eustis section in western nebraska the climate of the peoria loess steppe was relatively mild and in terms of annual precipitation relatively moist during the advance stages of woodfordian ice it was cold and dry during ice retreat the diversity and composition of mollusk species indicates that the extreme cold and dry climate was reached during the late phase of peoria time in mollusk zone mz3 although soil moisture during the growing season at that time was high the growing season was short and annual precipitation totals were low low values of magnetic susceptibility imply relatively rapid dust deposition during this interval judging from the current ecological tolerance of the species no closed forest existed in the area only scattered shrubs or isolated tree stands may have been present the late peoria mz3 assemblage compares favorably with the columella fauna of europe in contrast the early peoria mollusk assemblages mz1 and mz2 compare well with the european pleniglacial pupilla associations based on available 14 c dates from the studied region and on assumed relation of magnetic susceptibility to sedimentation rates the estimated age of the mz1 and mz2 zones is 24 000 to 16 000 yr whereas that of mz3 is 16 000 to 12 000 yr

a sedimentological and sequence stratigraphic reinterpretation of the upper cretaceous prairie canyon member mancos b and associated strata book cliffs area utah usa the mancos shale book cliffs eastern utah usa represents the open marine mudstones of the cretaceous western interior seaway and encloses the prairie canyon member which is located over 50 km seaward of interpreted contemporaneous highstand shoreline deposits in the blackhawk formation examination of the member reveals that it does not wholly represent offshore deposition as previously interpreted but instead contains three nearshore facies associations 1 tidally influenced fluvial channel fills 2 fluvial dominated delta fronts and 3 weakly storm influenced shorefaces tidally influenced fluvial channel fills are commonly stacked into multistory bodies that can be traced for tens of kilometers at discrete stratigraphic levels defining incised valley fill networks four such incised valley networks are identified at outcrop fluvial dominated deltas and weakly storm influenced shorefaces are eroded into by and lie at the down dip terminations of incised valley fills and are interpreted as forced regressive and lowstand shoreface deposits one incised valley fill appears to be onlapped by additional fluvial dominated deltas which represent pulses of shoreface progradation during an overall transgression forced regressive lowstand and transgressive shorefaces in the prairie canyon member differ significantly from highstand shorefaces in the blackhawk formation the former are sand poor and weakly wave storm influenced whereas the latter are sand rich and wave dominated this change in shoreface style reflects increased mud supply and an enhanced embayment paleogeography during periods of relative lowering of sea level

quaternary mollusc assemblages from the lower basin of salado river buenos aires province their use as paleoenvironmental indicators abstract quaternary mollusc assemblages preserved in the salado basin are described and analyzed in order to reconstruct past environments and evaluate spatial and temporal variations five localities were analyzed in which 48 998 individuals of eight continental gastropod species were recovered heleobia parchappii antillorbis nordestensis biomphalaria peregrina drepanotrema heloicum uncancylus concentricus pomacea canaliculata succinea meridionalis and miradiscops brasiliensis as well other species typical of marine estuarine environments have been found among which heleobia australis is highlighted based on changes in the composition and abundance of the assemblages different environments could be recognized quaternary mollusc assemblages have low taxonomic heterogeneity and spatial and temporal variations assemblages recovered from late pleistocene early holocene sediments are characterized by low species richness and abundance with a single species in numerous examples in the middle holocene the shells became more constant and more diverse late holocene assemblages have high species richness freshwater terrestrial and amphibious habits and show some differences among different localities several episodes of flooding have been identified through the record of fossiliferous horizons with high density of shells mainly heleobia parchappii these events that affected the area of influence of the salado river occurred at least during the late holocene

long term enso like events represented in the middle pleistocene shelf successions boso peninsula japan abstract millennial century and decadal scale stratigraphic cyclicities are described from transgressive shelf successions of the middle pleistocene ichijiku and kakinokidai formations ca 0 7 ma in the boso peninsula japan the ichijiku formation ca 400 m thick represents a shelf sandridge complex developed under the influence of the large meanders of the paleo kuroshio current and intertongues with outer shelf muddy deposits of the kakinokidai formation ca 170 m thick to the northeast most of the two formations are classified as a transgressive systems tract formed during the rise in glacioeustasy from oxygen isotope stages 18 to 17 three different types of cyclicities are identified in the transgressive shelf deposits the first cyclicity ca 3000 years duration is represented by coarsening upward units of the kakinokidai formation associated with the northeastward extension of the sandridge complex lower parts of each coarsening upward unit are characterized by intercalations of tempestites more than the upper parts the second cyclicity ca 250 years duration is defined by master bedding surfaces within sandridge deposits interpreted as formed in response to lateral migration of foresets of the sandridge complex the third cyclicity ca a few decades or shorter duration is defined as the units bounded by reactivation surfaces within large scale trough cross bedded sandstone units the three different types of cyclicities are interpreted to document fluctuations in the paths and speeds of the paleo kuroshio current in response to the large meanders oscillations of the large meanders of the modern kuroshio current every few to 10 years are interpreted to be in response to enso el nino southern oscillation events and are also associated with the decrease in frequency of typhoons in the western pacific if our stratigraphic interpretation is true the paleo kuroshio current controlled shelf successions document high frequency oscillations in paleoclimates responding to the long term enso like events in the western pacific during the middle pleistocene

mineralogy of antarctic ureilites and a working hypothesis for their origin and evolution abstract mineralogical and crystallographic data and electron microprobe analyses of silicate minerals for antarctic ureilites y74123 y74130 y74659 y790981 alha77257 alha78019 and alh82106 extend the chemical and textural variations among ureilites beyond those known for non antarctic ureilites low ca pyroxenes possibly orthopyroxene poikilitically enclosed in olivine and coexisting with mg rich pigeonites have been identified in y74659 and alha77257 coexisting low ca pyroxene pigeonite and augite together with the very fe rich olivine in ureilites were observed in y74130 almost fe free pigeonite and diopside coexist in alh82106 no systematic differentiation trend has been reconstructed from these data but the pyroxene pairs yield formation temperatures above 1200 c a weak anticorrelation between mno and feo delineated by these pyroxenes suggests that a reduction reaction is responsible for the chemical variations a working hypothesis for ureilite formation involves high temperature episoded and a planetesimal scale collision which might have facilitated compaction and recrystallization of mafic silicates during the episodes fe ni s eutectic melt and a partial melt rich in ca al and fe might have been lost from a carbonaceous chondrite like source material

late glacial and holocene malacofaunas from archaeological sites in the somme valley north france the first malacological successions covering the late glacial period and the early holocene are reported from archaeological sites in northern france five malacological zones s1 5 are recognized which are related to the regional lithostratigraphy upper palaeolithic mesolithic archaeology and to a radiocarbon chronology the zone s1 which contains an assemblage of low species diversity but with abundant vallonia allows attribution of the basal loess reworked as a rainwashed silt in the valley bottom to the early late glacial rather than the pleniglacial overlying the loessic sediments is an organic silt known as the belloy soil w at belloy which has yielded birch pollen but no pine allowing attribution to the early part of allerod phase of the late glacial the molluscan faunas from this level s2 are richer and more diverse helicopsis striata muller appears to be typical of this period above the allerod deposit is a minerogenic silt containing rhizomes but this is only represented in the valley floors the malacofaunas from this unit s3 are similar to those of the allerod silt but contain a higher proportion of hygrophilous taxa these faunas are assigned to the younger dryas a conclusion supported by radiocarbon dating of bones associated with the terminal upper palaeolithic industrie a pieces m churees which occur at the top of the unit the late glacial succession is overlain by organic silts of holocene age which at several sites have yielded mesolithic artefacts the molluscan faunas are much more diverse than the earlier late glacial assemblages and contain abundant shade demanding taxa s4 then a fall in species diversity and a reversion to faunas of open ground occur s5 comparison of these successions with similar sites in burgundy the paris basin and southeastern england demonstrate a closer affinity to the molluscan sequences of kent rather than to the french sites although late glacial molluscan faunas are still poorly known from france

high resolution paleotemperature proxy record for the last interglaciation based on norwegian speleothems two speleothems from a coastal lowland and an alpine cave site in northern norway grew in isotopic equilibrium during termination ii and marine isotope stage 5 150 000 80 000 yr b p as dated by the u series technique the stable isotope record 18o 13c displays a time resolution down to 20 yr the 18oc signal in the two speleothems appears to be mainly dominated by the meteoric signal i e there is a positive relationship between 18oc and temperature 18oc t 0 the fm 2 couplet a younger dryas type two step structure in termination ii at 132 000 5000 and 129 000 5000 yr is prominent in the speleothem record the record correlates well with details and gross features of the grip ice core and confirms the time scale and the unstable climate proposed for substage 5e the isotopic response in termination ii is delayed relative to the devil s hole record and is in accord with the specmap chronology but cooling at the end of substage 5e seems to be synchronous between devil s hole and the norwegian flowstones

stratigraphy of the kazusa group boso peninsula an expanded and highly resolved marine sedimentary record from the lower and middle pleistocene of central japan major climatic reorganizations including changes in the nature of glacial interglacial cycles through the pleistocene are a key issue for improving the understanding of earth s climate system highly resolved marine sedimentary records are essential to reconstruct the details of these past climatic changes and investigate the mechanisms responsible for them the kazusa group located in the central part of the japanese island chain is well exposed and contains a remarkably continuous and thick deep and shallow water marine sedimentary succession this group also contains well preserved marine microfossils pollen paleomagnetic reversal events geochemical signatures and a large number of tephra beds these features allow us to establish a robust chronological and stratigraphic framework for the kazusa group and provide a rare opportunity to study oceanic and terrestrial climatic and environmental changes at high resolution especially through the lower and lower middle pleistocene in the boso peninsula chiba prefecture the kazusa group is deeply incised yielding spectacular river cut exposures the matuyama brunhes paleomagnetic reversal is observed immediately above the widespread byakubi e byk e tephra in the chiba composite section within the kokumoto formation kazusa group because the matuyama brunhes boundary customarily serves as the primary guide for the lower middle pleistocene subseries boundary the chiba composite section is considered an excellent candidate for its global boundary stratotype section and point gssp this study reviews the published data for the kazusa group hitherto almost exclusively in japanese in order to place the chiba composite section within its broader depositional and chronostratigraphic context

experiments on bidisperse constant volume gravity currents propagation and sediment deposition laboratory experiments show that the propagation and sedimentation patterns of particle laden gravity currents are strongly influenced by the size of suspended particles the main series of experiments consisted of fixed volume releases of dilute mixtures containing two sizes of silicon carbide particles 25 m and 69 m mean diameter within a 6 m flume polydisperse experiments involved mixtures of five different particle sizes and variation of the amounts of the finest and coarsest particles all variables apart from the initial relative proportions of particles were identical in the experiments the effects of mixing different proportions of fine and coarse particles is markedly non linear adding small amounts of fine sediment to a coarse grained gravity current has a much larger influence on flow velocity run out distance and sedimentation patterns than adding a small amount of coarse sediment to a fine grained gravity current the experiments show that adding small amounts of fine particles to a coarse grained current results in enhanced flow velocities because the fine sediment remains suspended and maintains an excess current density for a much longer time thus the distance to which coarse particles are transported increases substantially as the proportion of fines in the flow is increased our experiments suggest that sandy turbidity currents containing suspended fines will be much more extensive than turbidity currents composed of clean sand

geostrophic circulation or shallow marine turbidity currents the dilemma of paleoflow patterns in storm influenced prograding shoreline systems abstract in ancient storm influenced prograding shoreline sequences sole marks mainly tool marks from hummocky crossstratified storm deposits are commonly oriented normal to paleoshoreline and the trend of paleobathymetric contours in the basin asymmetrical tool marks typically indicate flows directed offshore several workers have attributed their formation to storm generated shallow marine turbidity currents this interpretation conflicts with observations from modern shelves where storm driven circulation generally is geostrophically balanced and time averaged bottom currents approximately parallel bathymetric contours and the local shoreline the resolution of these apparently conflicting observations may lie in the realization that tool marks and many other small paleoflow indicators form almost instantly as the result of instantaneous flow conditions very near the bed beneath storm generated flows in the shallow ocean instantaneous and time averaged characteristics of the bottom boundary layer generally exhibit little similarity storm generated tool marks are formed by the movement of large tools within the thin less than 1 m inner boundary layer resulting from the superimposition of waves and currents the orientation of the peak instantaneous shear stress moving large tools under such combined flows mainly reflects wave orbital motions which typically are normal to shore the magnitude of stress is great y increased in the offshore direction and decreased in the onshore direction by superimposition of a steady current with an offshore component of flow but the direction of stress is only slightly affected in ancient storm influenced sequences therefore shore normal tool marks generally were not formed by turbidity currents rather their orientation is best attributed to shoaling waves approaching the coast at a very high angle asymmetrical tool marks are directed offshore due to enhanced shear stress on the offshore stroke of waves superimposed on a geostrophic current with an offshore flow component tool marks do not reflect the time averaged bottom flow direction in fact they provide almost no information concerning steady bottom currents in contrast high angle cross beds formed in coarser sediment by the migration of dunes and sandwaves although relatively rare in offshore storm deposits generally reveal approximately shore parallel flows in ancient systems cross beds closely reflect the time averaged flow direction in the outer boundary layer of a geostrophic current for three reasons 1 the net transport direction for sand moving as bed load beneath a combined flow lies between the directions of peak instantaneous shear stress and time averaged shear stress 2 large ripples disrupt the thin inner boundary layer and 3 long time intervals relative to wave induced velocity oscillations are required to form large ripples

climatic transfer function from quaternary molluscs in european loess deposits abstract correspondence and multiple regression analysis of terrestrial molluscs in the loess sections of achenheim alsace france has permitted the reconstruction of climatic variations during the last three glacial interglacial cycles back to 339 000 yr b p the sequence has been dated according to the specmap chronology of imbrie et al 1984 and the fossil faunas have been calibrated in relation to recent assemblages sampled in defined ecological conditions in sweden and france transfer functions that relate the abundances of different species to climate allow the reconstruction of temperature and precipitation estimates for the coldest february and warmest august months in present day alsace were obtained and variations in temperature between 13 and 2 c in winter and 10 and 17 c in summer were determined these results are consistent with those yielded by transfer functions using other continental fossils estimates differ for past precipitation summer precipitation is always less than present with values between 50 and 78 mm while modern august values are 76 mm higher winter estimates are always higher than the present mean between 76 and 33 mm while the recent february value is 34 mm comparisons between cycles show that the climatic patterns described for one cycle cannot be strictly applied to the others comparisons have been made with the pollen stratigraphy of la grande pile the nearest quantified sequence to achenheim and with some atlantic cores in order to study the magnitude of deviations from modern mean values of the climatic parameters

ureilite petrogenesis a limited role for smelting during anatexis and catastrophic disruption a popular model for ureilites assumes that during anatexis in an asteroidal mantle pressure buffered equilibrium smelting partial reduction coincident with partial melting engendered their conspicuous mafic silicate core mg diversity 75 96 mol several mass balance problems arise from this hypothesis smelting inevitably consumes a large proportion of any plausible initial carbon while generating significant proportions of fe metal and copious proportions of co gas the most serious problem concerns the yield of co gas if equilibrium smelting produced the ureilites entire 21 mol range in olivine core mg the proportion of gas within the asteroidal mantle assuming plausibly low pressure 80 bar should have reached 85 vol based on the remarkably stepwise cooling history inferred from ureilite texture and mineralogy a runaway co leaky process that can loosely be termed smelting appears to have occurred probably triggered by a major impact the runaway scenario appears likely because by le ch telier s principle co leakage would tend to accelerate the smelting process also the copious volumes of gas produced by smelting would have led to explosive mass leaky eruptions into the vacuum surrounding the asteroid loss of mass would mean diminution of interior pressure which would induce further smelting leading to further loss of mass basalt and so on such a disruptive runaway process may have engendered the ureilites distinctive reduced olivine rims but the only smelting according to this scenario was a short lived disequilibrium process that reduced only the olivine rims not the cores and the ureilites were cooling not melting during the abortive smelting episode

high resolution correlation patterns in the turbidite systems of the hecho group south central pyrenees spain detailed bed by bed correlations in sheetlike lobes and basin plain elements of the hecho group were carried out through a hierarchical decomposition based on three orders of correlation this procedure provides the most detailed correlation framework with chronostratigraphic significance first order decomposition is based on physical correlation by mapping of major megaturbidites second order decomposition consists in matching a series of marker beds within first order units leading to the definition of units several metres thick finally third order decomposition relies on the matching of serial features within second order packages number vertical arrangement and facies features of beds and further testing the coherence of the downstream evolution of facies in single beds sheetlike lobes and basin plain are closely related and display a distinctive sheet like geometry basin plain beds are deposited by the same flows that build the sheetlike lobes with the existence of a transitional facies change from the lobe to the basin plain thickening of some beds towards the basin plain due to ponding of the fine grained silt and mud divisions a diagnostic feature of the basin plain controls the sheet like stacking pattern by balancing the wedging out of thinner lobe beds upcurrent from or within the basin plain as a consequence the whole area can be geomorphically classified as a basin plain which comprises both lobe and basin plain facies associations

a salt oscillator in the glacial atlantic 1 the concept as shown by the work of dansgaard and his colleagues climate oscillations of one or so millennia duration punctuate much of glacial section of the greenland ice cores these oscillations are characterized by 5 c air temperature changes severalfold dust content changes and 50 ppm co2 changes both the temperature and co2 change are best explained by changes in the mode of operation of the ocean in this paper we provide evidence which suggests that oscillations in surface water conditions of similar duration are present in the record from a deep sea core at 50 n based on this finding we suggest that the greenland climate changes are driven by oscillations in the salinity of the atlantic ocean which modulate the strength of the atlantic s conveyor circulation

are ureilites residues from partial melting of chondritic material the answer from magpox calculations performed using magpox show that no bulk compositions having chondritic ca al ratio and within the range of chondritic si mg ratios can produce the olivine pigeonite ureilites which constitute 65 of those for which modal abundances are known as residues of single stage equilibrium partial melting calcium aluminum ratios of 2 3 5 ci are required in addition all the ureilites could not have formed from a single composition at various degrees of reduction because they show no correlation between pigeonite olivine ratio and mg ratio materials with various al mg ratios ranging from subchondritic to superchondritic are required if these materials are primitive i e created by nebular processes rather than planetary igneous processes they are unknown in the meteorite record excess accretion relative to chondrites of 5 10 mol of a high temperature condensate component which was itself almost completely depleted in corundum due to early fractionation could create the necessary compositions the plausibility that such processes occurred on a parent body sized scale is difficult to assess in contrast lodranites can be produced as residues of 3 30 equilibrium partial melting of an average ordinary chondritic composition at the appropriate level of reduction although many features of ureilites suggest that they are relatively primitive residues produced by low degrees of melting of chondritic materials and thus resemble lodranites and other groups of primitive achondrites their predominantly pigeonite olivine mineralogy remains difficult to explain within this simple scenario

how long and how stable was the last interglacial abstract surface ocean indicators in the north atlantic during marine isotope stage mis 5 correlate closely with the vegetational succession in northeastern france the melisey i silty layer which marks the end of the last interglacial biozone in la grande pile pollen record appears coeval with the polar front advance c24 registered in the core v29 191 by a sharply increased presence of ice rafted detritus and the cold water foraminifer neogloboquadrina pachyderma sinistral since this event is younger than the peak of mis 5d the last interglacial as recognized in northern france correlates not only with the mis 5e but also with a substantial part of mis 5d the last interglacial in la grande pile was twice as long as the holocene and the climate in its first half was apparently not less stable than during the current interglacial if the future natural climates were to develop as analogs of the past then the onset of the next glacial environments on land would be still many millennia ahead

kiloyear scale climate events and evolution during the last interglacial mu us desert china the fifth segment of the milanggouwan stratigraphical section mgs 5 in the mu us desert provides high resolution geological information on environmental variations during the last interglacial the analysis of grain content 50 mu m organic content sio2 al2o3 tofe and sio2 al2o3 tofe ratios in the mgs 5 suggest that there were 17 kiloyear scale climate fluctuations in the last interglacial including 9 warm events w1 w9 and 8 cold events c1 c8 dominated by the east asian summer monsoon and winter monsoon respectively the analysis also suggests that the eemian interglacial was unstable with 3 warm events w7 w9 and 2 cold events c7 c8 indicating that climate fluctuations affected the east asian monsoon in the mu us desert during the last interglacial the change cycles and the nature of the kiloyear scale climate events have a close temporal relationship with the greenland ice core oxygen isotope data suggesting that the climate forming mechanism was affected by polar weather north atlantic sea ice range of the eurasian ice front and movement of the arctic frontal all of which affect the intensity of the siberian mongolian high pressure region through the movement of the cold air mass c 2012 elsevier ltd and inqua all rights reserved

holocene environmental signals from mollusk assemblages in burgundy france abstract the malacofaunas of burgundy france reflect changes in climate and the activities of man during the holocene statistical analyses based on the shannon diversity index and correspondence analysis are used to describe the mollusk assemblages in a composite sequence based on three well dated sites the variation demonstrated by the mollusks suggests that a two step warming took place between 10 000 and 9000 and 8000 and 6000 yr b p in relative agreement with the timing of the deglaciation in the tropical atlantic ocean proposed by mix and ruddiman 1985 quaternary science reviews 4 59 108 high humidity partly associated with widespread inundations of the valleys between 10 000 and 8000 yr b p may be related to estimated variations in the rate of freshwater discharge to the atlantic ocean reported by fairbanks 1989 nature 342 637 642 the increasing impact of human activities on the environment during the past 2000 yr is indicated by the low diversity of the mollusk assemblages demonstrating the need for careful interpretation of the youngest holocene sediments in this region

evidence from polymict ureilite meteorites for a disrupted and re accreted single ureilite parent asteroid gardened by several distinct impactors ureilites are ultramafic achondrites that exhibit heterogeneity in mg and oxygen isotope ratios between different meteorites polymict ureilites represent near surface material of the ureilite parent asteroid s electron microprobe analyses of 500 olivine and pyroxene clasts in several polymict ureilites reveal a statistically identical range of compositions to that shown by unbrecciated ureilites suggesting derivation from a single parent asteroid many ureilitic clasts have identical compositions to the anomalously high mn mg olivines and pyroxenes from the hughes 009 unbrecciated ureilite here termed the hughes cluster some polymict samples also contain lithic clasts derived from oxidized impactors the presence of several common distinctive lithologies within polymict ureilites is additional evidence that ureilites were derived from a single parent asteroid in situ oxygen three isotope analyses were made on individual ureilite minerals and lithic clasts using a secondary ion mass spectrometer sims with precision typically better than 0 2 0 4 2sd for 18o and 17o oxygen isotope ratios of ureilitic clasts fall on a narrow trend along the ccam line covering the range for unbrecciated ureilites and show a good anti correlation with mineral mg sims analysis identifies one ferroan lithic clast as an r chondrite while a second ferroan clast is unlike any known meteorite an exotic enstatite grain is derived from an enstatite chondrite or aubrite and another pyroxene grain with 17o of 0 4 0 2 is unrelated to any known meteorite type ureilitic olivine clasts with mg s 85 which include the melt inclusion bearing hughes cluster ureilites thus melt was present in regions of the parent ureilite asteroid with a bulk mg 85 when the asteroid was disrupted by impact giving rise to two types of ureilites common ferroan ones that were residual after melting and less common magnesian ones that were still partially molten when disruption occurred one or more daughter asteroids re accreted from the remnants of the mantle of the proto ureilite asteroid polymict ureilite meteorites represent regolith that subsequently formed on the surface of a daughter asteroid including impact derived material from at least six different meteoritic sources

ejecta megaregolith accumulation on planetesimals and large asteroids megaregolith accumulation can have important thermal consequences for bodies that lose heat by conduction as vacuous porosity of the kind observed in the lunar megaregolith lowers thermal conductivity by a factor of 10 i have modeled global average ejecta accumulation as a function of the largest impact size with no explicit modeling of time in conjunction with an assumed cratering size distribution exponent b the largest crater constrains the sizes of all other craters that significantly contribute to a megaregolith the largest impactor mass ratio is a major fraction of the catastrophic disruption mass ratio and in general the largest crater s diameter is close to the target s diameter total accumulation is roughly 1 5 of and proportional to the target s radius global accumulations estimated by this approach are higher than in the classic housen et al 1979 study by a factor of roughly 10 this revision is caused mainly by higher typical largest crater size for b 2 the single largest crater typically contributes close to 50 of the total of new nonrecycled ejecta megaregolith can be destroyed by sintering a process whose pressure sensitivity makes it effective at lower temperature on larger bodies planetesimals 100 km in diameter may be surprisingly well suited about as well suited as bodies two to three times larger in diameter for attaining temperatures conducive to widespread melting a water rich composition may be a significant disadvantage in terms of planetesimal heating as the shallow interior may be densified by aqueous metamorphism and will have a low sintering temperature

isolated highstand shelf sandstone body of turbiditic origin lower kenilworth member cretaceous western interior book cliffs utah usa abstract an isolated highstand shelf sandstone body of turbiditic origin has been identified in the lower kenilworth member hatch mesa area book cliffs utah relative to most other marine mudstone encased isolated sandstone bodies the hatch mesa succession has an abundance of bouma like turbidite beds a greater proportion of mudstone and siltstone is thinner 6 20 m and is weakly coarsening upward these attributes in combination with locally abundant hummocky cross stratified sandstones a paucity of wave ripples in the background fair weather deposits carbonaceous matter in all facies a lack of clinoforms and a low diversity abundance trace fossil suite suggest deposition in a prodelta environment between fair weather and storm wave base a three component shoreface to shelf model consisting of delta front subaqueous channel and prodelta turbidite deposits is proposed to explain the depositional environment and setting of the hatch mesa succession regional correlation has demonstrated that the hatch mesa succession is time equivalent with the second parasequence in the kenilworth kps2 which is characterized by inner shelf turbidite bodies at a number of other localities paleogeographic reconstructions reveal that the hatch mesa succession was deposited at least 16 km basinward of the kps2 lower shoreface in approximately 20 m of water the kps2 hatch mesa sandstone body package is part of the early highstand systems tract indicating that isolated or stray sandstone bodies are not solely restricted to the falling stage or lowstand systems tracts

across shelf sediment transport interactions between suspended sediment and bed sediment 1 we use a two dimensional time dependent sediment transport model to quantify across shelf transport deposition and sorting during wave driven resuspension events characteristic of those that dominate sediment transport on many continental shelves decreases in wave orbital velocities as water depth increases and the resulting cross shelf gradient in bed shear stress favor a net offshore transport of sediment on wide flat shelves slopes 0 1 percnt these gradients are low and the depth to which the seabed is reworked depends mainly on bottom shear stress and local sediment availability on narrow steep shelves slopes 0 5 percnt however the gradient in bottom stress generates significant cross shelf suspended sediment flux gradients that create regions of net erosion and deposition while the magnitude of waves generally determines the water depth to which sediment can be resuspended erosional and depositional patterns on narrow shelves are sensitive to cross shelf gradients in wave energy nonlocal sediment availability and the direction and magnitude of the cross shelf current during energetic waves cross shelf divergence of suspended sediment flux can create a coarsened erosional area on the inner shelf that abuts a region of fine grained sediment deposition on the mid to outer shelf if currents are strongly shoreward however flux divergence leads to erosion over the entire shelf

reponses des malacofaunes terrestres quaternaires aux contraintes climatiques en europe septentrionale abstract quaternary land snails show two major responses to climatic variations emigration and ecophenotypism the former is the case of the great majority of stenotopic species examples of migration are determined through the study of malacological associations in northern france cooler phases are indicated by the immigration and development of nordic and alpine species of which the area of distribution was invaded by ice by contrast interglacial temperate periods corresponding to a recolonization of free environments are indicated by the immigration of forest or semiforest thermophilic species ecophenotypism concerns some eurythermal species they display morphological variations of the shell mainly variations in size which parallel climatic variations in pupilla muscorum the shell is large when the climate is cold and small when it is temperate examples of migration and ecophenotypism are provided by joint studies of the malacological associations and pupilla muscorum in the achenheim site alsace france

paleoclimatology of the achenheim series middle and upper pleistocene alsace france a malacological analysis abstract the loessic series of achenheim show an uninterrupted stratigraphical sequence dating from the middle and upper pleistocene they contain very abundant paleontological material especially land snails statistical analysis of the malacofaunas multivariate methods has allowed the reconstruction of the climatic evolution of that site during this period five cycles have been recognized which correspond to the glacial cycles b c d e and f comparison with the section of cerveny kopec czechoslovakia indicates the existence of a major climatic event during the pleniglacial of cycle d with a general expansion of the loess steppe in europe an environment which later never appeared in alsace the analogy of the climatic sedimentary sequences of cycle c suggests that alsace and central europe belong to the same geographical entity the development of alsace to an intermediary status between northwestern and central europe

formation of ureilites by nebular processes oxygen isotopic data are presented for 23 ureilites including 14 antarctic meteorites they show a much greater range in isotopic composition than those previously studied most noteworthy is the fact that unlike other achondrite groups the ureilites do not fall on a mass dependent isotopic fractionation trend but rather fall along an extrapolation of the 16o mixing line defined by components of allende and other c3 chondrites correlations between isotopic and chemical data imply that the isotopic and chemical variations are due primarily to processes in the solar nebula and not to igneous processes within a parent body the ureilite parent body accreted with isotopic and chemical heterogeneities which were not much modined by subsequent parent body processes the precursor materials were related in some way to the c3 carbonaceous chondrites

comment on parent body depth pressure temperature relationships and the style of the ureilite anatexis by p h warren maps 47 209 227 ureilites are carbon rich ultramafic olivine dominantly low ca pyroxene achondrites with poorly understood petrogenesis one major problem concerns the origin of extensive variation in feo content olivine core fo values ranging from approximately 75 to 95 among the individual ureilites the two main competing hypotheses to explain this variation are 1 equilibrium smelting in which ureilite fo values were established by pressure dependent depth linked carbon redox reactions on the ureilite parent body during partial melting or 2 nebular inheritance in which the variation in feo contents was derived from ureilite precursors and was preserved during partial melting the paper parent body depth pressure temperature relationships and the style of the ureilite anatexis by warren 2012 discusses a series of topics related to ureilite petrogenesis in each case an argument is presented within the context of smelting versus nonsmelting models collectively these arguments create the impression that there are many valid arguments against smelting the purpose of this comment is to point out flaws in some of these arguments and or to show that the issues they address are independent of smelting versus nonsmelting models both equilibrium smelting and nebular inheritance simple anatexis models face challenges in explaining all the properties of ureilites but both remain viable

eemian and early weichselian 140 60 ka paleoceanography and paleoclimate in the nordic seas with comparisons to holocene conditions paleoceanographic and paleoclimatic time series were extracted from norwegian iceland and greenland sea the nordic seas sediment sequences covering the time intervals 60 140 ka and 0 15 ka on the basis of stable isotope stratigraphy planktonic foraminiferal faunas and sedimentological methods the proxy temperature records from the norwegian iceland sea display a number of high frequency and high amplitude variations within the last interglacial the eemian indicating marked changes in heat flux at high northern latitudes eemian holocene comparisons document that the climate of the norwegian iceland sea in the last interglacial was less stable than that of the present interglacial and that the distribution of surface water masses in the eemian differed from that of the holocene within the greenland sea uniform cold conditions prevailed throughout both interglacials cooling of the nordic seas as well as the initial growth of the surrounding ice sheets began within the eemian interval before the main increase in global ice volume heat flux to the nordic seas was significantly higher during the interglacials than at any time during the early weichselian 60 113 ka and no marked stadial interstadial changes in sea surface temperature and deep water ventilation are documented in the early weichselian records contrary to the pattern found in north atlantic sediment records however fluctuations in planktonic foraminiferal content planktonic 13c and ice rafting on suborbital timescales mostly comparable in number and age to the stadial interstadial fluctuations in the greenland ice cores are demonstrated in our records the ice rafted detritus records provide a more detailed account of ice sheet variability than previously known for the early weichselian period and demonstrate that glaciers advanced to sea level somewhere around the nordic seas several times during this interval

a thermal model for the differentiation of asteroid 4 vesta based on radiogenic heating a finite element code has been developed to model the thermal history of asteroid 4 vesta this is the first attempt to model the thermal history of a differentiated asteroid through core and crust formation and subsequent cooling until geochemical closure is attained the results of the simulation are consistent with chronological measurements and other constraints provided by cumulate and noncumulate eucrites believed to have been derived from vesta the work solves two major problems with the hypothesis of heating by decay of26al an extinct radionuclide postulated to be a plausible heat source in the early solar system first the model demonstrates that it is possible to keep the mantle of vesta hot for 100 ma thereby explaining the observed difference in ages between cumulate and noncumulate eucrites second the simulation offers a possible explanation of why detectable excesses of26mg the decay product of26al are not observed in noncumulate eucrites the simulation draws a model chronology of vesta and predicts times relative to cai formation for accretion at 2 85 myr core formation at 4 58 myr crust formation at 6 58 myr and geochemical closure at 100 myr for a h chondrite asteroidal bulk composition decay of60fe is found to cause no perceptible difference in the thermal history of vesta even when sequestered into a central core although chondritic xenoliths have not been described in hed igneous lithologies the thermal model suggests the possibility that a veneer of unmelted near surface material should remain

multibeam bathymetric investigations of the morphology of sand ridges and associated bedforms and their relation to storm processes sable island bank scotian shelf abstract storm formed sand ridges are important morphologic features occurring on many continental shelves of the world our understanding of the morphology migration and the controlling processes over this type of sand ridges under different environmental settings is still limited in the present study an integrated approach of combining multibeam bathymetry survey seabed sampling sidescan seismic surveys and seabed instrumentation measurements was used to characterize the surficial geology and morphology of offshore sand ridges on sable island bank scotian shelf and to evaluate the relationship between sand ridge morphology migration and the storm processes on this storm dominated outer shelf bank multibeam data obtained at selected sites demonstrated the series of ne sw oriented sand ridges with an average height of 4 3 m and wavelength of 1 5 km sand ridges attain maximum spacing height and steepness in the intermediate depths sand ridge size and steepness also decrease from west to east and this decrease is correlated with decreasing dynamic condition sediment grain size and depth sand ridge profiles show weak easterly asymmetry this morphological asymmetry augments the sediment texture and grain size asymmetry to suggest eastward long term sand ridge migration and net sediment transport in the study area sand ridge asymmetry also shows strong local variation and the number of sand ridges asymmetric to the west is nearly equal to that asymmetric to the east the likely cause is the nearly equal number of major storms passing to the south versus to the north of the island so that the westerly and easterly peak storm driven currents associated with these storm path scenarios affect equally the sand ridges on sable island bank a suite of smaller bedforms were found superimposed on the sand ridges sand waves widely superimposed on both flanks of sand ridges mixed 2d and 3d megaripples commonly occurring in the sand ridge troughs and on the lower western flanks and large wave ripples ubiquitously found in the troughs of all megaripples surficial sediment is coarsest coarse sand with shell fragments in the sand ridge trough and becomes progressively finer eastward toward the sand ridge crest and down the eastern flank while best sorting occurs near the sand ridge crest box cores collected across sand ridges reveal characteristic storm event bed structure that reflects the development and migration of bedforms with the evolution of storms

geostrophic circulation or shallow marine turbidity currents the dilemma of paleoflow patterns in strom influenced prograding shoreline systems in ancient storm influenced prograding shoreline sequences sole marks mainly tool marks from hummocky crossstratified storm deposits are commonly oriented normal to paleoshoreline and the trend of paleobathymetric contours in the basin asymmetrical tool marks typically indicate flows directed offshore several workers have attributed their formation to storm generated shallow marine turbidity currents this interpretation conflicts with observations from modern shelves where storm driven circulation generally is geostrophically balanced and time averaged bottom currents approximately parallel bathymetric contours and the local shoreline the resolution of these apparently conflicting observations may lie in the realization that tool marks and many other small paleoflow indicators form almost instantly as the result of instantaneous flow conditions very near the bed beneath storm generated flows in the shallow ocean instantaneous and time averaged characteristics of the bottom boundary layer generally exhibit little similarity storm generated tool marks are formed by the movement of large tools within the thin less than 1 m inner boundary layer resulting from the superimposition of waves and currents the orientation of the peak instantaneous shear stress moving large tools under such combined flows mainly reflects wave orbital motions which typically are normal to shore the magnitude of stress is greatly increased in the offshore direction and decreased in the onshore direction by superimposition of a steady current with an offshore component of flow but the direction of stress is only slightly affected in ancient storm influenced sequences therefore shore normal tool marks generally were not formed by turbidity currents rather their orientation is best attributed to shoaling waves approaching the coast at a very high angle asymmetrical tool marks are directed offshore due to enhanced shear stress on the offshore stroke of waves superimposed on a geostrophic current with an offshore flow component tool marks do not reflect the time averaged bottom flow direction in fact they provide almost no information concerning steady bottom currents in contrast high angle cross beds formed in coarser sediment by the migration of dunes and sandwaves although relatively rare in offshore storm deposits generally reveal approximately shore parallel flows in ancient systems cross beds closely reflect the time averaged flow direction in the outer boundary layer of a geostrophic current for three reasons 1 the net transport direction for sand moving as bed load beneath a combined flow lies between the directions of peak instantaneous shear stress and time averaged shear stress 2 large ripples disrupt the thin inner boundary layer and 3 long time intervals relative to wave induced velocity oscillations are required to form large ripples