the benguela current and associated upwelling on the southwest african margin a synthesis of the neogene quaternary sedimentary record at dsdp sites 362 and 532

geostrophic transport in the benguela current region historical data from the region between the greenwich meridian and the african continental shelf are used to compute the offshore geostrophic transport of the benguela current at 32 s the benguela current is located near the african coast transporting about 21 sv 1 sv 106 m3 s 1 of surface water toward the north relative to a potential density surface lying between the upper branch of circumpolar deep water and the north atlantic deep watar two warm core eddies of probable agulhas current origin an observed west of the benguela current at 32 s near 30 s the benguela current turns toward the northwest and begins to separate from the eastern boundary it carries about 18 sv of surface water across 28 s the current then turns mainly toward the west to flow over a relatively deep segment of the walvis ridge south of the valdivia bank a surface current with northward surface of about 10 cm s 1 flows along the western side of the valdivia bank while another northward surface current flows at about 20 cm s 1 some 300 km west of the bank about 3 sv of surface now do not leave the cape basin south of the vaidivia bank but instead drift northward as a wide sluggish flow out of the northern end of the cape basin because of the more southerly seaward extensions of most of the benguela current there are no deep reaching interactions observed between this current and the cyclonic gyre in the angola basin east of the greenwich meridian beneath the surface layer about 4 5 sv of antarctic intermediate water are carried northward across 32 and 28 s by the benguela current essentially all of which turns westward to cross the greenwich meridian south of 24 s

a global view of martian surface compositions from mgs tes thermal emission spectrometer tes data from the mars global surveyor mgs are used to determine compositions and distributions of martian low albedo regions two surface spectral signatures are identified from low albedo regions comparisons with spectra of terrestrial rock samples and deconvolution results indicate that the two compositions are a basaltic composition dominated by plagioclase feldspar and clinopyroxene and an andesitic composition dominated by plagioclase feldspar and volcanic glass the distribution of the two compositions is split roughly along the planetary dichotomy the basaltic composition is confined to older surfaces and the more silicic composition is concentrated in the younger northern plains

results from the mars global surveyor thermal emission spectrometer the thermal emission spectrometer spectra of low albedo surface materials suggests that a four to one mixture of pyroxene to plagioclase together with about a 35 percent dust component provides the best fit to the spectrum qualitative upper limits can be placed on the concentration of carbonates 10 percent olivine 10 percent clay minerals 20 percent and quartz 5 percent in the limited regions observed limb observations in the northern hemisphere reveal low lying dust hazes and detached water ice clouds at altitudes up to 55 kilometers at an aerocentric longitude of 224 degrees a major dust storm developed in the noachis terra region the south polar cap retreat was similar to that observed by viking

early views of the martian surface from the mars orbiter camera of mars global surveyor high resolution images of the martian surface at scales of a few meters show ubiquitous erosional and depositional eolian landforms dunes sandsheets and drifts are prevalent and exhibit a range of morphology composition inferred from albedo and age as seen in occurrences of different dune orientations at the same location steep walls of topographic depressions such as canyons valleys and impact craters show the martian crust to be stratified at scales of a few tens of meters the south polar layered terrain and superposed permanent ice cap display diverse surface textures that may reflect the complex interplay of volatile and non volatile components low resolution regional views of the planet provide synoptic observations of polar cap retreat condensate clouds and the lifecycle of local and regional dust storms

mantle dynamics uplift of the tibetan plateau and the indian monsoon convective removal of lower lithosphere beneath the tibetan plateau can account for a rapid increase in the mean elevation of the tibetan plateau of 1000 m or more in a few million years such uplift seems to be required by abrupt tectonic and environmental changes in asia and the indian ocean in late cenozoic time the composition of basaltic volcanism in northern tibet which apparently began at about 13 ma implies melting of lithosphere not asthenosphere the most plausible mechanism for rapid heat transfer to the midlithosphere is by convective removal of deeper lithosphere and its replacement by hotter asthenosphere the initiation of normal faulting in tibet at about 8 3 ma suggests that the plateau underwent an appreciable increase in elevation at that time an increase due solely to the isostatic response to crustal thickening caused by india s penetration into eurasia should have been slow and could not have triggered normal faulting another process such as removal of relatively cold dense lower lithosphere must have caused a supplemental uplift of the surface folding and faulting of the indo australian plate south of india the most prominent oceanic intraplate deformation on earth began between about 7 5 and 8 ma and indicates an increased north south compressional stress within the indo australian plate a tibetan uplift of only 1000 m if the result of removal of lower lithosphere should have increased the compressional stress that the plateau applies to india and that resists india s northward movement from an amount too small to fold oceanic lithosphere to one sufficient to do so the climate of the equatorial indian ocean and southern asia changed at about 6 9 ma monsoonal winds apparently strengthened northern pakistan became more arid but weathering of rock in the eastern himalaya apparently increased because of its high altitude and lateral extent the tibetan plateau provides a heat source at midlatitudes that should oppose classical symmetric hadley circulation between the equator and temperate latitudes and that should help to drive an essentially opposite circulation characteristic of summer monsoons for the simple case of axisymmetric heating no dependence on longitude of an atmosphere without dissipation theoretical analyses by hou lindzen and plumb show that an axisymmetric heat source displaced from the equator can drive a much stronger meridianal monsoonlike circulation than such a source centered on the equator but only if heating exceeds a threshold whose level increases with the latitude of the heat source because heating of the atmosphere over tibet should increase monotonically with elevation of the plateau a modest uplift 1000 2500 m of tibet already of substantial extent and height might have been sufficient to exceed a threshold necessary for a strong monsoon the virtual simultaneity of these phenomena suggests that uplift was rapid approximately 1000 m to 2500 m in a few million years moreover nearly simultaneously with the late miocene strengthening of the monsoon the calcite compensation depth in the oceans dropped plants using the relatively efficient c4 pathway for photosynthesis evolved rapidly and atmospheric co2 seems to have decreased suggesting causal relationships and positive feedbacks among these phenomena both a supplemental uplift of the himalaya the southern edge of tibet and a strengthened monsoon may have accelerated erosion and weathering of silicate rock in the himalaya that in turn enhanced extraction of co2 from the atmosphere thus these correlations offer some support for links between plateau uplift a downdrawing of co2 from the atmosphere and global climate change as proposed by raymo ruddiman and froehlich mantle dynamics beneath mountain belts not only may profoundly affect tectonic processes near and far from the belts but might also play an important role in altering regional and global climates

dispersed organic matter in samples from the western continental shelf of southern africa palynofacies assemblages and depositional environments of late cretaceous and younger sediments abstract the composition and distribution of dispersed microscopic organic matter particles phytoclasts and palynomorphs in sediments and sedimentary rocks reflect factors that influenced their production in their original environments transport to depositional sites burial and post depositional changes thus they can be used as proxies for reconstructing provenance temporal and spatial paleoenvironmental conditions and diagenetic changes in this study phytoclasts and palynomorphs in 55 spot samples from upper cretaceous eocene miocene and uppermost pleistocene sediments on the western continental shelf of namibia and south africa were examined they were used to test lateral depositional facies inferred from unpublished micropaleontological analysis and to decipher any stratigraphic trends in the distribution of the organic particles in the sediments thirteen types of phytoclasts and palynomorphs were identified and analyzed in two ways visually with basic quantitative techniques and statistically with two multivariate techniques three components namely amorphous organic matter wood and black debris were visually and statistically significant average linkage cluster analysis of these three components and discrete changes in the amounts of marine palynomorphs and other terrigenously derived organic material such as spores and pollen brown black fragments and plant tissues delineated seven palynofacies assemblages by contrast principal components analysis revealed two groups of samples based on the amounts of amorphous organic matter and wood five groups of samples referred to as associations were identified visually from the pattern of organic matter distribution and compared with the statistical results a palynofacies depositional model is proposed to re evaluate the fluvial to inner shelf settings previously inferred for the sediments some clear stratigraphic trends were obvious in both sets of results such as the dominance of amorphous organic matter in turonian coniacian and uppermost pleistocene sediments and higher percentages of black debris in the older sediments these trends appear to be controlled more by provenance and depositional conditions than by age the dominance of amorphous organic matter in several uppermost pleistocene sediments deposited during a global fall in sea level were attributed to in situ physical and biological degradation of mostly marine algal material in an inner shelf setting

late quaternary paleoproductivity and deep water circulation in the eastern south atlantic ocean evidence from benthic foraminifera abstract two late quaternary sediment cores from the northern cape basin in the eastern south atlantic ocean were analyzed for their benthic foraminiferal content and benthic stable carbon isotope composition the locations of the cores were selected such that both of them presently are bathed by north atlantic deep water nadw and past changes in deep water circulation should be recorded simultaneously at both locations however the areas are different in terms of primary production one core was recovered from the nutrient depleted walvis ridge area whereas the other one is from the continental slope just below the coastal upwelling mixing area where present day organic matter fluxes are shown to be moderately high recent data served as the basis for the interpretation of the late quaternary faunal fluctuations and the paleoceanographic reconstruction during the last 450 000 years nadw flux into the eastern south atlantic ocean has been restricted to interglacial periods with the strongest dominance of a nadw driven deep water circulation during interglacial stages 1 9 and 11 at the continental margin high productivity faunas and very low epibenthic 13c values indicate enhanced fluxes of organic matter during glacial periods this can be attributed to a glacial increase and lateral extension of coastal upwelling the long term glacial interglacial paleoproductivity cycles are superimposed by high frequency variations with a period of about 23 000 yr enhanced productivity in surface waters above the walvis ridge far from the coast is indicated during glacial stages 8 10 and 12 during these periods cold nutrient rich filaments from the mixing area were probably driven as far as to the southeastern flank of the walvis ridge

global distribution composition and abundance of olivine on the surface of mars from thermal infrared data 1 we used spectral indexing and linear deconvolution to compare thermal infrared emission spectra of fo91 fo68 fo53 fo39 fo18 and fo1 olivine samples to mars global surveyor thermal emission spectrometer tes data over low albedo regions of mars the fo91 fo68 fo53 and fo39 spectral end members were confidently identified on mars a range of compositions wider than inferred from martian meteorites small less than hundreds of square kilometers occurrences of the fo91 spectral end member are present in the rims of the argyre and hellas impact basins and may represent martian mantle materials the fo68 spectral end member is common throughout the highlands chasmata outflow channels and nili fossae region the fo53 spectral end member occurs in eastern syrtis major the nili fossae region and smooth floored craters of the highlands although less abundant than fo68 and fo53 the distribution of the fo39 spectral end member suggests that some olivine on mars is more fe rich than olivine in martian meteorites global maps of olivine show that 1 materials containing 10 20 of olivine are common in the southern highlands of mars 2 olivine is most common near the topographic dichotomy boundary and 3 olivine becomes uncommon near the poles suggesting that it may be influenced by topography and or latitude climate olivine is found in early noachian to amazonian terrains some of which may be coeval with phyllosilicate and sulfate deposits detected by omega implying that any early noachian wet period of mars climate history may have been globally inhomogeneous or insufficient to weather the olivine that remains today

late miocene stable isotope stratigraphy of se atlantic odp site 1085 relation to messinian events abstract high resolution benthic oxygen isotope and xrf fe and ca records from site 1085 drilled in the mid cape basin odp leg 175 are used to investigate global climate changes during the late miocene in relation to messinian geological events the cyclic fluctuations of the time series at site 1085 enable us to establish a reliable chronology for the time interval 7 3 4 7 ma spectral analysis of the 18o record indicates that the 41 kyr period of orbital obliquity dominates the late miocene record a global climate record was extracted from the oxygen isotopic composition of benthic foraminifera both long and short term variabilities in the climate record are discussed in terms of sea level and deep water temperature changes the time interval 7 3 6 25 ma characterized by low amplitude 18o variations is followed by a period marked by maximum in the 18o values 6 25 5 57 ma at about 5 56 ma a rapid decrease in 18o values is documented that may reflect a warming of deep water temperature associated with a global warming period comparison between the timing of the oceanic isotope events and the chronology of the mediterranean salinity crisis suggest that global eustatic processes were not essential in the mediterranean salinity crisis history from our data we infer that the global warmth documented in the early mid pliocene probably started during the late miocene at 5 55 ma at the same time the onset of evaporite deposition in the central basin of the mediterranean sea took place sharp changes in the sedimentation rates mainly driven by terrigenous input at this site are observed during the messinian stage

genes diversity and geologic process on the pacific coast abstract we examine the genetics of marine diversification along the west coast of north america in relation to the late neogene geology and climate of the region trophically important components of the diverse west coast fauna including kelp alcid birds e g auks puffins salmon rockfish abalone and cancer crabs appear to have radiated during peaks of upwelling primarily in the late miocene and in some cases secondarily in the pleistocene phylogeographic barriers associated with mio pliocene estuaries of the mid california coast the pliocene opening of the gulf of california tectonic and eustatic evolution of the california bight as well as the influence of pleistocene and holocene climate change on genetic structure are assessed in a geologic context comparisons to east coast and western freshwater systems as well as upwelling systems around the globe provide perspective for the survey

tertiary sea level movements around southern africa sedimentological micropaleontological and seismic profiling data elucidate the history of tertiary sea level movements around southern africa these new data show that landward movement of the sea began in early paleocene time and continued into the early eocene the sea probably reached its maximum paleocene height during the early eocene and is today represented by outcrops up to at least 204 m and probably as high as 360 m above modern sea level a brief regressive pulse occurred during the middle eocene with renewed transgression in the late eocene a major regression followed probably spanning all of oligocene and early miocene times this regression exposed much of the continental shelf and is clearly represented on seismic reflection profiles by a widespread unconformity the major neogene transgression began in the middle miocene and probably reached its greatest extent in the late miocene or early pliocene the overall middle miocene to early pliocene transgression was interrupted by a brie

spectral evidence for weathered basalt as an alternative to andesite in the northern lowlands of mars mineral abundances derived from the analysis of remotely sensed thermal emission data from mars have been interpreted to indicate that the surface is composed of basalt surface type 1 and andesite surface type 2 1 the global distribution of these rock types is divided roughly along the planetary dichotomy which separates ancient heavily cratered crust in the southern hemisphere basalt from younger lowland plains in the north andesite 1 but the existence of such a large volume of andesite is difficult to reconcile with our present understanding of the geological evolution of mars here we reinterpret martian surface rock lithologies using mineral abundances from previous work1 and new mineralogies derived from a spectral end member set representing minerals common in unaltered and low temperature aqueously altered basalts our results continue to indicate the dominance of unaltered basalt in the southern highlands but reveal that the northern lowlands can be interpreted as weathered basalt as an alternative to andesite the coincidence between locations of such altered basalt and a suggested northern ocean basin implies that lowland plains material may be composed of basalts weathered under submarine conditions or weathered basaltic sediments transported into this depocentre

morphology and composition of the surface of mars mars odyssey themis results the thermal emission imaging system themis on mars odyssey has produced infrared to visible wavelength images of the martian surface that show lithologically distinct layers with variable thickness implying temporal changes in the processes or environments during or after their formation kilometer scale exposures of bedrock are observed elsewhere airfall dust completely mantles the surface over thousands of square kilometers mars has compositional variations at 100 meter scales for example an exposure of olivine rich basalt in the walls of ganges chasma thermally distinct ejecta facies occur around some craters with variations associated with crater age polar observations have identified temporal patches of water frost in the north polar cap no thermal signatures associated with endogenic heat sources have been identified

pulling apart the mid to late cenozoic magmatic record of the gulf of california is there a comondu arc the composition of the lithosphere can be fundamentally altered by long lived subduction processes such that subduction modified lithosphere can survive for 100 s myrs incorrect petrotectonic interpretations result when spatial temporal compositional trends of and source contributions to magmatism are not properly considered western mexico has had protracted cenozoic magmatism developed mostly in board of active oceanic plate subduction beneath western north america a broad range of igneous compositions from basalt to high silica rhyolite were erupted with intermediate to silicic compositions in particular showing calc alkaline and other typical subduction related geochemical signatures a major oligocene rhyolitic ignimbrite flare up 300 000 km3 switched to a bimodal volcanic phase in the early miocene 100 000 km3 associated with distributed extension and opening of numerous grabens extension became more focussed 18 ma resulting in localised volcanic activity along the future site of the gulf of california this localised volcanism known as the comondu arc was dominantly effusive and andesite dacite in composition past tectonic interpretations of comondu age volcanism may have been incorrect as these regional temporal compositional changes are alternatively interpreted as a result of increased mixing of mantle derived basaltic and crust derived rhyolitic magmas in an active rift environment rather than fluid flux melting of the mantle wedge above the subducting guadalupe plate

magnetostratigraphic biostratigraphic and stable isotope stratigraphy of an upper miocene drill core from the sale briqueterie northwestern morocco a high resolution chronology for the messinian stage we report a high resolution stable isotope carbonate magnetostratigraphic and biostratigraphic record from a 175 m drill core from the sale briqueterie which is part of the bou regreg section in northwestern morocco the sale drill core spans the interval from paleomagnetic chron c4n partim to c3r earliest gilbert which represents the time leading up to and including the isolation and desiccation of the mediterranean i e the messinian salinity crisis during chrons c3an and c3ar 6 935 to 5 894 ma the isotope and carbonate signals display quasi periodic variations with estimated periods of 40 and 100 kyr respectively we interpret the 40 kyr 18o variations as reflecting changes in global ice volume caused by obliquity induced changes 41 kyr in solar insolation in polar regions the 100 kyr carbonate variations probably represent long term modulation of the amplitude of the precessional cycle 21 kyr which is not resolved by our sampling frequency the cyclic nature of the oxygen isotope signal permits us to extend the isotope nomenclature of shackleton et al 1994a from stage tg24 in chron c3r earliest gilbert to stage c3ar 18o 18 at the base of chron c3ar 6 935 ma a major change in paleoceanographic conditions is recorded across the tortonian messinian boundary which we correlate to chron c3bn at 7 04 ma benthic foraminiferal 18o values increased by an average of 0 4 in two steps at 7 17 ma and 6 8 ma and 13c values decreased by 0 7 0 8 between 7 1 and 6 8 ma representing the late miocene carbon shift the first step in 18o values coincides with an inferred reversal in deep water circulation through the rifian corridor and the second correlates with the base of the tripoli formation and onset of crisis conditions in the mediterranean we suggest that the increase in 18o values represents at least in part an increase in global ice volume that lowered sea level and contributed to the establishment of a negative water budget in the mediterranean average 18o values remained high throughout most of chrons c3ar and c3an reaching maximum 18o values during isotope stages tg20 and 22 in chron c3r earliest gilbert the glacio eustatic falls associated with these events may have resulted in the complete isolation of the mediterranean from the world ocean shackleton et al 1994a following stage tg12 in the sale record there exists a trend toward progressively lower 18o values that may represent a series of marine transgressions that eventually reflooded the mediterranean and ended the salinity crisis

recognition of minor constituents in reflectance spectra of allan hills 84001 chips and the importance for remote sensing on mars reflectance spectra of splits 92 and 271 from the martian meteorite allan hills alh 84001 are presented and analyzed in this paper although the visible and infrared spectra of both chips show that the dominant mineralogy is low ca pyroxene the focus here is on identification of the minor constituents infrared spectra measured at multiple spots along the surface of chips 92 and 271 show subtle spectroscopic variations due to changes in the low ca pyroxene texture and composition and to the presence of secondary minerals absorption bands observed near 0 93 and 1 95 m are characteristic of low ca pyroxene strong mid infrared reststrahlen bands are observed near 9 and 19 5 m in all surface spectra and additional bands near 7 10 5 11 4 17 8 20 5 and 23 m are variable depending on the low ca pyroxene texture and the presence of secondary minerals selected spectra exhibit carbonate features near 4 6 4 7 1 and 11 3 m detailed analysis of these carbonate features indicates the presence of mg fe carbonate which is consistent with petrographic studies many of these spectra with strong carbonate features exhibit a magnetite feature near 17 9 m and a shoulder near 20 5 m that cannot be uniquely ascribed to one mineral spectroscopic identification of the minor carbonate and magnetite minerals in this probable piece of mars indicates that detection of small amounts of these minerals of possible biological significance will be possible using infrared hyperspectral analyses of the martian surface also of importance for remote sensing on mars is the result that mg fe and mg fe carbonates in a low ca pyroxene matrix should be distinguishable from one another in the spectral region measured by the thermal emmitance spectrometer tes

spectral evidence for the mineralogy of high albedo soils and dust on mars because of the lack of direct mineralogic data available for mars spectral remote sensing techniques and in particular earth based reflectance spectroscopy remain the primary source of this information presented here are laboratory observations which further constrain the mineralogy and origin of the high albedo soils and dust earth based observations show the reflectance spectra of classical bright regions to be fairly uniform with a strong fe3 o2 charge transfer absorption edge extending from the near uv through the visible this absorption is relatively smooth unlike those observed for crystalline ferric oxides which have superimposed fe3 crystal field bands dilution of ferric oxide with a spectrally more neutral medium montmorillonite weakens the charge transfer and crystal field absorptions together and does not serve to make the ferric oxide spectrum more mars like smoother nontronite ferric iron bearing smectite clay was also investigated for spectral agreement with telescopic observations pure nontronite has fe3 absorptions analogous to but different from ferric oxides as in the previous case the absorptions are very distinct and inappropriate for mars admixture of neither montmorillonite nor ferric oxide serves to improve the nontronite spectrum the conclusion is that nontronite is not a major component of martian soils although the presence of other iron poor clays cannot be totally excluded based on currently available observational data the best spectral analogs known for high albedo soil and dust are a specific type of palagonite from hawaii x ray amorphous weathering products of mafic volcanic glass the indication is therefore that ferric iron on mars is likely to occur in poorly defined crystallo graphic sites such as found in these amorphous materials these materials form slowly under semiarid conditions at ambient temperature even low temperature hydrothermal alteration of glass might provide enough ion mobility to favor some formation of crystalline clays over amorphous gels and may therefore not be the primary mechanism responsible for soil formation on mars the amorphous hawaiian soils exist metastably for thousands of years on earth similar materials on mars would be expected to survive considerably longer under the present cold and dry climatic conditions

dust coatings on basaltic rocks and implications for thermal infrared spectroscopy of mars 1 thin coatings of atmospherically deposited dust can mask the spectral characteristics of underlying surfaces on mars from the visible to thermal infrared wavelengths making identification of substrate and coating mineralogy difficult from lander and orbiter spectrometer data to study the spectral effects of dust coatings we acquired thermal emission and hemispherical reflectance spectra 5 25 m 2000 400 cm 1 of basaltic andesite coated with different thicknesses of air fall deposited palagonitic soils fine grained ceramic clay powders and terrestrial loess the results show that thin coatings 10 20 m reduce the spectral contrast of the rock substrate substantially consistent with previous work this contrast reduction continues linearly with increasing coating thickness until a saturation thickness is reached after which little further change is observed the saturation thickness of the spectrally flat palagonite coatings is 100 120 m whereas that for coatings with higher spectral contrast is only 50 75 m spectral differences among coated and uncoated samples correlate with measured coating thicknesses in a quadratic manner whereas correlations with estimated surface area coverage are better fit by linear functions linear mixture modeling of coated samples using the rock substrate and coating materials as end members is also consistent with their measured coating thicknesses and areal coverage a comparison of ratios of thermal emission spectrometer tes spectra of dark and bright intracrater and windstreak deposits associated with radau crater suggests that the dark windstreak material may be coated with as much as 90 areal coverage of palagonitic dust the data presented here also will help improve interpretations of upcoming mini tes and thermal emission imaging system themis observations of coated mars surface materials

cenozoic pelagic sr ca records exploring a link to paleoproductivity 1 recent studies have revealed that sr ca ratios of coccolithophores may be affected by productivity here we compile published sr ca data from bulk carbonate fine fraction sediment and planktonic foraminiferal sr ca records that span the past 60 myr and attempt to place these records into a paleoceanographic framework we account for changes in seawater sr ca ratios using the curve of lear et al 2003 and discuss our observations with respect to changes in the partitioning coefficient of sr through time we discuss limitations associated with postburial processes temporal changes in the coccolith planktonic foraminiferal rain ratio and the coccolith species composition of the sediment despite these caveats we are able to show that in the bulk and fine fraction carbonate records there are two broad periods of enhanced partitioning of sr relative to today the oligocene and the middle to late miocene early pliocene because these are two intervals for which we can cite evidence for a relatively productive ocean on the regional or global scale we believe that the sr ca ratios of bulk carbonate can be explained at least in part by the effects of oceanic nutrient levels on sr uptake during calcification of coccoliths which make up the vast majority of these sediments within the limits of the inferred seawater sr ca record the results of this study contribute a geologic perspective to recent laboratory and field studies that have raised the possibility that sr incorporation into biogenic calcite is controlled by biogeochemical processes

mineral and elemental indicators of post glacial changes in sediment delivery and deposition under a western boundary upwelling system cabo frio southeastern brazil abstract minerals and elements are important proxies that can provide information about variations in the delivery and deposition of coastal ocean sediments associated with past climate changes in this study postglacial changes in the accumulation of sediments on the upper shelf of southeastern brazil are linked to the evolution of regional paleoceanographic and continental paleoclimatic conditions during the last 14 4 kyr cal bp mineralogical and major and trace element analyses of a 14 c dated sediment core identify three main lithostratigraphic units of this core that reveal a succession of changes in sediment delivery and accumulation as postglacial sea level rose and holocene climate on land evolved the depositional setting has transitioned in response to the large sea level rise prior to 9 9 kyr cal bp from being a shallow water high energy environment to a deeper water one this location has since then been a lower energy environment that has persisted into modern times due to the high marine productivity associated with the cabo frio upwelling system in an oxygenated water column the sediments have shown a complex and dynamic redox condition making variations in redox sensitive trace elements indicative of changes in primary production and organic matter diagenesis at this location after sea level stabilized 9 kyr cal bp variations in fluxes of al fe ca and minerals were small indicating that climate driven changes had only secondary controls on delivery of detrital sediment components to the cabo frio shelf modern coastal upwelling conditions and the onset of mid shelf organic rich sediment deposition were established after 9 9 cal kyr bp

global mineral distributions on mars 1 determining the mineralogy of mars is an essential part of revealing the conditions of the surface and subsurface a deconvolution method was used to remove atmospheric components and determine surface mineralogy from thermal emission spectrometer data at 1 pixel per degree ppd minerals are grouped into categories on the basis of compositional and spectral similarity and global concentration maps are produced all binned pixels are fit well with rms errors of 0 005 in emissivity higher rms errors are attributed to short wavelength particle size effects on dust covered surfaces significant concentrations 0 10 of plagioclase high ca pyroxene sheet silicates high si glass and hematite are detected and display distributions consistent with previous studies elevated concentrations of plagioclase and high ca pyroxene are consistent with basaltic surfaces and are located in low albedo highlands regions north of 45 s significant concentrations of plagioclase and sheet silicates high si glass and low concentrations of high ca pyroxenes are consistent with andesitic surfaces and are concentrated in both southern and northern high latitude low albedo regions andesitic surfaces in the southern hemisphere have a lower spectral contrast than northern surfaces an isolated surface located in solis planum is spectrally distinct but compositionally similar to other surfaces interpreted to be andesitic in composition concentrations of olivine below the detection limit correctly identify its presence in two of three locations potassium feldspar low ca pyroxene basaltic glass olivine sulfate carbonate quartz and amphibole are not detected with confidence at 1 ppd the results presented here indicate a predominance of volcanic compositions within martian dust free surfaces

the early matuyama diatom maximum off sw africa benguela current system odp leg 175 abstract several sites of ocean drilling program leg 175 between 20 and 30 s 1081 1082 1083 1084 and 1085 in the benguela current system show a distinct opal and diatom maximum within the late pliocene and early quaternary spanning the lower half of the matuyama reversed polarity chron mdm matuyama diatom maximum this maximum is centered around 2 0 2 6 ma and follows a rapid increase of diatom deposition near 3 1 ma within the mdm we recognized intervals dominated by the antarctic subantarctic species thalassiothrix antarctica which have the aspect of diatom mats the mdm and the mats developed during a time of sustained southern ocean influence 3 2 1 6 ma probably reflecting a period of seasonally pulsed continuous advection of subantarctic waters into the benguela oceanic current the onset and cessation of the mdm raises questions about modes in the operation of the silica cycle and the relation of these to major oceanographic events a depositional model for the late pliocene is proposed which involves positional changes in a longshore system of fronts substantial equatorward excursions of subantarctic waters during mdm time and subsurface waters greatly enriched in silicate

classification of surface units in the equatorial region of mars based on viking orbiter color albedo and thermal data viking orbiter color albedo and thermal inertia data for the equatorial region of mars were utilized as a five dimensional data set to search for clusters that correspond to mappable surface units a principal components analysis shows that 84 of the variance within the data for the equatorial region 30 of equator can be carried along two vector directions these vector directions typify the dominant trend of martian surface materials the first direction indicates that as the surface materials become brighter at red wavelengths they also brighten at green and violet wavelengths the second direction implies that as the albedo increases the thermal inertia decreases these dominant trends were deemphasized by stretching the data from a five dimensional elliptical swarm into a hypersphere through the use of principal component techniques the decorrelated data were then plotted in a triangle diagram with red violet albedo and thermal inertia apices to facilitate discrimination of inherent clusters unit maps for the region within 15 latitude of the equator and bounded by 0 to 50 and 280 to 360 w longitude were generated on the basis of the clusters up to eight clusters can be identified and mixing between clusters appears to be important the three major clusters consist of bright red materials with low thermal inertia dark relatively gray materials with high inertia and materials with intermediate values of color albedo and thermal inertia mantling by aeolian deposits or volcanic materials is prevalent in the brightest reddest unit with the lowest thermal inertia while the darker grayer units with higher thermal inertia are dominated by marelike plains the mantling is apparent in viking orbiter images with resolutions from 8 to 30 m per pixel

effects of glass content and oxidation on the spectra of snc like basalts applications to mars remote sensing 1 we have investigated the effects of crystallization and oxidation on the visible and near infrared visnir and mid infrared mid ir spectra of materials with a shergotty nakhla chassigny snc basaltic composition in order to investigate potential links between martian visnir spectra martian mid ir spectra and snc meteorite data snc basalt samples of varying crystallinities were synthesized and subsequently oxidized in air at 700 c for 1 7 days and reflectance spectra of both fine 75 m and coarse 75 500 m basalt samples were obtained before and after oxidation the effects of crystallization on the spectral properties are readily observed in the unoxidized products in the visnir increasing crystallization is accompanied by an increasing influence of pyroxene absorptions and decreasing influence of glass absorptions in the mid ir changes in spectral properties with crystallization are due to the variations in relative amounts of glass pyroxene and plagioclase oxidation alters the glass and pyroxenes within the samples leading to changes in visnir and mid ir spectral shapes although distinct signatures of oxidation products are not always observed both spectral and electron microscopy data indicate that hematite is the dominant oxidation product in the pigeonite and glass of the samples in pigeonite hematite is present in nanophase form and leads to the diminishment of the diagnostic 1 and 2 m pyroxene absorptions in the visnir as well as pyroxene absorptions expressed between 800 and 1100 cm 1 in the mid ir in glass hematite forms a near surface layer that is detected with varying efficiencies in the visnir and mid ir depending on the crystallinity and particle size of the analyzed sample oxidized snc basalt samples of various crystallinities and fine grain sizes provide the best analogs to mars remote sensing data in the visnir and mid ir in the visnir partially crystalline oxidized snc basalts can reproduce martian dark region characteristics in the mid ir similarities exist between the spectra of a partially crystalline oxidized snc basalt and the basalt lithology detected by the thermal emission spectrometer tes the andesite lithology detected by tes is best matched by the spectrum of a fully crystalline oxidized snc basalt these results imply that plagioclase rich lithologies are not required by tes data and that observed variations in spectral character of dark regions across the martian surface can be explained by snc basalts influenced by oxidation coupled with variations in degree of crystallization

tectonic setting and terrane accretion of the archean zimbabwe craton the archean zimbabwe craton is made of a number of distinct tectonostratigraphic terranes assembled by plate tectonic processes the central tokwe terrane consists of 3 5 2 95 ga gneissic rocks and structurally complex inliers of possibly older greenstone belts these are overlain unconformably by a 2 9 2 8 ga assemblage of mafic and felsic volcanic rocks and conglomerates and a separate 3 0 2 7 ga southeastward thickening platform sequence of sandstone shale and limestone 2 7 ga greenstone belts form two distinctly different domains flanking the central terrane northwest of the ancient gneissic terrane ca 2 7 ga greenstone belts comprise a series of calc alkaline lavas and intercalated sedimentary rocks intruded by syn volcanic plutons southeast of the ancient gneissic complex 2 7 ga greenstone belts consist of thick piles of tholeiitic basalts overlying ultramafic lavas resting allochthonously over the shallow water platform sequence and older gneissic terrane this division of the zimbabwe craton is interpreted to show that the central tokwe terrane had a continental magmatic arc built on its northwestern edge as its southeastern margin rifted from another fragment forming the sea of umtali a passive margin sedimentary wedge formed on the rifted southeastern edge of this ancient continent and prograded onto the craton during sedimentary and tectonic loading of the craton margin the southeastern greenstone belts formed as thick oceanic crust oceanic plateau in this back arc basin and were later obducted on to the rift and passive margin sequence as the sea of umtali closed ca 2 7 ga this was followed by intrusion of granitic plutons of the chilimanzi suite ca 2 6 ga in a tectonic regime of intracontinental strike slip faulting representing a response to the zimbabwe kaapvaal continent continent collision crustal and lithospheric thickening during intrusion of these late granites may have played a role in stabilizing the zimbabwe craton and forming the lithospheric root

the latest miocene early pliocene biogenic bloom a revised indian ocean perspective abstract numerous investigations of neogene sediment sequences from the indian and pacific oceans have led to a paleoceanographic hypothesis that recently has been coined the biogenic bloom this hypothesis suggests that primary productivity increased substantially at indo pacific upwelling zones during the latest miocene early pliocene although it is clear that recognition of a widespread biogenic bloom provides a fundamental framework for understanding late neogene global change it also is apparent that investigations of this phenomena require syntheses of a variety of information from time correlated sediment sequences that span large oceanic regions late neogene polarity chron boundaries and nannofossil events are placed on a common and current time scale for 12 ocean drilling program odp sediment sequences in order to construct a coherent description of the biogenic bloom in the indian ocean carbonate mass accumulation rates mars were significantly higher than present day in the north and west indian ocean between 9 0 and 3 5 ma sediment deposited during this time interval also is dominated by planktic faunal assemblages that are indicative of high productivity and redox conditions that are explained by an increase in the supply of organic carbon further sediment of this age contains benthic faunal assemblages and chemical characteristics that are consistent with low dissolved o 2 in intermediate waters these observations collectively suggest that between 9 0 and 3 5 ma productivity in the north and west indian ocean was significantly higher than present day and the intermediate water oxygen minimum zone omz was more extensive than present day this paleoceanographic condition was most intense between 6 0 and 5 0 ma in the indian ocean comparison of the indian ocean sites with two locations in the pacific ocean suggests that the biogenic bloom was time coincident in the indian and pacific oceans the biogenic bloom therefore implies an important change in global nutrient cycling occurred during the latest miocene early pliocene although a satisfactory explanation for the change remains elusive

miocene to pliocene development of surface and subsurface temperatures in the benguela current system 1 the initiation of the benguela upwelling has been dated to the late miocene but estimates of its sea surface temperature evolution are not available this study presents data from ocean drilling program odp site 1085 recovered from the southern cape basin samples of the middle miocene to pliocene were analyzed for alkenone based u37k sstuk and glycerol dialkyl glycerol tetraether gdgt based tex86 temptex water temperature proxies in concordance with global cooling during the miocene sstuk and temptex exhibit a decline of about 8 c and 16 c respectively the temperature trends suggest an inflow of cold antarctic waters triggered by antarctic ice sheet expansion and intensification of southern hemisphere southeasterly winds a temperature offset between both proxies developed with the onset of upwelling which can be explained by differences in habitat alkenone producing phytoplankton live in the euphotic zone and record sea surface temperatures while gdgt producing thaumarchaeota are displaced to colder subsurface waters in upwelling influenced areas and record subsurface water temperatures we suggest that variations in subsurface water temperatures were driven by advection of cold antarctic waters and thermocline adjustments that were due to changes in north atlantic deep water formation a decline in surface temperatures an increased offset between temperature proxies and an increase in primary productivity suggest the establishment of the benguela upwelling at 10 ma during the messinian salinity crisis between 7 and 5 ma surface and subsurface temperature estimates became similar likely because of a strong reduction in atlantic overturning circulation while high total organic carbon contents suggest a biogenic bloom in the pliocene the offset between the temperature estimates and the cooling trend was reestablished

mars surface mineralogy from hubble space telescope imaging during 1994 1995 observations calibration and initial results visible to near infrared observations of mars were made with the hubble space telescope hst during 1994 1995 with the goals of monitoring seasonal variability of the surface and atmosphere and mapping specific spectral units to constrain the planet s surface mineralogy this paper presents the details of the collection and calibration of the data concentrating specifically on the near ir data that were obtained exclusively for the surface mineralogy aspect of our hst mars observing program we also present some initial results from the calibrated data set our calibration procedures included the standard pipeline processing steps supplemented by special procedures required for use with the linear ramp filters on the wide field planetary camera 2 instrument and an additional point spread function deconvolution procedure applied in order to realize the full potential spatial resolution of the images 23 to 64 km pixel between august 1994 and august 1995 the calibration results in a set of images projected onto a standard map grid and presented in radiance factor i f units having an estimated 5 photometric accuracy based on the performance of hst and comparisons with previous ground based and spacecraft mars spectra initial scientific analyses of these data reveal 1 distinct red blue color units within the classical bright regions similar to those seen in viking orbiter images and possibly related to variations in nanophase and or crystalline ferric mineral abundance 2 near ir spectral slope variations correlated with albedo on a large scale darker is bluer near ir slope but exhibiting wider variations among many of the small scale features visible in the data 3 an absorption at 860 nm that occurs in all regions but which is 3 to 5 stronger in many of the classical dark regions than in the bright regions possibly because of a greater abundance of a well crystalline ferric phase like hematite or a very low ca pyroxene or opx cpx mixture and 4 an absorption from pyroxene at 953 nm with a band depth that is inversely correlated with albedo bright regions 0 to 5 deep dark regions 7 to 15 deep and which shows the highest band depth values in individual craters calderas and other small geologic units that are resolved in the images

late quaternary palaeoceanography of the tasman sea the benthic foraminiferal view abstract the benthic foraminiferal content of four gravity cores from the east tasman plateau 2450 m and 2667 m water depth and the lord howe rise 1349 m and 1448 m water depth was examined in order to determine late quaternary palaeoceanographic changes in the tasman sea in all cores benthic foraminifera demonstrate the glacial interglacial cyclicity through changes in assemblages and abundance abundances range from about 400 to 1200 specimens per gram of dry sediment over the last 400 kyr abundance patterns differ between the northern between 31 s and 33 s and the southern sites between 43 s and 44 s in the southern cores a significantly increased benthic foraminiferal abundance indicates high nutrient flux and quality perhaps continuously during stage 5 the northern cores on the other hand display this signal for stage 6 this reversed pattern is recognizable for other glacial episodes as well as for interglacials but the trend is less distinctive enhanced sea surface productivity in the tasman sea during the last glacial cycle is recognized from benthic foraminiferal assemblages but the pattern appears highly variable and complex the data suggest that for the past relocation of recent high productive oceanographic features sensu yoder et al 1994 in the tasman sea such as the tasman front the subtropical convergence the east australian current and perhaps the east australian eddy field tranter et al 1982 are reflected in the benthic formainiferal abundances in the cores increased foraminiferal abundance during glacials on the lord howe rise indicate a slight northward shift of the tasman front data from the east tasman plateau show a more complex situation the faunal pattern in the cores probably reflect a southward shift of the eddy field during glacials and a slight northward shift of the subtropical convergence during interglacials

coupled productivity and carbon isotope records in the southwest pacific ocean during the late miocene early pliocene biogenic bloom biogenic components of sediment accumulated at high rates beneath frontal zones of the indian and pacific oceans during the late miocene and early pliocene the 13c of bulk and foraminiferal carbonate also decreased during this time interval although the two observations may be causally linked and signify a major perturbation in global biogeochemical cycling no site beneath a frontal zone has independent records of export production and 13c on multiple carbonate phases across the critical interval of interest deep sea drilling project dsdp site 590 lies beneath the tasman front tf an eddy generating jetstream in the southwest pacific ocean to complement previous 13c records of planktic and benthic foraminifera at this location late neogene records of caco3 mass accumulation rate mar ca ti ba ti al ti and of bulk carbonate and foraminiferal 13c were constructed at site 590 the 13c records include bulk sediment bulk sediment fractions 63 m and 5 25 m and the planktic foraminifera globigerina bulloides globigerinoides sacculifer with and without sac and orbulina universa using current time scales caco3 mars ca ti al ti and ba ti ratios are two to three times higher in upper miocene and lower pliocene sediment relative to overlying and underlying units a significant decrease also occurs in all 13c records all evidence indicates that enhanced export production the biogenic bloom extended to the southwest pacific ocean between ca 9 and 3 8 ma and this phenomenon is coupled with changes in 13c the chron c3ar carbon shift however caco3 mars peak ca 5 ma whereas elemental ratios are highest ca 6 5 ma foraminiferal 13c starts to decrease ca 8 ma whereas bulk carbonate 13c begins to drop ca 5 6 ma temporal discrepancies between the records can be explained by changes in the upwelling regime at the tf perhaps signifying a link between changes in ocean atmosphere circulation change and widespread primary productivity

seeing through the dust martian crustal heterogeneity and links to the snc meteorites through the application of new analytical techniques to high spatial resolution imaging spectrometer data the ferrous mineralogy of major volcanic terrains on mars is shown to consist of significant fractions of both low and high calcium pyroxene changes in the relative abundances of these pyroxenes are observed for units of different age and morphology even in regions with higher degrees of alteration and contamination from dust volcanic rocks with these characteristics are uncommon on earth but are typical of the basaltic snc meteorites shergottites nakhlites and chassignites thought to be from mars thus it is possible to infer even through the veil of dust that the snc meteorites have mineralogic affinities to major volcanic provinces on mars and are therefore truly representative of the heterogeneity observed on the surface of the red planet

spectroscopic analysis of martian meteorite allan hills 84001 powder and applications for spectral identification of minerals and other soil components on mars spectroscopic measurement and analysis of martian meteorites provide important information about the mineralogy of mars as well as necessary ground truths for deconvolving remote sensing spectra of the martian surface rocks the spectroscopic properties of particulate alh 84001 from 0 3 to 25 m correctly identify low ca pyroxene as the dominant mineralogy absorption bands due to electronic transitions of ferrous iron are observed at 0 94 and 1 97 m that are typical for low ca pyroxene a strong broad water band is observed near 3 m that is characteristic of the water band typically associated with pyroxenes weaker features near 4 8 5 2 and 6 2 m are characteristic of particulate low ca pyroxene and can be distinguished readily from the features due to high ca pyroxene and other silicate minerals the reflectance minimum occurs near 8 6 m for the alh 84001 powder which is more consistent with high ca pyroxene and augite than low ca pyroxene the dominant mid infrared ir spectral features for the alh 84001 powder are observed near 9 and 19 5 m however there are multiple features in this region these mid ir features are generally characteristic of low ca pyroxene but cannot be explained by low ca pyroxene alone spectral features from 2 5 5 m are typically associated with water organics and carbonates and have been studied in spectra of the alh 84001 split 92 powder and alh 84001 splits 92 and 271 chip surfaces weak features have been identified near 3 5 and 4 m that are assigned to organic material and carbonates another feature is observed at 4 27 m in many surface spots and in the powder but has not yet been uniquely identified spectroscopic identification of minor organic and carbonate components in this probable piece of mars suggests that detection of small amounts of organics and carbonates in the martian surface regolith would also be possible using visible infrared hyperspectral analyses laboratory spectroscopic analysis of martian meteorites provides a unique opportunity to identify the spectral features of minerals and other components while they are embedded in their natural medium

seven million years of glaciation in greenland glacial till glaciomarine diamictites and ice rafted detritus found in marine cores collected off the shore of southeast greenland record multiple late cenozoic glaciations beginning in the late miocene distinct rock assemblages and seismic stratigraphic control correlate the diamictites with glaciation of the southeast greenland margin glaciers advanced to the sea during several intervals in the pliocene and pleistocene north atlantic glaciation may have nucleated in southern greenland rather than further north because of the high mountains and the high levels of precipitation in this region

temporal variability in living deep sea benthic foraminifera a review the deep ocean environment is disturbed by various processes many of which involve episodic inputs of organic matter some inputs e g phytodetritus at mid high latitudes in the north atlantic and northeast pacific are seasonally pulsed others e g falls of whale carcasses are irregular and unpredictable but together they evoke a variety of responses from the benthic biota in the case of deep sea foraminifera only those responses arising from seasonal food pulses have been fairly well documented the population dynamics of deep sea benthic foraminifera total live populations and individual species appear to be controlled largely by two inversely related parameters the flux of organic matter to the seafloor and concentrations of oxygen in the sediment porewater organic matter food inputs are most intense along bathyal continental margins and their oxidation often leads to the depletion of oxygen in surface sediments under these conditions foraminiferal faunas are dominated by low oxygen tolerant infaunal species the abundance of which fluctuate in response to seasonally varying amounts of food and oxygen at some sites e g sagami bay off japan species migrate up and down in the sediments tracking critical oxygen concentrations where oxygen concentrations are consistently low less than about 0 5 ml l 1 as in parts of the california borderland foraminifera may undergo population increases solely in response to food pulses in the abyssal north atlantic and in some continental margin areas of this ocean organic matter inputs are weaker and do not lead to oxygen depletion within surface sediments these systems are food limited and seasonal population fluctuations reflect the availability of food phytodetritus rather than oxygen here the species which respond to phytodetritus are mainly epifaunal or shallow infaunal opportunists which represent a small proportion of highly diverse communities 2 or 3 out of 120 species per core of 25 5 cm2 surface area seasonal phytodetrital pulses to the deep seafloor and hence foraminiferal population dynamics are not entirely predictable being dependent on climatic and upper ocean processes they vary in intensity from year to year and occasionally e g at the porcupine abyssal plain pap in 1997 fail to materialise foraminiferal responses to irregular non seasonal organic matter inputs are poorly known however there is some evidence that whale falls turbidite deposits hydrothermal vents and seeps are exploited by species typical of organically enriched low oxygen environments rather than by a specialised fauna fossil foraminiferal assemblages from bathyal and abyssal environments may provide evidence for an increase or decrease in the seasonality of surface production as well as for longer term changes in palaeoproductivity however the accurate interpretation of this record depends on filling the many gaps which remain in our understanding of relations between benthic foraminiferal ecology and seasonal phenomena in the deep ocean

miocene history of the benguela current and antarctic ice volumes evidence from rhythmic sedimentation and current growth across the walvis ridge deep sea drilling project sites 362 and 532 the history of the northward growth and of the fluctuations of the benguela current from the middle miocene ca 14 ma to the uppermost late miocene ca 5 ma has been reconstructed from analyses of the coarse and clay fractions and geochemical analyses of the organic matter in sediments from deep sea drilling project sites 362 and 532 in the middle miocene the benguela current had not yet reached the walvis ridge and consequently no local upwelling occurred carbonate preservation was good during this period of low productivity rhythmic changes related to antarctic ice volumes were weak leading to slightly higher organic matter concentrations and higher montmorillonite illite m i ratios in sediments deposited during times of greater continental ice montmorillonite was carried north from the orange river by the benguela current whereas illite originated from the nearby namib desert in the early late miocene the benguela current reached the walvis ridge in colder periods and led to well developed rhythmic increases in opal which was transported from near coastal upwelling areas organic matter concentration carbonate dissolution and m i ratios were also enhanced during periods of greater ice volume during the late miocene farther northward migration of the benguela current led to a change in the uppermost miocene sediments opal contents and m i ratios were high during times of low ice volume rather than in colder times during the cold periods local winds from the namib desert increased the illite supply to the walvis ridge and depressed the m i ratio in these periods the benguela current flowed farther to the north reaching the angola basin as it did in quaternary glacial periods throughout these changes sediment organic carbon content was always enhanced in high ice volume periods from near bottom downslope transport of organic matter from shelf regions during regressions and carbonate dissolution in the sediments was increased as a result of oxidation of this organic matter

the messinian diatomite deposition in the mediterranean region and its relationships to the global silica cycle abstract diatomites constitute a widely represented lithology in the messinian sections of the circum mediterranean neogene marginal basins although traditionally interpreted as genuine evidence of the gradually restricted conditions that characterized the mediterranean just before the messinian salinity crisis their coeval occurrence with a global intensification of the opaline production in the world oceans late miocene early pliocene biogenic bloom suggests that an integrative analysis of the origins of these sediments is necessary a comprehensive analysis of the geological and paleontological records suggests that the synergistic intervention of abiotic tectonic and climate reconfigurations and biotic expansion of grass dominated opal rich biomes controlling factors may have promoted a remarkable enhancement of silica flux from continents to oceans which in turn can explain the opaline burst that occurred during the late miocene at both the global and mediterranean scale the finely laminated pattern and the rich fossil content of diatomaceous deposits that are usually considered to be byproducts of anoxic conditions are briefly discussed some studies seem to indicate that instead of anoxia the aggregation and sedimentation of diatom tests may play a critical role in these processes the lower messinian diatomites of the mediterranean region are generally interbedded with organic rich sediments sapropels clearly attesting prolonged precessionally controlled periods of basin stratification and bottom water anoxia or hypoxia a causal relationship between sapropel and diatomite deposition in the mediterranean is proposed considering the possible interplay between stratification adapted diatoms and anaerobic bacteria and their respective role in influencing the marine silica cycle

chronology causes and progression of the messinian salinity crisis the messinian salinity crisis is widely regarded as one of the most dramatic episodes of oceanic change of the past 20 or so million years 1 3 earliest explanations were that extremely thick evaporites were deposited in a deep and desiccated mediterranean basin that had been repeatedly isolated from the atlantic ocean1 2 but elucidation of the causes of the isolation whether driven largely by glacio eustatic or tectonic processes have been hampered by the absence of an accurate time frame here we present an astronomically calibrated chronology for the mediterranean messinian age based on an integrated high resolution stratigraphy and tuning of sedimentary cycle patterns to variations in the earth s orbital parameters we show that the onset of the messinian salinity crisis is synchronous over the entire mediterranean basin dated at 5 96 0 02 million years ago isolation from the atlantic ocean was established between 5 59 and 5 33 million years ago causing a large fall in mediterranean water level followed by erosion 5 59 5 50 million years ago and deposition 5 50 5 33 million years ago of non marine sediments in a large lago mare lake sea basin cyclic evaporite deposition is almost entirely related to circum mediterranean climate changes driven by changes in the earth s precession and not to obliquity induced glacio eustatic sea level changes we argue in favour of a dominantly tectonic origin for the messinian salinity crisis although its exact timing may well have been controlled by the 400 kyr component of the earth s eccentricity cycle

the late miocene onset of high productivity in the benguela current upwelling system as part of a global pattern abstract we have examined the history of the elevated primary productivity associated with the benguela current upwelling system off southwest africa using sediments from 7 5 to 4 8 ma at ocean drilling program site 1085 in the middle cape basin sedimentation rates are low until 6 9 ma low accumulation rates of benthic foraminifers and organic carbon indicate that biological productivity was also low paleoproductivity dramatically increased at 6 7 6 5 ma and was highly variable until 4 8 ma with productivity maxima during cooler periods the presence of radiolarian opal only between 5 8 and 5 2 ma suggests an interlude of silica rich intermediate water in the cape basin the onset of heightened productivity under the benguela current is mirrored by similar increases reported between 6 9 and 6 7 ma in the tropical eastern pacific the western and northern pacific and the indian ocean the similarity between the patterns at site 1085 and in the pacific and indian oceans suggests that the dramatic productivity increase off southwest africa is part of a global response to paleoceanographic changes

evolution of eastern pacific warm pool and upwelling processes since the middle miocene based on analysis of radiolarian assemblages response to indonesian and central american seaways a quantitative racholarian study at ocean drilling program site 1241 in the eastern tropical pacific enables us to reconstruct paleoceanographic changes that occurred since the latest middle miocene today this site is located just under the eastern pacific warm pool epwp based on the abundance variations of radiolarian characteristic species which are indicators of upwelling and thermocline changes it is suggested that three notable changes occurred at 10 6 9 8 and 4 2 ma in the region four distinct periods of oceanographic conditions bounded by these notable changes were characterized on the basis of the following 1 stratified seawater 12 0 to 10 6 ma 2 a shallowing of the thermocline and an increasing of upwelling 10 6 to 9 8 ma 3 significant inflow of warm water to the eastern tropical pacific caused by an intensified northern equatorial countercurrent necc resulting in the formation of epwp 9 8 to 4 2 ma and 4 the reduction of the epwp and the necc and an increase in upwelling 4 2 to 0 ma the timing of these paleoceanographic events indicated the strong relations with the opening and closing of the indonesian and central american panama seaways the reduction of the epwp this study and the deepening of the thermocline in western pacific at about 4 2 ma cannariato and ravelo 1997 chaisson and ravelo 2000 indicated a change from a state resembling el nino in the late miocene and the early pliocene time to a state resembling la nina by the late pliocene c 2009 elsevier b v all rights reserved

northeastern atlantic benthic foraminifera during the last 45 000 years changes in productivity seen from the bottom up we studied benthic foraminifera from the last 45 kyr in the 63 mu m size fraction in biogeochemical ocean flux studies bofs cores 5k 50 degrees 41 3 n 21 degrees 51 9 w depth 3547 m and 14k 58 degrees 37 2 n 19 degrees 26 2 w depth 1756 m at a time resolution of several hundreds to a thousand years the deepest site showed the largest fluctuations in faunal composition species richness and benthic foraminiferal accumulation rates the fluctuations resulted from changes in abundance of epistominella exigua and alabaminella weddellensis in the present oceans these species bloom opportunistically when a spring plankton bloom results in seasonal deposition of phytodetritus on the seafloor the phytodetritus species had very low relative abundances and accumulation rates during the last glacial maximum a strong increase in absolute and relative abundance of e exigua and a weddellensis during deglaciation paralleled the decrease in abundance of the polar planktonic foraminifer neogloboquadrina pachyderma s and the increase in abundance of warmer water planktonic species such as globigerina bulloides this strong increase in relative abundance of the phytodetritus species and the coeval increase in benthic foraminiferal accumulation rate were thus probably caused by an increase in the deposition of phytodetritus to the seafloor and thus probably of surface productivity when the polar front retreated to higher latitudes the abundance of phytodetritus species decreased during the younger dryas but not to the low levels of fully glacial conditions during heinrich events periods of excessive melt water formation and ice rafting benthic accumulation rates were very low as were the absolute and relative abundances of the phytodetritus species supporting suggestions that surface productivity was very low during these events in both cores pullenia and cassidulina species were common during isotope stages 2 3 and 4 as were bolivinid buliminid and uvigerinid species high relative abundances of these species have been interpreted as indicative either of sluggish deep water circulation or of high organic carbon fluxes to the seafloor in our cores relative abundances of these species are negatively correlated with benthic foraminiferal accumulation rates and we can thus not interpret them as indicative of increased productivity during glacials the percentage of these low oxygen species calculated on a phytodetritus species free basis decreased slightly at deglaciation at 5k but not at 14k this suggests that decreased production of north atlantic deep water during the last glacial might have slightly affected benthic foraminiferal faunas in the eastern north atlantic at 3547 m depth but not at 1756 m in conclusion major changes in deep sea benthic foraminiferal faunas over the last 45 000 years in our cores from the northeastern atlantic were the result of changes in surface water productivity not of changes in deep water circulation productivity was lower during the glacial probably because of extensive ice cover

chemical compositions at mars landing sites subject to mars odyssey gamma ray spectrometer constraints 1 the mars odyssey gamma ray spectrometer grs is the first instrument suite to return elemental abundances throughout the midlatitudes of mars concentrations of cl fe h k si and th have been determined to tens of centimeter depths as mass fractions with reasonable confidence comparing such data with or normalizing them to in situ compositional data is difficult due to issues such as dramatic differences in spatial resolution difficulties in convolving densities abundances and compositions of different regolith components and a limited number of elements observed in common we address these concerns in the context of the grs using si at pathfinder to normalize remote data in addition we determine representative in situ compositions for spirit both with and without columbia hills rocks opportunity and viking 1 landing sites using grs derived h content to hydrate the soil component our estimate of the si mass fraction at pathfinder with 13 areal fraction of rocks is 21 the composition of major elements such as si and fe is similar across the four landing sites while minor elements show significant variability areal dominance of soil at all four landing sites causes representative compositions to be driven by the soil component while proportionally large uncertainties of bulk densities dominate the net uncertainties grs compositional determinations compare favorably with the in situ estimates for cl and k and for si by virtue of the normalization however the grs determined fe content at each landing site is consistently higher than the in situ value

a 35 000 year record of changes in the eastern indian ocean offshore sumatra article i nfo we have examined the upper 276 cm of deep sea core bar9403 taken at a water depth of 2034 m offshore the southern portion of sumatra in the eastern indian ocean using several micropalaeontological proxies faunal counts and stable isotopes of oxygen and carbon of planktic and benthic foraminifers as well as floral counts of dinoflagellates were obtained to reconstruct conditions in the oceans over the last 35 000 years at times we found that when benthic foraminifers indicate high organic content values at the bottom of the ocean this is not paralleled by high productivity signals at the sea surface but instead must relate to changes in bottom water circulation as a result of slower water circulation the marine isotopic stages mis 3 1 are clearly differentiated by benthic and foraminiferal assemblages as well as dinoflagellates and their cysts mis 3 is characterised by a much sharper than today thermocline that was closer to the sea surface and by the absence of a low salinity barrier layer which today results from high monsoonal rains the absence of the latter persisted during the last glacial period mis 2 when bottom circulation must have been reduced and high percentages of organic matter occurred on the sea floor combined with low dissolved oxygen levels the deglaciation is marked by a change in salinity at the sea surface as seen by the dinoflagellates and planktic foraminifers and progressive alteration of the thermocline was detected by foraminifers suggesting a less productive deep chlorophyll maximum in contrast with mis 3 and 2 monsoonal activity commenced around 15 000 cal years ago and was well established 2000 years later the holocene is marked by a significant increase in river discharge to the ocean pulsed by the delivery of organic matter to the sea floor despite overall oligotrophic conditions at and near the sea surface induced by a permanent low salinity cap we did not identify obvious and persistent upwelling conditions offshore sumatra for the last 35 000 years

joint analysis of ism and tes spectra the utility of multiple wavelength regimes for martian surface studies utility of these data sets they need to be joined to provide pan spectral coverage of the surface of mars that will give information on different types of absorption processes in surface materials we have performed a test of this approach using ism and tes data to provide near infrared and thermal infrared coverage of the selected regions observed by both instruments gridding and registering the two data sets to a common reference allows investigations of regional and global properties of the surface here we investigate the variability in the spectral properties of low albedo regions particularly type i basaltic and type ii regions and relate these variations to probably mineralogic composition ism and tes data agree on the presence of pyroxenes in type i regions but may indicate a lack of pyroxene in the type ii material although this is inconclusive type i regions in general appear to be uniform in composition and surface variations are primarily controlled by mixing with dust temporal variations in surface reflectance make analysis of the differences in spectral properties between eastern and western syrtis major difficult but indicate that slope differences may not be due to intimate cementing of dark and light materials but rather due to penetrative oxidation of the surfaces of basaltic materials these results demonstrate that the complementary strengths of multiple wavelength regimes allow greater understanding of surface composition and processes

mars surface diversity as revealed by the omega mars express observations the observatoire pour la mineralogie l eau les glaces et l activite omega investigation on board the european space agency mars express mission is mapping the surface composition of mars at a 0 3 to 5 kilometer resolution by means of visible near infrared hyperspectral reflectance imagery the data acquired during the first 9 months of the mission already reveal a diverse and complex surface mineralogy offering key insights into the evolution of mars omega has identified and mapped mafic iron bearing silicates of both the northern and southern crust localized concentrations of hydrated phyllosilicates and sulfates but no carbonates and ices and frosts with a water ice composition of the north polar perennial cap as for the south cap covered by a thin carbon dioxide ice veneer

in situ compositions of martian volcanics implications for the mantle the primary objective of this analysis is to determine the mineralogic composition of relatively pristine terrains exposed on the surface of mars this analysis is conducted using imaging spectrometer data acquired in 1989 by the imaging spectrometer for mars ism instrument that was onboard the phobos ii spacecraft the ism instrument acquired some of the highest spectral 64 channels between 0 77 and 3 14 m and spatial resolution 22 km pixel observations to date of mars focused on the equatorial region relatively unaltered surfaces were identified in these data on the basis of their spectral properties low albedo weak spectral slope absence of ferric absorptions and were found in volcanic terrains of syrtis major valles marineris ophir planum and sinus meridiani oxia palus spectra representative of the diversity among terrains were extracted for detailed analysis using the modified gaussian model to determine the primary mafic mineralogy it was determined that the mafic mineralogy of the regions investigated is dominated by low calcium and high calcium pyroxene lcp hcp and that there was homogeneity within a given region but some heterogeneity between regions in the relative abundance of lcp to hcp the two pyroxene mineralogy is consistent with the mineralogies of the basaltic snc meteorites believed to have originated on mars two pyroxene volcanic mineralogies are indicative of large degrees of partial melting e g komatiites or a mantle source depleted in aluminum integration of these findings with previous studies of mars and the snc meteorites indicates that 1 the snc mineralogies are representative of large volcanic regions of mars with surface ages as old as 2 3 ga 2 the martian mantle was depleted in aluminum at least as long ago as the oldest terrain analyzed ophir planum and 3 there has been little evolution in the composition of mantle source regions as the 180 ma snc mineralogies are comparable to those of the oldest terrains analyzed

three and half million year history of moisture availability of south west africa evidence from odp site 1085 biomarker records ocean drilling program site 1085 provides a continuous marine sediment record off southern south west africa for at least the last three and half million years the n alkane 13 c record from this site records changes in past vegetation and provides an indication of the moisture availability of sw africa during this time period very little variation and no apparent trend is observed in the n alkane 13c record suggesting stable long term conditions despite significant changes in east african tectonics and global climate slightly higher n alkane 13c values occur between 3 5 and 2 7 ma suggesting slightly drier conditions than today between 2 5 and 2 7 ma there is a shift to more negative n alkane 13c values suggesting slightly wetter conditions during a 0 2 ma episode that coincides with the intensification of northern hemisphere glaciation inhg from 2 5 to 0 4 ma the n alkane 13c values are very consistent varying by less than 0 5 and suggesting little or no long term change in the moisture availability of south west africa over the last 2 5 million years this is in contrast to the long term drying trend observed further north offshore from the namib desert and in east africa a comparison of the climate history of these regions suggests that southern africa may have been an area of long term stability over the last 3 5 myrs

paleoproductivity from benthic foraminifera abundance glacial to postglacial change in the west equatorial pacific surface productivity is correlated with the rate of accumulation of benthic foraminifera on the deep sea floor as a rule of thumb for each 1 mg of organic carbon arriving at the sea floor one benthic foram shell 150 m is deposited the correlation can be used to reconstruct organic flux to the sea floor in the past and hence the productivity of past oceans applying the appropriate equations to box core data from the ontong java plateau in the western equatorial pacific we found that productivity during the last glacial maximum exceeded present productivity by a factor of between 1 5 and 2 0 with intermediate values for the mid transition period accumulation of benthic foraminifera was depressed on top of the plateau during the glacial and transitional period presumably because increased winnowing removed part of the food supply

quantitative compositional analysis using thermal emission spectroscopy application to igneous and metamorphic rocks the mineral composition of a suite of igneous and metamorphic rocks was determined using the thermal infrared emission spectra of these rocks in a linear spectral deconvolution algorithm this algorithm assumes that the infrared spectrum of each rock is a linear mixture of the component mineral spectra weighted by volume abundance a diverse suite of 36 common rock forming and accessory minerals was used in the deconvolution the model was tested by comparing the mineralogy derived from the infrared spectrum with petrographically estimated abundances for 45 igneous and 51 metamorphic rock samples the mineral abundances derived from these two techniques agree to within 67 15 for the primary minerals feldspar pyroxene quartz and calcite dolomite and 69 17 for secondary minerals such as micas and amphiboles these differences are comparable to the error for traditional thin section mode estimates which are 65 15 for major minerals and 5 for minor minerals the detection limit for the primary and secondary minerals found in the rocks analyzed ranged from 5 to 10 each major rock type studied here was easily distinguished by its spectral characteristics the best results in both the qualitative determination of the rock type and dominant minerals and the quantitative reproduction of absorption features and mineral composition were obtained for igneous rock samples for metamorphic rocks pelite and quartzo feldspathic samples gave slightly better results than calcareous or mafic samples a controlled analysis in which the end member suite was reduced based on an initial estimate of the rock type only improved the results by several percent for most primary and secondary minerals the quality of the obtained results demonstrates that a linear deconvolution of infrared emission spectra provides an accurate rapid technique for determining the quantitative mineral composition of rock samples in a laboratory and has application to future in situ measurements

analysis of terrestrial and martian volcanic compositions using thermal emission spectroscopy 2 application to martian surface spectra from the mars global surveyor thermal emission spectrometer atmospherically corrected thermal infrared spectra of large regions of the martian surface from the mars global surveyor thermal emission spectrometer mgs tes previously have been interpreted to represent two general spectral classes one class represents a basalt to basaltic andesite composition and the other class represents a basaltic andesite to andesite composition we have performed new linear deconvolutions of the two martian surface type spectra with an end member set tailored to represent volcanic rock types our preparatory study of laboratory spectra of terrestrial volcanic rocks acquired at 2 cm 21 sampling convolved to tes spectral sampling 10 cm 21 shows little degradation in deconvolution results when compared to results acquired using the higher spectral resolution data indicating that the deconvolution technique is valid for analyzing data at tes resolution our spectral fits to the martian data agree well with previous models and do not exhibit any notable deviations from the martian spectra that would indicate the absence of any significant end members in our model modal mineralogies obtained with these new spectral fits also compare favorably within the previously stated uncertainties to prior results the newly derived modal mineralogies are used with new and traditional classification schemes for volcanic igneous rocks introduced in a companion paper wyatt et al this issue to classify the martian compositions our results substantiate the previously proposed hypothesis that these two spectral classes on the martian surface represent volcanic compositions with distinguishable differences in silica content ranging from basalt to andesite

the african landscape through space and time it is generally accepted that cenozoic epeirogeny of the african continent is moderated by convective circulation of the mantle nevertheless the spatial and temporal evolution of africa s basin and swell physiography is not well known here we show how continental drainage networks can be used to place broad constraints on the pattern of uplift through space and time first we assemble an inventory of 710 longitudinal river profiles that includes major tributaries of the 10 largest catchments river profiles have been jointly inverted to determine the pattern of uplift rate as a function of space and time our inverse model assumes that shapes of river profiles are controlled by uplift rate history and modulated by erosional processes which can be calibrated using independent geologic evidence e g marine terraces volcanism and thermochronologic data our results suggest that modern african topography started to develop 30 myr ago when volcanic swells appeared in north and east africa during the last 15 20 myr subequatorial africa was rapidly elevated culminating in the appearance of three large swells that straddle southern and western coasts our results enable patterns of sedimentary flux at major deltas to be predicted and tested we suggest that the evolution of drainage networks is dominated by rapid upstream advection of signals produced by a changing pattern of regional uplift an important corollary is that with careful independent calibration these networks might act as useful tape recorders of otherwise inaccessible mantle processes finally we note that there are substantial discrepancies between our results and published dynamic topographic predictions

late pliocene climate in the southeast atlantic preliminary results from a multi disciplinary study of dsdp site 532 abstract site 532 on the walvis ridge was sampled at 4000 to 800 year intervals from 2 24 to 2 60 ma spanning the three large glacial advances of the late pliocene an age model was created by correlating the oxygen isotope record to site 607 with linear interpolations between tie lines the resultant age model differs from that in the site reports by more than 800 000 years due to misidentification of a magnetic boundary sedimentation rates varied by an order of magnitude at this site with minimum accumulation during glacial events interglacial intervals were charactrized by high marine production and high summer precipitation on land while glacials had very low production and arid continental climate during the large glacial events stages 96 100 conditions of low production and continental aridity reached their greatest intensity but there is no evidence of a permanent mode shift in either marine or terrestrial records calcite concentration has a strong variation at obliquity frequencies with maxima during interglacials but occasionally shows a large amplitude at precessional frequencies as well so that high concentrations occur in a few glacial intervals as a result color variation is not a reliable guide to glacial scale cycles at this site composition of the phytoplankton assemblage is diverse and highly variable and we have not been able to distinguish a clear indicator of upwelling related production spectral analysis reveals obliquity and precessional signals in the pollen data while several diatom records contain combination tones indicating that these data represent a complicated response to both local and high latitude forcing

high resolution reflectance spectra of mars in the 2 3 μm region evidence for the mineral scapolite spatially resolved reflectance spectra of mars in the 2 2 to 2 4 m spectral region were obtained in august 1988 using the nasa 3 m infrared telescope facility the spectra show weak absorption features due to martian atmospheric carbon monoxide and a surface mineral both co and the mineral absorptions are composed of overlapping narrow features but in many locations such as hellas chryse eden and moab the mineral absorptions are quite strong at least 3 times stronger than at the most absorbing wavelengths of co near 2 33 m therefore co complicates the analysis of the surface mineral but does not always overwhelm its signature model removal of the martian atmospheric co has been performed and the remaining absorption bands are identified as scapolite relatively strong absorptions that match bands in the spectrum of scapolite and have little or no co absorption interference are seen near 2 41 2 39 and 2 29 m absorption also occurs at the scapolite bands at 2 36 and 2 33 m but the analysis is complicated by uncertainty in the atmospheric co removal at these wavelengths weaker scapolite bands are seen at 2 44 and 2 23 m where there is virtually no atmospheric interference the scapolite bands observed on mars are due to hco3 and hso4 ions in the scapolite structure the bicarbonate and bisulfate contents appear to vary with location the scapolite in hellas is more bisulfate rich relative to that in the chryse moab eden area other locations contain little arabia syrtis major hellespontica and isidis or no scapolite e g margaritifer ausonia and erythraeum the calculated abundances are unconstrained because the amounts of hco3 and hso4 in the martian scapolites as well as their grain sizes are not known if the scapolites contain about 3 wt of each near the maximum possible the scapolite abundances probably range from about 5 wt scapolite at eden and hellas 3 5 at chryse moab and oxia palus 2 3 at arabia syrtis major and isidis to less than 2 at hellespontica syrtis minor and margaritifer assuming a relatively large grain size of 50 100 m if the characteristic grain sizes are smaller or the hco3 and hso4 contents are lower the scapolite abundances required to match the observed band depths would be higher the mineral bands are apparent in many of the mars spectra measured so it appears to be widely but not uniformly distributed the newly observed fine structure also varies greatly in both depth and spectral detail with location on mars thus there appears to be regional variations in composition the mineral phases appear to reflect local or regional geology and are not primarily contained in the homogeneous globally redistributed aeolian dust higher spectral resolution martian spectra in the 2 3 m region as well as at 3 9 m are needed to confirm the scapolite identification and to constrain its abundance

middle to late miocene fluctuations in the incipient benguela upwelling system revealed by calcareous nannofossil assemblages odp site 1085a middle to late miocene calcareous nannofossil data of odp site 1085 from the eastern south atlantic off namibia were analysed to document spatial and temporal changes in surface ocean circulation upwelling initiation and associated productivity our data show that calcareous nannofossils constitute a significant part of the carbonate fraction throughout the investigated interval from 12 5 to 7 7 million years ma highest numbers of calcareous nannofossils up to 38 000 10 6 nannofossils g 1 sediment were observed during the intervals 9 9 to 9 7 and 8 7 to 8 0 ma these elevated numbers of calcareous nannofossils may generally be linked to the initiation of upwelling at about 10 ma in the studied region in contrast diminished numbers of calcareous nannoplankton as in the interval 9 6 to 9 0 ma probably characterise time intervals of weaker productivity resulting in a decrease of nannofossil carbonate contents in the sediments of site 1085 this decrease in nannofossil production could be one possible explanation for the major caco3 depression in between 9 6 and 9 0 ma coccoliths of the genus reticulofenestra are the most abundant taxa their occurrences are characterised by changes in the investigated time interval in addition coccolithus pelagicus calcidiscus leptoporus and umbilicosphaera spp contribute a common part of the assemblage calcareous nannofossils account for more than half of the carbonate with peak contribution up to 80 at 8 8 ma d 2005 elsevier b v all rights reserved

effects of chemical weathering on infrared spectra of columbia river basalt and spectral interpretations of martian alteration abstract we investigated the mineralogy of basalt weathering rinds and fresh basaltic rocks using visible near infrared vnir 0 4 2 5 m and thermal emission 6 30 m spectroscopy to 1 constrain the effects of chemical weathering on rock spectra and 2 further understand the context of infrared spectra of mars which may contain evidence for weathered rocks and particulates derived from them vnir spectra of weathered rock surfaces are generally redder and brighter than fresh surfaces thermal infrared spectra of weathered basalts show evidence for aluminous opal and clay minerals or clay precursor mineraloids in natural surfaces supporting vnir observations generally do not show the same evidence for neoformed clays or silica because of their textural occurrence as thin coatings and microfracture fill and possibly due to poor crystallinity of the aluminosilicate weathering products in this context spectral trends observed at mars such as the detection of low to moderate 10 25 abundances of silica and clay that are observed in the thermal infrared but not in the vnir are therefore consistent with trends observed for natural rock surfaces in the laboratory the combined use of thermal infrared and vnir suggest that vast areas of martian dark regions contain sandy rocky basaltic materials with weathering rinds and thin coatings that could have formed in conditions of relatively low water rock ratios

miocene salmon oncorhynchus from western north america gill raker evolution correlated with plankton productivity in the eastern pacific abstract miocene salmon were more specialized than modern salmon in their feeding apparatus computed tomography scans of two late miocene pacific salmon reveal unusually long closely spaced and numerous gill rakers plankton straining structures in the pharynx middle miocene oncorhynchus rastrosus also has more numerous and more finely spaced gill rakers than living species the fossils described here including one new species appear to be related to modern sockeye salmon and chum salmon differing most in the numbers and morphology of gill rakers these structural adaptations to plankton feeding in a group of fish otherwise adapted to fish predation are concordant with oceanographic evidence for remarkably high plankton productivity in the north pacific ocean during the middle miocene

thermal emission spectra of mars 5 4 10 5 μm evidence for sulfates carbonates and hydrates we have obtained spectra of the thermal emission from mars in the 5 4 10 5 m wavelength domain at a resolving power of about 60 from the kuiper airborne observatory spectra were obtained for several large spots on mars whose ground temperatures and air masses through the martian atmosphere differed significantly these data were taken at two times during the flight by taking the ratio of the spectral flux from one spot to that of a second spot we obtained results that were independent of uncertainties in the instrument s spectral response and the transmission of the earth s atmosphere these data as well as spectral fluxes of single spots based using the star tau as a calibration standard show a number of emission and absorption features they are present in sets of spectra taken at two different times some of the absorption features are due to gaseous co2 in the martian atmosphere the remainder of the absorption and emission features are due to minerals present in the airborne dust and on the surface comparison of the strength of features seen at similar times but with three different air masses and ground temperatures suggests that the emission features arise primarily from surface emissivity spectral variations and that the absorption features arise from components of the atmosphere based on comparisons of the observed features with laboratory data for a broad ensemble of minerals spectra of other solar system bodies and relevant compositional information about mars we have made the following tentative identifications of the observed features emission features at 7 8 and 9 7 m are attributed to surface silicates an emission feature at 6 1 m is attributed to a molecular water component of the surface material an absorption band at 8 7 m as well as possibly one at 9 8 m is ascribed to sulfate or bisulfate anions probably located in a distorted crystalline site and an absorption band at 6 7 m is attributed to carbonate or bicarbonate anions located in a distorted crystalline site although we cannot totally rule out a nitrate origin for this feature we have simulated these spectra with radiative transfer programs for the atmosphere and surface these simulations indicate that the sulfate and carbonate bearing minerals are contained in the same particles of the airborne dust as the dominant silicate minerals that the dust optical depth was about 0 6 at a reference wavelength of 0 3 m over the area of the observed spots and that sulfates and carbonates constitute about 10 15 and 1 3 by volume of the airborne dust respectively these results imply that minerals formed by weathering processes represent major reservoirs of volatile species on current mars

sea level events in the south pacific linked with the messinian salinity crisis cores drilled through the carbonate cap of niue a mid oceanic carbonate platform in the south pacific contain an unusually well resolved stratigraphic section of the latest miocene at 35 to 140 m depth below sea level intensely leached and chalky intervals associated with pronounced 18 o and 13 c depletions mark the position of dissolution unconformities representing eight episodes of eustatic falls that outstripped the local rate of subsidence we demonstrate on the basis of sr isotope chronostratigraphy that these eustatic changes are correlative with the messinian salinity crisis events in the mediterranean sea level changes of about 10 m amplitude commenced at 6 14 ma and culminated in a large sea level fall that reached at least 30 m at 5 26 ma corresponding to the miocene pliocene boundary evaluation of the sea level history reported here and the contemporaneous mediterranean events supports the model of coupling between tectonic and eustatic factors that caused the onset and demise of the salinity crisis the available evidence suggests that during messinian time glacio eustatic falls and rises are likely to have modulated the connection between the atlantic and the mediterranean and influenced the evaporite deposition and may have contributed significantly to the final phase of isolation and desiccation of the mediterranean and its subsequent refilling during the zan clean deluge

eocene oligocene transition in the southern ocean history of water mass circulation and biological productivity high resolution records of carbon and oxygen isotopes and benthic foraminiferal accumulation rates for the eocene oligocene section at ocean drilling program site 689 maud rise weddell sea paleodepth about 1500 m were used to infer variations in paleoproductivity in relation to changes in climate and ventilation of the deeper water column the benthic foraminiferal abundance and isotope records show short term fluctuations at periodicities of 100 and 400 ka implying orbitally driven climatic variations both records suggest that intermediate depth water chemistry and primary productivity changed in response to climate during the eocene productivity increased during cold periods and during cold to warm transitions possibly as a result of increased upwelling of nutrient rich waters in the oligocene in contrast productivity maxima occurred during intervals of low d18o values presumably warmer periods when a proto polar front moved to the south of the location of site 689 this profound transition in climate productivity patterns occurred around 37 ma coeval with rapid changes toward increasing variability of the oxygen and carbon isotope and benthic abundance records and toward larger amplitude d18o fluctuations therefore we infer that at this time temperature fluctuations increased and a proto polar front formed in conjunction with the first distinct pulsations in size of the antarctic ice sheet we speculate that this major change might have resulted from an initial opening of the drake passage at 37 ma at least for surface and intermediate water circulation

evolutionary changes in the biometry of the fossil radiolarian stichocorys peregrina lineage in the eastern equatorial and eastern north pacific abstract stichocorys peregrina riedel contributes to paleoceanography as a valuable stratigraphic tool for correlation of deep sea siliceous sediments in world oceans and as a paleoceanographic indicator this paper documents the evolutionary morphologic changes of the s peregrina lineage from the middle miocene to late pliocene in the eastern equatorial and eastern north pacific iodp site u1335 and odp site 887 respectively the size and shape changes show that there are at least two geographical variations in the s peregrina lineage in the eastern equatorial pacific two significant morphological shifts took place about 11 0 and 7 0 ma but the morphology remained relatively stable from 7 0 to 3 0 ma coincident with morphological changes in the s peregrina lineage were changes in biogenic productivity these changes suggest that there is a close correspondence between major paleoceanographic events in the late neogene and evolutionary changes of the s peregrina lineage in the low latitudes in the high latitudes the ratio of the third segment to fourth segment in width and height showed a maximum from 9 5 to 8 0 ma and decreased stepwise at about 8 0 and 6 5 ma however the radiolarian data in the high latitudes do not show a clear relationship between the paleoceanographic events and size variation of this lineage the evolutionary transition from stichocorys delmontensis to s peregrina can be used as a primary biostratigraphic marker in the low latitudes however it is not easy to use the evolutionary transition for biostratigraphic correlation and age determination in the high latitudes because there is no obvious change in the ratio of the third to fourth segment widths that can be used to distinguish s delmontensis from the descendant s peregrina

the surface of syrtis major composition of the volcanic substrate and mixing with altered dust and soil syrtis major is an old low relief volcanic plateau near the equatorial regions of mars it is a persistent low albedo feature on the planet and is thought to contain a high abundance of exposed bedrock and or locally derived surface material and debris spatially resolved variations in surface spectral properties and therefore composition are investigated with data from the imaging spectrometer for mars ism instrument ism obtained 128 wavelength channel spectra from 0 76 to 3 16 m for contiguous pixels approximately 22 22 km in size across much of the plateau the value and spatial distribution of four primary spectral variables albedo continuum slope wavelength of the ferric ferrous band minimum area of the ferric ferrous absorption are mapped and coregistered to viking digital photomosaics analysis of these maps shows that although there is a high degree of overall spectral variability on the plateau the key indicators of mafic mineralogy are relatively homogeneous detailed examination of reflectance spectra from representative areas across the plateau indicate the volcanic surface is dominated by augite bearing basalts and the pyroxene composition in the basalts is estimated to be 0 275 0 075 ca ca fe mg and 0 3 0 1 fe fe ca mg additional mineral components may include olivine feldspar and glass most of the spectral variability on the plateau is interpreted to result from mixing of volcanic bedrock and or locally derived surface material and debris with highly altered dust and soil in western syrtis major the altered material is a transient component on the surface or occurs in large spatially coherent patches e g crater rims in eastern syrtis major it is apparent that the dust components are firmly fixed to the basaltic substrate as a stable oxide rind or coating

late cenozoic evolution of the outer continental shelf at the head of the cape canyon south africa abstract cenozoic sedimentary successions have a restricted distribution both onshore and offshore along the passive western margin of southern africa and much controversy and uncertainty remains on the geological evolution of this margin siliciclastic authigenic and biogenic sediments varying in age from cretaceous to holocene recovered from a number of vibrocores collected between 200 and 500 m water depth at the head of the cape canyon provide the basis for an integrated bio sr isotopic and lithostratigraphic study the study area is underlain by unconsolidated middle cretaceous interbedded woody quartzose sand and kaolinitic mud a large regional erosional hiatus separates the upper oligocene to lower miocene carbonate sediments from these cretaceous sediments the upper oligocene to lower miocene 18 1 27 2 ma carbonate succession records third order sea level fluctuations superimposed on an overall marine transgression the interpreted late oligocene depositional environments imply increased bottom water activity over time and the peak in phosphogenesis at 23 6 26 1 ma indicates the onset of warm water upwelling calcareous deposition ended at around 18 ma when downwarping of the continental shelf associated with uplift of the continental interior resulted in the seaward tilt of the carbonate succession to greater water depths increased terrigenous input is recorded as inner shelf prograding quartzose delta front deposits following uplift of the interior uplift combined with a long term marine regression resulted in the widespread erosion of middle to upper miocene successions generally recovered only as reworked glauconite carbonate fluorapatite cfa mixed mineral pellets above the erosional hiatus glauconite rich sediments indicate overall low accumulation rates and multiple reworking events of organic rich clayey sediments during the middle to late miocene early pliocene onset of cold water upwelling at least intermittently by 15 ma established hydrographic conditions similar to the benguela upwelling system with a coast parallel mudbelt present on the middle shelf a middle pliocene marine regression reworked 15 8 9 1 ma inner shelf quartzose delta front sediments across the outer shelf late pliocene early pleistocene uplift of the continental interior resulted in the fault controlled incision of the head of the cape canyon along the seaward flank of the buoyant agulhas columbine basement block uplift increased quaternary terrigenous sedimentation on the shelf where the facies distribution was clearly controlled by canyon head bathymetry high frequency glacio eustatic sea level fluctuations resulted in late quaternary erosion and slumping across the outer shelf and the continued downcutting of the cape canyon lowstand shelly gravels are common including the last glacial maximum shell lag which grades into a faecal pellet rich holocene mud drape over much of the study area the late cenozoic evolution of the western margin recorded in the complex condensed sediment record of the study area is characterised by low sediment accumulation rates and multiple reworking events the integrated stratigraphic interpretation emphasises the importance of eustasy tectonic activity fluvial sediment input palaeoceanographic and climatic changes

nature and distribution of surficial deposits in chryse planitia and vicinity mars color images of bright red dust deposits at the mutch memorial station were acquired at variable incidence angles during sol 611 subsolar longitude 70 northern spring season after removing effects due to atmospheric scattering and absorption the data were used to estimate the independent variables in the hapke 1986 photometric function in blue green and red coordinates the vector representing the space radiance factor of the landing site extracted from viking orbiter images acquired on sol 609 is separated by a euclidean distance of only 0 022 units and an angle of only 1 5 from the vector estimated from the station data for the orbiter lighting and viewing geometries this result implies that light reflected from dust exposures dominates the orbiter signal multiplicative and additive atmospheric terms cancel one another and surface roughness is a second order effect in the orbiter data dust radiance factors computed from station data are most like laboratory spectra for fine grained hawaiian palagonite and are indistinguishable from earth based spectra of classical bright areas color composites of orbiter images show that the dust is found immediately south of acidalia planitia and in association with topographic barriers such as craters and cliffs examination of viking infrared thermal mapper data shows that the dust deposits typically do not have distinctive thermal inertia signatures implying that the deposits are optically thick hundreds of micrometers but thinner than the diurnal thermal skin depth centimeters dark gray material with thermal inertia values 8 12 10 3 cal cm 2 s 1 2 k 1 indicative of sand grain sizes 0 5 1 5 mm dominates the acidalia planitia lowlands and parts of kasei vallis this material also occurs as dark streaks extending from craters in xanthe terra and oxia palus space radiance factors of dark gray material are similar to spectra of mafic rock mixed with a minor amount of palagonitelike material material that is darker than but just as red as the dust deposits occurs in lunae planum xanthe terra and oxia palus areas of intermediate elevation multiple phase angle orbiter images suggest that the dark red exposures are a mixture of bright red and dark gray materials with the dark red exposures being relatively rough at a subpixel scale as compared to exposures of the other two materials thus only two types of materials can be detected in the data covering the study area palagonitelike dust and mafic rock fragments thermal inertia values 4 8 10 3 cal cm 2 s 1 2 k 1 for the dark red material are consistent with the presence of fine to medium sand size particles 0 10 0 5 mm such material should be easily moved by winds the lack of aeolian features implies that the dark red deposits are not composed of loose material rather they are probably more eroded versions of blocky soil or duricrust cemented dust and rock fragments exposed at the station both bright red dust aeolian suspension load and dark gray materials saltation traction loads migrate over the dark red substrate the overall distribution of the surficial units is controlled by topography at a variety of length scales lower wind threshold friction velocities associated with higher atmospheric densities in lowlands keep dust from accumulating and duricrust from forming while higher threshold velocities in highlands lead to net accumulation of dust local topographic obstacles craters walls ridges perturb wind flow and lead to local accumulation or erosion at a variety of elevations in addition the bright red dust ubiquitously found between exposures of dark gray and dark red materials may accumulate as the wind velocity gradient decreases at the transition from smoother dark gray exposures to rougher dark red exposures the distribution of the materials must also be modulated by climatic variations induced by quasi periodic oscillations in obliquity eccentricity and spin axis direction constraining these surficial deposits to be 1 ma

determining the modal mineralogy of mafic and ultramafic igneous rocks using thermal emission spectroscopy the modal mineralogies of 20 mafic and ultramafic igneous rocks were determined from their thermal infrared emission spectra using a linear deconvolution approach which uses a library of end member mineral spectra to model a bulk rock spectrum over 90 of the modes obtained from thermal emission spectra agree with modes obtained by traditional optical analyses to within the stated error of the optical analyses 5 15 vol library spectra of several compositions within a solid solution series e g plagioclase feldspars labradorite and bytownite were commonly used in each best fit model and are assumed to represent in combination a composition in the rock for which an identical mineral spectrum was unavailable in the library the accuracy of this assumption was evaluated by calculating a weighted average solid solution composition for plagioclase and or pyroxenes from the library minerals used in the model best fit of 14 rocks and comparing these compositions to the actual chemistries measured by electron microprobe or the optically estimated an the derived solid solution compositions are generally within 10 15 an or mg of the measured composition modal data derived from the spectra via the deconvolution were summed and converted to weight percent wt oxides for comparison to standard bulk chemistry data sio2 al2o3 and na2o k2o were generally slightly overestimated and feo and mgo were typically slightly underestimated modes and wt oxides were plotted on standard rock type classification diagrams and provide broadly accurate classifications demonstrating that the linear deconvolution technique is successful at deriving useful mineralogical information from thermal infrared emission spectra of bulk rock samples furthermore convolution of the laboratory data to spectral resolutions comparable to remote sensing instruments specifically the mars global surveyor thermal emission spectrometer demonstrates only a 5 vol increase in modal uncertainty for minerals present in abundances 10 vol this study thus provides a strong foundation for the application of this technique to mafic igneous sample spectra from both laboratory and remote sensing instruments