comparison of water column co2aq with sedimentary alkenone based estimates a test of the alkenone co2 proxy 1 the stable carbon isotopic compositions of alkenones have been used to interpret the long term history of the partial pressure of atmospheric carbon dioxide pco2 although extensive water column and culture studies document the potential utility and limitations of this approach to date the accuracy of pco2 values derived from sedimentary alkenones remains untested for this study we establish holocene aged alkenone based co2aq estimates co2aq alk from 20 sites along a central pacific ocean transect and compare them against both observed modern water column co2aq and estimated preindustrial concentrations at the depth of alkenone production at each site although the co2aq alk track measured water column values they are conspicuously lower than modern values across the subtropics this offset likely reflects the contributions of anthropogenic co2 in modern surface waters relative to preindustrial concentrations at the time of alkenone production when a model based estimate of anthropogenic co2 is removed from the modern observed values a majority 84 of co2aq alk falls within 20 of modeled preindustrial values consistency between the modeled and alkenone based estimates of preindustrial co2 levels points to the relative accuracy of the alkenone co2 method across a wide range of ocean and biogeographic regimes provided that phosphate concentrations at the depth of haptophyte production are reasonably constrained it further suggests that light limited growth and or active carbon uptake if they occur have a negligible effect on reconstructed co2aq

monsoon related variations in zaire congo sediment load and influence of fluvial silicate supply on marine productivity in the east equatorial atlantic during the last 200 000 years two sediment cores from the zaire fan and the angola margin have been investigated for their composition of terrigenous and biogenic constituents respectively for the late quaternary kaolinite feldspar ratios and variations of terrigenous element ratios of zr ti k rb and al reveal that the composition of zaire river sediment load has fluctuated in tune with precessional variations of boreal summer insolation in particular the correspondence of high kaolinite feldspar and al k ratios with low latitude insolation maxima strongly corroborates the assumption that west african monsoonal precipitation and chemical weathering was enhanced during periods of increased central african heating the most striking feauture observed is that opal accumulation has been 2 to 10 times higher in zaire fan sediments than outside in continental margin sediments off angola although biogenic ba and corg fluctuations from both areas indicate that changes of total paleoproductivity were of the same magnitude in the zaire river plume and off angola from this we infer that the contribution of biogenic opal production to total paleoproductivity has been significantly higher within the zaire river plume than in the oceanic upwelling regime farther to the south off angola over the last 200 000 years the pattern of opal accumulation rates with respect to that of marine organic carbon implies that enhanced opal production off the zaire river to a great extent was the result of additional fluvial supply of dissolved silica during humid climates characterized by more intense chemical weathering on the continent while total paleoproductivity created by oceanic upwelling was high in periods of increased zonal trade wind intensity at precessional insolation minima and during cold more arid glacial climate conditions we presume that paleoproductivity off the zaire was controlled by the following two sources of nutrients 1 marine nutrients including nitrate and phosphate as well as the uptake of ba on particulate corg caused by upwelling and 2 silica mainly delivered by the zaire river dissolved silicate hence our results underline the importance of dissolved silicate in large rivers for marine silicate cycling in the tropical to subtropical atlantic at a millenial timescale

response of the tropical atlantic thermocline to late quaternary trade wind changes we applied the modern analog technique to foraminiferal counts from three equatorial atlantic gravity cores to estimate paleothermocline depths in the eastern and western tropical atlantic during the past 250 kyr the eastern equatorial core geob 1105 4 is characterized by variations in the 23 kyr cycle whereas the western sediment cores show a dominant periodicity at the 41 kyr band the phase relationships with respect to insolation and ice volume suggest that thermocline fluctuations in the east are primarily driven by the intensity of the monsoon due to variations in low latitude insolation in contrast changes of the thermocline depth in the western tropical atlantic which lead global ice volume at the 41 kyr band by 3 4 kyr seem to depend on the strength of the se trade winds in response to the meridional temperature gradients in the south atlantic

robust geochemical indices for redox and weathering on a granitic laterite landscape in central uganda abstract most geochemical studies of laterite formation have been based on detailed examinations of a small number of hopefully representative profiles due to spatial variability in bedrock composition and geomorphic processes that sort materials by size density and other properties experimental designs developed for the geochemical analysis of single soil profiles are of limited use in landscape investigations in this study of a laterite landscape on a granitic rock in uganda we used element concentrations from neutron activation analysis naa to develop a suite of robust geochemical indices for landscape scale analysis of weathering and oxidation reduction redox processes in laterite formation to capture k feldspar weathering the k hf ratio served as a good proxy for feldspar zircon mineral ratios while k na ratios indexed feldspar concentration to quartz using principal components analysis we derived an index of rare earth elements ree leaching relative to th and an index of heavy to light ree hree lree fractionation we used the fe sc ratio to ascertain the absolute redox vs relative weathering fe accumulation in laterite formation with absolute fe accumulation also associated with lower fe as ratios mn ce ba nodules and concretions were identified by characteristically high ce values with individual ce values as high as 5000 g g 1 the relatively large amounts of k feldspar k avg is 4000 g g 1 and low degree of hree lree fractionation suggest that this landscape is weathered less than generally assumed the fe and mn derived indices highlight the important role of oxidation reduction processes in iron accumulation overall our findings suggest that the current ferricrete mantled hilltops were formerly located on a lower poorly drained part of the landscape

carbon isotopic fractionation ep of c37 alkenones in deep sea sediments its potential as a paleonutrient proxy 1 we compared ocean atlas values of surface water po43 and co2 aq against the carbon isotopic fractionation ep of alkenones obtained from surface sediments of the south atlantic and the central pacific pacific data are from pagani et al 2002 we observed a positive correlation between ep and 1 co2 aq which is opposite of what would be expected if the concentration of co2 aq were the major factor controlling the carbon isotopic fractionation of c37 2 alkenones instead we found inverse relationships between ep and po43 for the two ocean basins for the atlantic ep 4 6 po43 15 1 r 0 76 for the pacific ep 4 1 po43 13 7 r 0 64 suggesting that ep is predominantly controlled by growth rate which in turn is related to nutrient concentration the similarity of the slopes implies that a general relationship between both parameters may exist using the relationship obtained from the south atlantic we estimated surface water nutrient concentrations for the past 200 000 years from a deep sea sediment core recovered off angola low ep values indicating high nutrient concentrations coincide with high contents of total organic carbon and c37 alkenones low surface water temperatures and decreased bulk 15n values suggesting an increased upwelling of nutrient rich cool subsurface waters as the main cause for the observed ep decrease

glacial interglacial co2 change the iron hypothesis several explanations for the 200 to 280 ppm glacial interglacial change in atmospheric co2 concentrations deal with variations in southern ocean phytoplankton productivity and the related use or nonuse of major plant nutrients an hypothesis is presented herein in which arguments are made that new productivity in today s southern ocean 7 4 1013g yr 1 is limited by iron deficiency and hence the phytoplankton are unable to take advantage of the excess surface nitrate phosphate that if used could result in total southern ocean new production of 2 3 1015 g c yr 1 as a consequence of fe limited new productivity holocene interglacial co2 levels preindustrial are as high as they were during the last interglacial 280 ppm in contrast atmospheric dust fe supplies were 50 times higher during the last glacial maximum lgm because of this fe enrichment phytoplankton growth may have been greatly enhanced larger amounts of upwelled nutrients may have been used and the resulting stimulation of new productivity may have contributed to the lgm drawdown of atmospheric co2 to levels of less than 200 ppm background information and arguments in support of this hypothesis are presented

long chain alkenones and alkyl alkenoates and the fossil coccolith record of marine sediments long chain n c37 c39 alkenones and alkyl alkenoates are biological markers for sediment inputs of algae from the class prymnesiophyceae which includes the coccolithophorids these compounds have been recognized in many recent and ancient marine sediments but in only a few living algal species notably the ubiquitous coccolithophorid emiliania huxleyi the proven value of long chain alkenones in palaeotemperature assessment prompts an evaluation of their sedimentary record especially their correspondence with coccolithophorid fossils in ancient marine sediments synthesis of available micropalaeontological and molecular data suggests that morphologically related species of the genera crenalithus dictyococcites emiliania gephyrocapsa pseudoemiliania and reticulofenestra all belonging to the family gephyrocapsaceae were potential biological sources of alkenones and alkyl alkenoates in marine sediments deposited since the eocene 45 ma the occurrence of alkenones in cenomanian and albian sediments devoid of nannofossils may be presumed to reflect contributions from ancestors of the gephyrocapsaceae although an investigation of cretaceous samples containing both coccoliths and alkenones would provide further evidence of this proposed correspondence the combination of palaeontological and molecular chemotaxonomic information offers a novel approach to the evaluation of the phylogenetic lineages that link living and extinct algae

long term tropical morphogenesis of new caledonia southwest pacific importance of positive epeirogeny and climate change extensive mapping of relict lateritic landsurfaces over the 1600 m of relief of mainland new caledonia is used to evaluate long term morphogenesis of the island since its emergence in the oligocene the results support the interpretation of the lateritic levels as abandoned stepped remnant landsurfaces that may be grouped into eight island scale erosion levels recording episodic lowering of base level the separation of the erosion levels results from the combination of positive epeirogenic movements of the new caledonia continental ridge and long term neogene climate variability which is recorded by the contrasted erosion and weathering patterns of the three youngest levels and tentatively correlated with known global and regional paleoclimatic events

10be and ba concentrations in west african sediments trace productivity in the past particle reactive elements are scavenged to a higher degree at ocean margins than in the open ocean due to higher fluxes of biogenic and terrigenous particles in order to determine the influence of these processes on the depositional fluxes of10be and barium we have performed high resolution measurements on sediment core geob 1008 3 from the congo fan because the core is dominated by terrigenous matter supplied by the congo river it has a high average mass accumulation rate of 6 5 cm kyr biogenic10be and ba concentrations were calculated from total concentrations by subtracting the terrigenous components of10be and ba which are assumed to be proportional to the flux of al2o3 the meanba al weight ratio of the terrigenous component was determined to be 0 0045 the unusualy high terrigenous10be concentrations of 9 1 109 atoms g al2o3 are either due to input of particles with high10be content by the congo river or due to scavenging of oceanic10be by riverine particles the maxima of biogenic10be and ba concentrations coincide with maxima of the paleoproductivity rates time series analysis of the10be and of ba concentration profiles reveals a strong dominance of the precessional period of 24 kyr which also controls the rates of paleoproductivity in this core during the maxima of productivity the flux of biogenic ba is enhanced to a larger extent than that of biogenic10be applying a model for coastal scavenging we ascribe the observed higher sensitivity of ba to biogenic particle fluxes to the fact that the ocean residence time of ba is approximately 10 times longer than that of10be

reconstruction of past nutrient utilization in the eastern angola basin based on sedimentary 15n 14n ratios the 15n records of two sediment cores from the angola basin have been used to investigate past changes in nutrient utilization in the surface waters of this highly productive region low 15n 14n ratios in the cores from 3000 m water depth generally correspond to low sea surface temperatures and high sedimentary organic content demonstrating a link between upwelling productivity and the degree of nitrate depletion glacial 15n was lower by 0 5 0 7 and paleoproductivity was elevated by around 30 relative to interglacial periods indicating that although productivity was higher nitrate was less depleted during glacial than interglacial periods more pronounced than the glacial interglacial changes in 15n values of both cores are precession related 23 kyr fluctuations these cyclic 15n variations which are in phase with those of paleoproductivity and sea surface temperature indicate that changes in trade wind driven upwelling intensity and the advection of cold nutrient rich water from the south drive nutrient availability and productivity off the southwest coast of africa no strong evidence was found from sedimentary 15n values for denitrification in the water column in the angola basin during the past 180 kyr

200 000 yr diatom records from atlantic upwelling sites reveal maximum productivity during lgm and a shift in phytoplankton community structure at 185 000 yr abstract time series of diatom accumulation rates dar and assemblage composition for the last 200 000 yr from the atlantic major coastal upwelling loci of the eastern boundary currents and eastern equator are compared together with independent proxies of export production to upper ocean productivity and to nutrient concentration and utilization fluctuations in dar are concomitant at all sites and in good correspondence to the other independent productivity proxies indicating glacial periods as the most productive times of the past 200 000 yr in both hemispheres of the eastern atlantic maximum productivity about one order of magnitude higher than at present occurred at the last glacial maximum lgm despite the atlantic similarities in both coastal and equatorial upwelling types important regional and site specific variations emerge in the southern hemisphere site a contradiction of proxies diatoms and corg is noted at the base of stage 6 185 000 yr the good correlation found between the corg and the benthic foraminifera fluxes is interpreted as a reflection of a shift in the phytoplankton community structure related to either a change in the n p si ratio or similar nutrient conditions associated with increased water column stratification

coccolith sr ca as a new indicator of coccolithophorid calcification and growth rate 1 polyspecific coccolith separates from core top sediments in the eastern equatorial pacific show variations of 15 in sr ca ratios across the equatorial upwelling zone with sr ca highest at the equator and decreasing off axis these variations cannot be due to changes in the sr ca of seawater which varies by less than 2 in the surface ocean variations in sr ca of coccolith sediments are similar to variations in primary productivity and alkenone estimated coccolithophorid growth rates in overlying surface waters and to caco3 rain rates measured in sediment traps because of these relationships and because calcification rate exerts a strong control on sr ca in abiogenic calcites we suggest that the observed sr ca variations in coccoliths may be strongly controlled by coccolithophorid growth and calcification rates although temperature may also influence coccolith sr ca to a lesser degree changes in dissolution intensity and coccolith assemblages appear to exert a minor influence if any on coccolith sr ca in these sediment core tops if further work confirms relationships between coccolith sr ca and coccolithophorid productivity sr ca records of past changes in coccolithophorid productivity may be useful in reconstructing past variations in the rain ratio of organic to carbonate carbon an important control on deep ocean ph and partitioning of co2 between the atmosphere and ocean in addition coccolith sr ca might provide an independent record of past changes in coccolithophorid growth rates which in combination with data on the carbon isotopic fractionation in coccolithophorid organic matter may permit more reliable calculations of past dissolved co2 in the surface ocean

the δ13c of equatorial atlantic surface waters implications for ice age pco2 levels carbon isotopic records of nutrient depleted surface water place constraints on the past fertility of the oceans and on past atmospheric pco2 levels the best records of nutrient depleted 13c are obtained from planktonic foraminifera living in the thick mixed layers of the western equatorial and tropical atlantic ocean we have produced a composite stacked globigerinoides sacculifer 13c record from the equatorial atlantic which exhibits significant spectral power at the 100 000 and 41 000 year milankovitch periods but no power at the 23 000 year period similar to the record presented by shackleton and pisias 1985 surface deep ocean 13c produced with the g sacculifer record leads the 18o ice volume record however the glacial interglacial amplitudes of 13c differ between our record and shackleton and pisias 1985 record although large changes in 13c occur in the equatorial atlantic during early stages of the last three glacial cycles surface deep 13c at glacial maxima 18o stage 2 late stage 6 and late stage 8 was only about 0 2 greater than during the subsequent interglacial our results imply that nutrient driven pco2 changes account for about one third of the pco2 decrease observed in ice cores and consequently 13c should not be used as a proxy pco2 index enough variance in the ice core pco2 records remains to be explained that conclusions about pco2 and ice volume phase relationships should also be reexamined as much as 40 ppm pco2 change still has not been accounted for by models of past physics and chemistry of the ocean

late quaternary sedimentation on the eastern walvis ridge se atlantic hpc 532 and four piston cores five sediment cores from the eastern walvis ridge have been investigated by means of a quantitative coarse fraction analysis 40 m numerous biogenous terrigenous and authigenic particles have been distinguished the variations in composition suggest the following conclusions core walda ks 12 from the northern flank of the walvis ridge consists entirely of a slump which contains mainly glacconite sands and biogenous opal foraminiferal skeletons and terrigenous matter the sediments in the other four cores comprise the late quaternary oxygen isotope stages 1 6 there are several levels at the transition from warm to cold intervals where benthos plankton foraminiferal ratios increase from 10 up to 50 90 here imperforate benthonic foraminifera decrease strongly dissolution of planktonic foraminifera can only partly explain this finding lateral supply of benthos or the influence of reduced oxygen content in the bottom water might have played an additional role calcium carbonate dissolution as revealed by the fragmentation of planktonic foraminifera shows intermediate values in coldest and warmest periods dissolution maxima occur at warm cold stage boundaries dissolution minima have been found at the transition from cold to warm periods upwellinginfluence is reflected in varying amounts of biogenous opal in interglacial periods the influence of upwelling is strong in all cores with an increase in intensity to the east core v19 259 it is explained by eddies of upwelled water which drifted westward under the influence of the westward turning benguela current in glacial periods the influence of upwelling at the core sites was very reduced the benguela current problably was close to the continent and turned westward only at 17 s thus it did not affect the core sites climate in the near coastal area has been arid in the latitude of 20 s throughout the investigated time slice accumulation rates reflect the position of the cores hpc 532 and circe gb 211 are in the area of the sediment filled trough which forms the walvis ridge terrace here accumulation rates are 2 to 3 times higher in stages 2 4 and 5 than in v19 259 and walda ks 09 which are from the steeper flank of the terrace outside the trough mean values of calcium carbonate dissolution are similar in all cores lower caco3 content in v19 259 and lower sand fraction percentages are explained by lateral supply of fine grained terrigenous matter in the area of core v19 259 which probably received insoluble material from the kuene shelf area by the n s flowing countercurrent

river patterns and their meaning abstract rivers are largely responsible for shaping the earth s continental landscapes river patterns the spatial arrangements of channels in the landscape are determined by slope and structure at site and sector scale channel morphology varies spatially and in time but river patterns and drainage texture or the frequency of stream lines per unit area together determine the intricacy or otherwise of topography most river patterns evolve through natural selection slope induces the formation of such patterns as parallel radial and distributary while structure produces straight angular trellis and annular arrangements once established patterns tend to persist nevertheless at many sites the usual patterns have been disturbed and patterns that are anomalous in terms of slope and structure have been produced by diversion tectonism volcanism glaciation mass movements and human activities by antecedence superimposition inheritance or underprinting by the persistence of deeply eroding rivers which encounter alien structures and by climatic change river patterns provide clues to underlying structure and to the chronology of events they have also proved significant in the search for minerals

the carbon isotopic record of the c37 2 alkenone in the south atlantic last glacial maximum lgm vs holocene the carbon isotopic fractionation ep of the c37 2 alkenone was analysed for 19 south atlantic sediment samples from the last glacial maximum lgm our study covers the equatorial and subtropical ocean including the coastal upwelling regions off south africa the equatorial upwelling and the oligotrophic western basins the results were compared to the holocene ep records from the respective core locations andersen n muller p j kirst g schneider r r 1999 alkenone 13c as a proxy for past pco2 in surface waters results from the late quaternary angola current in fischer g wefer g eds use of proxies in paleoceanography examples from the south atlantic springer berlin pp 469 488 benthien a andersen n schulte s muller p j schneider r r wefer g 2002 carbon isotopic composition of the c37 2 alkenone in core top sediments of the south atlantic ocean effects of co2 and nutrient concentrations glob biogeochem cycles 16 10 1029 2001gb001433 generally alkenone ep was lower during the lgm compared to the holocene higher glacial ep values were only found in sediments from the angola basin and in one sample from the eastern crest of the walvis ridge considering present understanding of lgm holocene changes in surface water conditions i e nutrient level primary productivity phytoplankton assemblages the observed glacial interglacial difference in ep indicates that multiple factors controlled the isotopic fractionation in alkenone producing algae depending on the regional setting in the oligotrophic areas of the south atlantic the lower than holocene glacial ep values can be partly explained with a decrease in surface water pco2 during the lgm in contrast the holocene to lgm decrease in ep values in the coastal upwelling areas as well as in the eastern tropical atlantic most probably reflects much higher glacial haptophyte growth rates induced by an increase in surface water nutrient concentrations the exceptional opposite trend of the ep differences in the angola basin can be explained by a shift in the phytoplankton community towards a greater dominance of diatoms under glacial conditions thus leaving less nutrients available for haptophytes in this way the isotopic record of alkenones indicate lower haptophyte growth rates during the lgm although other palaeoceanographic proxies point to enhanced productivity and higher nutrient levels

letter to the editorcomment on 10be and26al evidence for exceptionally low rates of australian bedrock erosion and the likely existence of pre pleistocene landscapes bierman and turner 1995

cool climate lateritic and bauxitic weathering it is commonly held that laterites and bauxites form under tropical climates although some workers have suggested lateritic weathering was not representative of tropical climates the assertion is still almost universally made early tertiary 56 34 ma basalts are widespread in the monaro region of new south wales they overlie and enclose fluvial and lacustrine sediments hyaloclastites and tuffs and the upper parts of many flows are bauxitized the basalts are up to about 200 m thick and in one section comprise 22 flows eight tuffs and hyaloclastites two dolerites and nine interflow bauxitic profiles this region in the eastern australian highlands was tectonically stable and had probably been at its present elevation for some 50 100 ma immediately before the beginning of volcanism and during the extrusion and bauxitization of the earlier flows the region was at 57 5 s latitude climates were wet cool to cold and thermally seasonal and the region was well forested paleomagnetic studies sh

micromorphology and geochemistry of groundwater silcretes in the eastern south downs uk groundwater silcretes have been recognised recently as major terrestrial silicon sinks and yet their origins are poorly understood this paper aims to further understanding of the micro fabric geochemistry and formation of groundwater silcretes through detailed analyses of silcrete boulders from the south downs sussex uk in depth petrological investigations of silcrete blocks identified three varieties of silcrete across the study area saccharoid hard and pebbly conglomeratic or silcrete breccia similar to those elsewhere in england silcrete fabrics were universally simple and preserved host material structures optically continuous quartz overgrowths were the dominant cement and developed on framework grains in the absence of silt and clay sized particles finer grained silica cements occurred in isolated patches and as vein or cap like geopetal features these caps and veins formed through the silicification of illuviated clay rich material that entered the host sediment prior to or in the early stages of overgrowth formation titanium contents were related to the amount of fine grained silica and appear to reflect variations in host material chemistry subsequent to silicification the silcretes were altered by at least two phases of ferrunginisation characterised by the ingress of iron minerals and partial fabric dissolution or replacement the study reveals strong similarities in the micromorphology and geochemistry of groundwater silcretes in the study area and those developed in sandy host sediments in neighbouring parts of northwest europe variations that do occur could be explained by differences in the host sediment geological setting or tectonic history of the respective basins or sub basins suggesting that there may be a common mechanism for silcrete formation across northwest europe silcrete development appears to be related to the release of silica accompanying acid leaching of the host material or adjacent strata in the south downs this probably resulted from oxidisation of pyrite in the argillaceous and lignitic sediments overlying the host sands it is envisaged that palaeoenvironmental conditions were of limited importance for silcrete development and that there was no specific era of formation with phased development accompanying landscape evolution through the neogene into the pleistocene

relative and absolute dating of land surfaces abstract the dating of land surfaces has long posed problems for geomorphologists relative methods stratigraphic geomorphic topographic are sound and convincing exhumed forms may complicate identification and relationships for both epigene and etch forms have been buried and exhumed but in tectonically undisturbed areas the higher surfaces are older than those preserved at lower levels also surfaces have an age range the relationship of surfaces with volcanic deposits old shorelines and genetically related sedimentary sequences provides sound ages and correlation with dated duricrusts and faults is also useful there are no temporal limits to relative dating for the methods are equally applicable to the dating say of proterozoic surfaces as of those of pleistocene age the disadvantage of such methods is that the necessary evidence is frequently either not preserved or not exposed the so called absolute physical numerical methods and especially those based on exposure age dating with in situ cosmogenic radionuclides are appealing because they produce direct numerical ages and appear to be widely applicable but there are severe temporal limitations and sampling problems complicate and may invalidate interpretation absolute age determinations must be consistent with the stratigraphic and geomorphologic settings the best results are obtained when physicists and earth scientists pool their knowledge and experience a background in local and regional geology is especially important

oxygen isotope dating of the australian regolith australia has had a long and complex history of intense surficial weathering and this has led to the extensive development of laterites bauxites and deeply weathered profiles of a variety of ages across the continent1 2 a detailed knowledge of the age s of such weathering phenomena is of great importance for the reconstruction of australia s post palaeozoic geomorphic and palaeoclimatic history however in many instances absolute geo chronological information is not obtainable using conventional techniques here we describe and evaluate a new method that can provide an estimate of the age of intensely weathered profiles based on the oxygen isotope composition of minerals developed by deep weathering lateritization processes this method allows the definition of four ages of weathering in eastern australia from the late palaeozoic to the present and suggests that some profiles previously thought to be late cretaceous or tertiary in age may be of pre late mesozoic age the oxygen isotope data indicate that the minerals used in this study have retained their original isotopic composition for periods of up to 250 million years despite the continued presence of meteoric waters of progressively higher 18o content during this interval

tertiary coastal dunes of the eucla basin australia abstract on the northeast margin of the nullarbor plain in western south australia there is preserved an assemblage of coastal aeolian landforms that includes coastal dune dune ridge and possible beach ridge one of these landforms is the ooldea range a 650 km long coastal dune that lies 25 300 km from the present coast these landforms are believed to have formed at the end of the eocene after maximum marine transgression in the eucla basin the ooldea barton and paling ranges formed in a tectonically stable region of topographically subdued terrain their orientation and position may be related in part to crustal fractures that were active during initial break up of australia and antarctica the large quantities of sand required for their construction were supplied to the coast by rivers which drained a hinterland of various suitable source rocks growth may have begun as chains of barrier islands which amalgamated to form large coast parallel dunes during progradation these coastal dunes provide evidence about climate at and after the time of their formation their formation indicates an atmospheric circulation of at least moderate intensity and prevailing winds with a major westerly component this occurred at a time when the climate is likely to have been temperate if the interpretation of the dunes age is correct they may be viewed as landforms bearing testimony to the global change in climate which occurred at the end of the eocene their excellent preservation in the landscape today some 34 37 million years after formation is remarkable implied is a degree of aridity for much of the remainder of the cainozoic this appears to have been more significant in the nullarbor plain region than in the southeastern part of australia other factors responsible for their preservation are likely to include vegetation cover the permeability of their quartz sands subsequent history of sea level and hydrodynamics of the basin

the use of duricrusts and topographic relationships in geomorphological correlation conclusions based in australian experience though there are many possible pitfalls duricrusted surfaces provide morphostratigraphic markers which are useful in preliminary extrapolation and correlation at the local and regional scales especially if other factors such as landscape evolution and topographic relationships are also considered particular reference is made to ferruginous and siliceous cappings close stratigraphic dating of the duricrusts allows regional differentiation but correlations are preferably intra rather than inter regional and are at best general and involve age ranges rather than narrow time frames problems broached include type of landscape development the relation of surface and duricrusts and the temporal equivalence of duricrust facies i e duricrusts of similar chemical tendencies but contrasted morphology the roles of duricrusts in relief inversion surface preservation and climatic interpretation are also mentioned

the influence of air and sea exchange on the carbon isotope distribution in the sea we explore here the influence of the temperature dependence of isotope fractionation between atmospheric co2and ocean co2 on the distribution of carbon isotopes in the ocean this is accomplished by an analysis of departures from the expected redfield tie between po4 and 13c we find that for the surface ocean the temperature influence largely compensates for the biologic influence in the deep ocean the temperature influence imprinted at the sites of deepwater formation reduces somewhat the biologically induced difference between the carbon isotope ratios for deep waters produced in the northern atlantic and in the antarctic these same features are reproduced in the hamburg ocean model in order to assess the impact of changes in the ratio of ocean mixing rate to wind speed we have made a model run in which co2 exchange rates between air and sea were everywhere doubled as expected the influence of the thermodynamic effect on the oceanic carbon isotope distribution is magnified

cenozoic landscape development within the central iberian chain spain abstract in the central iberian chain spain covering an area of some 7400 km 2 up to seven stepped erosion surfaces are determined from aerial photographs and field observations these planation surfaces situated between 1000 and 1600 m a s l are separated by erosional scarp slopes most parts of the erosion surfaces are developed on mesozoic limestones and form stepped rims around the main elevations of the iberian chain it is proposed that the surfaces were formed by erosional events associated with periods of uplift related to eocene miocene compressional tectonic activity the palaeogene uplift was related with syntectonic sedimentation in internal basins with up to 3500 m of accumulated thickness during the neogene middle miocene pliocene post tectonic period the lowered synclinal areas formed residual internally drained basins that were filled with non marine deposits mainly clays and limestones the filling of the internally drained sedimentary basins located within the iberian chain onlapped onto the ancient erosional surfaces covering the lower younger levels the recent landscape evolution of the whole area is controlled by the capture of the internal basins and the dissection of the ancient relief by the present day fluvial network this process is related with the transition from internal to external drainage of the ebro basin

reconstructing calcification in ancient coccolithophores individual coccolith weight and morphology of coccolithus pelagicus sensu lato we have adapted an existing method to estimate coccolith calcite weight using birefringence beaufort 2005 to suit the large coccoliths of coccolithus pelagicus which are only partially birefringent under cross polarised light microscopy fossil and sediment trap material from the south tasman rise region of the southern ocean was used for calibration and validation our approach was tested with only the coccolith central area ca considered for measurement to avoid relying on the less robust proximal shields thus our results are relative and intend to quantify intra specific variations in volumetric calcite weight expressed as a weight index wi our results were overall consistent with mass estimation based on distal shield lengths however the wi approach clearly has the advantage in exploring allometric scaling between coccolith size and weight as well as in measuring the degree of calcification in similarly sized morphotypes combining wi and morphometry data distal shield length dsl we demonstrate subtle but statistically significant changes in shape and thus calcification degree both within and between the tested coccolithus populations most strikingly it appears that modern coccolithus populations in the southern ocean are on average more heavily calcified than their fossil counterparts

the origin and implications of some erosional landforms etching is a mechanism of landform development involving two stages or phases first a regolith develops as a result of interaction between groundwaters and country rock the surface of contact between the two called the weathering front develops a relief as bedrock weaknesses are exploited by chemical corrosion second the regolith is stripped to expose the weathering front as an etch surface etch forms are widely distributed but are especially well developed and preserved in the relatively stable shield lands they range in scale from the plains and hills of inselberg landscapes to minor features such as boulders gutters basins flared slopes scarp foot depressions and pitted surfaces many etch forms have two ages one related to the period of subterranean preparation the other to the exposure of the erstwhile weathering front many are developed in a variety of rock types as well as in a considerable range of climatic settings etching carries several implications for landform interpretation

palaeogeographical influence on late eocene biosiliceous sponge rich sedimentation southern western australia late eocene nearshore shallow marine environments within the bremer and western eucla basins of southern western australia were characterized by the thick deposition of spongolite and spiculite deposits epibenthic sponge communities dominated estuaries and topographically complex basin margin embayments archipelagos while cool water carbonates with up to 10 sponges accumulated in open shelf environments the transition from a biosiliceous to calcareous epibenthos was related to the degree of palaeogeographical protection within basement protected embayments there was an offshore gradation from shoreface spongolite and pure spiculite to a muddy spiculite facies towards central embayment areas calcareous fossils are rare throughout embayment facies but rapidly increase in more open outer archipelago areas this depositional relationship occurred along 2000 km of the late eocene southern australian coastline palaeogeographical protection from strong currents acted in concert with 1 a planar low gradient inland topography with sluggish run off supplying fine grained sediment nutrients and abundant dissolved silica and 2 a microtidal setting weak to moderate swells and opposing wind and coriolis surface current forcing which inhibited water exchange between embayments estuaries and the open shelf this situation led to an embayment water chemistry that encouraged prolific sponge growth calcareous spiculites record the mixing front between these embayment waters and normal open shelf waters supporting cool water carbonates

the laterite profile ferricrete and unconformity summary the laterite profile consists of ferricrete overlying saprolite examples from our field observations and from the literature demonstrate that in many if not all cases ferricrete consists of detrital material younger than the underlying weathering zone s from which it is separated by an unconformity heretofore a detrital origin for ferricretes although occasionally mentioned has not been sufficiently considered the laterite originally described by buchanan is saprolite and does not harden significantly on exposure to the air some definition of laterite would exclude this original type material because of relief inversion ferricrete is now often exposed in high situations such as plateau margins relief inversion may have occurred at many times and places and individual occurences of ferricrete are not necessarily parts of a former widespread erosion surface

carbon isotopic composition of the c37 2 alkenone in core top sediments of the south atlantic ocean effects of co2and nutrient concentrations 1 we have analyzed the stable carbon isotopic composition of the diunsaturated c37 alkenone in 29 surface sediments from the equatorial and south atlantic ocean our study area covers different oceanographic settings including sediments from the major upwelling regions off south africa the equatorial upwelling and the oligotrophic western south atlantic in order to examine the environmental influences on the sedimentary record the alkenone based carbon isotopic fractionation ep values were correlated with the overlying surface water concentrations of aqueous co2 co2 aq phosphate and nitrate we found ep positively correlated with 1 co2 aq and negatively correlated with po43 and no3 however the relationship between ep and 1 co2 aq is opposite of what is expected from a co2 aq controlled diffusive uptake model instead our findings support the theory of bidigare et al 1997 that the isotopic fractionation in haptophytes is related to nutrient limited growth rates the relatively high variability of the ep po4 relationship in regions with low surface water nutrient concentrations indicates that here other environmental factors also affect the isotopic signal these factors might be variations in other growth limiting resources such as light intensity or micronutrient concentrations