3d nanopores modeling using tem tomography dolostones upper triassic abstract transmission electron microscopy tomography temt stands as a novel and alternative tool to tridimensionally model the nano scale pores of rocks in this study it is flanked with traditional mercury capillary injection porosimetry micp nitrogen adsorption porosimetry np and scanning electron microscopy sem analysis to test a sample belonging to an upper triassic dolostone cropping out in northern calabria micp revealed low values of porosity and permeability 2 3 and the 0 11 md respectively nanopores account for the 94 of the pore volume whereas the remaining 6 is represented by micropores the integrated micp and np pore size distribution psd shows the presence of a dominant pore diameter population coincident with 50 nm with minor peaks at diameters of 12 m 850 25 13 6 2 nm however since the psd peaks of the two techniques do not match a comparison of the two curves is necessary to better characterized the overlapping area sem imaging analysis showed the presence of nano scale intercrystalline and intracrystalline pores the first corresponds with the spaces among dolomite crystals and as suggested by the np analysis shows a wedge slit morphology the second appears with a prevailing polygonal section or as tight microfractures since sem provides exclusively two dimensional images the morphology and development of these pores was obtained through temt 3d reconstruction the 3d model showed the presence of open cavities fractures and blind isolated pores cavities cross the entire dolomite crystals and can present a constant sub prismatic pores or variable channel section funnel shaped pores that can reduce its aperture as observed of also more than a ten factor e g from 300 nm to 20 nm fractures commonly developing on the existing cleavage surfaces cut the crystal faces for 300 350 nm reducing its aperture maximum of 20 30 nm from the edge towards the inner part of the crystal lastly blind isolated pores can assume diameters and thickness of 250 nm they show a sub cubic morphology and can be filled by solid liquid or gaseous inclusions

paleovegetation simulations of lowland amazonia and implications for neotropical allopatry and speciation paleovegetation modeling simulations of the lowland amazon basin were made to assess the relative importance of glacial climate and atmospheric co2 for altering vegetation type and structure as well as to explore the potential physiological mechanisms underlying these ecosystem level responses modeling results support the view that widespread invasion of grasslands into the amazon lowlands during the last glaciation was not likely glacial cooling was probably responsible for maintaining glacial forest cover via its effects in reducing photorespiration and decreasing evapotranspiration which collectively improve plant carbon and water relations modeling results confirm that leaf area index lai a common proxy for canopy density is highly sensitive to independent and interactive changes in climate and low concentration of atmospheric co2 and the results show considerable region to region variation during the last glaciation heterogeneous variations in glacial vegetation lai may have promoted allopatric speciation by geographically isolating species called vicariance in the forest sub canopy the proposed vicariance hypothesis incorporating spatial variations in canopy density conforms to many of the essential tenets addressed by previous neotropical speciation models but also helps to overcome some of their inconsistencies c 2001 university of washington

an 15 000 year record of el nino driven alluviation in southwestern ecuador debris flows have deposited inorganic laminae in an alpine lake that is 75 kilometers east of the pacific ocean in ecuador these storm induced events were dated by radiocarbon and the age of laminae that are less than 200 years old matches the historic record of el nino events from about 15 000 to about 7000 calendar years before the present the periodicity of clastic deposition is greater than or equal to 15 years thereafter there is a progressive increase in frequency to periodicities of 2 to 8 5 years this is the modern el nino periodicity which was established about 5000 calendar years before the present this may reflect the onset of a steeper zonal sea surface temperature gradient which was driven by enhanced trade winds

neogene and quaternary history of vegetation climate and plant diversity in amazonia the neotropical amazonian and andean plant diversity developed mainly during the tertiary in amazonia miocene oral diversity seems considerably higher than today during the neogene tropical taxa entered newly created montane area and montane taxa entered the tropical lowlands the general decrease of temperature during the upper neogene and especially during the quaternary glacial periods may have caused considerable extinctions in the lowlands representation of pollen of apparently principally montane taxa podocarpus hedyosmum in miocene pliocene and quaternary sediments of amazonia and surroundings is still di cult to interpret in terms of temperature decrease at low elevation changes in precipitation may have profound impact on the composition of vegetation communities ilex and melastomataceae increase signi cantly in many glacial pollen records increase of weinmannia in amazonian pollen records seems the best indicator of downward migration of montane vegetation belts a temperature lowering at sea level of 4 5 13c during the last glacial maximum lgm seems reasonable it may have caused a downslope migration of some 700 m of the lower montane vegetation belt lower montane arboreal species may have been able to grow in higher elevation areas 500 m of amazonia increasing background pollen values of montane taxa in the area di erence between a cool and wet middle pleniglacial 60 28 ka bp and a cold and dry upper pleniglacial 28 14 ka bp thus including the lgm is evident in andean and amazonian records statements about environmental conditions of the ice age amazon should be speci ed chronologically the middle pleniglacial is a time of accumulation of uvial sediments the upper pleniglacial is a time of incision of the rivers in their sediments sedimentation started again in the lateglacial since ca 13 ka bp and the holocene when lake levels rose again based on simpli ed considerations of precipitation changes and evaporation we estimate that lgm rainfall may have been reduced by values of ca 45 10 amazonian and cordilleran lakes dried up dry rain forest was locally replaced by savanna savanna forest or cerrado type vegetation dry rain forest savanna forest and pure savanna was locally replaced by extensive semi desert dune formations lower rio branco area in present day central amazonia the present day centers of higher rainfall 2500 mm surrounded by areas of lower rainfall are refuge areas of the very wet rain forest and of the very high plant diversity 300 plant species per 0 1 ha and they should have been that equally or more during the dry climate intervals plant diversity of drier forests is in the order of 100 150 species per 0 1 ha both extinction and speciation in isolation under precipitation and temperature stress may have taken place in these refugia 2000 elsevier science ltd all rights reserved

high resolution image treatment in ichnological core analysis initial steps advances and prospects abstract ichnological studies have become popular during the last decades particularly those associated with the development of two major concepts the ichnofacies model and ichnofabric approach they have driven ichnology into diverse fields of earth sciences including paleoecology sedimentology paleoceanography and basin analysis as well as applied fields for the oil and gas industry and aquifer characterization whereas early ichnological analyses focused on outcrops later the number of ichnological studies on well cores increased noticeably still ichnological research on cores is hampered by certain limitations i e mainly narrow exposed surface and the characterization of ichnological properties is complicated when cores are involved to facilitate ichnological analysis in cores from modern deposits several techniques among them x rays magnetic resonance and computed tomography have been used with the development of computer software a new high resolution image treatment has emerged as a powerful tool in different branches of ichnological studies especially for cores from modern marine deposits because applications are numerous and perhaps not familiar to all the scientific community this paper provides an overview of the usefulness of image treatment in ichnological analysis its first steps and subsequent development the novel techniques most recently used in the study of cores from modern marine deposits and some challenges for future research

applications of organic geochemistry to paleolimnological reconstructions a summary of examples from the laurentian great lakes the organic matter content of lake sediments contains information that helps to reconstruct past environmental conditions evaluate histories of climate change and assess impacts of humans on local ecosystems the elemental isotopic and molecular compositions of organic matter buried in sediment provide evidence of the biota that have lived in a lake and its catchment area and they serve as proxies of organic matter delivery and accumulation sedimentary records from the north american great lakes provide examples of applications of organic geochemistry to paleolimnological reconstructions the records of these lakes date from retreat of the laurentide ice sheet around 12 ka include the mid holocene hypsithermal and show consequences of recent human changes low corg ntotal ratios indicate that most of the sediment organic matter in the great lakes is from algal production yet changes in biomarker molecule compositions also show that varying amounts of land plant organic matter have been delivered to the lakes elevated algal productivity that accompanies nutrient enrichments of lake waters is recorded as excursions to less negative 13c values in the organic matter of sediments that were deposited in the 1960s and 1970s increased organic carbon mass accumulation rates mirror the isotopic excursions in most parts of the great lakes accumulations of petroleum residues and pyrogenic polycyclic aromatic hydrocarbons in sediments identify fluvial and eolian delivery of organic matter components to different parts of the great lakes emerging applications of multiple and novel organic geochemical proxies to paleolimnological reconstructions are promising yet some potentially important measurements remain underutilized

organic geochemical proxies of paleoceanographic paleolimnologic and paleoclimatic processes abstract organic matter constitutes a minor fraction of marine and freshwater sediments yet its important contribution to the sedimentary record can be used to reconstruct marine and continental paleoenvironments the organic matter content of sediments is the residue of past biota the amounts and types of organic matter present in sediments consequently reflect environmental conditions that impacted ecosystems at different past times general sources of the organic matter are inferred from bulk properties such as elemental compositions carbon and nitrogen stable isotope ratios rock eval pyrolysis data and organic petrography details of organic matter origins are refined by analyses of biomarker molecular compositions source changes are proxies for fluctuations in sea level oceanic surface currents and continental climates algal paleoproductivity rates are indicated by organic carbon mass accumulation rates and carbon and nitrogen stable isotopic compositions these parameters record past availability of nutrients and therefore are proxies of surface mixing in the oceans and amount of land runoff to lakes sea surface paleotemperatures are recorded by the number of carbon carbon double bonds in lipid biomarkers produced by marine algae larger proportions of the double bonds are proxies for the cooler surface waters that accompanied periods of global glaciation and intervals of enhanced upwelling the 13c and d values of plant organic matter record past concentrations of carbon dioxide in the atmosphere and changes in delivery of atmospheric moisture respectively diagenesis which causes the concentration and composition of organic matter in sedimentary settings to differ from those of the original biologically synthesized materials can bias organic geochemical paleoenvironmental records the magnitude of this potential source of misinformation must always be considered and evaluated comparison of multiple organic geochemical proxies of past conditions helps to compensate for the effects of diagenetic alterations and thereby to improve interpretations of paleoenvironmental change

a vegetation and fire history of lake titicaca since the last glacial maximum fine resolution fossil pollen and charcoal analyses reconstruct a vegetation and fire history in the area surrounding lake titicaca 3810 m peru bolivia since ca 27 500 cal yr bp hereafter bp time control was based on 26 accelerator mass spectrometer ams radiocarbon dates seventeen ams dates and 155 pollen and charcoal samples between ca 17 500 bp and ca 3100 bp allow a centennial scale reconstruction of deglacial and early to mid holocene events local and regional fire signals were based on the separation of two charcoal size fractions 180 m and 179 65 m charcoal abundance correlated closely with the proportion of woody taxa present in the pollen spectra little or no pollen was detected in the sedimentary record prior to ca 21 000 bp very cold climatic conditions prevailed with temperatures suggested to be at least 5 8 c cooler than present increases in pollen concentration suggest initial warming at ca 21 000 bp with a more significant transition toward deglaciation ca 17 700 bp between 17 700 bp and 13 700 bp puna brava is progressively replaced by puna and sub puna elements the most significant changes between the pleistocene and the holocene floras were largely complete by 13 700 bp providing an effective onset of near modern conditions markedly earlier than in other andean records fire first occurs in the catchment at ca 17 700 bp and becomes progressively more important as fuel loads increase no evidence is found of a rapid cooling and warming coincident with the younger dryas chron a dry event between ca 9000 bp and 3100 bp with a peak between 6000 and 4000 bp is inferred from changes in the composition of aquatics and the marsh community as pollen of cyperaceae is replaced by poaceae apiaceae plantago and the shrub polylepis human disturbance of the landscape is evident in the pollen spectra after ca 3100 bp with the appearance of weed species

deglaciation and holocene climate change in the western peruvian andes pollen charcoal magnetic susceptibility and bulk density data provide the first paleoecological record spanning the last 33 000 years from the western cordillera of the peruvian andes sparse super puna vegetation existed before 30 000 cal yr b p around lake compuerta 3950 m elevation prior to a sedimentary hiatus that lasted until c 16 200 cal yr b p when sedimentation resumed a glacial foreland or super puna flora is represented in which polylepis was a significant element glacial outwash marked by high sedimentary magnetic susceptibility increased from c 16 200 cal yr b p and reached a peak at c 13 200 cal yr b p between c 12 500 cal yr b p and 10 000 cal yr b p magnetic susceptibility was reduced vegetation shifts suggest a cool dry time consistent with regional descriptions of the younger dryas event deglaciation resumes by 10 000 cal yr b p and the last ice is lost from the catchment at 7500 cal yr b p during the early holocene warm and dry period between 10 000 and 5500 cal yr b p alnus expanded in downslope forests alnus declined in abundance at 5500 cal yr b p when wetter and cooler conditions returned and human activity intensified maize zea mays pollen first occurred in the core at 2600 cal yr b p indicating a minimum age for local agriculture an increase in alnus pollen abundance at 1000 cal yr b p could be due to human activity or perhaps due to a regional climate change associated with cultural turnover elsewhere in the andes at this time

amazonia during the last glacial abstract new data on the vegetational history and quaternary geology of amazonia permit an improved reconstruction of past environments in amazonia during the last glacial period although limited data from rondonia carajas and guyana show that in certain areas savanna type vegetation and savanna forest had replaced the rain forest during the late pleniglacial ca 22 000 13 000 yr b p the amazonian forest may have been split up into one major west amazonian and several other medium size forest areas this suggests a decline in rainfall of 500 to 1000 mm a reduction of 25 to 40 temperatures may also have been 2 to 6 c 4 2 c lower than today possibly substancially influencing amazonian vegetation during the humid middle pleniglacial 55 000 26 000 yr b p rivers carried a lot of water and sediment resulting in the deposition of lower terrace sediments with one dry interruption around 40 000 yr b p carajas and katira in carajas there is evidence of dry periods ocurring at about 40 000 yr b p and during the early pleniglacial ca 60 000 yr b p rivers carried little water and incised into the low terrace sediments during the dry late pleniglacial water levels rose during the late glacial 13 000 10 000 yr b p or at the beginning of the holocene 10 000 yr b p sedimentation in and of the present inundation valleys commenced after that

a 750 year fire history based on lake sediment records in central yellowstone national park usa a 750 year fire history was reconstructed for the central plateau of yellowstone national park from the deep water sediments of five lakes the charcoal record from a large lake provided a chronology of regional fires data from four small lakes were used to study local and extralocal fires the co occurrence of abundant charcoal and high magnetic susceptibility values at the same stratigraphic level was used as evidence of a local catchment fire and a charcoal peak without high magnetic susceptibility was ascribed to an extralocal fire or a local fire without a related erosion event the fire history was compared with the dendrochronologic fire record for the last 450 years and the close agreement provided the justification to extend the chronology back in time large areas of the region burned in ad 1988 c 1700 c 1560 and c 1440 from c 1220 to 1440 and c 1700 to 1987 intermediate to small areas burned the near absence of fires in the twentieth century prior to the large fires of 1988 is evi

organism substrate interactions and astrobiology potential models and methods abstract organism substrate interactions and their products biogenic structures are important biosignatures on earth this study discusses the application of ichnology the study of organism substrate interactions to the search for present and past life beyond earth three main questions are addressed 1 why to look for biogenic structures i e traces and ichnofabrics beyond earth 2 what biogenic structures to expect on other planets moons and asteroids 3 how to study extraterrestrial biogenic structures review of terrestrial evidence highlights a set of properties that make traces and ichnofabrics important for the search of potential extraterrestrial life trace fossils preserve the activity of soft bodied organisms biogenic structures are resilient to processes that obliterate other biosignatures i e mechanical and chemical degradation diagenesis tectonism and metamorphism traces are very visible biosignatures traces indicate environment and behaviour traces can be universal biosignatures i e biosignatures ideally suited for detecting any type of life a model of organism substrate interactions beyond earth is here proposed expected extraterrestrial traces are those that manifest behaviours that allow to maintain homeostasis excavations meandering traces and biodeposition structures most of the existing rovers and orbiters provide basic instruments for searching these traces it is here suggested that the search for extraterrestrial biogenic structures by rovers would also benefit from artificial adjustable lighting gpr lidar and drilling equipment with optical televiewer in this study open access databases of rover and orbiter imagery have been searched for traces and ichnofabrics but no unquestionable evidence of biogenic structures beyond earth has been found besides those produced by humans this sounds along the lines of the famous fermi paradox if the universe is teeming with aliens where are their traces results of this search show that habitable environments are not the only place to look for biogenic structures non habitable environments such as moons without atmosphere can favour the preservation of shallow tier traces the better preservation potential of traces compared to other biosignatures greatly widens the issue of planetary protection including the interaction between astronauts or vehicles and the substrate may produce disturbances although this study highlights a new direction of study with the tools and concepts of ichnology dialogue between the astrobiological and ichnological communities is needed to use its full potential and possibly answer one of the major questions of science does life exist beyond earth

biogenically enhanced permeability a petrographic analysis of macaronichnus segregatus in the lower cretaceous bluesky formation alberta canada a detailed petrographic analysis was conducted on several core samples from the cretaceous aged bluesky formation in the la glace area in alberta canada within the gas producing zone of these upper shoreface sediments a fine to mid medium grained chert rich litharenite is intensely bioturbated with macaronichnus segregatus petrographic analysis showed that the burrow mantle is generally lined with dark colored iron rich mainly chert shale clasts and organic grains fragments whereas the burrow fill contained mainly quartz and light colored chert fragments the reason for the dark colored grain segregation of the tracemaker is unclear but in the bluesky formation presented in this study grain segregation has improved the reservoir quality by effectively resorting compaction and cement resistant chert and quartz into the burrow fill primary reservoir quality can be preserved in the presence of chert as pore occluding quartz overgrowths do not form on chert fragments as they do on monocrystalline quartz thus leaving open well connected primary pores and hence elevated permeability chert fragments are resistant to the effects of mechanical compaction and are not easily squeezed into adjacent pore spaces as are ductile rock fragments further research is needed to test the chemical constituents of the grains that modern tracemakers ingest this may lead to a better understanding of why sands burrowed with macaronichnus and similar burrowed sediment can have elevated reservoir quality

observations on late pleistocene cooling and precipitation in the lowland neotropics although accurate reconstructions of amazonian palaeoclimates are central to under standing the distribution and history of neotropical biodiversity current reconstructions based on proxy data are discordant and subject to intense debate we review some current thinking in amazonian climatology and incorporate some new ideas in an attempt to explain the apparently con tradictory records of palaeoprecipitation from across the amazon basin we suggest that palaeoecol ogists need to recognise that organised convective radiation the process that induces most wet season rainfall in amazonia should be treated as a phenomenon related to but separate from the passage of the inter tropical convergence zone itcz decoupling itcz migration from larger con vective activity provides a mechanism to account for observed palaeoclimatic heterogeneity patterns of observed precipitation change are consistent with the long term persistence of closed forest across much of amazonia indicating that the greatest changes in precipitation during the last glacial max imum came during the wet season which would have little negative impact on forest extent neo tropical cooling at the last glacial maximum lgm is widely accepted although the estimates of that cooling range between 1 c and 5 c in answering the basic question what is meant by cooling we observe that interhemispheric ice mass asymmetry may have caused cooling to be manifested differently according to location a terrestrial cooling of ca 5 c as well as radiative cooling and event based cooling combined to induce vegetation change probably both absolute temperature and mean monthly minima were reduced by polar air incursions in the northern neotropics how ever in the southern neotropics mean monthly minima were reduced by more frequent incursions of patagonian air masses but absolute minima may have been largely unchanged copyright 2004 john wiley sons ltd

using magnetic resonance imaging and petrographic techniques to understand the textural attributes and porosity distribution in macaronichnus burrowed sandstone abstract magnetic resonance images are paired with petrographic data to evaluate the textural characteristics of rocks dominated by macaronichnus segregatis a trace fossil that is commonly associated with rocks deposited in shallow marginal marine sedimentary environments mri techniques used revealed the three dimensional geometry of the trace fossil burrows are typically horizontal and in plan view range between straight sinuous meandering and spiral geometries changes in burrow morphology may be related to population density and patchy resource distribution the pairing of mri and petrographic data helped map the distribution of porosity in the burrowed rock because mri images represent complex composites of nuclear spin density and mr relaxation times each of which is related to pore size stronger mr signals must be calibrated to known porous zones by integrating petrographic data with mr data the complex distribution of porosity and its relationship to the matrix show that this fabric represents a dual porosity permeability system and may affect the resource reservoir or aquifer quality of similarly burrowed sedimentary rocks future research should elaborate upon the porosity permeability model for this and similar fabrics

biogenic chaos cryptobioturbation and the work of sedimentologically friendly organisms abstract biogenic chaos from an ichnological point of view can be defined as total bioturbation of sediment by infaunal organisms such that the original sedimentary fabric and associated sedimentary structures are entirely destroyed the truth however is that not all forms of thorough bioturbation are purely destructive as improbable as it initially sounds sediment can be pervasively potentially 100 bioturbated and yet have suffered remarkably little distortion of the original bedding in nature there exist many different levels of organism communities historically the study of any natural system begins with the most obvious attention grabbing elements only later do the more innocuous aspects come to be discovered and appreciated ichnology shows a similar historical pattern the most obvious aspects of the science the discrete burrow or track forms have been well studied for many years only recently have more subtle biogenic disturbances such as micro borings bacterial trails meiofaunal burrows infaunal tiering etc gained attention likewise another level of bioturbation cryptobioturbation exists and is becoming more evident in the rock record owing to its diminutive and obscure nature cryptobioturbation has not received widespread attention as the name implies cryptobioturbation is characteristically small in scale and exceedingly subtle in expression what sets it apart from other forms of bioturbation however is its tendency to preserve rather than to destroy the sediment s primary physical structure the fabric that results from cryptobioturbation can have significant influence on resulting permeability and porosity trends in some systems where both cryptically bioturbated sandstone and generally unburrowed sandstone are present mini permeameter measurements show that numerous heterogeneities are retained in the unburrowed sandstone resulting in a wide range of permeabilities in contrast cryptically bioturbated sandstone intervals show that these heterogeneities are less pronounced and the resulting permeability curve is more uniform the effect of cryptobioturbation does not result in enhanced permeabilities but rather diminishes internal heterogeneities leading to a more uniform permeability distribution

modelling runoff and erosion for a semi arid catchment using a multi scale approach based on hydrological connectivity runoff and erosion processes are often non linear and scale dependent which complicate runoff and erosion modelling at the catchment scale one of the reasons for scale dependency is the influence of sinks i e areas of infiltration and sedimentation which lower hydrological connectivity and decrease the area specific runoff and sediment yield the objective of our study was to model runoff and erosion for a semi arid catchment using a multi scale approach based on hydrological connectivity we simulated runoff and sediment dynamics at the catchment scale with the lapsus model and included plot and hillslope scale features that influenced hydrological connectivity the semi arid carcavo catchment in southeast spain was selected as the study area where vegetation patches and agricultural terraces are the relevant sinks at the plot and hillslope scales respectively we elaborated the infiltration module to integrate these runoff sinks by adapting the parameters runoff threshold and runoff coefficient which were derived from a rainfall simulation database the results showed that the spatial distribution of vegetation patches and agricultural terraces largely determined hydrological connectivity at the catchment scale runoff and sediment yield for the scenario without agricultural terraces were respectively a factor four and nine higher compared to the current situation distributed hydrological and erosion models should therefore take account of relevant sinks at finer scales in order to correctly simulate runoff and erosion sedimentation patterns

amazonian paleoecological histories one hill three watersheds abstract data from the hill of six lakes in the northwestern brazilian amazon region provide three records of paleoclimatic and vegetation change in lowland amazonia that span the last 170 000 years three lakes verde pata and dragao which occupy separate watersheds on the hill provide the most detailed image yet obtained of ice age conditions in lowland amazonia well dated sedimentary records for fossil palynological charcoal cation and pigment data are presented the data indicate the continuous presence of mesic forest throughout the last ice age oscillations of lake level are recorded and the lowstands are attributed to reduced precipitation inputs to systems delicately balanced between water loss leakage through the floor of the basin and gain precipitation gross stratigraphy algal remains and paleochemistry suggest that the stands of high and low lake level were cyclic apparently correlating precessional orbital variation times of lake lowstand coincide with wet season december january february djf insolation minima the strongest of eight lowstand cycles occurred ca 35 000 to 27 000 cal bp even during lowstand episodes pollen is well preserved and provides a clear signal of uninterrupted forest cover the principal lowland elements are continuously present in the record suggesting the long term quaternary availability of the lowland forest biome in this region however during the late pleistocene the forest changed in composition with the expansion or invasion of montane floral elements creating communities of the mesic forest biome without modern analogs while precipitation cycles were causing lake levels to rise and fall the principal influence on vegetation appears to have been cooling in the late pleistocene the population expansion of montane elements at lower elevations is consistent with a cooling of 4 5 c

digital terrain modelling a review of hydrological geomorphological and biological applications the topography of a catchment has a major impact on the hydrological geomorphological and biological processes active in the landscape the spatial distribution of topographic attributes can often be used as an indirect measure of the spatial variability of these processes and allows them to be mapped using relatively simple techniques many geographic information systems are being developed that store topographic information as the primary data for analysing water resource and biological problems furthermore topography can be used to develop more physically realistic structures for hydrologic and water quality models that directly account for the impact of topography on the hydrology digital elevation models are the primary data used in the analysis of catchment topography we describe elevation data sources digital elevation model structures and the analysis of digital elevation data for hydrological geomorphological and biological applications some hydrologic models that make use of digital representations of topography are also considered

proximal distal ichnofabric changes in a siliciclastic shelf early pliocene guadalquivir basin southwest spain abstract the lower pliocene deposits cropping out along the atlantic coast of cadiz in the conil cabo roche area formed on a shelf gently deepening towards the w nw up to five types of facies can be recognized distributed in belts from proximal to distal parts of the shelf 1 coarse grained sandstone with trough cross stratification facies on the most proximal parts of the shelf inner shelf deposits 2 medium grained sandstone with low angle planar cross stratification facies deposited in a more distal position due to storm currents transporting sediment offshore this facies intercalates with the previous trough cross bedded sandstone 3 massive fine grained sandstone and siltstone facies laterally and vertically related with the previous facies type and representing sediments formed in the middle shelf close to the storm wave base 4 tabular sandstone bed facies corresponding to storm bed deposits intercalated within the two previous facies 5 greenish bluish shale facies accumulated on the outer shelf below storm wave base three ichnofabrics associated with these facies are recognized 1 the two cross bedded facies are dominated by a macaronichnus ichnofabric characterized by macaronichnus and bichordites traces that represent colonization of a shifting sandy substrate by polychaetes macaronichnus tracemakers and by sea urchins bichordites producers 2 a rosselia ichnofabric consisting of vertical traces of rosselia cross cutting macaronichnus characterizes the interval of massive fine grained sandstone and silt facies and interbedded tabular sandstones this ichnofabric formed under high sedimentation rates with rosselia traces exhibiting stacked patterns that indicate vertical readjustment following deposition 3 massive fine grained sandstone and silt facies are distinguished by a cylindrichnus ichnofabric this fabric was produced by the activity of a moderately diverse community dominated by sessile burrow dwelling probably superficial detritus feeding polychaetes rosselia and cylindrichnus tracemakers and vagile deposit feeding polychaetes planolites producers in addition infaunal deposit detritus feeders producing spreiten structures teichichnus are found in distal areas pervasive indistinct mottling of the sediment of this facies was probably due to the activity of very shallow burrowers in the uppermost sediment tiers this proximal distal replacement of ichnofabrics reflects the change of benthic communities across the shelf this distribution does not fit the traditional seilacherian ichnofacies model for soft ground shallow marine settings in which proximal vertical dwelling burrows of the skolithos ichnofacies dominate high energy environments in the pliocene of cadiz shallow tier burrows of deposit detritus feeders characterize the high energy facies instead which fit better with the cruziana ichnofacies this deviation can be related with the particular palaeoenvironmental conditions thus vagile opportunistic deposit feeders colonized the dune foreset when the dunes were stable and the progradation of the structure favored the preservation of the traces

deriving indicators of soil degradation from soil aggregation studies in southeastern spain and southern france soil degradation is perceived as a major threat in the mediterranean region due to changes in land use and possible future climate change soil aggregation parameters are used here to demonstrate their potential as a key indicator for land degradation studies the monitoring of these indicators offers a means of establishing the vulnerability and resilience of geo ecosystems soil aggregation stability and distribution were studied on soils with an open shrubby vegetation cover from several places in southeastern spain and southern france by applying drop tests and determining aggregate size distributions aspect and vegetation cover were incorporated in the soil sampling several indices were derived from these analyses to indicate the degree of soil aggregation this was done by referencing to a base level of aggregation bare soil aggregation it was found that soil aggregates were more stable and were often coarser under vegetation when compared to their immediate surrounding bare areas a similar slightly less clear effect was noted on n facing exposed slopes when compared to s facing exposed slopes long term changes were found by studying cultivated land abandoned fields and land covered by semi natural vegetation on comparable substrate and comparable land units it is clear that soil aggregation and aggregate stability increases with time years it is argued that soil aggregation indices can be used as a key indicator for degradation processes at a fine scale with implications for runoff and sediment generating processes at the hillslope scale

a carbon storage perspective on alluvial sediment storage in the rhine catchment abstract floodplains are important sinks in terms of the sediment and carbon flux in fluvial systems despite the large amount of detailed geomorphological studies which include measurements on total organic carbon little is known of the coupling of long term carbon and sediment flux and on the amount of carbon storage in floodplains therefore the influence of the sedimentary facies in fluvial systems was investigated based on a statistical analysis of 1948 organic carbon measurements in different parts of the rhine catchment the analysis allows to develop a conceptual carbon budget model of fluvial systems which was coupled with a holocene alluvial sediment budget to estimate the holocene sequestration rates of carbon storage in floodplains averaged over the rhine catchment the sedimentary carbon sequestration ranges between 3 4 to 25 4 g m 2 yr 1 with more reasonable values between 5 3 to 17 7 g m 2 yr 1 compared to the recent particulate carbon export these values are in the same order of magnitude but somewhat smaller indicating that approximately the same amount of the exported carbon may be stored in floodplains however compared to sedimentary carbon sequestration rates obtained elsewhere the presented values are at the lower limit corresponding to the lower mean holocene soil erosion and floodplain accumulation rates

paleo environmental change in amazonian and african rainforest during the lgm abstract the paper provides new and comparative insight into the ecological history of the two largest continental tropical forest areas during the last glacial maximum lgm the tropical forest regions are of particular interest because they present a large source of heat and have been shown to have significant impact on the extra tropical atmospheric circulation they are also the most intense land based convective centers thus especially from the tropics paleoecological information is needed as benchmarks for climate modeling the african data for lgm climates were published earlier including the reconstructed paleoprecipitation patterns deduced from ssts the tropical south american lgm data were interpreted from pollen geochemical and 18o stable oxygen isotope data from brazil and selected surrounding areas the available terrestrial data are consistent with the sst derived precipitation data for the tropical forests in brazil and for africa however the impact of lgm climate extremes was less severe in the amazon than in the congo basin the lgm humid forest area including evergreen and semi deciduous forest types in africa was probably reduced by 84 in contrast the amazon humid forest area probably shrank to 54 of their present day extension still there are different interpretations with respect to the amount of reduction of the amazon forest area during the lgm although direct information about lgm climates in amazonia is still limited the more detailed map obtained in the present work however allows a more reliable characterization of the last glacial tropical environment than previously published for the amazon region

evidence for the development of a superpermeability flow zone by bioturbation in shallow marine strata upper jubaila formation central saudi arabia abstract superpermeability super k flow zones in carbonate reservoirs are thought to be controlled by bioturbation related burrow networks e g burrow pores of thalassinoides to improve the current understanding this study investigated thalassinoides and associated passive fill in the upper jubaila member of the upper jurassic jubaila formation central saudi arabia analysis of the elemental and mineralogical compositions of powder samples from the passive fill and burrow matrix and thin sections of selected burrow matrix samples were conducted to determine the origin of the passive fill the goal herein is to infer the flow properties of the bioturbated strata of the upper jubaila member based on the occurrence of this passive fill in the burrow pores of the thalassinoides compared to the burrow matrix the analyzed passive fill exhibit marked differences in elemental composition suggesting a much younger and different origin than that of the marine carbonates of the upper jubaila member a cao plus mgo concentration below 28 and an elevated sio2 plus al2o3 concentration above 45 suggest a clay dominated passive fill the reddish and brownish colorations of the passive fill are attributed to the presence of iron oxyhydroxides as indicated by the elevated fe2o3 concentration a mean of 5 8 1 7 and a mineralogical composition with elevated percentages of goethite and hematite the normalized rare earth element ree pattern of the passive fill is consistent with that of lithogenous siliciclastic sources which are likely deposited in a well oxygenated environment as suggested by the redox sensitive elements and normalized rees these sources probably originate in hot humid environment as indicated by the chemical index of alteration cia 80 the above geochemical data suggest that the passive fill was derived from soils similar to mediterranean terra rossa soils and postdate the formation of burrow pores in the thalassinoides bearing strata this could have occurred after exposure of the upper jubaila member terra rossa soil most likely reached the thalassinoides bearing strata from the surface through vertical fractures and karst features filled burrow pores fractures along bedding plains and even intercrystalline pores the occurrence of terra rossa soil in the burrows and intercrystalline pores of the thalassinoides bearing strata implies that the pore system of the upper jubaila member possessed connected pathways that enabled soil infiltration followed by simultaneous precipitation in the burrows and intercrystalline pores the presence of these connected burrow pores containing shafts with diameters ranges from 1 to 5 cm suggests a superpermeable storage capacity and presence of a superflow unit in the upper jubaila member this study provides an excellent example to better understand the controls of super k zones in carbonate reservoirs

determination of pore size distribution in sedimentary rocks by proton nuclear magnetic resonance abstract the distribution of pore sizes in sedimentary rocks can be determined from laboratory measurements of proton nuclear magnetic resonance nmr longitudinal relaxation t 1 in water saturated rocks the details of the longitudinal relaxation curve are converted into a t 1 distribution curve by approximating the data with a sum of single exponential decays the non linear least squares minimization procedure includes a regularization term that reduces excursions in the computed density function thus producing smooth and robust results the t 1 distribution curve is scaled to pore size distributions by a phenomenological parameter that describes the strength of the proton interaction between the fluid and the pore wall this parameter is relatively constant in sandstones but is an order of magnitude less with greater variability in carbonates there is excellent qualitative and quantitative agreement between pore size distributions determined by nmr and independently determined information on pore sizes for a variety of sedimentary rocks the laboratory derived t 1 distributions are used to estimate the irreducible water saturation in sandstones by identifying the fraction of pores less than 4 m in diameter

palaeoenvironmental and palaeogeographical implications of modern macaronichnus segregatis like traces in foreshore sediments on the pacific coast of central japan traces produced by modern animals provide useful information for our understanding of comparable trace fossils this paper reports on a polychaete worm euzonus producing traces which fall within the definition of the ichnotaxon macaronichnus segregatis observation on the wave dominated pacific sandy coast of central japan revealed that this animal and its trace occur exclusively in sediments of the mid foreshore portion of the beach owing to such a limited occurrence of the modern trace the ichnofossil m segregatis might be useful as an indicator of mid foreshore environment the longer axes of modern m segregatis like traces on a bedding plane are arranged perpendicular to the shoreline and accordingly its fossil counterpart can be utilized for reconstructions of the ancient shoreline orientation in support of this assumption a similar mode of m segregatis occurrence is reported from pleistocene shallow marine deposits in japan

linking spatial patterns of soil organic carbon to topography a case study from south eastern spain a key uncertainty in our understanding of the global carbon cycle is the lateral movement of carbon through the terrestrial system soils are the major storage of carbon in the terrestrial biosphere and the inventory of soil organic carbon soc is required for greenhouse gas inventories and carbon mitigation projects the aim of this study is to characterize spatial patterns of the concentrations of topsoil total organic carbon toc in a semi arid mediterranean area in south eastern spain and to assess their relationship to topography we adopt a remote sensing based approach for the spectral determination and quantification of toc with a complete coverage of bare soil surfaces digital terrain analysis and geostatistical techniques are applied to analyze the spatial patterns of toc at different spatial scales we show that accumulation of topsoil soc is dependent on topographic position at the landscape scale with highest values found in valley bottoms at the hill slope scale differences among terrain classes exist regarding the topographic controls on soc while positive correlation between the topographic wetness index twi and toc can be observed on steep slopes that correlation is not significant on wide pediments small scale spatial variability is large on ridges steep slopes and valley bottoms while soc distribution on pediments is relatively homogeneous these differences are most likely governed by the presence of vegetation patches and variable runoff and sediment transport rates among the terrain classes the successful application of hyperspectral remote sensing for the spatial estimation of soc concentrations suggests that it is a promising technique to advance soc inventories in semi arid and arid regions

absence of last glacial maximum records in lowland tropical forests abstract environmental conditions of the lowland tropical forests during the last glacial maximum lgm between ca 20 000 and 18 00014c yr b p are reevaluated in terms of dating control and lithology analyzed in seven pollen records from south america the reevaluation shows that probably in none of the published records are lgm sediments present or abundant this conclusion is based on the occurrence of abrupt lithologic changes coupled with changes in sedimentation rate interpolated from radiocarbon dates these findings suggest that the lgm was represented probably by a hiatus of several thousand years indicative of drier climates than before or after

beyond the stony veil reconstructing the earth s earliest large animal traces via computed tomography x ray imaging abstract trace fossils are superb lines of evidence for examining the ancient biologic world because they offer an opportunity to infer behavioral ecology of organisms however traces can be difficult to parse from their matrix which leads to the loss of important morphological and behavioral data this is especially true for the earliest marine animal traces from the ediacaran period 635 541 ma which are usually small

variations of the amazonian rainforest environment a sedimentological record covering 30 000 years abstract two cores css 2 and css 10 were collected from two lakes situated in the carajas area 6 35 s 49 30 w that show different stages of silting up the results of geochemical and petrographic organic analyses backed up by 14 c radiometric dating lead to a reconstruction of the variations in the hydrological regime of these lakes over the last 30 000 years evidence is revealed for a period of drying up characterized by a sedimentary hiatus between 22 000 and 13 000 14 c years bp followed by a period of refilling between 13 000 and 11 000 14 c years bp 15 400 12 900 cal years bp the latter interval is primarily characterized by a mainly clastic sedimentary input rich in quartz kaolinite and iron hydroxides leading on to the authigenic formation of siderite this type of sedimentation implies the erosion of the small catchment basin during periods of transition between arid and humid climatic regimes from 8000 to 4000 14 c years bp 8900 4500 cal years bp as well as from 2700 to 1500 14 c years bp 2780 1360 cal years bp special hydrological conditions prevailed they are characterized in the sedimentary record by the presence of micro laminae containing wood charcoal interlayered with sponge spicule material this interlamination reflects the rapid alternation of dry and humid periods a comparison with the results obtained by pollen analysis shows that sedimentological indicators once filtered for strictly local effects can provide a full record of the regional scale variations in the environment

southern oscillation signal in south american palaeoclimatic data of the last 7000 years abstract during strong el nino events rainfall anomalies and changes in wind patterns are observed in different regions of south america along the central brazilian coast during the 1983 el nino year the frontal systems were blocked to the south provoking a reversal of the longshore sand transport long duration reversals of longshore transport were also recorded in holocene beach ridge terraces from the rio doce coastal plain this led to the formulation of a model relating these reversals of longshore transport to el nino like conditions el nino like conditions are past average climate situations that generate the same perturbations as the strong el nino events observed during the last decade they are likely to correspond to the long duration low phase of the southern oscillation to confirm this hypothesis we compared the holocene beach ridge record with other palaeoenvironmental records from regions where strong el nino events would have a substancial signal as well 1 water level fluctuations of lake titicaca 2 a pollen and sediment record in an eastern amazonian lake 3 changes of the rio xingu discharge in eastern amazonia and 4 variations of sand supply at the rio piura and rio chira outlets in the sechura desert the occurrences of el nino like conditions were numerous before 3900 3600 yr b p absent between 39003600 and 2800 2500 yr b p and infrequent after 2800 2500 yr b p

mapping soil depth classes in dry mediterranean areas using terrain attributes derived from a digital elevation model abstract modern land management increasingly demands quantitative information on spatially variable soil properties traditional soil survey maps do not provide this information in this paper we report on the application of terrain attributes to mapping soil depth classes at high spatial resolution over large areas under dry mediterranean conditions soil data were collected in 111 georeferenced field plots of 30 m 30 m more or less equally distributed over three lithological units phyllites shales and limestones topographic attributes were computed from a digital elevation model at 30 m resolution a principal components analysis was carried out on the map overlays of the terrain attributes in order to obtain uncorrelated topographic factors that enabled us to apply a probability approach using the maximum likelihood classifier with the field plots as a dispersed training area predictions were made of mean soil depth class and the probability of occurrence of shallow or deep soils a cross validation revealed a 65 81 and 61 accuracy for the three maps of the shale area a 50 55 and 40 for the maps of the phyllite area and a 78 72 and 75 accuracy for the maps of the limestone area explanations for both the good results in the shale and limestone areas and the poor results in the phyllite area focus on the effects of the spatial scale of topographic variation sediment transport mechanisms and the impact of land use

variations of sea surface temperature wind stress and rainfall over the tropical atlantic and south america abstract empirical orthogonal functions e0fs and composite analyses are used to investigate the development of sea surface temperature sst anomaly patterns over the tropical atlantic the evolution of large scale rainfall anomaly patterns over the equatorial atlantic and south america are also investigated the eof analyses revealed that a pattern of anomalous sst and wind stress asymmetric relative to the equator is the dominant mode of interannual and longer variability over the tropical atlantic the most important findings of this study are as follows atmospheric circulation anomalies precede the development of basinwide anomalous sst patterns over the tropical atlantic anomalous sst originate off the african coast simultaneously with atmospheric circulation anomalies and expand westward afterward the time lag between wind stress relaxation strengthening and maximum sst warming cooling is about two months anomalous atmospheric circulation patterns over northern tropical atlantic are phase

large thin slicing a new method for the study of fabrics in lithified sediments this paper outlines a new method for the study of sedimentary fabrics in well lithified facies the technique involves the cutting of large thin slices of rock that can then be viewed in transmitted light the utility of this methodology is demonstrated in sandstone soft siltstone and even schist the technique is particularly pertinent to sedimentary geologists studying lithologically homogeneous sediments in which physical and biogenic sedimentary fabrics are difficult to discern due to a lack of contrast

pleistocene precipitation balance in the amazon basin recorded in deep sea sediments abstract terrigenous sediments from ceara rise in the western tropical atlantic ocean record pleistocene amazon basin climate variability iron oxides and oxyhydroxides in this region originate mainly from chemically leached amazon lowland soils concentrations of goethite and hematite in the terrigenous fraction consistently peak during transitions from glacial to interglacial periods suggesting an increased proportion of erosive products derived from the amazon lowlands compared to the physically weathered highlands lowland amazon basin precipitation changes monitored by the percentage of goethite relative to total iron oxides lead ice age extremes with maximum aridity during ice growth and maximum precipitation during ice melt rapid climate changes over the amazon basin may reflect shifts in the position of the intertropical convergence zone forced by northern hemisphere insolation at precessional 1 23 000 yr 1 and obliquity 1 41 000 yr 1 frequencies variance in the orbital eccentricity bands 1 100 000 and 1 413 000 yr 1 may be explained by nonlinear amplification of insolation forcing at precessional frequencies the early response of amazon precipitation to insolation ahead of high latitude ice volume 18o at all orbital frequencies suggests that tropical aridity is part of the chain of events leading to ice ages rather than a response to glacier oscillations

a new procedure for gridding elevation and stream line data with automatic removal of spurious pits abstract a morphological approach to the interpolation of regular grid digital elevation models dems from surface specific elevation data points and selected stream lines is described the approach has given rise to a computationally efficient interpolation procedure which couples the minimization of a terrain specific roughness penalty with an automatic drainage enforcement algorithm the drainage enforcement algorithm removes spurious sinks or pits yielding dems which may be used to advantage in hydrological process studies the drainage enforcement algorithm has also been found to significantly increase the accuracy of dems interpolated from sparse but well chosen surface specific elevation data moreover it facilitates the detection of errors in elevation data that would not be detected by more conventional statistical means and forms a sound physical basis for cartographic generalization

effect of phycosiphoniform burrows on shale hydrocarbon reservoir quality unconventional gas tight gas coalbed methane and shale gas has become an increasingly significant source of energy economic production from such low permeability reservoirs relies upon identifying regions of the reservoir that will yield the highest gas production rates currently available gas recovery technologies are highly dependent on the fracturability of the reservoir zones of enhanced brittleness and permeability within shale gas reservoir horizons are a prerequisite for successful shale gas recovery such brittle zones are directly linked with increased quartz and or carbonate content within the mudstone in mudstones with high clay mineral content quartz may be concentrated and redistributed as a result of burrowing activities of infaunal organisms high quality porosity and permeability zones in shale petroleum reservoirs may be present in the form of silty and sandy tortuous strips of selectively concentrated grains of quartz that constitute burrow halos grain selective burrows therefore can improve reservoir capacity permeability and fracturability and thus control the storativity of the shale petroleum reservoir this study presents three dimensional reconstructions of three different types of phycosiphon like burrows and investigates the possible fluid flow paths caused by the ichnofabric the volumetric approach to the bioturbation generated by phycosiphoniform burrow makers used herein shows that the volume of sediment that becomes more porous and more permeable media within such bioturbated interval can range from 13 to 26 of the total volume the quartzose strips of sediment caused by bioturbation are highly tortuous and interconnected vertically and horizontally thereby increasing both horizontal and vertical permeability additionally the quartz frameworks created by the burrows may locally increase fracturability within otherwise nonbrittle mudstones

the significance of deep water cryptic bioturbation in slope channel massive sand deposits of the lower rio dell formation eel river basin california abstract deep water massive featureless sands are commonly interpreted as indicators of flow conditions during or shortly after deposition and are almost never interpreted to reflect post depositional homogenization due to bioturbation deep water deposits of the lower rio dell formation pliocene eel river basin nw california however reveal previously unrecognized cryptically bioturbated fabrics in massive sandstone and mudstone this study represents the first detailed documentation of cryptically bioturbated massive appearing sandstone in deep water channelized environments although fluid escape contributed to some of the massive appearing textures in the rio dell formation we present criteria for recognizing cryptic bioturbation fabrics 1 tubes with lithologically distinctive concentric linings or infillings 2 meniscate backfill in burrows 3 lithologically distinctive spreite 4 concentric grain orientations and 5 grains realigned adjacent to tubular structures using biostratigraphic data detailed stratigraphic descriptions core photos and photomicrographs we document ichnofabrics associated with two main lithofacies and their bounding surfaces 1 diffuse muddy siltstone lithofacies e g planolites phycosiphon schaubcylindrichnus 2 massive sandstone lithofacies e g cryptic bioturbation planolites 3 lithofacies crossers 4 burrows that prefer the top of sand base of mud interface e g planolites skolithos and 5 a glossifungites demarcated discontinuity at the base of the massive sand lithofacies we also establish two main lithofacies associations with characteristic sedimentologic traits we use relative percentages of the lithofacies associations to interpret slope channel depositional facies distal channel margin proximal channel margin and channel axis by comparing ichnologic characteristics to depositional facies we conclude that proximity to the channel axis appear to control the degree and type of bioturbation observed in the massive appearing deposits distal channel margin deposits preserve the smallest burrows highly developed cryptic bioturbation fabrics and the most complete sequence of background bioturbation proximal channel margin and channel axis deposits record larger burrows but incomplete cryptic bioturbated fabrics and an overall smaller proportion of preserved background bioturbation

hydroclimate influences on modern pollen rain of upland southeastern amazonia for accurate interpretations of palaeopalynological data it is important to understand the influence of the current vegetation composition and characteristics on the formation of the palynological

three dimensional imaging of earth and planetary materials x ray computed tomography neutron computed tomography and magnetic resonance imaging are driving novel scientific advances by enabling rapid non destructive three dimensional examination and analysis of earth and planetary materials discoveries catalyzed by these approaches range across fields from environmental geology to petroleum geology hydrology to soil science paleontology to petrology and geodynamics to meteoritics they have impacted our understanding of hydrocarbon reservoirs contaminant transport climate change co2 sequestration the evolution of life crustal uplift mantle metasomatism planetary differentiation and more three dimensional imaging is likely soon to become an essential component of every investigator s toolkit especially as instruments and facilities emerge that are optimized for increasingly sophisticated geological applications of these techniques and as access to them expands

the history of south american tropical precipitation for the past 25 000 years long sediment cores recovered from the deep portions of lake titicaca are used to reconstruct the precipitation history of tropical south america for the past 25 000 years lake titicaca was a deep fresh and continuously overflowing lake during the last glacial stage from before 25 000 to 15 000 calibrated years before the present cal yr b p signifying that during the last glacial maximum lgm the altiplano of bolivia and peru and much of the amazon basin were wetter than today the lgm in this part of the andes is dated at 21 000 cal yr b p approximately coincident with the global lgm maximum aridity and lowest lake level occurred in the early and middle holocene 8000 to 5500 cal yr b p during a time of low summer insolation today rising levels of lake titicaca and wet conditions in amazonia are correlated with anomalously cold sea surface temperatures in the northern equatorial atlantic likewise during the deglacial and holocene periods there were several millennial scale wet phases on the altiplano and in amazonia that coincided with anomalously cold periods in the equatorial and high latitude north atlantic such as the younger dryas

hydrological processes in a small arid catchment scale effects of rainfall and slope length many studies have been concerned with the scale issue in geomorphology and hydrology most studies focus on the possibility of data transfer from small to large watersheds less attention has been given to the scale problem within very small watersheds where differences in slope length may seriously affect the spatial distribution and extent of runoff contributing areas to the channel it is usually assumed that runoff and erosion increase as slope length and angle increase however field observations in the negev highlands show positive relationships between slope length and deposition rates regardless of slope angles short hillslopes are devoid of colluvial mantle while thick colluvial deposits with well developed soil profiles indicative of long term stability are found at the base of long hillslopes the hypothesis advanced is that temporal variations in effective rainfall control the spatial structures of surface properties that further enhance the effects of temporal variations in rainfall long term monitoring of rainfall and runoff 1982 1998 conducted at spatial scales varying from few hundreds of m2 up to 0 3 km2 show a decrease in runoff at the hillslope scale the low efficiency of runoff and erosion processes on long hillslopes is because the concentration time required for continuous flow along such slopes is longer than the duration of most effective rain showers prevailing in the area field data lead to the notion that runoff and erosion models in which a positive relationship between slope length and angle and runoff and erosion rates is assumed should not be applied to arid and semiarid areas more attention should be given in latter areas to the complex hydrological relationships between rainfall scales and spatial scales the implications of data obtained regarding the spatial distribution of areas contributing to channel flow at a geological time scale and under changing climatic conditions are discussed

spatial patterns of soil water balance on intensively cultivated hillslopes in a semi arid environment the impact of rock fragments and soil thickness during past decades a diverse system of subsistence agriculture in south east spain annual rainfall of less than 300 mm has been overturned in favour of large scale plantations of almond trees without consideration for topography and related spatial patterns in soil hydrological properties the objective of this paper is to investigate the spatial pattern in soil physical properties induced by this cultivation system and to highlight its impacts on the water balance soil properties were recorded along hillslopes with shallow soils developed on slates and greywackes in the upper part of the guadalentin drainage basin murcia region frequent tillage of these almond plantations covering entire hillslopes has resulted in denudation by tillage erosion on the topographic convexities as well as transport of rock fragments and fine earth along the slopes these processes have created a systematic spatial pattern of soil thickness and rock fragment content shallow and stony soils on the topographic convexities and deep soils with a rock fragment mulch in the concavities at the foot of the slopes at the same time a negative relationship between rock fragment content and fine earth bulk density was observed the impact of this spatial pattern in soil properties on the water balance was evaluated using the pattern one dimensional hydrological and plant growth model the model simulates the water balance of soil profiles covering the observed variation in soil thickness stoniness and bulk density the model results indicate that the highest rates of infiltration evaporation and drainage as well as the lowest rates of overland flow are restricted to shallow soils on the hilltops in contrast the deeper soils in the valley bottoms produce a more stable moisture regime than shallower soils which tend to saturate and dry out quickly these model results are in agreement with the spatial patterns of almond productivity an asymptotic increase with soil thickness copyright c 2000 john wiley sons ltd

lateritic crusts and related soils in eastern brazilian amazonia abstract the upland soils of carajas and paragominas in eastern brazilian amazonia are made up of yellow to reddish earthy clayey to clayey materials which cover iron aluminum aluminum iron and aluminum lateritic crusts these materials are closely related to each other and to lateritic evolution and are comprised by three horizons described from the base to the top as lower intermediary and upper horizons that are identified by the type amount and size of the lateritc fragments embedded into a matrix that increases towards the top the three horizons show a strong lithological vertical transition into themselves and the degradation degree increases toward the top of the profiles where the main characteristics are the same geochemical signatures between the horizons of every profile and the change in the mineralogical composition from hematite gibbsite to gibbsite al goethite in the n5 and ib and from gibbsite to kaolinite quartz in paragominas these transformations support a lateritic crust chemical reworking which allows for its transformation into a friable and soft in situ matrix and then into soil in a progressively weathering process which started in amazonia probably in the miocene after the formation and exposure of the main lateritic crusts to landsurface

a 25 000 year tropical climate history from bolivian ice cores ice cores that were recovered from the summit of sajama mountain in bolivia provide carbon 14 dated tropical records and extend to the late glacial stage lgs oxygen isotopic ratios of the ice decreased 5 4 per mil between the early holocene and the last glacial maximum which is consistent with values from other ice cores the abrupt onset and termination of a younger dryas type event suggest atmospheric processes as the probable drivers regional accumulation increased during the lgs during deglaciation and over the past 3000 years which is concurrent with higher water levels in regional paleolakes unlike polar cores sajama glacial ice contains eight times less dust than the holocene ice which reflects wetter conditions and extensive snow cover

late quaternary changes in amazonian ecosystems and their implications for global carbon cycling abstract the current role of amazonia in the terrestrial carbon budget is the focus of intensive scientific interest in large part due to its potential to accelerate global warming however its role in mediating co2 changes over millennial time scales since the last glacial maximum lgm has generally been overlooked and is the subject of speculation recent advances in our understanding of the late quaternary history of amazonian ecosystems offers an opportunity to make more informed inferences about late quaternary changes in the magnitude of amazon carbon storage than has hitherto been possible therefore in this paper we reconstruct changes in the magnitude of amazon carbon storage over the last 21 000 years since the lgm by reference to recently published palaeohydrological and palaeoecological data and compare these data with results from simulations using a process based terrestrial ecosystem model for the mid holocene and the lgm building on these results further we interpret changes in tropical forest biomass in the context of late quaternary polar ice core records of atmospheric methane and carbon dioxide concentrations palaeo data and model simulations show that amazonia was predominantly forested at the lgm although there is evidence for savanna expansion near the margins of the basin and southern amazonia may have been covered by deciduous semi deciduous dry forests rather than evergreen rain forests we estimate amazon c storage at the lgm to be only 135 gt c 50 smaller than today but find that its proportion of the entire terrestrial carbon store was almost twice that of today the model shows that between the lgm and the mid holocene there is a significant increase in evergreen broad leaf forests at the expense of deciduous forests and a 67 increase in total amazon c storage attributable to rising temperatures and atmospheric co2 levels although our results indicate that the amazon basin was dominated by rain forests throughout the holocene rain forest cover expanded in the late holocene at the expense of savannas and total amazon carbon storage is simulated to have risen by 22 between the mid holocene 225 gt c and the present day pre industrial 225 gt c comparison of these amazon carbon fluxes with palaeo data from other parts of the world suggests that contrary to previous hypotheses the terrestrial biosphere acted as a net carbon sink throughout the holocene and that the observed co2 rise from 260 to 285 ppmv between 8 and 1 ka bp revealed by the antarctic taylor dome ice core record may have been driven by release of carbon from the oceans rather than land

computer modeling bioturbation the creation of porous and permeable fluid flow pathways computer modeling of trace fossils skolithos thalassinoides planolites zoophycos and phycosiphon and ichnofacies skolithos cruziana and zoophycos ichnofacies is undertaken to assess the impact of bioturbation on porosity and permeability trends in sedimentary media model volumes are randomly populated with the digitally modeled trace fossils to test for connectivity between burrows the probability of vertical and lateral interconnections is compared with bioturbation intensity the results of the simulations indicate that biogenic flow networks develop at low bioturbation intensity between 10 and 27 5 bioturbation bi 2 however the efficiency of connectivity is controlled by the architecture of the burrows for all trace fossil and ichnofacies models regardless of trace fossil orientation continuous horizontal and vertical connectivity across the sediment volume is achieved within a 0 to 10 range in bioturbation in subsurface aquifers and petroleum reservoirs the presence of bioturbation can significantly influence fluid flow in particular for marine sedimentary rocks where burrows are more permeable than the surrounding matrix a greater degree of three dimensional burrow connectivity can produce preferred fluid flow pathways through the rock recognizing these flow conduits may enable optimization of resource exploitation or may contribute to increasing reserve estimates from previously interpreted nonreservoir rock

early warming of tropical south america at the last glacial interglacial transition glaciation in the humid tropical andes is a sensitive indicator of mean annual temperature here we present sedimentological data from lakes beyond the glacial limit in the tropical andes indicating that deglaciation from the last glacial maximum led substantial warming at high northern latitudes deglaciation from glacial maximum positions at lake titicaca peru bolivia 16 s and lake junin peru 11 s occurred 22 000 to 19 500 calendar years before the present several thousand years before the bolling allerod warming of the northern hemisphere and deglaciation of the sierra nevada united states 36 5 to 38 n the tropical andes deglaciated while climatic conditions remained regionally wet which reflects the dominant control of mean annual temperature on tropical glaciation

palaeoecology of macaronichnus segregatis degiberti reconstructing the infaunal lives of the travisiid polychaetes abstract macaronichnus segregatis degiberti a relatively large ichnosubspecies of macaronichnus segregatis is an almost straight to gently curved cylindrical fossilized burrow oriented horizontal to oblique to the bedding plane it is interpreted as a pascichnial trace fossil formed through selective sand feeding and excretion of a free living polychaete such as a relatively large travisiid formerly classified as opheliid or scalibregmatid polychaete travisia while the other ichnosubspecies i e m s segregatis m s lineiformins m s meandriformis and m s spiriformis are commonly 2 5 mm in diameter and occur exclusively in foreshore deposits m s degiberti attains a diameter of up to 15 mm and shows wide environmental distribution ranging from tidal channels tidal sand bars tidal sandridges tidal flats upper to lower shorefaces bioturbated sandy shelves shelf storm sheets to shelf sand ridges the core of m s degiberti consisting mainly of light mineral rich sand grains is composed of alternating lamellae of light mineral rich and heavy mineral rich sands arranged oblique to the bedding plane on the other hand the mantle composed mainly of heavy mineral rich sands has a smooth outline or evenly spaced lobes flanked on both sides the morphology of the mantle lobes and core lamellae suggests repeated pulses of sediment probing and excreting behaviour of the tracemaker two or more burrows of this ichnosubspecies tend to occur adjacently sometimes intertwining as travisia develops directly lacking any planktic larval stages aggregations of the burrows can be interpreted to reflect the burrowers interindividual exploratory behaviour with the aim of copulation travisia also known as a stink worm secretes volatile chemical substances that might act as sex pheromones to attract other individuals for reproduction within the substrate therefore a new category of ethological classification of trace fossils sequorichnia sequor follow and ichnia traces for exploration of other individuals is proposed here this is the first record of interindividual exploratory behaviour of infaunae

differential responses of hillslope and channel elements to rainfall events in a semi arid area the degree of hydrological connectivity of hillslope elements in a semi arid climate was studied at the season and event timescales field data were obtained in rambla honda a medalus project field site situated in se spain on micaschist bedrock and with 300 mm annual rainfall the season timescale was assessed using correlation analysis between soil moisture and topographic indices the event timescale was studied by a quasi continuous monitoring of rainfall soil moisture runoff and piezometric levels results show that widespread transfers of water along the hillslope are unusual because potential conditions for producing overland flow or throughflow are spatially discontinuous and extremely short lived during extreme events runoff coefficients may be locally high ca 40 on slope lengths of 10 m but decrease dramatically at the hillslope scale 10 on slope lengths of 50 m two mechanisms of overland flow generation have been identified infiltration excess and local subsurface saturation from upper layers the former occurs during the initial stages of the event while the latter which is quantitatively more important takes place later and requires a certain time structure of rainfall intensities that allow saturation of the topsoil and the subsequent production of runoff hillslopes and alluvial fans function as runoff sources and sinks respectively permanent aquifers are lacking in rambla honda variable proportions of hillslope areas may contribute to flash floods in the main channel but their contribution to the formation of saturated layers within the sediment fill is very limited

late quaternary climate history of the bolivian altiplano abstract sediment cores and outcrops from the bolivian altiplano are used to interpret late pleistocene holocene paleoclimates and lake evolution based on a multi proxy approach ostracod content palynology sedimentology and radiocarbon dating despite the different sensitivity of the lacustrine basins to environmental changes interpreting the records in terms of paleohydrology climate and more especially timing of events is difficult notwithstanding these problems lake titicaca in the north and lake pocoyu lake poopo salars of coipasa and uyuni in the south reveal a similar evolution in general trends through the course of time during the minchin phase until 30 26 kyr bp the altiplano was wetter than present the last glacial maximum ca 26 14 kyr bp marked by cooler drier conditions was followed by a return to a wetter climate interrupted by short arid events between ca 14 and 10 5 kyr bp another cycle of aridity between 10 5 and 8 kyr bp took place abruptly just after the humid tauca phase the mid holocene is interpreted as climatically unstable with an alternation of humid and dry episodes since 3 9 kyr bp wetter conditions have persisted and intensified to the present the data are interpreted in terms of changes in inter tropical convergence zone extension summer precipitation and in polar air mass intensity winter precipitation

terrestrial sedimentation and the carbon cycle coupling weathering and erosion to carbon burial this paper examines the linkages between the carbon cycle and sedimentary processes on land available data suggest that sedimentation on land can bury vast quantities of organic carbon roughly 1015 g c yr 1 to evaluate the relative roles of various classes of processes in the burial of carbon on land terrestrial sedimentation was modeled as a series of 864 scenarios each scenario represents a unique choice of intensities for seven classes of processes and two different global wetland distributions comparison was made with presumed preagricultural conditions the classes of processes were divided into two major component parts clastic sedimentation of soil derived carbon and organic sedimentation of autochthonous carbon for clastic sedimentation masses of sediment were considered for burial as reservoir sediment lake sediment and combined colluvium alluvium and aeolian deposits when the ensemble of models is examined the human induced burial of 0 6 1 5 1015 g yr 1 of carbon on land is entirely plausible this sink reaches its maximum strength between 30 and 50 n paddy lands stand out as a type of land use that warrants future study but the many faces of rice agriculture limit generalization in an extreme scenario paddy lands alone could be made to bury about 1 1015 g c yr 1 arguing that terrestrial sedimentation processes could be much of the sink for the so called missing carbon is reasonable such a hypothesis however requires major redesign of how the carbon cycle is modeled unlike ecosystem processes that are amenable to satellite monitoring and parallel modeling many aspects of terrestrial sedimentation are hidden from space

late quaternary vegetation and climate change in the amazon basin based on a 50 000 year pollen record from the amazon fan odp site 932 hemipelagic sediments from the amazon deep sea fan odp site 932 5 12 7 n 47 1 8 w and continental shelf provide a 50 000 yr long pollen record of amazon basin vegetation the age model for hole 932a is constrained by eight magnetic remanence intensity features one paleomagnetic excursion and three ams14c dates alchornea melastomataceae myrtaceae and moraceae urticaceae are dominant taxa in the pollen record between 40 200 and 19 800 cal yr b p andean taxa such aspodocarpusandhedyosmum increase in abundance between 19 800 and 11 000 cal yr b p and prior to 40 200 cal yr b p the holocene pollen assemblage derived from amazon river and continental shelf sediments is dominated by secondary growth taxa such ascecropia climatic factors influencing the development of glacial and interglacial tropical vegetation are considered by comparing marine with terrestrial records of vegetation change this comparison shows that the amazon basin forests were not extensively replaced by savanna vegetation during the glacial period contradicting the refugia hypothesis

late pleistocene temperature depression and vegetation change in ecuadorian amazonia abstract paleoecological pollen phytolith and wood analyses of sediments radiocarbon dated 33 000 to 26 000 yr b p from two sites in ecuadorian amazonia provide data that suggest a cooling of ca 7 5 c below present in equatorial lowlands from 33 000 to 30 000 yr b p a period of warning followed in which novel species assemblages a blend of montane and lowland floral components persisted for at least 4000 years these data of forest community change from sites lying within the postulated glacial rain forest napo refugium provide the strongest paleoecological refutation of the refugial hypothesis yet obtained the large temperature depression at ca 30 000 yr b p allows the possibility that if maximum cooling at the equator was synchronous with the last glacial maximum lgm of the northern hemisphere freezing temperatures would have been experienced in parts of lowland amazonia between 25 000 and 18 000 b p

biogenically enhanced reservoir properties in the medicine hat gas field alberta canada abstract spot minipermeametry and micro ct analytical techniques were employed to evaluate the effect s of bioturbation on porosity and permeability distributions in reservoir facies of the highly prolific medicine hat gas field of alberta canada this study focuses on five cm scale samples that occur at different stratigraphic positions and intersect discrete bioturbated horizons within the medicine hat member spot minipermeability results demonstrate that permeability in bioturbated sandstones is up to two orders of magnitude greater than those of the muddy matrix thus corresponding to a dual porosity fluid flow system graphing bioturbation intensity versus measured permeability indicates that burrows are well connected horizontally and provide flow conduits micro ct models reveal that burrowed sandstones are isolated and planiform in character rare interpenetrations from vertically oriented trace fossils serve to interconnect these hydraulically isolated strata results show that bioturbated sandstones possess reservoir properties comparable to those associated with laminated sandstones yielding an anisotropic porous medium understanding the impact of trace fossils on porosity permeability distributions in the medicine hat gas field can be used to identify potential reservoir from previously interpreted non reservoir rock and ultimately improve reserve estimations

tropical climate changes at millennial and orbital timescales on the bolivian altiplano tropical south america is one of the three main centres of the global zonal overturning circulation of the equatorial atmosphere generally termed the walker circulation1 although this area plays a key role in global climate cycles little is known about south american climate history here we describe sediment cores and down hole logging results of deep drilling in the salar de uyuni on the bolivian altiplano located in the tropical andes we demonstrate that during the past 50 000 years the altiplano underwent important changes in effective moisture at both orbital 20 000 year and millennial timescales long duration wet periods such as the last glacial maximum marked in the drill core by continuous deposition of lacustrine sediments appear to have occurred in phase with summer insolation maxima produced by the earth s precessional cycle short duration millennial events correlate well with north atlantic cold events including heinrich events 1 and 2 as well as the younger dryas episode at both millennial and orbital timescales cold sea surface temperatures in the high latitude north atlantic were coeval with wet conditions in tropical south america suggesting a common forcing

differences in hillslope runoff and sediment transport rates within two semi arid catchments in southeast spain this paper focuses on hillslope runoff and sediment transport within two catchments in southeast spain five monitoring sites were established on hillslope concavities throughout the two catchments the techniques used were mini crest stage recorders spray painted lines sediment traps and tipping bucket rain gauges established during previous research results show that a storm event in the rambla nogalte on 30 june 2002 of 83 0 mm was responsible for a maximum runoff depth of 12 cm and a maximum hillslope sediment transport of 1886 cm3 m 1 the same storm in the rambla de torrealvilla produced 53 4 mm of rainfall on the 1 july 2002 had a maximum runoff depth of 26 cm and resulted in 2311 cm3 m 1 of sediment transport there is evidence to suggest that measured sediment transport is related to runoff and a qualitative estimate of morphological runoff zones mrz sediment transport and depth of runoff varied dramatically with lithology marl sites produced most runoff and sediment transport followed by the sites of mixed red and blue schist then blue schist these results are important for understanding the behaviour of slopes and show that for short lived storms with high but not rare rainfall intensities and total rainfall amounts runoff can cause significant hillslope sediment transport in semi arid areas

patterns of rock fragment cover generated by tillage erosion abstract intensively cultivated areas in the upper part of the guadalentin catchment southeast spain show a systematic spatial pattern of surface rock fragment cover rc the objective of this paper is to quantify and to explain this spatial rock fragment cover pattern therefore a map of an intensively cultivated area of 5 km2 was digitised and for each pixel total topographic curvature was calculated next rock fragment cover was determined photographically at 35 sites with a range of total slope curvatures a linear relation between total curvature and rock fragment cover was found except for narrow concavities it was hypothesised that this pattern can be explained by a significant net downslope movement of rock fragments and fine earth by tillage the displacement distances of rock fragments by tillage with a duckfoot chisel were measured by monitoring the displacement of tracers painted rock fragments and aluminium cubes on 5 sites having different slopes the rare of tillage erosion for one tillage pass with a duckfoot chisel expressed by the diffusion constant k equals 282 kg m for up and downslope tillage and only 139 kg m for contour tillage nomograms indicate that mean denudation rates in almond groves due to tillage erosion 3 to 5 tillage passes per year can easily amount to 1 5 2 6 mm year for contour tillage and up to 3 6 5 9 mm year for up and downslope tillage for a field 50 m long and having a slope of 20 these figures are at least one order of magnitude larger than reported denudation rates caused by water erosion in similar environments hence tillage erosion contributes significantly to land degradation the downslope soil flux induced by tillage not only causes considerable denudation on topographic convexities hill tops and spurs and upper field boundaries but also an important sediment accumulation in topographic concavities hollows and valley bottoms and at lower field boundaries kinetic sieving i e the upward migration of rock fragments by the tines of the duckfoot chisel also concentrates the largest rock fragments in the topsoil in such a way that a rock fragment mulch develops in narrow valleys and at the foot of the slopes these results clearly indicate that tillage erosion is the main process responsible for the observed rock fragment cover pattern in the study area since the study area is representative for many parts of southern spain where almond groves have expanded since 1970 the results have a wider application they show to what extent intensive tillage of steep slopes has contributed to the increase in soil degradation to changes in hillslope morphology i e strong denudation of convexities development of lynchets and rapid infilling of narrow valley bottoms and to the development of rock fragment cover patterns which control the spatial variability of the hydrological and water erosion response within such landscapes

neogene and quaternary development of the neotropical rain forest the forest refugia hypothesis and a literature overview abstract the upheaval of the northern andes in miocene and pliocene time changed the drainage system in northern south america significantly and caused the present day rain forest areas of choco and the lower magdalena valley became separated from amazonas plant diversity may have reached the highest level in the miocene or pliocene and excessive present day phytodiversity may be regarded as a legacy of the tertiary rather than an evolutionary product of the quaternary in the quaternary strong temperature oscillations related to the series of ice ages were superposed on the late tertiary forest dynamics which included river displacement and latitudinal migrations of the equatorial rain belt caloric equator with the rhythm of the precession cycle of orbital climate forcing the hypothesis that claims a permanent rain forest cover all over the amazon basin during the last glacial is in contrast with the forest refugia hypothesis which accepts replacement of rain forest by savanna or savanna forest during dry climatic intervals both scenarios have been evidenced by pollen records in this paper it is suggested that both hypotheses are not necessarily conflicting and apparently did occur in different parts of the amazon basin and in different periods depending on the climatological constraints a compilation of the most important literature concerning the vegetational climatic and environmental history of the rain forest areas of amazonas and choco and surrounding dry ecosystems has been included

radiocarbon calibration curve spanning 0 to 50 000 years bp based on paired 230 th 234 u 238 u and 14 c dates on pristine corals abstract radiocarbon dating is the most widely used dating technique in the world recent advances in accelerator mass spectrometry ams and sample preparation techniques have reduced the sample size requirements by a factor of 1000 and decreased the measurement time from weeks to minutes today it is estimated that more than 90 percent of all measurements made on accelerator mass spectrometers are for radiocarbon age dates the production of 14 c in the atmosphere varies through time due to changes in the earth s geomagnetic field intensity and in its concentration which is regulated by the carbon cycle as a result of these two variables a radiocarbon age is not equivalent to a calendar age four decades of joint research by the dendrochronology and radiocarbon communities have produced a radiocarbon calibration data set of remarkable precision and accuracy extending from the present to approximately 12 000 calendar years before present this paper presents high precision paired 230 th 234 u 238 u and 14 c age determinations on pristine coral samples that enable us to extend the radiocarbon calibration curve from 12 000 to 50 000 years before present we developed a statistical model to properly estimate sample age conversion from radiocarbon years to calendar years taking full account of combined errors in input ages and calibration uncertainties our radiocarbon calibration program is publicly accessible at http www radiocarbon ldeo columbia edu along with full documentation of the samples data and our statistical calibration model

biogeochemical indicators of environmental changes from 50 ka to 10 ka in a humid region of the brazilian amazon abstract we present a geochemical record of a 113 6 cm sediment core lpt v from lagoa da pata which is located in the forested upper rio negro basin the record reveals significant changes in the environmental history of amazonia during the late quaternary the results of biogeochemical analyses revealed three hydrological and climatic regimes from 50 000 to 10 000 cal yr bp the first phase between 50 000 and 26 300 cal yr bp was characterized by a relatively wet climate as suggested by relatively high total organic carbon toc and chlorophyll derivate concentrations indicating high productivity linked to a high lake level a decrease of the toc and chlorophyll derivate accumulation rates between 43 100 cal yr bp and 26 300 cal yr bp marks a decrease in the productivity linked to a reduced lake level indicating a decrease in moisture at the end of this phase the second phase between 26 300 and 15 300 cal yr bp was characterized by a decrease in productivity reaching a minimum at 21 950 cal yr bp as indicated by a minima in sedimentary chlorophyll and toc accumulation rates values of 13 c increased by 5 in relation to the preceding phase indicating an influence of the c 4 organic matter high iron concentrations and accumulation rates related to intense erosion of the lateritic crust in the watershed were observed all of the observations indicate a dry phase during this period a third phase from approximately 15 300 to 10 000 cal yr bp was characterized by an increase in lacustrine productivity as shown by an increased in toc and chlorophyll derivate concentrations and accumulation rates these increases likely correspond to a lake level rise due to a wetter climate

ichnological analysis the common ground between ichnofacies workers and ichnofabric analysts abstract this work compares the approaches taken by the two schools of applied ichnology ichnofacies and ichnofabric analysts and proposes an integrated approach for future improvement there are many similarities between the two approaches which mainly differ in the resolution at which ichnological analysis is undertaken ichnofabric work is by necessity performed on a bed by bed basis and interpreted at a scale consistent with that of the sedimentologist s facies ichnofacies studies in contrast seldom report bed by bed changes in ichnological content instead highlighting bedset to facies association scale changes in ichnology through comparison with summary models of ichnological trends this work highlights the fact that workers from both schools utilize the same tools with slightly different emphases to reach their ichnological conclusions contention between the two schools has in recent years centred upon which is the better method for studying trace fossils an artificial construct that detracts from the fact that both are extremely useful to sedimentological and palaeoenvironmental studies ichnofabric analysis is in addition a highly effective means of documenting bioturbated sedimentary fabrics as the basis for petrophysical studies ichnofacies and ichnofabric analysts use the same toolbox of ichnological methods to determine ancient palaeoenvironments the scale of observation is generally different but the results closely comparable the recognition of key stratal surfaces on ichnological grounds is also possible with both methodologies ichnofacies analysts look to recognise glossifungites ichnofacies firmgrounds in offshore mudstones ichnofabric studies would look to recognise overprinting of fabrics created by groups of organisms from different palaeoenvironments but associated with the same key surface it is proposed that the terms ichnofacies method and ichnofabric analysis are abandoned in favour of a neutral ichnological analysis method encompassing the approaches and terminology of both to produce a unified scientifically rigorous user friendly methodology

use of low cost multistripe laser triangulation mlt scanning technology for three dimensional quantitative paleoichnological and neoichnological studies abstract the purpose of this paper is to test the application of a new low cost 2995 00 us multistripe laser triangulation mlt scanner and three dimensional 3d software for semiquantitative and quantitative analyses of ichnofossils and modern traces the goal of this research is to improve on existing analytical techniques and apply new methods to 3d digital models of ichnofossils and modern traces objectives are to 1 provide researchers with new ways to develop and test hypotheses quantitatively in the fields of paleoichnology neoichnology sedimentology and soil science and 2 discuss uses advantages and limitations of mlt technology related to ichnology we scanned and created digital models of a variety of mostly continental ichnofossils and modern terrestrial traces produced by invertebrates and vertebrates visual methods applied include making uniformly colored specimen surfaces stereo pairs anaglyph stereo images animations and cross sections quantitative methods applied include measuring distances tortuosity indices and angles and producing contour maps of tracks two of the most useful properties measurable from digital models are surface area sa and volume v these are used rarely in ichnology because they are difficult to measure with traditional methods we use sa to calculate area exploited and introduce a method of quantifying surface roughness adapted from research on soil surfaces we measure v of burrows tracks and coprolites as well as introduce a new measure termed volume exploited we hypothesize that different tracemakers make burrows with characteristic v to sa ratios this is partially supported by statistical tests of previously published data we also use v to sa ratios to determine relative compactness a metric adapted from building physics digital models ensure perpetuity of specimens because they preserve 3d data that can be used to make physical copies placed in museums and disseminated easily to researchers and educational institutions of all levels data from digital models can be used to interpret ichnocoenoses bioturbation rates and pedogenic properties and processes in soils and paleosols note that mlt scanning digitizes only surfaces of objects so it is best suited for exogenic traces and casts of endogenic traces

early local last glacial maximum in the tropical andes the local last glacial maximum in the tropical andes was earlier and less extensive than previously thought based on 106 cosmogenic ages from beryllium 10 dating from moraines in peru and bolivia glaciers reached their greatest extent in the last glacial cycle 34 000 years before the present and were retreating by 21 000 years before the present implying that tropical controls on ice volumes were asynchronous with those in the northern hemisphere our estimates of snowline depression reflect about half the temperature change indicated by previous widely cited figures which helps resolve the discrepancy between estimates of terrestrial and marine temperature depression during the last glacial cycle

accumulation of organic carbon in five brazilian lakes during the holocene abstract a comparative study was made of organic carbon accumulation in five lacustrine environments in brazil large open water lake ponds with floating meadows and marshes the most representative cores were used to calculate the accumulation of total organic carbon toc in the sediment over the past 12 000 cal years bp carbon accumulation rates were determined using the toc concentration sediment in situ density 14 c calibrated ages and the interpolated sedimentation rate cm year 1 or sediment accumulation rate g m 2 year 1 the c n ratio and microscopic observations were used to characterise the sedimentary organic matter recent toc accumulation in the lakes was estimated at 7 41 g m 2 year 1 by averaging the last 500 years this variation roughly correlated with the present day ratio of watershed area vs lake area indicating that nutrient input is important for the modern accumulation of organic matter the accumulation rates were greatest in lakes with floating macrophytes the largest lake dom helvecio with a strong thermal stratification low primary production and low carbon accumulation had relatively well preserved organic matter when its low watershed area lake area ratio was considered the general increase in carbon accumulation during the holocene followed the expansion of lakes and the development of a wetter climate due to a growing penetration of the atlantic and amazonian wet air mass over brazil driven by insolation changes this change in carbon accumulation was not controlled by the higher water and nutrient inputs alone more organic matter was decomposed when lake levels were low at the beginning of the holocene some lakes were also influenced by higher inputs of allochthonous organic matter during the early and middle holocene these inputs included high concentrations of charcoal fragments lake morphology and its changes as the lake level rose as well as the nature of primary producers strongly influenced the carbon accumulation rates our understanding of how climate changes are linked to changes in the lacustrine environment should not be based on measuring organic matter alone but requires a good description of the organic matter and other limnological parameters

reservoir quality along a homoclinal carbonate ramp deposit the permian upper dalan formation south pars field persian gulf basin abstract permo triassic carbonate successions host some of the largest oil and gas reserves in the arabian plate including the world s largest gas reservoirs of the upper dalan and the kangan formations in the south pars gas field persian gulf basin both formations are stratigraphically equivalent to the upper khuff formation which has been long recognized as a major oil and gas reservoir in the arabian peninsula the permian upper dalan formation is composed mainly of mixed carbonate evaporite sequences that formed on a laterally continuous homoclinal carbonate ramp with significant variations in reservoir heterogeneity and quality they can be grouped in 18 microfacies high reservoir qualities are found within high energy shoal environments with a tendency of the best reservoir quality to occur towards the basin in a mid ramp setting in contrast low energy tidal flat environments exhibit the poorest reservoir quality reservoir quality from lagoonal environments is diverse diagenesis has significantly affected reservoir properties by both enhancing and destroying original porosity and permeability bivariate plots of porosity and permeability values combined with thin section petrography indicate that pore filling pervasive and poikilotopic anhydrite cements had the greatest negative impact on the reservoir quality whereas dolomitization and dissolution of grains and cements played the most positive role two third order sequence stratigraphic cycles link lithologies and depositional environments to sea level fluctuations hsts are associated with better reservoir characteristics than tsts

late quaternary vegetation and coastal environmental changes at ilha do cardoso mangrove southeastern brazil abstract a 190 cm mangrove sediment core from the ilha do cardoso state park state of sao paulo southeastern brazil was analyzed for pollen diatoms as well as carbon and nitrogen isotopes the goal was to determine the dynamics of the coastal terrestrial aquatic ecosystems vegetation history and climate change in this region of the brazilian atlantic rainforest during the late pleistocene and holocene the values for total organic carbon toc from 3 up to 40 c n ratios from 10 up to 130 and 15n 0 to 8 are associated with well preserved aquatic and terrestrial organic matter and possibly influenced by nitrogen cycling e g denitrification that caused 15n enrichment between 40 000 cal yr b p and 23 000 cal yr b p depleted 13c values 28 0 are also observed and indicate the predominance of c3 plants during this time interval the pollen analysis reveals the presence of the genera ilex alchornea weinmannia myrsine symplocos drimys and podocarpus on a site currently occupied by mangrove vegetation these data suggest that in the past prevailed a colder and more humid climate than today with a low relative sea level from 23 000 cal yr b p to 2200 cal yr b p a sedimentary hiatus likely occurred related to an erosive event associated to the post glacial sea level rise since at least 2200 cal yr b p sediments are marked by relatively low c n ratios from 2 to 27 exhibit more enriched 13c from 26 0 to 24 0 and 15n up to 7 values and are characterized by the presence of marine diatoms this indicates the return of the marine coastal line to its current position and consequently the development of mangrove

determination of black carbon by chemical oxidation and thermal treatment in recent marine and lake sediments and cretaceous tertiary clays abstract several sample treatments and analytical methods for the measurement of black carbon in a wide variety of sediments were considered in which the removal of organic carbon is a critical step in the procedure a comparison between chemical oxidation and thermal treatment was conducted and the latter was shown to be inappropriate due to the polymerisation of organic matter using acid dichromate oxidation reactive kerogen was separated from black carbon in a variety of lake and marine and recent and ancient sediments with relatively small and quantifiable losses 1 6 of black carbon under carefully controlled reaction conditions

some factors controlling gully growth in fine grained sediments a model applied in southeast spain abstract gullies in the guadalentin catchment se spain are formed in a variety of lithologies ranging from schists to marls there are clear differences in valley and channel morphology between these two types gully erosion in schists produces large amounts of clastic material that restricts sediment transport leading to a relatively smooth transition from gullies to hillslopes and to broad alluvial valley bottoms with laterally migrating channels gullies in marls contain only limited gravels so gully extension leads to sharply incised gully heads a two dimensional model has been developed to investigate and simulate the distribution of gully heads in the guadalentin the model runs on a smooth initial surface with an added fractal perturbation without some perturbation of the initial surface or material properties symmetry prevents the formation of any channels fractal perturbation was used here to provide initial irregularities at all scales this paper explores the dependence of model response on the form of the sediment transport law initially sediment transport was considered to be transport limited and so depends on the relationship between wash and creep splash this was modified by i altering the exponents for gradient and area to conform with experimental results ii adding a critical tractive power for the initiation of rillwash iii including a more explicit treatment of mass movements iv including terms to reduce the dependence of the model on the computational grid size v providing a basis for explicitly integrating from individual storms to average long term behaviour and most critically vi introducing the effective bedload fraction ebf as a simplifying concept to allow for the selective transportation of eroded sediment this modification allows the model to represent removal of fines in marl rich catchments without the need to introduce a fully explicit travel distance formulation the steep gully heads and vertical side walls developed in marl catchments in the guadalentin basin are qualitatively well represented by the model preliminary tests showed that steep walled gullies are generated where the ebf falls to below about 0 5 if a tractive power threshold is also introduced gentler headcuts are produced selective transportation is thus seen as the critical determinant of steep headcuts in gully systems

runoff generation sediment movement and soil water behaviour on calcareous limestone slopes of some mediterranean environments in southeast spain abstract an interpretation of soil hydrology and erosion data obtained from limestone areas in southeast spain is presented in the framework of recent hypotheses on runoff generation mechanisms in mediterranean environments the main objective is to synthesise and harmonise the data in theoretical concepts or behavioural models of hydrological functioning of mediterranean limestone slopes for this purpose data were collected in a typical limestone area with climatic characteristics ranging from subhumid to semiarid several sites were chosen with comparable slopes vegetation and soils along a transect of 20 km to carry out several research projects the data discussed in this paper consist of information on water redistribution within the soil profiles obtained from long duration up to 5 h rainfall simulation experiments with continuous monitoring of soil moisture at different depths runoff and sediment concentration data were obtained i from rainfall simulation experiments with different antecedent soil moisture conditions and ii as natural results from open gerlach plots on runoff and sediment movement over 4 years three conceptual models of water redistribution during the infiltration process could be observed two of them imply nonuniform water redistribution within the soil profile due mainly to macropore flow caused by specific soil surface characteristics at the plot scale runoff generated in bare patches is mainly hortonian in plots with previously wetted soils or soils with high infiltration capacities the generated runoff implies the saturation of the upper soil both types of runoff are discontinuous through time and space the runoff generation mechanisms at the slope scale have been synthesised into two conceptual models a hortonian discontinuous runoff model that takes place in the most degraded slopes or during high intensity rain events and a mixed runoff generation model in less degraded slopes or in previously wet soils where infiltration excess runoff as well as saturation excess runoff can happen on the same slope in both cases slopes behave as a patchwork of runoff and runon areas the size of the runoff or runon patches is dependent on the climatological conditions these control the hydrological disconnection between different parts of the slopes hortonian and saturation runoff can both be generated and infiltrated downslope

a 24 700 yr paleolimnological history from the peruvian andes abstract a new paleolimnological dataset from lake pacucha 13 s 3095 m elevation in the peruvian andes provides evidence of changes in lake level over the past 24 700 yr a late glacial highstand in lake level gave way to an early holocene lowstand this transition appears to have paralleled precessional changes that would have reduced insolation during the wet season the occurrence of benthic salt tolerant diatoms and caco3 deposition suggest that the lake had lost much of its volume by c 10 000 cal yr bp pronounced holocene oscillations in lake level included a second phase of low lake level and heightened volatility lasting from c 8300 to 5000 cal yr bp while a polymictic lake formed at c 5000 cal yr bp these relatively wet conditions were interrupted by a series of drier events the most pronounced of which occurred at c 750 cal yr bp paleolimnological changes in the holocene were more rapid than those of either the last glacial maximum or the deglacial period

palaeobiology of schaubcylindrichnus heberti comb nov from the lower jurassic of northeast england abstract the distinctive species of palaeophycus known as palaeophycus heberti is characterised by its thick burrow wall and passive burrow fill this species is typically associated with intensely bioturbated heterolithic sandstones and mudstones deposited in shoreface to offshore marine palaeoenvironments three dimensional analysis of specimens attributed to p heberti based on closely spaced serially ground surfaces has revealed a number of hitherto unknown morphological elements more comparable to the ichnogenus schaubcylindrichnus thereby creating schaubcylindrichnus heberti comb nov schaubcylindrichnus burrows are typically passively filled and have a thick burrow wall composed of sand rich annular rings the three dimensional reconstructions importantly demonstrate that the gross morphology is a broad open u shape which is inconsistent with the ichnogeneric diagnosis of palaeophycus s heberti differs from all other species of schaubcylindrichnus in that the burrow wall is mineralogically heterogeneous rather than purely quartzose the ichnogeneric diagnosis is thus emended to accommodate s heberti

large macaronichnus in modern shoreface sediments identification of the producer the mode of formation and paleoenvironmental implications abstract the trace fossil macaronichnus segregatis is an intrastratal trail occurring in shallow marine deposits previous studies have shown that this trace fossil can be used as a powerful indicator of ancient sea level shoreline orientation beach morphodynamics and paleoceanographic conditions here we describe another type of macaronichnus an incipient large macaronichnus isp which is 5 12 mm in diameter from upper shoreface deposits of a modern sandy beach in western japan the burrow is produced by selective sand grain feeding of the opheliid polychaete travisia japonica although the detailed mechanism remains unclear based on the distribution of t japonica and other travisia species large macaronichnus isp seems to be more widely distributed across tidal flats the upper lower shoreface the continental shelf and possibly even the deep sea floor the distribution of the large burrow is quite different to that of the standard m segregatis it is therefore necessary to distinguish between the sizes of the burrows in order to use the ichnogenus macaronichnus as a paleoenvironmental indicator