intercalibration of astronomical and radioisotopic time the 40ar 39ar radioisotopic dating technique is one of the most precise and versatile methods available for dating events in earth s history but the accuracy of this method is limited by the accuracy with which the ages of neutron fluence monitors dating standards are known calibrating the ages of standards by conventional means has proved difficult and contentious the emerging astronomically calibrated geomagnetic polarity time scale apts offers a means to calibrate the ages of 40ar 39ar dating standards that is independent of absolute isotopic abundance measurements seven published 40ar 39ar dates for polarity transitions nominally ranging from 0 78 to 3 40 ma are based on the fish canyon sanidine standard and can be compared with apts predictions solving the 40ar 39ar age equation for the age of the fish canyon sanidine that produces coincidence with the apts age for each of these seven reversals yields mutually indistinguishable estimates ranging from 27 78 to 28 09 ma with an inverse variance weighted mean of 27 95 0 18 ma normalized residuals are minimized at an age of 27 92 ma indicating the robustness of the solution

volcano hazards and potential risks on st paul island pribilof islands bering sea alaska abstract volcano hazards and potential risks on st paul island alaska are assessed on the basis of the recent volcanic history of the island the long term frequency of volcanic eruptions is estimated using a count of 40 identifiable vents considered to represent separate eruptions assuming regular temporal spacing of these events during the period 360 000 to 3230 y b p the estimated mean recurrence time is 0 11 10 3 eruption year and the eruptive interval is approximately 8900 years volcano hazards on st paul are associated exclusively with the eruption of low viscosity alkali basaltic magma the most important are lava flows tephra fallout and base surges other hazards include volcanic gases seismicity and ground deformation associated with dike intrusion beneath rift zones and explosive lava water interactions along coastal regions and water saturated ground the general characteristics of past volcanism on st paul indicate that the most likely styles of future eruptions will be 1 hawaiian style eruptions with fire fountains and pahoehoe lava flows issuing from one of two polygenetic shield volcanoes on the island 2 strombolian style scoria cone building eruptions with associated tephra fallout and eruption of short pahoehoe lava flows and 3 explosive surtseyan style phreatomagmatic eruptions initiating at some point along st paul s insular shelf given the relatively restricted range in volcanic phenomena on st paul the most significant question regarding volcano hazard and risk assessment is whether future eruptions will be confined to the same region on the island as the most recent activity if future activity follows the recent past resulting volcano hazards will most likely be located at inland areas sufficiently far from habitation that they will pose little threat to life or property an important caveat however is that st paul is constructed almost entirely from the products of volcanic eruptions with vents located all over the island thus a new vent could form at any place on the island including st paul s insular shelf and areas farther offshore because of the remote location of st paul in the storm lashed bering sea risks related to volcano hazards may be greater than they would be in a different setting where more stable meteorological conditions prevail and access by monitoring and relief groups is less challenging

quantification of spatial gradation of slope positions transition between slope positions e g ridge shoulder slope back slope foot slope and valley is often gradual quantification of spatial transitions or spatial gradations between slope positions can increase the accuracy of terrain parameterization for geographical or ecological modeling especially for digital soil mapping at a fine scale current models for characterizing the spatial gradation of slope positions based on a gridded dem either focus solely on the parameter space or depend on too many rules defined by topographic attributes which makes such approaches impractical the typical locations of a slope position contain the characteristics of the slope position in both parameter space and spatial context thus the spatial gradation of slope positions can be quantified by comparing terrain characteristics spatial and parametrical of given locations to those at typical locations based on this idea this paper proposes an approach to quantifying the spatial gradation of slope positions by using typical locations as prototypes this approach includes two parts the first is to extract the typical locations of each slope position and treat them as the prototypes of this position and the second is to compute the similarity between a given location and the prototypes based on both local topographic attributes and spatial context the new approach characterizes slope position gradation in both the attribute domain i e parameter space and the spatial domain i e geographic space in an easy and practicable way applications show that the new approach can quantitatively describe spatial gradations among a set of slope positions comparison of spatial gradation of a horizon sand percentages with the quantified spatial gradation of slope positions indicates that the latter reflects slope processes confirming the effectiveness of the approach the comparison of a soil subgroup map of the study area with the maximum similarity map derived from the approach also suggests that the quantified spatial gradation of slope position can be used to aid geographical modeling such as digital soil mapping c 2009 elsevier b v all rights reserved

freshwater carbonates within a late triassic siliciclastic fluvial system in a gondwana rift basin the maleri formation india abstract spring related carbonates are valuable repositories for information on physical and biotic environments of the past however for mesozoic and earlier records their use is limited due to their low preservation potential and difficulties in accurate identification of the carbonate type this study aims to characterise the source of carbonate clasts preserved as thin beds of cross bedded grainstones in late triassic siliciclastic fluvial deposits the maleri formation pranhita godavari rift basin india the microfabric and stable isotopic compositions of the grainstones and thin and discontinuous beds of impure limestones of this formation are presented here these features help in identifying the freshwater carbonate precipitating environments that existed in an ancient continental rift basin though such deposits are not primarily preserved in this case the microfabric of the carbonate grains provides evidence for carbonate precipitation in aquatic environment related to karstic springs taking together the microfabric stable isotopic compositions as well as the associated geological and palaeontological information it could be shown that the calcium carbonate precipitation took place in palustrine pools related to tufa like spring systems and in alluvial swamps under a pluvial climatic setting this research thus demonstrates that carbonate grains derived from spring related carbonate deposits formed mainly near the margins of rift basins can be incorporated into nearby siliciclastics if interpreted correctly they can be used in reconstructing ancient karstic carbonate environments even when in situ primary record is not preserved therefore making it possible to access the information stored in freshwater carbonates

landform classification and soil distribution in hummocky terrain saskatchewan canada this study presents a classification of distinct three dimensional landform elements and examines the relationship between these landform elements and selected soil morphological properties of udic boroll soils in southern saskatchewan canada the classification is based on defined ranges of three criteria derived from topographic data gradient profile downslope curvature and plan across slope curvature seven landform elements are recognized convergent shoulders divergent shoulders convergent backslopes divergent backslopes convergent footslopes divergent footslopes and level elements all of the elements are easily identified in the field the thicknesses of a horizons and depths to calcium carbonate of the soils were consistently greater in convergent versus divergent elements in the same profile group e g shoulders and showed an overall increase in the sequence shoulders backslopes level footslope elements distinct groups of elements emerge from a statistical analysis of the differences between individual and bivariate means of soil morphological properties associated with each landform element the differences in soil properties among the elements can be largely explained by differences in water movement and distribution in hillslope systems the results of the study highlight the need to consider land surface morphology during the development of research designs for soil related studies

sedimentation and recent history of a freshwater wetland in a semi arid environment loboi swamp kenya east africa loboi swamp is a 1ae 5k m 2 freshwater wetland situated near the equator in the kenya rift valley the climate is semi arid precipitation is 700 mm year 1 and evapotranspiration is 2500 mm year 1 some of the wetland water is currently used for irrigation an interdisciplinary study was conducted on the geology hydrology pedology and biology of the wetland to determine its origin and history and to assess its longevity under present hydrological conditions sedimentary records from two piston cores 1ae8 and 4 m long indicate that the present wetland developed during the late holocene on a lowrelief alluvial plain floodplain deposits sandy silts are capped with wetland sediments organic rich clay and peat which began to form at 700 bp the swamp is dominated by typha domingensis pers 80 and floating cyperus papyrus l 20 it is fed by warm springs t 35 c ph 6ae4 6ae9 emanating from grid faults of the rift floor water compositions suggest that sources are dominated by shallow meteoric water with little contribution from deeper geothermal fluids siderite concretions in the floodplain silts reflect the fe reducing conditions that developed as the surface became submerged beneath the water table the pollen record captured both local and more regional vegetation showing the prevailing dry rift valley climate despite development of the wetter conditions on the valley floor the diatom record also suggests a dramatic change in local hydrology the combined biological records of this semi arid wetland indicate an abrupt change to wetter conditions most probably as a result of a regional change in climate rift tectonics provided accommodation space maintained the wetland at or below the water table and enabled spring recharge the size of the modern wetland has been reduced by about 60 since 1969 which suggests that the system may now be under hydrological stress due to anthropogenic impacts from land use change

palaeoenvironmental reconstruction of the late cretaceous sânpetru formation haţeg basin romania using paleosols and implications for the disappearance of dinosaurs abstract paleosols of the late cretaceous s npetru formation ha eg basin romania are the subject of macroscopic microscopic and geochemical investigation in order to reconstruct the palaeoenvironmental and palaeoclimatic conditions in which dinosaurs lived study of overbank deposits present in an 860 m thick stratigraphic interval of the s npetru formation exposed along the sibisel valley reveals the presence of one facies and five different pedotypes 1 finely laminated gray green mudstones and siltstones interpreted as pond deposits 2 bioturbated gray green mudstones lacking macroscopic pedogenic features interpreted as very poorly developed hydromorphic paleosols 3 bioturbated gray green mudstones containing carbonate concretions interpreted as poorly developed hydromorphic paleosols 4 mottled gray green mudstones containing carbonate concretions and limited illuvial clay accumulation interpreted as moderately developed paleosols characterized by a high but fluctuating watertable 5 bioturbated brown red mudstones lacking macroscopic pedogenic features other than the occasional mottles interpreted as poorly developed paleosols that formed on the higher and better drained floodplains and 6 bioturbated brown red mudstones containing carbonate nodules interpreted as moderately developed calcareous paleosols that formed on distal floodplain settings although limited exposure prevents the documentation of lateral relationships of pedotypes the presence of paleosol profiles that display characteristics of two different pedotypes suggests that they represent a lateral continuum on the landscape related to local differences in hydrology and relief i e catena the pedotype assemblage reveals that the s npetru landscape was a mosaic of wetlands seasonal wetlands and better drained floodplain habitats similar to the present day indogangetic plains pedogenic features and paleosol geochemistry indicate that the maastrichtian climate of romania was subhumid the distribution of pedotypes through the s npetru formation reveals small and large scale palaeoenvironmental changes associated with the shifting of a complex mosaic of wet and dry habitats in response to shifts in river position on the alluvial plain however a major palaeoenvironmental change occurs in the upper s npetru formation where the region was transformed into extensive wetlands such dramatic changes coincide with river competence increase change in palaeocurrent directions and dearth of macrovertebrate remains which had been previously misinterpreted as evidence for the disappearance of dinosaurs at the cretaceous tertiary boundary these palaeoenvironmental changes induced by tectonism are responsible for the shift from preservation of macrofossils concentrated by hydraulic processes into conspicuous lenticular bonebeds in the lower s npetru formation to preservation of microfossil and more rarely macrofossil remains in hydromorphic calcareous paleosols in the upper s npetru formation the consequences of palaeoenvironmental changes on vertebrate preservation mode must be considered in the search for fossils and interpretation of the fossil record

sedimentology and stable isotopes from a lacustrine to palustrine limestone deposited in an arid setting climatic and tectonic factors miocene pliocene opache formation atacama desert chile abstract field relations petrography gis and geochemistry of a late miocene pliocene limestone the opache formation calama basin atacama desert chile shows that depositional facies diagenetic histories and isotopes differ from eastern to western parts of the basin we recognize two facies lacustrine characterized by ostracod diatom mudstone and wackestone and palustrine characterized by both shallow water and pedogenic features gis analysis of the basin topography reveals an intrabasinal low in the eastern area and steeper hydrological gradients to the west with the calama constriction restricting flow between east and west petrography and geochemical results confirm that the calama constriction influenced depositional parameters ponding groundwater to the east forming a shallow lake and creating palustrine conditions to the west our analyses indicate that lake waters were less enriched in 13c or 18o than palustrine waters even though petrologic studies show that the lacustrine carbonates have a complex diagenetic history derived from groundwater rich in dissolved minerals this seemingly contrary observation can be reconciled if an important source of water for the western carbonates was sourced from the pacific ocean and was less evolved whereas eastern limestones precipitated from water which had become depleted in 18o during transport from the east today moisture from the pacific very rarely if ever reaches inland as far as calama indicating that during the late miocene mid pliocene breakdown in the temperature inversion due to weakened or absent upwelling in the cold coastal pacific current allowed moisture from the pacific to reach inland this changing atmospheric circulation pattern may have also affected upper level airflow that today blocks eastern sourced moisture from crossing the andes allowing it to reach farther westward into the atacama region during the late miocene pliocene together these moisture sources were sufficient to produce carbonate rich palustrine and lacustrine environments in the calama basin

chemical sedimentology and paleoenvironmental history of lake olduvai a pliocene lake in northern tanzania lake olduvai was a saline highly alkaline closed basin lake in which lacustrine sediments of bed i and lower bed ii of olduvai gorge were deposited between ca 1 92 and 1 70 ma the lake consisted of a lacustrine area the central basin cb surrounded by lake margin terrain that was alternately flooded and dried the lacustrine deposits consist largely of authigenic clay and carbonate minerals zeolites k feldspar chert and pyrite claystones of the cb and most of the eastern lake margin elm terrain consist chiefly of mg rich authigenic illite smectite and interlayered illite smectite i s these clays were formed penecontemporaneously with detrital clay deposition by interaction of the detrital clays with the saline highly alkaline water the lake olduvai clays average 65 70 mg 2 sio 2 and alkali ions from lake water and the remaining 30 35 is detrital clay lacustrine clays of the elm indicate that this area was flooded by saline water for substantial periods of time hominids occupied the elm at times of lower lake levels when the clays were dried calcite is the most abundant carbonate mineral and occurs chiefly as sand size euhedral crystals dispersed in claystone and less commonly as calcite crystal limestones and nodules the sand size calcite crystals were formed diagenetically at shallow depths possibly from a gaylussite and or micritic calcium carbonate precursor dolomite occurs chiefly in the form of dolostones some of which are probably of replacement origin the oxygen isotope composition of lake water and pore fluid of the cb varied over 11 as determined from calculated delta 18 o h 2 o values of authigenic minerals clay minerals were formed chiefly in the more saline waters sand size calcite crystals were generated mostly from less saline pore fluids and limestone nodules were formed chiefly from dilute pore fluid dolostones were formed from fluids of varying salinity hydrogeology of the central basin was complex and postdepositional fluid movements are documented by differing delta 18 o h 2 o values for different authigenic minerals of the same samples pore fluids moved within the lake deposits for a considerable period of time after deposition as shown by 18 o values of quartz and k feldspar formed at different times downward flow of lacustrine fluids is indicated by zeolitic alteration of the underlying tuffaceous alluvial deposits lake olduvai became overall shallower during the deposition of bed i and the subaerial exposure increased leading to occasional playa conditions these changes very likely resulted from increasing aridity and tectonic activity the lake that deposited lower bed ii was larger than that responsible for upper bed i and episodes of wetter climate alternated with drier periods in which salinity and probably temperatures were higher than in the bed i lake

orientated plant fragments revealing tidal palaeocurrents in the fumanya mudflat maastrichtian southern pyrenees insights in palaeogeographic reconstructions abstract leafy axis fragments of frenelopsis sp leaves of sabalites longirhachis unger kvacek et herman and logs are common in the maastrichtian of the basal tremp formation in the vallcebre syncline southern pyrenees the largest plant remains i e leaves of s longirhachis and logs appear scattered and randomly orientated whereas the smallest plant remains i e frenelopsis sp are aligned in a clear east west trend this orientation based on 117 measurements is consistent with the basin palaeogeography which was an e w elongated foreland trough that confined tidal palaeoflow and deposits such as tidal bores in the absence of usual sedimentary indicators e g tractive structures and base marks the accurate study of fossil plant orientations can largely assist palaeoflow determinations in palaeogeographic reconstruction

the flk zinj paleolandscape reconstruction of a 1 84 ma wooded habitat in the flk zinj amk ptk ds archaeological complex middle bed i olduvai gorge tanzania abstract we have analyzed the phytolith content of 37 samples from the paleosol capped by tuff ic dated 1 84 ma within middle bed i at olduvai gorge tanzania samples were obtained from different trenches sampling an area of about 25 ha to document the paleovegetation associated with the abundant faunal remains and hominin artifacts in flk amk ptk and ds sites the analysis reveals the abundance of globular granulate and forest indicator phytoliths from 3 to 86 relative to the total number of phytoliths in the assemblages attributed to woody plants and of short cell grass phytoliths up to 22 the presence of palm phytoliths up to 57 attests for meso haline soils in the area in agreement with the presence of the saline alkaline olduvai paleolake and one or more groundwater discharge areas freshwater springs and or wetland phytoliths provide botanical evidence for a mixed paleovegetation dominated by forest and woodland with patches of open spaces occupied by grasses prior to the deposition of tuff ic the presence of fern phytoliths in some assemblages suggest shaded and humid habitat which supports the presence of freshwater watercourses or springs that might have attracted hominins and other animals yet we have found that our phytolith extractions residues also include micrometric zeolites chabazite clinoptilolite phillipsite which attest that the phytolith signal in the zinj paleosols is certainly affected by dissolution this study completes the spatial analysis of the area and reveals that the wooded area extends north south and west of flk zinj with palm trees preferentially located in the periphery like the zinj amk and ds sites the phytolith inferred distribution of plants does not support the hypothesis that topography was influential in the location of these sites particularly given that trees and or shrubs were dominant all over rather it is the presence of freshwater ponds that seem to have been the attractive factor for hominins at this particular place and time

lava flow volume and morphology from digitised contour maps a case study at mount etna sicily abstract the volume and morphology of a lava flow field can be measured by mapping and comparing the topography before and after lava emplacement contour maps are a widely available source of topographic data containing a record of the geomorphological changes at volcanoes due to lava emplacement this paper explores the use of 1 25 000 scale digitised contour maps for mapping two lava flows of diverse eruption history and morphology at mount etna sicily we find that subtracting dems created from these maps gives a good representation of volume and shape for thicker lava flows 10 m mean thickness in the case of the 1983 lava flow however thinner

facies model of a semiarid freshwater wetland olduvai gorge tanzania the sedimentology and stratigraphy of a freshwater wet land in early pleistocene 1 75 ma volcaniclastic deposits olduvai gorge tanzania are characterized using texture mineralogy micro fossils and stratigraphic description to create a depositional facies model the freshwater wetland was located on the margin of a semi arid closed basin containing a playa lake the lake margin deposits are dominated by two distinct lithologies waxy claystones and earthy sediments waxy sediments are olive green dense claystones that con tain authigenic minerals such as trona and represent a fluctuating saline alkaline lake hay 1976 earthy sediments are beige friable siltstones that contain siliceous microfossils bone fragments and minor pebbles they represent the freshwater wetland microfossils from the earthy sediments and diatomites indicate freshwater marsh biota with some rare salt tolerant species associated lithofacies are diatomite carbonate and sandstone interpretation of vertical and lateral lithofacies variations in the 2 km 2 wetland based on 50 excavations identified seven distinct sub environments spring deposits perennial marsh pool ephemeral wet land fringing wetland wetland channel and ephemeral stream the stratigraphic sequence estimated to represent an 40 50 kyr long interval indicates that persistent 10 3 yr wet periods prevailed dur ing the deposition of thick waxy clays when the lake expanded and flooded the wetlands and equally long intervening dry periods caused the lake to contract allowing the flourishing of wetlands and accretion of earthy sediment the lithofacies associations in the olduvai paleo wetland provides an important first step in the development of a de positional environmental model for freshwater wetlands that can be tested elsewhere particularly in arid and semiarid settings

mixed geothermal and shallow meteoric origin of opal and calcite beds in pliocene lower pleistocene axial fluvial strata southern rio grande rift rincon hills new mexico u s a abstract exposed in upper pliocene fluvial strata in the eastern rincon hills and adjacent jornada del muerto basin southern rio grande rift new mexico usa are five laterally continuous beds 0 2 to 1 0 m thick of opal ct which straddle the east rincon hills normal fault four of these opal beds change basinward over 1 km or less to white friable lithofeldspathic sand with opal glaebules and then to microcrystalline calcite the opal and calcite generally replaced fine sand at shallow depths although two beds locally precipitated from standing water 87sr 86sr values 0 71301 to 0 71724 of the opal beds are consistent with precipitation from an advecting high temperature geothermal fluid that flowed through bedrock and or from a high temperature geothermal fluid derived from a deep crustal source carbon and oxygen isotopic values 13cpdb 7 1 to 0 6 18opdb 9 1 to 5 6 of the calcite beds lie between and overlap those of paleozoic carbonate and pliocene paleosol calcite suggesting precipitation from a mixture of a high temperature geothermal fluid that interacted with paleozoic carbonates and shallow meteoric groundwater for which paleosol calcite is a proxy the geothermal fluids are interpreted to have upwelled along the east rincon hills fault flowed laterally at or just below the surface and precipitated opal in response to rapid cooling and evaporation downflow precipitation of opal glaebules occurred as a result of decreasing silica concentrations and perhaps by mixing with shallow meteoric groundwater from which calcite precipitated probably by co2 degassing

desert wetlands in the geologic record abstract desert wetlands support flora and fauna in a variety of hydrologic settings including seeps springs marshes wet meadows ponds and spring pools over time eolian alluvial and fluvial sediments become trapped in these settings by a combination of wet ground conditions and dense plant cover the result is a unique combination of clastic sediments chemical precipitates and organic matter that is preserved in the geologic record as ground water discharge gwd deposits gwd deposits contain information on the timing and magnitude of past changes in water table levels and therefore are a potential source of paleohydrologic and paleoclimatic information in addition they can be important archeological and paleontological archives because desert wetlands provide reliable sources of fresh water and thus act as focal points for human and faunal activities in some of the world s harshest and driest lands here we review some of the physical sedimentological and geochemical characteristics common to gwd deposits and provide a contextual framework that researchers can use to identify and interpret geologic deposits associated with desert wetlands we discuss several lines of evidence used to differentiate gwd deposits from lake deposits they are commonly confused and examine how various types of microbiota and depositional facies aid in reconstructing past environmental and hydrologic conditions we also review how late quaternary gwd deposits are dated as well as methods used to investigate desert wetlands deeper in geologic time we end by evaluating the strengths and limitations of hydrologic and climatic records derived from gwd deposits and suggest several avenues of potential future research to further develop and utilize these unique and complex systems

freshwater limestone in an arid rift basin a goldilocks effect abstract the olduvai basin 3 s situated just west of the east african rift system in northern tanzania contains a two million year record of paleoclimate and paleoenvironmental change as well as a rich archive of vertebrate paleontology including hominins milankovitch precession cycles 20 kyr regulate the mean annual precipitation 250 700 mm yr and the 2500 mm yr evapotranspiration results in a negative hydrologic balance despite persistent aridity extensive deposits of freshwater limestone punctuate the stratigraphic record between 2 and 1 ma lake olduvai occupied the basin and its sediments are a proxy for climate driven cycles three limestones 1 84 1 80 and 1 36 ma in age which formed within lake margin floodplains adjacent to the lake were studied to determine their depositional environment using field relations sedimentary structures fossils petrography and stable isotope and major element geochemistry the three limestones are similar in that they contain peloidal micrite siliciclastic detrital grains and rhizoconcretions abundant faunal remains gastropods ostracods charaphytes and fish indicate that ponded water was relatively fresh and alkaline geochemical and stable isotope data indicate two types of groundwater sourced carbonate producing waters a deeper sourced fluid that was enriched in iron and manganese due to extended water rock interactions and a shallower groundwater that traveled through alluvial fan deposits regional faults tapped the deeper groundwater producing carbonate at spring sites while seeps associated with basinward changes in alluvial fan slopes drew on shallower groundwater sources isotope compositions indicate that fault related waters experienced some evaporation as water moved away from the spring sites while compositions of the seep related carbonate remained relatively constant pedogenic alteration and meteoric calcite cementation affected the carbonate when the spring and seep sites dried out secondary strontium rich dolomite precipitated within the limestones during burial under paleo lake olduvai sediments and fluids during periods of lake expansion integrating these data within the geological context of regional paleoclimatic and local environmental change indicates that the freshwater carbonates formed periodically when the conditions were just right i e a goldilocks effect carbonates near the basin center formed from groundwater flowing under a hydraulic head from faults or fractures during the falling limbs of milankovitch cycles when the lake was in recession carbonates near the basin margin formed from an increased rate of groundwater seepage that occurred only on the rising limbs of cycles in both contexts the continuous flow of groundwater with surface evaporation and co2 degassing optimizes the conditions for limestone formation in this arid environment these results help explain the formation of freshwater limestones in the rift basin link the carbonates to specific portions of milankovitch cycles and document that localized sources of potable water were present for use by hominins in olduvai gorge during an important period of human evolution

vegetation landscape at dk locality olduvai gorge tanzania abstract the olduvai gorge palaeoanthropological site in northern tanzania encompasses about two million years of earth history the sedimentary facies of palaeolake olduvai have been used to reconstruct lake transgressions and regressions up to total drying out interpreted to reflect wet dry climate cycles although multidisciplinary research has been conducted during the past decades to reconstruct the palaeoenvironments and palaeolandscapes of the gorge very few focused on the dk site located about 2 km farther east in the gorge we present here a vegetation study at dk for bed i the oldest stratum based upon the phytolith and diatom recovery of the basalt lava to tuff ib stratigraphic interval these results have been analysed in relation to the different facies in which they occur sandy diamictite sandstone sandy waxy claystone waxy claystone and sandy diatomite the phytolith results from diamictite samples indicate a similar vegetation composition during these more arid periods conversely waxy claystone and sandy waxy claystone samples show a higher diversity in the vegetation composition the diatoms were indicative of a fresh water pool environment thus the dk site would have provided plant foods for hominins such as fruits from trees and shrubs and starch rich rhizomes and tubers from sedges and reeds overall the results at dk site present a different vegetation landscape in comparison to previously published phytolith results from other olduvai stratigraphic levels and regions

late quaternary environmental changes in the upper las vegas valley nevada abstract five stratigraphic units and five soils of late pleistocene to holocene age crop out in dissected badlands on corn creek flat 30 km northwest of las vegas nevada and at tule springs nearer to las vegas the record is dominantly fluvial but contains evidence of several moister marsh forming periods the oldest unit b dates perhaps to the middle wisconsin and the more widespread unit d falls between 30 000 and 15 000 yr b p unit d therefore correlates with pluvial maximum lacustrine deposits elsewhere in the great basin standing water was not of sufficient depth or extent during either period to form lake strandlines between 14 000 and 7200 yr b p unit e standing surface water gradually decreased a trend also apparent in great basin pluvial lake chronologies during the same period groundwater carbonate cementation and burrowing by cicadas cicadae accompany the moist phase units after 7200 yr b p increased wind action decreased biotic activity and at least 25 m of water table lowering accompanied widespread erosion of older fine grained deposits based on pack rat midden and pollen evidence this coincides with major vegetation changes in the valley from sagebrush dominated steppe to lower mohave desertscrub

paleoenvironmental reconstruction of a paleosol catena the zinj archeological level olduvai gorge tanzania abstract paleosols record paleoclimatic processes in the earth s critical zone and are archives of ancient landscapes associated with archeological sites detailed field micromorphologic and bulk geochemical analysis of paleosols were conducted near four sites at olduvai gorge tanzania within the same stratigraphic horizon as the zinjanthropus paranthropus boisei archeological site paleosols are thin

laser 40ar39ar ages of tephra from indian ocean deep sea sediments tie points for the astronomical and geomagnetic polarity time scales tephra layers within deep sea sediment cores are valuable stratigraphic markers which can be radiometrically dated with high precision by the laser 40ar39ar technique two neogene ash layers from ocean drilling program odp site 758 have been dated these layers are located within detailed oxygen isotope and paleomagnetic stratigraphies which have previously been assigned ages based on the astronomically derived geomagnetic polarity time scale adgpts 7 10 28 we use the radiometric dates from the ash layers to independently evaluate the ages assigned to oxygen isotope stage 19 1 and the paleomagnetic reversals marking the brunhes matuyama boundary and the termination of the nunivak event ash d 20 21 yields an age of 800 20 ka which is consistent with an adgpts age of 780 ka for the overlying brunhes matuyama transition and with the astronomical age for oxygen isotope stage 19 1 ash i located near the top of the nunivak subchron bears evidence of excess 40ar an error weighted mean of five plateau ages gives an apparent age of 4 519 012 ma but an errorchron through a subset of the data suggests a possible eruption age of 4 43 03 ma the plateau age is in agreement with the adgpts 7 10 28 and the errorchron age is in agreement with the time scale of baksi 29 the laser 40ar39ar ages of both ashes are significantly older than the ages from the radiometrically derived time scale rdgpts of mankinen and dalrymple 3 which is primarily based upon a large dataset of k ar dated paleomagnetic poles it is essential to reconcile the adgpts with the rdgpts because radiometric age tie points are the best hope of extending the adgpts to times before 5 ma an analysis of the expected and actual variance for the astronomical and mankinen and dalrymple 3 time scales suggests that only a handful of low k ar ages may have biased the original gpts it is not necessary to invoke general systematic errors in the ar dating system to explain the discrepancies between the rdgpts and adgpts

evidence for fractionation of quaternary basalts on st paul island alaska with implications for the development of shallow magma chambers beneath bering sea volcanoes abstract st paul island is the youngest volcanic center in the bearing sea basalt province we have undertaken a field petrographic and geochemical study of select st paul volcanic rocks in order to better understand their differentiation specifically to test the hypothesis that magmas erupted from individual bering sea basaltic volcanoes are not related by shallow level processes such as crystal fractionation petrographically all of the st paul volcanic rocks are olivine plagioclase and clinopyroxene phyric textural features and modal contents of olivine phenocrysts however vary widely throughout the spectrum of basalt compositions although differing in size and abundance olivine phenocrysts in all rock compositions are euhedral and commonly skeletal suggesting rapid growth during ascent or eruptive quenching none however display reaction textures with surrounding groundmass liquid compositionally the st paul volcanic rocks are basalts and tephritic basalts and all have high contents of normative nepheline 8 to 16 concentrations of many major and incompatible trace elements display no clear correlations with bulk rock sio2 and mgo contents or modal abundances of phenocrysts suggesting that much of the compositional diversity of these magmas reflects variable mantle sources and degrees of partial melting similarly chondrite normalized ree patterns show variable degrees of light ree enrichment lan 70 90 that do not correlate with bulk rock mg numbers in contrast concentrations of compatible trace elements ni cr and co are positively correlated with mgo contents and modal percentages of olivine phenocrysts maximum forsterite contents of olivine phenocryst cores in most st paul rocks decrease with decreasing bulk rock mg number and are similar to the calculated equilibrium range this is evidence that the high mg numbers are magmatic and do not result from olivine accumulation instead major and compatible trace element mass balance calculations support derivation of the low mg number lavas from the high mg number lavas mainly by olivine fractionation which in turn implies that st paul magmas may have temporarily resided in crustal magma chambers prior to eruption

aquatic biomarkers record pleistocene environmental changes at paleolake olduvai tanzania abstract several hypotheses invoke climatic variability as a driving force for hominin evolution thus high resolution records of climate and environmental variability from anthropologically significant locations can help test these hypotheses sedimentary sequences recovered by the olduvai gorge coring project ogcp help evaluate climatic and environmental changes at olduvai gorge tanzania through the analyses of various biogeochemical proxies the stratigraphic sequence of ogcp core 2a can be correlated with horizons associated with hominins and is chronologically constrained by distinctive dated horizons such as the bed i basalt and tuff ib the lacustrine interval from 76 6 to 86 9 m depth is ideally suited for high resolution analyses of biogeochemical proxies as it is rich in organic carbon 1 toc the hydrogen isotopic composition of nc31 in this interval of ogcp core 2a records the effects of precession driven wet dry cycles on the terrestrial environment that led to alternations between woodland and grassland ecosystems comparable to those documented by previous investigations of outcrop analogues at olduvai here we examine stratigraphic variations in the abundance of biomarkers c28 steradienes c17 and c23 n alkanes c27 and c28 a norsteranes fern 8 ene and chromans derived from aquatic organisms algae cyanobacteria sponges macrophytes etc to determine the response of paleolake olduvai to climate variability in general these aquatic biomarkers reflect the productivity of the lake environment and exhibit the same precession driven wet dry cycles recorded by terrestrial biogeochemical signatures however they also provide evidence of abrupt

paleoclimatic and paleoenvironmental framework of flk north archaeological site olduvai gorge tanzania abstract the multi component flk north archaeological site was discovered over 50 years ago and its interpretation has been highly controversial since explanations of the dense bone and stone tool accumulation range from a site on a featureless lake margin that is dominantly anthropogenic in origin to a site near a freshwater wetland that is dominated by carnivore activity e g felids and hyenas flk north occurs stratigraphically between the ng eju tuff 1 818 0 006 ma and tuff if 1 803 0 002 ma and is composed of 9 distinct levels analysis of newly recovered fossil bones and artifacts has shown that the bones of large animals are largely the product of felid hunting and feeding behavior followed by hyena gnawing and breakage of some bones the expanded sample of felid prey remains is significant for understanding the contrasts between the mortality profiles of fossil assemblages produced by carnivores and those produced by hominins geologic mapping in the environs of the site has revealed rich sedimentological and paleoecological records and a thin but persistent tuff here named kidogo tuff that is 1 5 m below tuff if electron microprobe analyses of the tuff mineralogy revealed a unique geochemical fingerprint that permits its use for correlation of widely separated outcrops and facilitates the high resolution reconstruction of the landscape at the time of site formation the 9 archaeological levels comprise a relatively continuous record through a milankovitch precession cycle dry wet dry as the lake receded into the central basin during the dry part of the cycle surface water supplies dwindled and groundwater fed springs and wetlands became the dominant freshwater supply the flk north archaeological record essentially ended when level 1 was covered with 0 4 m of tuff if in a violent volcanic eruption of nearby mt olmoti however the overlying bed ii sediments contain scattered archaeological material and a freshwater carbonate deposit that is similar to those found associated with other bed ii archaeological sites e g vek hwk and hwke the recognition of the ecological association of springs wetlands and archaeological remains is a powerful predictive tool for locating new archaeological sites in this region that is known for hominin remains

40ar 39ar geochronology of flood basalts from the kerguelen archipelago southern indian ocean implications for cenozoic eruption rates of the kerguelen plume the 6500 km2 kerguelen archipelago formed on the northern kerguelen plateau nkp 4 105 km2 which is a shallow submarine plateau belonging to the kerguelen large igneous province in the southern indian ocean flood basalts make up 85 of the archipelago and are interpreted as the most recent volcanism 40 ma from the kerguelen hotspot which has erupted basalt for the last 115 million years based on 40ar 39ar incremental heating of acid leached groundmass separates we report isochron ages ranging from 29 26 0 87 ma to 24 53 0 29 ma for 15 basalts from five stratigraphic sections from diverse regions of the archipelago the oldest dated basalt from the archipelago 29 ma is much younger than the 40 ma age of conjunction between the hotspot and the southeast indian ridge basalt eruption seems to have ceased shortly after 24 ma although small volume highly evolved lavas and plutons continued to form in the archipelago the basalt age data suggest an average lava accumulation rate of 1 6 0 9 km my during the oligocene the archipelago s volumetric eruption rate 0 009 km3 yr is lower than estimates made for the cretaceous kerguelen plateau 1 7 km3 yr and the ninetyeast ridge hotspot track 0 18 km3 yr suggesting that the late cenozoic extrusive activity of the kerguelen plume is waning cenozoic volcanism attributed to the kerguelen plume occurs over a diffuse area with quaternary eruptions at heard and mcdonald islands and within the kerguelen archipelago the decreasing eruption rate and areally diffuse volcanism may be explained by the thick lithosphere of the cretaceous kerguelen plateau overriding and insulating the plume however if the undated nkp which underlies the archipelago formed during the cenozoic then the crustal production rate of the plume from 40 ma to the present 0 25 km3 yr would be similar to the crustal production rate 0 23 km3 my previously estimated for the formation of the ninetyeast ridge 82 38 ma

magma eruption rates constrained by 40ar 39ar chronology and gis for the ceboruco san pedro volcanic field western mexico 40ar 39ar geochronology is coupled with quantitative volume determinations utilizing field mapping digital elevation models orthophotos and geographic information system gis software to constrain magma eruption rates at the ceboruco san pedro volcanic field 1600 km2 in the western trans mexican arc ages are reported for 40 volcanic units including volcan ceboruco an active andesitic stratovolcano peripheral domes shields cinder cones and fissure fed flows after a hiatus of 3 m y volcanic activity recommenced to produce 80 5 3 5 km3 of magma at a rate of 63 m3 km2 per year over the past 0 8 m y however 75 of this volume erupted in the past 100 k y including the 51 2 5 km3 of volcan ceboruco equivalent to an eruption rate of 377 m3 km2 per year there have been at least two stages of cone building activity at volcan ceboruco the main edifice is composed of 38 km3 of precaldera andesites the youngest dated at 45 8 ka their eruption was followed by a hiatus interrupted by a plinian eruption at 1 ka the plinian eruption and subsequent lava flows are andesite to dacite in composition and constitute 13 km3 of the total volume of volcan ceboruco overall the relative proportions of lava types erupted in the past 0 8 m y are 18 19 basaltic andesite 56 60 andesite 18 22 dacite and 3 rhyolite the peripheral lavas are each of small volume geochemically diverse and show little evidence of prior storage in an upper crustal chamber the eruptive sequence proportions of lava types phenocryst assemblages textures and geochemistry imply that the lavas do not reflect the differentiation of a single parental liquid in a long lived magma chamber the distinct geochemical signatures were present prior to magma emplacement in the upper crust whereupon subsequent degassing and crystallization led to variable phenocryst abundances and assemblages

local variance for multi scale analysis in geomorphometry increasing availability of high resolution digital elevation models dems is leading to a paradigm shift regarding scale issues in geomorphometry prompting new solutions to cope with multi scale analysis and detection of characteristic scales we tested the suitability of the local variance lv method originally developed for image analysis for multi scale analysis in geomorphometry the method consists of 1 up scaling land surface parameters derived from a dem 2 calculating lv as the average standard deviation sd within a 3 3 moving window for each scale level 3 calculating the rate of change of lv roc lv from one level to another and 4 plotting values so obtained against scale levels we interpreted peaks in the roc lv graphs as markers of scale levels where cells or segments match types of pattern elements characterized by relatively equal degrees of homogeneity the proposed method has been applied to lidar dems in two test areas different in terms of roughness low relief and mountainous respectively for each test area scale levels for slope gradient plan and profile curvatures were produced at constant increments with either resampling cell based or image segmentation object based visual assessment revealed homogeneous areas that convincingly associate into patterns of land surface parameters well differentiated across scales we found that the lv method performed better on scale levels generated through segmentation as compared to up scaling through resampling the results indicate that coupling multi scale pattern analysis with delineation of morphometric primitives is possible this approach could be further used for developing hierarchical classifications of landform elements

siliceous islands in a carbonate sea modern and pleistocene spring fed wetlands in ngorongoro crater and oldupai gorge tanzania abstract a biogenic mechanism is proposed that produces a diagnostic geochemical signature of perennial spring fed wetlands in arid basins especially the saline and alkaline volcanic basins of east africa respiration by vegetation and decay of organic matter within marshes in ngorongoro crater tanzania locally increases aqueous equation the resulting lowered ph inhibits the precipitation of calcite and decreases the rate of silica dissolution steep geochemical gradients are produced these are represented mineralogically by siliceous biomineralization within the perennial marsh and carbonate precipitation in surrounding ephemeral wetlands mudflats and lacustrine environments as a test of this model of geochemical sedimentation the mineralogy of the early pleistocene siliceous earthy claystone of oldupai gorge is consistent with its interpretation as a paleo spring wetland deposit because such deposits are expressions of the paleo water table this approach has potential applications in many studies of basin paleohydrology paleoclimatology paleoecology and archaeology

the 40ar 39ar chronology and eruption rates of cenozoic volcanism in the eastern bering sea volcanic province alaska from the aleutian arc front to the arctic circle we estimate that about 750 km 3 of magma were erupted in the volcanic centers that we have studied all within the past 6 0 ma several discrete eruption episodes have been identified with the new 40 ar 39 ar data at circa 6 0 ma imuruk volcanic field circa 3 5 ma teller volcanic field circa 2 5 1 5 ma st george island circa 1 0 ma st lawrence island and the youngest activity which started at circa 0 7 ma and continued throughout region until historic times combining age information with volume estimates reveals that the intensity of volcanic activity in the bering sea volcanic province has increased through time with only about 15 of lava erupted before 3 ma and about 30 of all late cenozoic magma erupted within the last 500 ka eruption rates also increase toward more recent times from the 6 ma imuruk basalts which erupted at the rate of 70 15 m 3 km 2 yr 1 t o the 0 7 ma nunivak island and st michael volcanic field basalts which erupted at a rate of 165 25 m 3 km 2 yr 1 high volumes of erupted lava accompanied by high eruption rates for the youngest volcanic rocks suggest significant changes in the melting rates which are best explained by either an evolving tectonic regime or significant changes in the melting processes

orbital rhythms monsoons and playa lake response olduvai basin equatorial east africa ca 1 85 1 74 ma the lithostratigraphy at the pliocene pleistocene boundary exposed in olduvai gorge east africa was used to determine the duration and cause of climate variations wet dry periods the area has rich paleontological and archaeological records and the time interval is a critical period in human evolution five episodes of lake expansion and contraction can be interpreted from a stratigraphic interval defined by tuffs between ca 1 85 and 1 74 ma suggesting precession controlled cyclicity the geochronometry of the sequence was determined using the paleomagnetic record top of subchron cn2 1 785 ma the ages of two tuffs tuff ib and tuff if and sedimentation rates insolation w m 2 variations calculated as a function of eccentricity and precession predict five cycles of varying insolation 10 between 2 0 and 1 5 ma rainfall would have increased by one third between dry and wet portions of each 21 000 k y cycle this study represents the first dated terrestrial record at the pliocene pleistocene boundary with sufficient resolution to link lake cycles a climate proxy to astronomic forcing the wet dry climate pendulum may have been a factor in the natural selection processes of hominin evolution and the first wave of hominin migrations out of africa 1 8 ma

sedimentary geology and human origins a fresh look at olduvai gorge tanzania abstract recent field work at olduvai gorge tanzania using sedimentary geology in particular high resolution paleoenvironmental reconstruction and isotope geochemistry has revealed that freshwater was in proximity to a number of the rich fossil sites in beds i and ii 2 0 1 0 ma this paper presents the first geological evidence for springs associated with archaeological sites in this semiarid rift basin the springs appear to be limited to a small area within the basin and were likely connected to faults that acted as conduits for groundwater tufas associated with ten archaeological sites have stable isotope signatures occurring in a cluster bounded by 18o ratios from 6 to 1 and the 13c ratios from 5 to 2 the 18o values cluster around 4 that of precipitation in the region indicating a meteoric source the longevity of the spring record reflects a hydrologic system that apparently persisted for hundreds of thousands of years previous landscape reconstructions depicted the archaeological sites on the lake margin of paleo lake olduvai as an alkaline playa the discovery of springs at or near the archaeological sites provides fresh insights for interpreting hominin behavior during this key time in evolution with respect to procuring food water and materials for stone tools as well as hominin adaptation to climate change and paleoenvironmental change the idea that spring deposits may be in proximity to archaeological sites could lead to discovery of new sites at other hominin fossil localities in the east african rift system ears

wetland diagenesis and traces of early hominids olduvai gorge tanzania lateral variations in whole rock and clay geochemistry of basal bed ii claystones in olduvai gorge tanzania reflect water quality differences across the eastern lacustrine plain 1 75 myr ago bulk ba sr and na2o k2o mgo al2o3 range from 1 4 to 4 2 and from 0 7 to 1 4 respectively and indicate leaching of lacustrine claystones beneath freshwater wetlands at times following lake retreat bulk mgo al2o3 0 3 1 0 and molar mg al 0 5 3 9 ratios of 0 2 m clays reflect alteration of mg rich lacustrine clays these indicators point to freshest conditions near locality 43 of hay 1976 hwk east leakey 1971 moderate conditions to the east locality 40 mck and high salinity and alkalinity to the west localities 85 vek 45 flk clay geochemistry and artifact abundances are well correlated r 0 67 p 0 005 suggesting a relationship between paleo water quality and hominid paleoecology this pattern is consistent with predictions of greatest artifact discard loss around freshwater sources where scavanging opportunities were greatest for hominids this quantifies a relationship between artifact density distribution and a paleoecological proxy over landscape scales for the first time in early stone age archaeology in contrast fossil bone abundance is uncorrelated r 0 14 p 0 6 reflecting more complex taphonomic processes quantitative tests of landscape scale land use models are important for understanding early hominid behavior and its evolution

sedimentology of ancient coastal wetlands insights from a cretaceous multifaceted depositional system coastal wetlands are prominent modern environments widely studied in geomorphology and ecology but the term coastal wetland is still barely used for the sedimentological classification of ancient deposits the depositional system studied here leza formation cameros basin early cretaceous n spain includes diverse carbonate and clastic facies deposited at the sea land transition and is an illustrative example of the wide array of sedimentary environments that may occur in coastal wetlands systems the studied system was composed mainly of carbonate water bodies whose salinity ranged from fresh to brackish and near marine and which had variable input of clastic material due to their lateral connection with alluvial fans in addition the system also included carbonate water bodies with stronger marine influence tide influenced oolitic areas and relatively restricted evaporative settings the deposits of all these environments occur alternating with each other throughout a unit 30 280 m thick and they range from continental to marine conditions in a relatively small area approximately 10 km 3 30 km thus this sedimentological study of the leza fm provides an ideal opportunity to investigate challenging ancient deposits with both continental and marine features comparison with other modern and ancient coastal settings allows the conclusion that coastal wetland may be the most accurate sedimentological classification for the leza fm since it was not part of a major coastal system e g delta or estuary a series of general sedimentological characteristics of coastal wetland deposits are gathered from the cretaceous case study and from the modern and ancient examples examined these characteristics include predominance of shallow water facies common subaerial exposure and edaphic features great variety of interrelated continental transitional and marine environments with contrasting hydrodynamic and hydrochemical conditions and low diversity biotic communities including both continental and marine fossils as well as fossils of ambiguous affinities

potassium argon geochronology of a basalt andesite dacite arc system the mount adams volcanic field cascade range of southern washington high precision k ar dating and detailed mapping have established an eruptive chronology for a cascade stratovolcano and its surrounding array of coeval basaltic centers mount adams is a 200 km 3 andesitic cone that stands at the center of a coeval 1250 km 2 quaternary volcanic field that contains 60 discrete vents k ar ages were measured for 74 samples from 63 of the 136 volcanic units defined in the course of the mapping within analytical error there are no discrepancies between k ar ages and stratigraphic sequence major activity began in the area ca 940 ka and inception of the central stratovolcano took place at ca 520 ka a plot of cumulative volume erupted versus time shows that between 940 and 520 ka the eruptive rate was 3 k y and 80 of the products were basaltic andesites are volumetrically dominant and were emplaced in three main cone building episodes centered at 500 450 and 30 ka at eruptive rates of 1 6 5 km 3 k y at a lower rate of 0 05 0 1 km 3 k y the magmatic system remained almost continuously active between the main pulses although breaks in activity as long as 30 k y are permitted by the k ar data andesitic dacitic activity in the focal region and dominantly basaltic activity on the periphery have coexisted for 520 k y and their products are interstratified the last main episode of cone construction occurred ca 40 10 ka the oldest andesite identifiably derived from within the present day edifice having an age of 33 14 ka andesites forming the south summit rim and the true summit have ages of 13 8 ka and 15 8 ka respectively the time volume composition data bear upon several fundamental questions concerning the long term behavior of arc volcanoes stratovolcanoes commonly grow in spurts but can stay active between the widely spaced episodes of peak productivity large stratocone systems may remain active for half a million years subdivision of complex stratovolcanoes into eruptive or constructional stages without detailed mapping geochronology and compositional data should be treated skeptically discussion of volumetric eruptive rates can be misleading without an adequate time scale stratovolcanoes need never develop large upper crustal magma chambers basalt erupts peripherally but its ascent is suppressed beneath stratovolcanoes by deep crustal domains of magma storage and hybridization that form where concentrated injection of basalt amplifies crustal melting

east asia seismotectonics magmatism and mantle dynamics abstract in this article we review the significant recent results of geophysical studies and discuss their implications on seismotectonics magmatism and mantle dynamics in east asia high resolution geophysical imaging revealed structural heterogeneities in the source areas of large crustal earthquakes which may reflect magma and fluids that affected the rupture nucleation of large earthquakes in subduction zone regions the crustal fluids originate from the dehydration of the subducting slab magmatism in arc and back arc areas is caused by the corner flow in the mantle wedge and dehydration of the subducting slab the intraplate magmatism has different origins the continental volcanoes in northeast asia such as changbai and wudalianchi seem to be caused by the corner flow in the big mantle wedge bmw above the stagnant slab in the mantle transition zone and the deep dehydration of the stagnant slab as well the tengchong volcano in southwest china is possibly caused by a similar process in bmw above the subducting burma microplate or indian plate the hainan volcano in southernmost china seems to be a hotspot fed by a lower mantle plume associated with the pacific and philippine sea slabs deep subduction in the east and the indian slab s deep subduction in the west down to the lower mantle the occurrence of deep earthquakes under the japan sea and the east asia margin may be related to a metastable olivine wedge in the subducting pacific slab the stagnant slab finally collapses down to the bottom of the mantle which may trigger upwelling of hot mantle materials from the lower mantle to the shallow mantle beneath the subducting slabs and cause the slab plume interactions some of these issues such as the origin of intraplate magmatism are still controversial and so further detailed studies are needed from now

anthropocene and early human behavior when is the baseline for anthropocene the first indications of human impact on earth closely relate to early human behavior and use of resources first agricultural societies modified the landscap

automated segmentation of hillslope profiles across ridges and valleys using a digital elevation model abstract we developed a three step algorithm to automate the recognition and segmentation of hillslopes across ridges and valleys using a gridded digital elevation model dem the first step involves the delineation of a side slope profile by locating the lower and upper boundaries in the second step the cross profile pattern of a ridge or a valley floor which is defined and bounded by a pair of side slopes is examined in order to distinguish upland flats from ridges and lowlands from valley floors the width and gradient of these landform units are also measured in the third step a side slope profile is segmented into lower mid and upper slopes with a line simplification algorithm to identify changes and breaks in the slope in this step the footslope and crestslope can also be distinguished within the lower and upper slopes respectively using a 15 m dem this method was applied to five sites in low to high relief fluvial landscapes in japan the results showed good agreement 86 9 2 7 with manual slope segmentation indicating the effectiveness of our algorithm

3d s velocity model of the lithosphere asthenosphere system beneath the bering sea the 3d s velocity structure for the bering sea region is determined from dispersion analysis rayleigh waves from which the most conspicuous features of the crust and upper mantle from 0 to 400 km depth will be revealed in the depth range from 0 to 5 km this model shows the distribution of the sedimentary basins present in the study area in terms of s velocity for the bering shelf the s velocity values decrease southward indicating the presence of deep sedimentary basins in the southern bering shelf in the depth range from 5 to 30 km the s velocity model shows clearly the division of the bering sea basin in three sub basins the aleutian basin the bowers basin and the komandorsky basin produced by the bowers ridge and the shirshov ridge in this model the low s velocity pattern determined for the bering shelf confirms that its crust is similar to a continental type crust no an oceanic crust the moho map determined in the present study from the 3d s velocity model is the first moho map calculated for the bering sea region in this map the crust beneath the bering shelf shows thicker thickness than a typical oceanic crust from which is concluded that this crust must be considered as a transitional crustal structure in the depth range from 30 to 100 km the aleutian basin shows a pattern of high s velocity that can be correlated with the origin of this basin because this basin is considered as formed by the entrapment of a piece of pacific plate in the depth range from 45 to 60 km the low s velocity pattern shown for the eastern aleutian arc is associated to the active arc volcanoes present in this region from the s velocity model the asthenosphere beneath the study area is firstly determined from 100 to 180 km depth for the depth range from 80 to 400 km the high s velocity pattern determined for the eastern aleutian arc allows the modeling imaging of the subducting pacific slab in terms of s velocity this pattern of high s velocity is not visible beneath the western aleutian arc because the pacific plate is not subducting beneath the bering sea in the western aleutian arc

palaeovegetation changes recorded in palaeolake olduvai ogcp core 2a 2 09 2 12 ma naibor soit formation olduvai gorge tanzania abstract for five decades olduvai gorge has been a key site to reconstruct and understand the relationship between environmental and landscape conditions and use of affordances by early african hominin populations following the first olduvai gorge coring project ogcp during 2014 a multiproxy microbiological analysis which includes phytoliths pollen diatoms sponge spicules and chrysophyte cysts was undertaken on samples collected from various borehole cores the aim of the study is to better understand palaeoenvironmental and palaeovegetation conditions and changes through time and their relationship to hominin presence and evolution this study details the first palaeobotanical and palaeoenvironmental study of borehole 2a at olduvai gorge it represents the as yet oldest known sedimentary sequence in the olduvai basin for a portion of the pre bed i naibor soit formation this is a unit that is not accessible in any natural exposures in olduvai gorge and has only recently been encountered by drilling here we present the results from a particularly phytolith prone portion between 2 09 ma and 2 12 ma phytolith results indicate a savannah environment dominated by grasses where poaceae were a key component and where the c3 pooideae grasses were mostly dominant alternating with c4 grasses oscillations between grass subfamilies c3 pooideae c4 chloridoideae and c4 panicoideae to lesser degrees indicate five substantial climatic shifts varying between more humid and arid conditions associated with phytoliths freshwater indicators such as diatoms sponge spicules and chrysophyte cysts were also identified suggesting the presence of wetlands in the lake catchment area pollen is extremely rare in the sediments but when present comprises fungal spores and poaceae pollen thus supporting the wetland and grassland reconstructions respectively these results offer for the first time a whole picture of the palaeovegetation and associated palaeoenvironments for this pre bed i period together with previous results from other areas and chronological periods they improve our understanding of the evolution and adaptation of early hominins and their close relationship to the surrounding landscape

paleopedology and paleohydrology of a volcaniclastic paleosol interval implications for early pleistocene stratigraphy and paleoclimate record olduvai gorge tanzania abstract a cumulative red paleosol interval developed on volcaniclastic parent material under semiarid conditions in olduvai gorge tanzania it contains a complex history of pedogenesis that was affected by 1 episodic pyroclastic and debris fan processes and 2 episodic expansions and contractions of an adjacent alkaline lake and the associated fluctuations in the water table the paleosol interval is 130 320 cm thick represents 25 ka of the 50 kyr duration of lowermost bed ii and is defined by early pleistocene 1 75 ma tuffs if and iia the paleosol interval records a paleocatena related to both landscape and drainage the slope position on a pyroclastic fan relative to an alkaline lake the proximity to freshwater wetlands and the position of water table biogenic paleosol structures include grass and sedge root traces zeolite rhizocretions and soil fauna termite and ant traces abundant pedogenic features sensitive to soil moisture conditions including redoximorphic mottles in the paleosol matrix fe oxide glaebules grain and pore coatings illuviated clay grain and pore coatings and vadose siliciclastic and zeolite crystal silt record episodic water table fluctuations the geochemistry of whole rock samples distinguishes two parent materials early low ti zr weathered volcaniclastic sediment and late high ti zr tuffaceous sediment which represent two distinct pedogenic phases the lower paleosol developed at both sites whereas the upper paleosol developed only at the upslope site mass balance calculations indicate greater weathering higher eh and ph and greater zeolite precipitation at the upslope site than at the downslope site these relationships are compatible with the upslope site having had a lower overall water table and better drained conditions than the downslope site which had a higher water table and poorly drained conditions the lower paleosol provides evidence of a fluctuating water table consistent with a wetter climate followed by a prolonged arid period the upper paleosol began to form after a return to wetter conditions and ended under arid conditions the position of the olduvai subchron c2n 1 942 1 785 ma in bed i directly beneath the paleosol interval is used to make a tentative correlation at 1 75 ma with global climate dust records wet dry cycles

application of vertebrate trace fossils to palaeoenvironmental analysis abstract this is a review of the main uses of vertebrate trace fossils ichnofabrics and ichnofacies in the palaeoenvironmental analysis of sedimentary sequences the article accounts for the significant developments produced in the last three decades including the application of the ichnofacies concept to vertebrate trace fossils recognition of footprints in cross sectional view and their distinction from inorganic structures and burrow fills is first discussed the response of different substrates showing contrasting water content and imprinted by different animals or devices is compared in terms of the morphology of the resultant footprint trackways with sand crescents are typical of aeolian cross strata and are absent in associated flat lying to low angle deposits thick packages of highly bioturbated sandy dune and interdune sediments have been interpreted as reflecting periods of increased rainfall neoichnological observations in modern lake basins suggest that distinct zones can be recognized in the margins of fossil ponds and lakes including onshore shoreline and shallow subaqueous zones abundant flamingo like footprints and flamingo nest mounds are good indicators of alkaline and or saline lake waters hippopotamus trails are found closely associated with modern and fossil freshwater wetlands dinosaur and pterosaur swim traces from lacustrine and fluvial deposits can be used to estimate water depth turtle crocodile amphibian hippopotamus and fish swim traces allow one to infer a subaqueous substrate certain modern intertidal fish feeding traces are oriented with the predominant tidal current and can be used as palaeocurrent indicators the preferential orientation of tetrapod trackways in lacustrine and fluvial deposits is analyzed vertebrate trace fossils can help to infer discharge variability in fluvial channels the descriptions of vertebrate ichnofabrics are commonly limited to heavily bioturbated beds due to trampling by vertebrates and to a few examples of ichnofabrics with discrete trace fossils the nature and implications of the recognized vertebrate ichnofacies are still being debated and have a limited utility in palaeoenvironmental analysis the distinction of a potential vertebrate burrow ichnofacies in carbonate bearing palaeosols is proposed to represent well drained soils developed under arid or semiarid climate

wetland sedimentation and associated diatoms in the pleistocene olorgesailie basin southern kenya rift valley abstract the olorgesailie basin in the southern kenya rift valley contains a variety of lacustrine wetland and terrestrial facies that were laid down during the last 1 2 million years this study integrates diatom ichnofossil and rhizolith silica and carbonate evidence in order to identify and characterize shallow wetland deposition at the top member 14 ca 493 ka of the olorgesailie formation a key feature of these deposits is the presence of facies with aquatic indicators diatoms that are overprinted by ichnofossils and rhizoliths that suggest drier conditions diatom floras include several fresh water aulacoseira spp and saline indicators such as thalassiosira rudolfi t faurii cyclotella meneghiniana and anomoeoneis sphaerophora the main indicators of shallow fresh to mildly saline waters include epithemia argus rhopalodia gibberula encyonema muelleri and synedra spp three main suites of ichnofossils indicate varying water table depths during their formation these consist of 1 horizontal tunnels that suggest saturated substrates 2 vertical burrows formed in substrates with relatively lower water tables and 3 termite hymenopteran and beetle ichnofossils that indicate dry substrates member 14 of the olorgesailie formation also contains carbonate and siliceous rhizoliths which occur both together and separately four possible models are suggested to explain the silica and carbonate rhizolith formation 1 a complex of spring fed marshes and dry areas 2 ephemeral wetlands and floodplains 3 wetlands with abundant organic decay and 4 initial carbonate rhizoliths that were replaced by silica preservation of cellular structures and the reworking and incorporation of rhizoliths in overlying younger strata suggest that they formed early during diagenesis

basaltic volcanism in the bering sea geochronology and volcanic evolution of st paul island pribilof islands alaska abstract the evolution of a pleistocene to holocene basaltic volcanic field in the back arc region of the aleutian subduction system is investigated at st paul island alaska one of the youngest eruptive centers in the bering sea basalt province new 40ar 39ar and 14c age determinations indicate that subaerial volcanic activity forming the island began as early as 540 ka and has continued nearly to the present the youngest eruption occurred approximately 3230 years bp magmas erupted on st paul are basaltic with mgo contents ranging from 14 to 4 wt and phenocryst assemblages of olivine clinopyroxene plagioclase all are alkalic the surface of st paul is composed mainly of numerous tephra cones surrounded by coalescing low viscosity pahoehoe lava flows a central highland spans the island from east to west and is constructed of relatively young eruptive centers where rocks show a minimum of weathering and little deformation by faulting in contrast older lava flows forming the wave eroded base of the island are gently to moderately tilted and faulted geochronologic stratigraphic and geochemical data indicate that eruptive styles on st paul evolved from early mostly effusive eruptions of chemically little evolved lavas that form the base of the island to more explosive monogenetic scoria cones to polygenetic centers forming shields by repeated effusive eruptions of evolved low viscosity lavas localization of the monogenetic and polygenetic centers appears to be related to east west and northeast southwest trending fault and fissure systems with polygenetic centers located at intersections of major structures the combined volcanic and compositional changes on st paul island suggest that the magmatic system as a whole may be trending toward eruption of more evolved magmas related to the progressive development of crustal magma chambers in which crystal fractionation and magmatic differentiation are occurring

tufa as a record of perennial fresh water in a semi arid rift basin kapthurin formation kenya lithological and biological features of a fossiliferous tufa in the kapthurin formation baringo kenya reveal the presence of a lush wetland in a semiarid environment during the middle pleistocene ca 500 ka in this portion of the east african rift valley four geological sections each between 3 m and 8 m in thickness exposed over a distance of 0ae5 km reveal a 1 to 2 m thick paludal tufa which is composed of three carbonate beds two dark grey silty claystones and a reddish brown silty palaeosol high resolution stratigraphic analysis carbonate petrography stable isotope and elemental geochemistry clay mineralogy and fossil remains molluscs ostracods diatoms and charophytes reveal a ground water fed system that fluctuated in depth and periodically disappeared altogether oxygen isotope ratios d 18 o of tufa matrix range from 4ae5 to 8ae0 vienna pee dee belemnite and become more positive up section indicating the decreasing influence of fault related fluids and increasing residence time or freshness of wetland water rather than evaporative enrichment this spring was situated on a lake margin during low lake levels thrived during periods of increased ground water input and was ultimately replaced by an alkaline lake the wetland would appear to have existed during a cool interval within the generally warm marine isotope stage 13 or perhaps during the warm second half of marine isotope stage 13 the ground water source of this wetland arose through a fault system thus the position of the tufa deposit is controlled structurally but the timing and duration of the wetland system may have been influenced by both climatic and tectonic factors

paleoenvironmental and paleoecological reconstruction of a freshwater oasis in savannah grassland at flk north olduvai gorge tanzania the records of early hominins are commonly localized both temporally and spatially even in archaeologically rich basins like olduvai gorge tanzania the flk north site was discovered in 1960 but the reason for the exact location of this dense concentration of fossils and stone tools on a lake margin flat has not been explained we present new geological and geochemical information from six excavations in upper bed i which revealed up to 1 4 m thick carbonate deposits attesting to the presence of freshwater springs in the area surrounding flk north the 18o signatures of the tufa are typical for meteoric water that has evolved during evaporation tuff if that caps the sequence was deposited on uneven topography with the highest area a low relief ridge between two faults at the archaeological site and lowest areas being sites of groundwater discharge the model proposed here is that rainfall on adjacent highlands was transported to the basin where faults acted as conduits for water similar hydrogeological settings at modern lakes manyara and eyasi currently support lush groundwater forest and woodland despite arid climate flk north may have been an oasis offering freshwater and shelter for consuming meat by both carnivores and hominins

thermochronologic constraints on late cretaceous to cenozoic exhumation of the bendeleben mountains seward peninsula alaska in the bendeleben mountains seward peninsula mid cretaceous granites are exposed in an uplifted block bounded on its south side by an e w striking normal fault the bendeleben fault has well preserved scarps 4 7 m in height that offset holocene moraines seismic activity young normal faulting and quaternary basaltic volcanism are all evidence of active extension south of the bendeleben fault there is a 3 4 km deep basin fifteen apatite u th he ages from granitic samples of the footwall yield an eocene weighted mean age of 41 3 4 8 ma biotite 40ar 39ar ages from the country rock of the bendeleben pluton are 81 83 ma in spite of the young fault scarps hefty and pecube thermal modeling results illustrate that rapid exhumation of the bendeleben mountains occurred in the late cretaceous eocene and slowed since the oligocene a weak age elevation relationship of apatite he ages and a lack of correlation between age and distance from the fault indicate that exhumation was accomplished with minimal block rotation on a steeply dipping long lived normal fault timing of extension in the seward peninsula can be correlated with deformation in the offshore hope basin where seismic reflection lines document early tertiary large magnitude normal faulting followed by minor post miocene reactivation the faulting observed in the bendeleben mountains is part of an extensional system that spans a large portion of the bering strait region the tectonic model proposed in previous studies suggests that clockwise rotation of the bering block relative to north america is the cause of extensional deformation in western alaska

a fuzzy logic slope form system for predictive soil mapping of a landscape scale area with strong relief conditions abstract we studied an improved slope form system using a fuzzy logic method to assess and map soil fertility of a mountain region in northern vietnam that has strong relief conditions the lack of good soil mapping techniques in vietnam has brought about insufficient soil information which often leads to false recommendations for land use and crop planning the reviewed literature describes soil mapping techniques using fuzzy logic method but all of them are applied for mapping areas that have gentle relief conditions that are unlikely to be applicable to the mountainous soils in our study area in this paper we introduce a detailed slope form system that significantly describes the complexity of terrain characteristics of the area to be mapped and provides more detail about the variability of the soil fertility of the area nine basic slopeforms were used to characterize for each of upper middle and foot slope positions making the list 27 slopeforms together with crest and valley the total unit number is 29 we investigated soils of the area and classified them into the major soil groups and calculated soil property indices for all of them we identified four major environmental parameters affecting soil formation and soil quality geology elevation slope inclination and land use the findings indicated that soil fertility differs at slope positions soils located at upper slope positions where agricultural activity only started recently are more fertile than those found at middle slope positions soils located at foot slope positions where eroded sediments accumulate also have high levels of fertility compared to those on the middle slope the improved slope form system then became an important additional environmental parameter for this soil mapping work at a same comparable category i e slope position geology soil group elevation slope gradient straight slopeforms are an indicator for better soil fertility compared to convex and concave forms although the findings could not specify soil fertility variability for all 29 slopeforms they did emphasize the major differences in soil fertility and soil formation based on three major forms of convex straight and concave with other factors taken into account such as slope inclination geology and elevation we expect our results to be used by scientists and local authorities in deriving more effective land use and crop options for land use management strategies for the northern vietnam s mountain regions

hominin use of springs and wetlands paleoclimate and archaeological records from olduvai gorge 1 79 1 74 ma abstract an interdisciplinary study of the geologic and archaeological records of a 50 ky year period at the plio pleistocene boundary in olduvai basin tanzania revealed that a small groundwater fed wetland was a consistent focus of hominin activity during periods of climate change wet dry cycles paleoenvironmental analysis of sedimentary records from 33 excavations in lowermost bed ii lmb ii olduvai gorge 3 s revealed evidence of significant climate fluctuations that produced two and one half lake cycles between 1 79 and 1 74 ma the region experienced wet dry cycles in response to combined astronomical forcing effects of eccentricity 100 ky cycle and precession of the equinox 19 and 23 ky cycles rhythmic variability of the monsoon system produced wet periods followed by a transition into dry periods followed by a transition back into wet climate a high resolution study of the stratigraphy documented a groundwater fed wetland complex 1 km2 that flourished during low lake levels dry periods and was drowned during high lake levels wet periods stratigraphic analysis temporal changes of 916 artifacts from 13 excavations selected from a landscape transect across alluvial fan spring wetland and lake margin environments showed no notable differences in artifact type frequency and raw material type when comparing wet periods as a group and dry periods as a group however a lateral shift of hominin activity on the landscape did occur between wet and dry periods the oldowan tool kit did not vary at spring sites between wet and dry periods whereas the tool kit did vary at other lake margin sites between wet and dry periods both analyses suggest that climate affected the location of an activity not type of activity these data suggest that oldowan hominins adapted their land use patterns to exploit spring wetland resources available during dry periods a switch from wet to dry conditions likely altered surface and groundwater systems affecting food and potable water availability forcing hominins to adjust their subsistence patterns

s wave velocity structure of the upper mantle beneath the arctic region from rayleigh wave dispersion data abstract a new model of the upper mantle structure of the arctic region based on a representative dataset of rayleigh wave group velocity dispersion curves from 10 to 250 s period is presented a surface wave tomography procedure is used to image the group velocity distributions local dispersion curves are constructed and inverted to vertical s wave velocity sections up to the depth of 500 km results are presented in two forms as horizontal slices of s wave velocity variations relative to the average velocities at several mantle depths and as 2d velocity sections along three profiles crossing different tectonic units the model shows lateral and vertical velocity variations over the whole depth range within the study area the most prominent velocity heterogeneities are localized in the uppermost mantle up to the 200 km depth in this depth range the velocity anomalies are strongly correlated with the main tectonic structures the calculated s wave velocity distribution demonstrates that the upper mantle of the continental shields is characterized by high s wave velocities and contains regional velocity anomalies associated with small scale blocks low mantle velocities are attributed to the areas with high level of tectonic and seismic activity significant difference in deep velocity structure of the marginal seas and deep water oceanic basins of various ages is revealed the obtained model suggests some insights into the geodynamical evolution of the lithosphere of the arctic region

object representations at multiple scales from digital elevation models in the last decade landform classification and mapping has developed as one of the most active areas of geomorphometry however translation from continuous models of elevation and its derivatives slope aspect and curvatures to landform divisions landforms and landform elements is filtered by two important concepts scale and object ontology although acknowledged as being important these two issues have received surprisingly little attention this contribution provides an overview and prospects of object representation from dems as a function of scale relationships between object delineation and classification or regionalization are explored in the context of differences between general and specific geomorphometry a review of scales issues in geomorphometry ranging from scale effects to scale optimization techniques is followed by an analysis of pros and cons of using cells and objects in dem analysis prospects for coupling multi scale analysis and object delineation are then discussed within this context we propose discrete geomorphometry as a possible approach between general and specific geomorphometry discrete geomorphometry would apply to and describe land surface divisions defined solely by the criteria of homogeneity in respect to a given land surface parameter or a combination of several parameters homogeneity in its turn should always be relative to scale

paleoenvironmental interpretation of lake margin deposits using δ13c and δ18o results from early pleistocene carbonate rhizoliths olduvai gorge tanzania isotope analyses of lake margin rhizoliths from paleo lake olduvai ca 1 75 ma form the basis of a new model proposed here for interpreting stable isotope values of phreatic rhizolith carbonates average 18o and 13c values from rhizoliths formed in transgressive lacustrine waxy claystones are relatively low low 18o averages 5 5 reflect meteoric water values consistent with increased precipitation during wet periods that would increase the outflow of fresh water from subsurface seeps and shift a brackish groundwater zone lakeward low 13c averages 4 1 could indicate little atmospheric exchange high plant decay and or increased groundwater low 13c flow higher averages in 18o 3 6 and 13c 2 0 occur during dry periods and lake regressions earthy claystones when hydraulic head is reduced the lake recedes and water within the wetlands is subjected to intense evaporation and gas exchange with the atmosphere the isotope ratios of the rhizoliths from lowermost bed ii change in response to groundwater hydrology on milankovitch time scales but the isotopes also provide evidence of shorter term decadal to centennial scale climate fluctuations the orbitally driven climate changes are recorded faithfully by lithologic variations and stable isotope patterns

fossil spring deposits in the southern great basin and their implications for changes in water table levels near yucca mountain nevada during quaternary time fossil spring deposits are common in the southern great basin and their distribution provides important constraints on the hydrologic response of the regional water table to climate change this information is crucial because the proposed high level nuclear waste repository at yucca mountain will be located 200 400 m above the modern water table water tables will rise in response to a future return to glacial climates but the magnitude of the change and the consequences for radionuclide travel times and overall repository integrity are key uncertainties increased recharge during past pluvial periods in the spring mountains and sheep range caused water tables to rise and ground water to discharge over broad expanses of the las vegas valley system and in nearby pahrump sandy and coyote springs valleys in contrast other valleys in the region contain only small areas of pleistocene discharge resulting from local damming of ground water by faults that cut valley alluvium in these instances which include the valley wells area and piute and northern coyote springs valleys smaller ranges such as the clark and new york mountains supplied the moisture the change in water table levels since the last full glacial period varies between and within valleys from as little as 10 m in several areas to 95 m in the coyote springs valley at yucca mountain the water table has probably changed by 115 m in response to climate change the spring deposits and the mollusk faunas found with them often misinterpreted as lacustrine in origin share many essential features with active spring systems in northeast nevada deposits associated with discharge mainly consist of pale brown silt and sand that is entrapped by dense stands of phreatophytes covering valley bottoms when water tables are high pale green mud containing a mix of aquatic semiaquatic and moist terrestrial mollusks accumulates in wet meadows and marshes associated directly with spring discharge the record in subbasins of the las vegas valley system is dominated by late wisconsin age sediments although pond sediments and alluvium belonging to at least one older pre wisconsin pluvial period are also locally exposed deposits from two even earlier episodes of spring discharge both of which also occurred during rancholabrean time 10 to 450 ka are exposed in the pahrump chicago piute and coyote springs valleys and in the valley wells the records from the pahrump and coyote springs valleys are especially well exposed and likely extend back to at least early pleistocene time

paleolandscape and paleoenvironmental interpretation of spring deposited sediments in dakhleh oasis western desert of egypt abstract iron rich sediments in dakhleh oasis western desert of egypt have been recognized as spring mounds and as archaeological sites where paleolithic materials have been recovered detailed sedimentologic investigation and mapping of these features reveal that spring mound sediments were deposited in a shallow vegetated wetland formed by the discharge of iron rich nubian aquifer waters along the southern margin of the oasis controlled largely by localized faulting and the variable paleotopography of the basin floor the spring sediments represent peri lacustrine or lake independent features and can be differentiated from fully lacustrine deposits on the basis of their sedimentary characteristics as well as the presence of goethite and jarosite in a region where authigenic deposition during pleistocene pluvial activity principally resulted in tufas and lacustrine marls spring mound formation incorporated sediment through the ponding of surface water aeolian entrapment by local vegetation and the formation of iron precipitates in a low energy oxidative and acidic environment that was not dependent upon surface water inputs into the dakhleh basin the potentially interpluvial nature of this water resource makes it an important sedimentary archive for archaeological investigations in the basin the dakhleh spring mounds record a unique groundwater controlled paleoenvironment providing the first evidence of a bog iron in egypt and one of the few occurrences of iron rich wetland remnants in the modern sahara

automated classification of landform elements using object based image analysis this paper presents an automated classification system of landform elements based on object oriented image analysis first several data layers are produced from digital terrain models dtm elevation profile curvature plan curvature and slope gradient second relatively homogenous objects are delineated at several levels through image segmentation these object primatives are classified as landform elements using a relative classification model built both on the surface shape and on the altitudinal position of objects so far slope aspect was not used in classification the classification has nine classes peaks and toe slopes defined by the altitudinal position or the degree of dominance steep slopes and flat gentle slopes defined by slope gradients shoulders and negative contacts defined by profile curvatures head slopes side slopes and nose slopes defined by plan curvatures classes are defined using flexible fuzzy membership functions results are visually analyzed by draping them over dtms specific fuzzy classification options were used to obtain an assessment of output accuracy two implementations of the methodology are compared using 1 romanian datasets and 2 berchtesgaden national park germany the methodology has proven to be reproducible readily adaptable for diverse landscapes and datasets and useful in respect to providing additional information for geomorphological and landscape studies a major advantage of this new methodology is its transferability given that it uses only relative values and relative positions to neighboring objects the methodology introduced in this paper can be used for almost any application where relationships between topographic features and other components of landscapes are to be assessed

soil landscape modelling using fuzzy c means clustering of attribute data derived from a digital elevation model dem this study explores the use of fuzzy c means clustering of attribute data derived from a digital elevation model to represent transition zones in the soil landscape the conventional geographic model used for soil landscape description is not able to properly deal with these fuzzy c means clustering was applied to a hillslope within a small drainage basin in southern spain cluster validity evaluation was based on the coefficient of determination of regressing topsoil clay data on membership grades the resulting clusters occupied spatially contiguous areas we found a high degree of association with measured topsoil clay data r a 2 0 68 for three clusters and a weighting exponent of 2 1 location of the clusters coincided with observable terrain characteristics therefore we concluded that the coefficient of determination of regressing soil sample data on membership grades efficiently supports deciding upon the optimum fuzzy c partition the study confirms that fuzzy c means clustering of terrain attribute data enhances conventional soil landscape modelling as it allows representation of fuzziness inherent to soil landscape units

late wisconsin groundwater discharge environments of the southwestern indian springs valley southern nevada abstract badland exposures in the indian springs valley southern nevada contain evidence of formerly widespread spring and seep discharge the stratigraphic position and appearance of most of these deposits suggests correlation with late wisconsin 30 000 to ca 10 000 yr b p marsh sediments in nearby las vegas valley previously all these deposits have been loosely described as lacustrine because of the presence of extensive green mudstones associated with aquatic mollusks however this association also typifies modern groundwater discharge environments in many basins of northeast nevada such as the steptoe valley basins often without hydrographic closure such analogs best explain the origin of late wisconsin fine grained deposits in the unclosed southwestern arm of the indian springs valley key features of these depositional systems are the lack of shoreline deposits the presence of a broad belt of subaerially deposited plae brown silts surrounding spring wet meadow and marsh deposits and the intermixture of terrestrial and aquatic mollusks in most horizons where mollusks occur

mapping recent lava flows at westdahl volcano alaska using radar and optical satellite imagery field mapping of young lava flows at aleutian volcanoes is logistically difficult and the utility of optical images from aircraft or satellites for this purpose is greatly reduced by persistent cloud cover these factors have hampered earlier estimates of the areas and volumes of three young lava flows at westdahl volcano including its most recent 1991 1992 flow we combined information from synthetic aperture radar sar images with multispectral landsat 7 data to differentiate the 1991 1992 flow from the 1964 flow and a pre 1964 flow and to calculate the flow areas 8 4 9 2 and 7 3 km 2 respectively by differencing a digital elevation model dem from the 1970 1980s with a dem from the shuttle radar topography mission srtm in february 2000 we estimated the average thickness of the 1991 1992 flow to be 13 m which reasonably agrees with field observations 5 10 m lava flow maps produced in this way can be used to facilitate field mapping and flow hazards assessment and to study magma supply dynamics and thus to anticipate future eruptive activity based on the recurrence interval of recent eruptions and the results of this study the next eruption at westdahl may occur before the end of this decade

topographic analyses of k lauea volcano hawai i from interferometric airborne radar we analyze digital topographic data collected in september 1993 over a 500 km2 portion of k lauea volcano hawai i by the c band 5 6 cm wavelength topographic synthetic aperture radar topsar airborne interferometric radar field surveys covering an 1 km2 area of the summit caldera and the distal end of an 8 m thick a flow indicate that the 10 m spatial resolution topsar data have a vertical accuracy of 1 2 m over a variety of volcanic surfaces after conversion to a common datum topsar data agree favorably with a digital elevation model dem produced by the u s geological survey usgs with the important exception of the region of the ongoing eruption which postdates the usgs dem this dem comparison gives us confidence that subtracting the usgs data from topsar data will produce a reasonable estimate of the erupted volume as of september 1993 this subtraction produces dense rock equivalent dre volumes of 392 439 and 90 106 m3 for the pu u k pa ianah and episode 50 53 stages of the eruption respectively these are 124 89 and 94 of the volumes calculated by staff of the hawaiian volcano observatory hvo but do not include lava of k pa ianah and episodes 50 53 that flowed into the ocean and are thus invisible to topsar accounting for this lava increases the topsar volumes to 124 159 and 129 of the hvo volumes including the 2 m uncertainty derived from the field surveys produces topsar derived volumes for the eruption as a whole that range between 81 and 125 of the usgs derived values the vesicularity and ocean corrected topsar volumes yield volumetric eruption rates of 4 5 4 5 and 2 7 m3 s for the three stages of the eruption which compare with hvo derived values of 3 6 2 8 and 2 1 m3 s respectively our analysis shows that care must be taken when vertically registering the topsar and usgs dems to a common datum because c band topsar penetrates only partially into thick forest and therefore produces a dem within the tree canopy whereas the usgs dem is adjusted for vegetation

vegetation of northern tanzania during the plio pleistocene a synthesis of the paleobotanical evidences from laetoli olduvai and peninj hominin sites abstract more than 40 years of scientific investigations of the hominin bearing plio pleistocene sediments of northern tanzania have provided a number of paleobotanical data which taken as a whole provide today a way to investigate vegetation changes between 4 and 1 ma at a time when our early ancestors emerged here i have integrated the data from all vegetation proxies obtained for the paleontological sites of laetoli olduvai and peninj i e macroscopic plant remains pollen and phytolith assemblages carbon and oxygen isotopic ratios measured on carbonates and organic biomarkers this important yet discontinuous botanical record suggests some similarities between past and present day vegetation at the regional scale afromontane forests with olea podocarpus juniperus hagenia abyssinica in the highlands and wooded grasslands with grasses and drought adapted acacia commiphora capparidaceae and chenopodiaceae and or amaranthaceae in the lowlands were present in the southern serengeti crater highlands region since 4 ma grasses of the c 4 photosynthetic type made their first appearance in the record at 3 7 ma i e during the mid pliocene 700 ky before major p co 2 and temperature decline c 4 grasses became dominant in the vegetation soon after 3 66 ma probably in response to reduced precipitation at 2 6 ma phytolith and isotope indicate grassland with abundant c 4 xerophytic grasses that document strong aridity during the intensification of northern hemisphere glaciation period 2 7 2 5 ma after 2 ma the detailed and diverse record at olduvai indicates complex vegetation patterns linked to oscillating precipitation varying lake levels and the presence of geological faults hence despite low basin averaged reconstructed paleo precipitation amounts of 250 700 mm y c 4 grasslands closed woodlands wetlands and palm groves co occurred on short spatial scales near saline lake olduvai freshwater wetlands and palm rich woodlands occurred in highly localized areas on the lake margins where aquifer barriers and or outcrops caused by geologic faults allowed groundwater discharge botanical evidence of paleo springs at laetoli olduvai and peninj includes the marked presence of typha cattail and hyphaene palm tree in association with acacia pollen grains and at olduvai abundant forest indicator phytoliths and organic and isotopic biomarkers at olduvai freshwater wetlands were most developed when lake level and fluvial competence where low i e during dry periods when wet dry climate variability was extreme in east africa 1 9 1 7 ma freshwater springs may therefore have offered a sustainable habitat i e refuge for several species including hominins and favored hominin and artifact concentration at these specific places particularly during environmentally stressful times

sediment geochemistry mineral precipitation and clay neoformation on the mkuze river floodplain south africa abstract the mkuze wetland system situated in northern kwazulu natal is south africa s largest freshwater wetland area and acts as a major sink for naturally occurring solutes within the landscape the mineralogy and geochemistry of 135 sediment samples from two transect sites on the mkuze river floodplain were investigated to identify processes involved in the control of solute concentrations results show that clastic sediment is dominated by silt and fine sand with clay mineralogy comprising primarily fe rich smectite smectite is concentrated within the lower zone of sediment profiles where it is believed to be neogenetic in origin smectite neoformation is typically associated with the precipitation of caco 3 and sio 2 which results from the evapotranspirative concentration of groundwater solutes evapotranspiration locally lowers water table elevation and plays an important role in controlling the geochemical behaviour of fe and mn seasonal water level fluctuations result in the accumulation of fe and mn oxyhydroxides which likely favours smectite neoformation the precipitation of minerals and immobilisation of solutes within the mkuze river floodplain sediments has important implications for the long term development of the geomorphology and ecology of the wetland system as it has potential to alter sediment properties groundwater composition salinity vegetation distribution and topographic relief