terminal classic drought in the northern maya lowlands inferred from multiple sediment cores in lake chichancanab mexico we present new density records from sediment cores taken along a depth transect in lake chichancanab mexico the data reveal in great detail the climatic events that comprised the terminal classic drought tcd and coincided with the demise of classic maya civilization between ca 750 and 1050 ad in shallow water cores the tcd is marked by a condensed gypsum horizon in deeper water sections it is expanded and represented by numerous interbedded gypsum and organic rich strata the tcd was not a single two century long megadrought but rather consisted of a series of dry events separated by intervening periods of relatively moister conditions we estimate the tcd occurred between ca 770 and 1100 ad and included an early phase ca 770 870 ad and late phase ca 920 1100 ad the intervening 50 year period ca 870 920 ad was relatively moister each dry phase is represented by multiple gypsum density bands interbedded with organic rich sediment that indicate alternating dry and wet conditions spectral analysis revealed significant periods around 213 50 and 27 years despite uncertainty regarding the ages of these events their pattern is robust and generally consistent with other proxy records under the same climate regime such as the marine cariaco basin off northern venezuela science 299 2003 1731

hydrogen isotope ratios of lacustrine sedimentary n alkanes as proxies of tropical african hydrology insights from a calibration transect across cameroon abstract hydrogen isotope values d of sedimentary aquatic and terrestrial lipid biomarkers originating from algae bacteria and leaf wax have been used to record isotopic properties of ancient source water i e precipitation and or lake water in several mid and high latitude lacustrine environments in the tropics however where both processes associated with isotope fractionation in the hydrologic system and vegetation strongly differ from those at higher latitudes calibration studies for this proxy are not yet available to close this gap of knowledge we sampled surface sediments from 11 lakes in cameroon to identify those hydro climatological processes and physiological factors that determine the hydrogen isotopic composition of aquatic and terrestrial lipid biomarkers here we present a robust framework for the application of compound specific hydrogen isotopes in tropical africa our results show that the d values of the aquatic lipid biomarker n c17 alkane were not correlated with the d values of lake water carbon isotope measurements indicate that the n c17 alkane was derived from multiple source organisms that used different hydrogen pools for biosynthesis we demonstrate that the d values of the n c29 alkane were correlated with the d values of surface water i e river water and groundwater which on large spatial scales reflect the isotopic composition of mean annual precipitation such a relationship has been observed at higher latitudes supporting the robustness of the leaf wax lipid d proxy on a hemispheric spatial scale in contrast the d values of the n c31 alkane did not show such a relationship but instead were correlated with the evaporative lake water d values this result suggests distinct water sources for both leaf wax lipids most likely originating from two different groups of plants these new findings have important implications for the interpretation of long chain n alkane d records from ancient lake sediments in particular a robust interpretation of palaeohydrological data requires knowledge of the vegetation in the catchment area as different plants may utilise different water sources our results also suggest that the combination of carbon and hydrogen isotopes does help to differentiate between the metabolic pathway and or growth form of organisms and therefore the source of hydrogen used during lipid biosynthesis

three dimensional numerical modeling of slip rate variations on normal and thrust fault arrays during ice cap growth and melting 1 changes in the volumes of ice caps considerably alter the stress state of the lithosphere by generating a transient signal that is added to the tectonic background stress field these stress field changes in turn affect crustal deformation and in particular the slip behavior of existing faults here we use three dimensional finite element models to investigate how arrays of normal and thrust faults near a growing and subsequently melting ice cap are influenced in their slip evolution the results show that regardless of fault dip both types of faults experience a decrease in their slip rate during ice cap advance and an increase in their slip rate during ice cap retreat if they are located beneath the ice cap in contrast faults outside the ice cap that are loaded on their footwall or hanging wall only show the opposite pattern their slip rate increases during glacial loading and decreases during subsequent unloading if the load is located along strike of the fault that is at one of its tips the slip behavior of normal and thrust faults is different the normal fault shows a slip rate increase during unloading the thrust fault during loading our results explain the location and timing of deglaciation induced paleoearthquakes in scandinavia and the contrasting slip histories reported from normal faults in the basin and range province which are located at different positions relative to the former yellowstone ice cap more generally our findings imply that a uniform slip behavior of faults in formerly glaciated regions should not be expected

variation in p wave modulus with frequency and water saturation extension of dynamic equivalent medium approach abstractwe have developed a new modeling approach for the complex valued p wave modulus of a rock saturated with two phase fluid accounting for the variation with frequency and water saturation our method is based on the dynamic equivalent medium approach theory which predicts p wave modulus dispersion due to mesoscopic scale wave induced fluid flow wiff although the application of the original theory was limited to small fluctuation media we have extended it to also be applicable for high fluctuation media such as partially saturated rock our modification and extension consists of two components the first is introducing a scaling by the rigorous bounds for p wave velocity dispersion by mesoscopic scale wiff the second is to develop a model representing the effective patch size of stiffer fluid that controls the location of the dispersion curve we have found that the spatial correlation length of heterogeneity of saturated rock used in the original theory does not appropriately capture the effec

holocene climate variability in texas usa an integration of existing paleoclimate data and modeling with a new high resolution speleothem record abstract delineating the climate processes governing precipitation variability in drought prone texas is critical for predicting and mitigating climate change effects and requires the reconstruction of past climate beyond the instrumental record we synthesize existing paleoclimate proxy data and climate simulations to provide an overview of climate variability in texas during the holocene conditions became progressively warmer and drier transitioning from the early to mid holocene culminating between 7 and 3 ka thousand years ago and were more variable during the late holocene the timing and relative magnitude of holocene climate variability however is poorly constrained owing to considerable variability among the different records to help address this we present a new speleothem nbj reconstruction from a central texas cave that comprises the highest resolution proxy record to date spanning the mid to late holocene nbj trace element concentrations indicate variable moisture conditions with no clear temporal trend there is a decoupling between nbj growth rate trace element concentrations and 18o values which indicate that i the often direct relation between speleothem growth rate and moisture availability is likely complicated by changes in the overlying ecosystem that affect subsurface co2 production and ii speleothem 18o variations likely reflect changes in moisture source i e proportion of pacific vs gulf of mexico derived moisture that appear not to be linked to moisture amount

diagenetic and sedimentological controls on the composition of organic matter preserved in california borderland basin sediments compound specific radiocarbon 14c contents stable carbon isotopes and abundances of phytoplankton and vascular plant derived lipid biomarkers alkenones and fatty acids were obtained from santa barbara basin and santa monica basin sediments along with radiocarbon contents of planktic foraminifera and total organic carbon we investigated core top and prebomb sediment intervals at sites from the flanks and depocenters of the basins deposited under contrasting bottom water oxygen concentrations bulk organic matter generally has the lowest radiocarbon levels of all sediment constituents measured whereas planktic foraminifera tend to be the most radiocarbon enriched alkenones are systematically depleted in radiocarbon with respect to foraminifera short chain c14 c 16 c 18 fatty acids decrease rapidly in absolute abundance and relative to longer chain c24 homologues from core top to prebomb samples the loss of short chain fatty acids with depth is associated with 13c depletion of short chain fatty acids indicating preferential preservation of terrestrially derived fatty acids short chain fatty acids tend to be more 14c enriched relative to alkenones in core top sediments whereas longerchain homologues are generally the most radiocarbon depleted of the lipids studied here less refractory compounds e g short chain fatty acids are thus enriched in radiocarbon with respect to more recalcitrant biomarkers alkenones long chain fatty acids the lower 14c content of more refractory compounds reflects a larger proportion of laterally supplied preaged material greater preservation of labile organic compounds observed at the depocenters than in flank sediments results in the presence of younger biomarkers underlining the important influence of selective degradation of labile compounds on their radiocarbon ages

fundamentals of seismic rock physics during the past 50 years or so tremendous progress has been made in studying physical properties of rocks and minerals in relation to seismic exploration and earthquake seismology during this period many theories have been developed and many experiments have been carried out some of these theories and experimental results have played important roles in advancing earth sciences and exploration technologies this tutorial paper attempts to summarize some of these results

displacement rates of normal faults previous estimates of displacement rates on individual faults have been limited to neotectonic faults and averaged over time intervals of about 200 kyr or less1 2 3 4 5 these estimates have been highly variable which has led to a belief that longer term displacement rates on individual faults are likely to be variable as well here we report estimates of long term normal fault displacement rates averaged over time intervals ranging from 1 to 40 myr and based on observed decreases in displacement of progressively younger horizons intersected by syn sedimentary faults we find that displacement rates are remarkably stable over these longer time periods and within a given fault system the rates are strongly dependent on the relative size of the fault as measured by cumulative vertical displacement taken together these results indicate that faults become large relative to nearby faults by having higher displacement rates even when small rather than as a consequence of having been active for longer our analyses also show that high regional strain rates tend to be accommodated by high fault displacement rates rather than high fault densities

growth of faults by accumulation of seismic slip the accommodation of large strains in the upper crust is largely achieved by the accumulation of displacement on faults observation shows that as a fault accumulates displacement it grows in size i e its surface area and its length increase here we address the question for an increase in the amount of displacement on a fault by how much would the length of the fault change it is argued by cowie and scholz 1992a that the displacement on a fault is linearly related to the length of the fault this simple result is expanded upon in this paper by assuming that a fault accumulates displacement by repeated earthquakes two different approaches are presented the first approach considers the balance that must be achieved between the energy available for deformation and the work involved in creating new fault surface area as the fault grows the available energy is provided by changes in strain energy when the fault slips the second approach is to construct a geometrical model for fault growth using the scaling relationship between the slip during a single earthquake and the length of the rupture the total displacement on a fault is the sum of the slips contributed by many earthquakes the usefulness of these two approaches is that the growth of a fault over geologic time can be described by parameters that can be obtained from earthquake and fault data the models presented here predict that 1 the maximum amount a fault can grow in a single earthquake that ruptures the entire fault is of the order of 1 of its previous length and 2 the work of faulting may account for 10 of the total energy available during an earthquake the energy lost from the system is accounted for by work done against friction and seismic radiation consequences of fault growth for the segmentation and thus seismogenic potential of a fault over geologic time are discussed using predictions of the theory

active tectonics of the aegean region the aegean sea and its surrounding regions comprise one of the most rapidly deforming parts of the alpine himalayan mountain belt though the deformation of the belt as a whole is related to thc northward move ment of africa arabia and india relative to eurasia the tectonics of the aegean region itself is dominated by strike slip and extensional motions the actively deforming part of the aegean region is not large about 700 x 700 km2 compared with that in asia yet it has had an influence on our views of continental tectonics disproportionate to its size and comparable perhaps only to tibet fundamental contributions from the aegean have been made to many topics including

high resolution stalagmite climate record from the yucatan peninsula spanning the maya terminal classic period the decline of the classic maya civilization was complex and geographically variable and occurred over a 150 year interval known as the terminal classic period tcp c e 800 950 paleoclimate studies based on lake sediments from the yucatan peninsula lowlands suggested that drought prevailed during the tcp and was likely an important factor in the disintegration of the classic maya civilization the lacustrine evidence for decades of severe drought in the yucatan peninsula however does not readily explain the long 150 year socio political decline of the classic maya civilization here we present a new absolute dated highresolution stalagmite 18o record from the northwest yucatan peninsula that provides a much more detailed picture of climate variability during the last 1500 years direct calibration between stalagmite 18o and rainfall amount offers the first quantitative estimation of rainfall variability during the terminal classic period our results show that eight severe droughts lasting from 3 to 18 years occurred during major depopulation events of classic maya city states during these droughts rainfall was reduced by 52 to 36 the number and short duration of the dry intervals help explain why the tcp collapse of the mayan civilization occurred over 150 years

landsliding and the evolution of normal fault bounded mountains much of the tectonic and climatic history in high relief regions such as the mountains of the western u s basin and range province is contained in the morphology of hillslopes drainage networks and other landforms that range in scale from 10 1 to 101km to understand how these landforms evolve we have developed a numerical landscape evolution model that combines a detailed tectonic displacement field with a set of physically based geomorphic rules bedrock landsliding long recognized as a significant geomorphic process in mountainous topography is for the first time explicitly included in the rule set in a series of numerical experiments we generate synthetic landscapes that closely resemble mountainous topography observed in the basin and range the production of realistic landscapes depends critically on the presence of bedrock landslides and landsliding yields rates of long term erosion that are comparable in magnitude to those of fluvial erosion the erosive efficiency of bedrock landsliding implies that hillslopes may respond very quickly to changes in local base level and that fluvial erosion is the rate limiting process in steady state experimental landscapes our experiments generate power law distributions of landslide sizes somewhat similar to both field and laboratory observations thus even a simple model of bedrock landsliding is capable of quantitatively reproducing mountainous topography and landslide distributions and represents a significant step forward in our understanding of the evolution of normal fault bounded ranges

seismic velocity inversion for patchy and homogeneous fluid distribution conditions in shallow unconsolidated sands abstractknowledge of homogeneous and heterogeneous fluid distribution conditions in unconsolidated sediments is important for the selection of remediation techniques for groundwater contamination however for unconsolidated sediments fluid distribution conditions from laboratory tests on core samples may not be representative of in situ conditions we have developed a seismic inversion method to determine in situ fluid distribution conditions that involves inverting experimental seismic p and s wave velocities using hertz mindlin and biot gassmann models with different averaging methods wood and hill averages and different fluid distribution condition assumptions this method can determine whether seismic velocity versus depth profiles are better explained assuming heterogeneous or homogeneous saturation conditions in shallow 1 m depth unconsolidated sands during the imbibition and drainage of shallow unconsolidated sands we have observed nonmonotonic relationships between p wave velocity and w

leaf waxes as recorders of paleoclimatic changes during the paleocene eocene thermal maximum regional expressions from the belluno basin abstract paired assessments of carbon 13 c lipids and hydrogen isotopic compositions of leaf wax lipids 2 h lipids from warm intervals in earth s history have been used to investigate the relationship between greenhouse gases hydrological cycle and global warming modern studies however show that 2 h lipids can exhibit significant variability due to secondary factors including differences in biosynthetic fractionation and 2 h enrichments in soil and leaf water to evaluate the intrabasinal variability of sedimentary compound specific isotopic records we generated new carbon and hydrogen isotopic compositions of leaf wax lipids for the paleocene eocene thermal maximum petm 55 ma from cicogna creek belluno basin northern italy and compared results with published petm records from the proximal forada creek section similar isotopic trends are observed at both localities the magnitude of the negative carbon isotope excursion at cicogna is 2 5 pre event 2 h enrichment recorded in the forada section is missing at cicogna likely due to a disturbed interval at the paleocene eocene boundary a 2 h depletion of 10 15 during the body of the petm at cicogna is observed in several petm sections implicating a primary change in the global hydrological cycle given the proximity of cicogna and forada isotopic compositions of paleo meteoric water are expected to be similar however a 15 offset between the records is apparent possible reasons include differences in vegetation biomarker transport and precipitation altitude underscoring the complexity of using a single record for zonal reconstructions and data model comparisons ultimately this study shows that while 2 h 1 h trends can be applied for paleoclimate analysis with reasonable certainty absolute magnitudes can be biased by secondary local factors

pre aged plant waxes in tropical lake sediments and their influence on the chronology of molecular paleoclimate proxy records sedimentary records of plant wax hydrogen ddwax and carbon d 13 cwax stable isotopes are increasingly applied to infer past climate change compound specific radiocarbon analyses however indicate that long time lags can occur between the synthesis of plant waxes and their subsequent deposition in marginal marine sediments the influence of these time lags on interpretations of plant wax stable isotope records is presently unconstrained and it is unclear whether such time lags also affect lacustrine sediments we present compound specific radiocarbon 14 cwax data for n alkanoic acid plant waxes n c26 to n c32 from 1 a sediment core from lake chichancanab yucatan peninsula mexico 2 soils in the lake chichancanab catchment and 3 surface sediments from three other lakes in southeastern mexico and northern guatemala 14 cwax ages in the surface sediments are consistently older than modern and may be negatively correlated with mean annual precipitation and positively correlated with lake catchment area 14 cwax ages in soils surrounding lake chichancanab increase with soil depth consistent with deep subsoil horizons being the primary source of lacustrine aged plant waxes which are likely delivered to lake sediments through subsurface transport plant waxes in the lake chichancanab core are 350 1200 years older than corresponding ages of bulk sediment deposition determined by 14 c dates on terrestrial plant macrofossils in the core a ddwax time series is in closer agreement with other regional proxy hydroclimate records when a plant wax 14 c age model is applied as opposed to the macrofossil based core chronology inverse modeling of plant wax age distribution parameters suggests that plant waxes in the lake chichancanab sediment core derive predominantly from millennial age soil carbon pools that exhibit relatively little age variance 200 years our findings demonstrate that high temporal resolution climate records inferred from stable isotope measures on plant waxes in lacustrine sediments may suffer from possible chronologic distortions as a consequence of long residence times of plant waxes in soils they also underscore the importance of direct radiocarbon dating of these organic molecules

long stored soil carbon released by prehistoric land use evidence from compound specific radiocarbon analysis on soppensee lake sediments compound specific radiocarbon c 14 analyses allow studying the fate of individual biomarkers in ecosystems in lakes with small catchments terrestrial biomarkers have the potential to be used fo

role of climate changes for wind gap formation in a young actively growing mountain range wind gaps in actively growing mountain ranges are unique geomorphological features testifying to the competition between tectonics and fluvial incision although it is clear that these landforms reflect the defeat of rivers during sustained rock uplift the role of climate changes in their formation has never been explored here we use a coupled tectonics landscape evolution model to show that temporal changes in precipitation rate exert an important control on wind gap formation in models with a constant precipitation rate rivers flowing across a growing range are either defeated at an early stage or they abandon their valleys very late if at all if precipitation varies wind gaps form mostly 100 200 ka after a transition to drier conditions because of sediment aggradation upstream of the range our results suggest that the pliocene quaternary aridification of central asia contributed to wind gap formation in active mountain ranges in the foreland of northeastern tibet this article is protected by copyright all rights reserved

hydrogen isotope ratios of recent lacustrine sedimentary n alkanes record modern climate variability abstract hydrogen isotope ratios were measured on n alkanes n c12 to n c31 extracted from recent lake surface sediments along a n s european transect to test if modern climate variability is recorded in these biomarkers d values of the n alkanes are compared to d values of meteoric water from the iaea gnip database spanning a range from 119 in northern sweden to 41 in southern italy to lake water d values and to mean annual temperatures varying between 2 0 c in the north and 13 7 c in the south d values of the short chained n alkanes n c12 to n c20 excluding algal derived n c17 and n c19 are higher in the north and lower in the south the isotopic fractionation e for hydrogen between meteoric water and the short chained n alkanes is increasing from n to s by more than 100 and is significantly correlated to mean annual temperature for n c16 and n c18 this suggests that these n alkanes may originate from a different source in the northern lakes possibly due to petroleum contamination or are synthesized using a different biochemical pathway the n c17 and n c19 alkanes of algal origin the n c21 and n c23 alkanes originating from water plants and the long chain n alkanes n c25 n c27 n c29 and n c31 of terrestrial origin clearly correlate with d values of meteoric water lake water and mean annual temperature indicating that they excellently record the d value of meteoric water the mean hydrogen isotope fractionation ec17 w of 157 sd 13 between n c17 and meteoric water is fairly constant over the wide range of different climates and lake environments suggesting only minor influence of environmental factors on this biochemical fractionation this suggests that d values of n c17 are suitable to reconstruct the isotopic composition of source water the mean fractionation between the long chain n alkanes and water is 128 sd 12 the mean difference of 31 between both e values is likely due to evaporative enrichment of deuterium in the leaf water if this is the only influence on the enrichment the difference between the d values of terrestrial and aquatic compounds might be suitable to reconstruct terrestrial evapotranspiration of the lake environment

the growth of fault bounded tilt blocks a series of uniformly tilted fault bounded blocks is a common feature in actively extending regions such as the basin and range province if the tilted blocks were produced by rigid domino style rotation one would predict large voids at either end of a series of these blocks using tilt data and a simple flexural calculation we suggest that much of the apparent rigid behavior could also be produced by internal block deformation in our model of normal fault growth isostatic elastic uplift of the footwall is coupled with hanging wall downdrop within the region between faults resulting in the appearance of a tilted rigid block we present tilt data sampled at varying distances from several block defining faults within the northeast basin and range province tilt measurements between a series of 30 km spaced block defining faults are found to be uniform while tilts between more widely spaced faults exhibit a pattern of tilt that diminishes to zero in less than 30 km using a simple flexural calculation for internal block deformation we show that for this region the patterns of tilt are consistent with a flexural length scale of 8 12 km and deflections of 2 4 km these estimates are compatible with both the lower limit to seismicity and basin depth determined from earthquake and seismic reflection studies

migration of activity within normal fault systems examples from the quaternary of mainland greece abstract we examine five areas of mainland greece where active extension occurs on sub parallel systems of normal faults and where geomorphological and stratigraphic evidence indicates that the faulting has migrated basinwards into the original hanging walls in several cases within the late quaternary by comparing fault slip rates estimated from geomorphological data with current extension rates known from geodetic measurements it appears that the newest faults can account for effectively all the present day motions fault migration of this sort is easy to recognize in young systems close to sea level because vertical movements of footwalls and hanging walls are obvious and reveal which faults are currently most active but is less easy to confirm away from reliable reference levels or in older terrains with poorer time resolution it is probably more common than is appreciated and has a profound effect on syn rift sedimentation and erosion patterns fault migration is probably an inevitable consequence of the interplay between stresses generated by the fault related topography and the ultimate strength of major faults it is likely to be further encouraged in places where lower crustal flow or rotations about a vertical axis are important however it is not clear why migration should preferentially occur into the hanging walls as observed in central greece

d h variation in terrestrial lipids from santa barbara basin over the past 1400 years a preliminary assessment of paleoclimatic relevance we analyzed d h ratios of common terrestrial leaf wax lipids in a 1400 year sediment core from the santa barbara basin sbb to test whether they accurately record terrestrial climate in southern california the d h ratios of long chain n alkanes vary substantially with depth but are poorly correlated with other terrestrial climate proxies interference from fossil hydrocarbons may be at least partly responsible long chain n alkanoic acids exhibit nearly constant downcore d h ratio values this constancy in the face of known climatic shifts presumably reflects a substantial residence time for leaf wax compounds in terrestrial soil and or on the basin flanks alternatively the isotopic composition of meteoric waters in southern california may not covary with climate particularly aridity however the d values of n c22 and n c24 fatty acids commonly attributed to terrestrial aquatic sources are partially correlated with southern california winter palmer drought severity index a tree ring based climatic proxy r 2 0 25 p 0 01 on multi centennial scales with an inferred ca 215 year time lag the improved correlation of these biomarkers can be explained by the fact that they are not stored in terrestrial soil nor are subject to interference from fossil hydrocarbons our study indicates that the sbb is unlikely to preserve high resolution leaf wax d h records that can serve as quantitative paleoclimate proxies though some qualitative information may be retained more generally the sources of lipids in marginal marine basins need to be carefully evaluated prior to attempting paleoclimate reconstruction based on the leaf wax d h proxy

seismic attenuation in porous rocks with random patchy saturation saturation of porous rocks with a mixture of two fluids has a substantial effect on seismic wave propagation in particular partial saturation causes significant attenuation and dispersion of the propagating waves due to the mechanism of wave induced fluid flow such flow arises when a passing wave induces different fluid pressures in regions of rock saturated by different fluids most models of attenuation and dispersion due to mesoscopic heterogeneities imply that fluid heterogeneities are distributed in a regular way however recent experimental studies show that mesoscopic heterogeneities have less idealized distributions and that the distribution itself affects attenuation and dispersion based on an approximation for the coherent wavefield in random porous media we develop a model which assumes a continuous distribution of fluid heterogeneities as this continuous random media approach assumes that there will be a distribution of different patch sizes it is expected to be better suited to modelling experimental data we also show how to relate the random functions to experimentally measurable parameters

a multitracer study of radionuclides in lake zurich switzerland 2 residence times removal processes and sediment focusing residence and settling times of particles and particle reactive nuclides evaluated from in situ tracer studies can be used as diagnostic indicators of trace element pathways in lakes natural e g 210pb 7be and 10be and artificial i e chernobyl 137cs radionuclide fluxes through lake zurich at 50 and 130 m depth from 1983 to 1987 atmospheric fluxes of the same nuclides and fluxes of 10be during 1987 allowed the calculation of nuclide residence times as well as particle settling and transit velocities in lake zurich the residence time of 210pb in the lake is approximately 1 month and hence of the same order as the residence times of particles and stable pb steady state residence times for 7be were calculated as 150 170 days while non steady state instantaneous removal residence times ranged from 50 to 800 days polonium 210 was removed from lake zurich with removal times of 10 26 months indicating slow removal processes or efficient recycling in the lake water transit velocities of particles calculated from the attenuation of chernobyl 137cs fluxes at 50 m and 130 m depth during early may 1986 were 17 m d 1 while 2 4 5 m d 1 was calculated as an effective settling velocity from the attenuation of 7be fluxes at 130 m depth as compared to 50 m depth model calculations reveal that the overall removal process of atmospherically deposited 7be from the water column to the sediments is mainly controlled by the adsorption coagulation step and not by the rate of particle settling extra inputs of 10be 210pb or 137cs into the lower trap i e rebound flux originating from episodic lateral inputs of fine particles with a high content of 210pb 10be and 137s were observed during the lake stratification period i e summer this novel observation of summertime radionuclide and sediment focusing is different from previously described wind generated resuspension and focusing effects caused by river plumes and lake sediments during the stagnation period boundary and focusing effects for radionuclide bearing particles are proposed to explain observed summertime enhancements of longer lived nuclide fluxes at 130 m depth as well as the decrease in calculated effective settling velocities

slip on normal faults induced by surface processes after the cessation of regional extension insights from three dimensional numerical modelling abstract in regions of active extension normal faulting generates topography that is continuously modified by erosion sediment transport and deposition as shown by previous numerical models with full coupling between tectonics and surface processes the redistribution of mass at the earth s surface accelerates the rate of faulting by affecting the stress state of the crust it remains unknown however how fault slip evolves as a result of ongoing surface processes if regional extension as the main driver of faulting ceases here we use three dimensional finite element modelling to show that surface processes acting on normal fault bounded mountain ranges may sustain fault slip for millions of years even after regional extension has stopped the models consist of two successive phases during the first phase the normal fault accumulates displacement owing to an extensional boundary condition while erosion and sediment deposition are active on the model surface at the beginning of the second phase extension of the model is stopped while the surface processes remain active the results show that in most models normal faulting continues during the second phase at rates of 20 to 70 m ma for more than 1 ma in some experiments normal slip is maintained for 3 ma whereas in other models a short phase of normal faulting is followed by slow reverse slip the maximum amount of normal slip in different experiments reaches up to 90 m during the second model phase if erosion is intensified by increasing the diffusion constant by a factor of 5 the fault accumulates the additional normal slip at a faster rate i e during a shorter time period in contrast a five fold variation of the fluvial erosion constant does not significantly affect the fault slip evolution variations of the fault dip and length have a similar effect on the duration of the phase with additional normal slip as variations of the diffusion constant the fault slip evolution is correlated with the temporal evolution of the erosion and sedimentation rates which decrease more or less gradually after the end of extension ultimately the fault slip behaviour is controlled by the evolution of the differential stress which varies through time due to the redistribution of mass on the model surface that is induced by erosion sediment transport and deposition our results imply that individual normal faults may remain active even if regional extension ceases because surface processes continue to modify the fault generated topography

slip acceleration on normal faults due to erosion and sedimentation results from a new three dimensional numerical model coupling tectonics and landscape evolution abstract although it is well accepted that mass redistribution on earth s surface due to erosion and sedimentation affects the rate of crustal deformation the influence of surface processes on the slip behaviour of individual faults remains poorly understood here we use the new tool casqus which combines landscape evolution modelling with three dimensional tectonic models to investigate how erosion and sediment deposition affect fault behaviour in extensional tectonic regimes a systematic set of experiments with models consisting of an isostatically responding elastic upper crust containing a single normal fault shows that the slip accumulation on the fault is accelerated by erosion and sedimentation depending on fault geometry extension rate and parameters controlling erosion and sediment deposition the slip rate of the normal fault is up to 15 higher when surface processes are taken into account the slip acceleration can be explained by an increase in the differential stress caused by erosion of the fault footwall and sedimentation in the hanging wall which alter the faulting induced flexure of the crust we observe a similar slip rate increase in a more complex model of a growing horst bounded by three faults of different length our results show that a positive feedback exists between surface processes and tectonics and imply that geologically derived fault slip rates that integrate over several earthquake cycles may contain a contribution from surface processes

northern hemisphere controls on tropical southeast african climate during the past 60 000 years the processes that control climate in the tropics are poorly understood we applied compound specific hydrogen isotopes d and the tex86 tetraether index of 86 carbon atoms temperature proxy to sediment cores from lake tanganyika to independently reconstruct precipitation and temperature variations during the past 60 000 years tanganyika temperatures follow northern hemisphere insolation and indicate that warming in tropical southeast africa during the last glacial termination began to increase 3000 years before atmospheric carbon dioxide concentrations d data show that this region experienced abrupt changes in hydrology coeval with orbital and millennial scale events recorded in northern hemisphere monsoonal climate records this implies that precipitation in tropical southeast africa is more strongly controlled by changes in indian ocean sea surface temperatures and the winter indian monsoon than by migration of the intertropical convergence zone

improved understanding of velocity saturation relationships using 4d computer tomography acoustic measurements a recently developed laboratory method allows for simultaneous imaging of fluid distribution and measurements of acoustic wave velocities during flooding experiments using a specially developed acoustic sample holder that combines high pressure capacity with good transparency for x rays it becomes possible to investigate relationships between velocity and fluid saturation at reservoir stress levels high resolution 3d images can be constructed from thin slices of cross sectional computer tomography scans ct scans covering the entire rock core volume and from imaging the distribution of fluid at different saturation levels the x ray imaging clearly adds a new dimension to rock physics measurements it can be used in the explanation of variations in measured velocities from core scale heterogeneities computer tomography gives a detailed visualization of density regimes in reservoir rocks within a core this allows an examination of the interior of core samples revealing inhomogeneities porosity and fluid distribution this mapping will not only lead to an explanation of acoustic velocity measurements it may also contribute to an increased understanding of the fluid flow process and gas liquid mixing mechanisms in rock immiscible and miscible flow in core plugs can be mapped simultaneously with acoustic measurements the effects of core heterogeneity and experimentally introduced effects can be separated to clarify the validity of measured velocity relationships

escarpment evolution on high elevation rifted margins insights derived from a surface processes model that combines diffusion advection and reaction experiments with a surface processes model of large scale 1 1000 km long term 1 100 m y erosional denudation are used to establish the controls on the evolution of a model escarpment that is related to the rifting of a continent the model describes changes in topographic form as a result of simultaneous short and long range mass transport representing hillslope diffusive processes and fluvial transport advection respectively fluvial entrainment is modeled as a first order kinetic reaction which reflects the credibility of the substrate and therefore the fluvial system is not necessarily carrying at capacity one dimensional and planform models demonstrate that the principal controls on the evolution of an initially steep model escarpment are 1 antecedent topography drainage 2 the timescale or equivalently a length scale in the fluvial entrainment reaction 3 the flexural response of the lithosphere to denudation and 4 the relative efficiencies of the short and long range transport processes when rainfall and substrate lithology are uniform a significant amount of discharge draining over the escarpment top causes it to degrade only when the top of the model escarpment coincides with a drainage divide can escarpment retreat occur for these conditions an additional requirement for retreat of a model escarpment without decline is a long reaction time scale for fluvial entrainment this corresponds to a substrate that is hard to detach by fluvial erosion and therefore to fluvial erosion that is not transport limited continuous backtilting of an escarpment due to flexural isostatic uplift in response to denudational unloading helps maintain the scarp top as a divide it is essential if the escarpment gradient is to be preserved during retreat in a uniform lithology low flexural rigidities promote steep and slowly retreating escarpments for given rainfall and substrate conditions the morphology of a retreating model escarpment is determined by the ratio of the short range diffusive and long range advective transport efficiencies a low ratio which is interpreted to correspond to a relatively arid climate and weathering limited conditions promotes steep sharp topped escarpments with straight main slopes and escarpment retreat occurs over a wide range of height scales a high ratio interpreted to correspond to a more humid temperate climate produces a convex upper slope and concave lower slope morphology and only major escarpments are predicted to preserve a high scarp gradient lithological contrasts in the model produce more complex morphologies and predict the formation of scarps crowned by an erosionally resistant caprock however resistant caprocks are not an essential requirement for model scarps to retreat we conclude that the inferred controls and model behavior are both consistent with the present day morphology of rifted continental margins and with modern conceptual models of landscape evolution

geomorphology of active faulting and seismic hazard assessment new tools and future challenges by witold zuchiewicz and jerzy zasadni 2012 intended for this volume young tectonics of the outer western carpathians in the light of some morphometric indices in this paper we test the applicability of some morphometric indices commonly used in tectonic geomorphological studies to the area of the outer western carpathians representing an alpine fold and thrust belt this belt was shaped largely in miocene times and shows traces of pliocene quaternary tectonic activity consisting mainly in some remnant folding and faulting this is indicated by scarce examples of faulting within quaternary strata numerous cases of clast fracturing owing to palaeoearthquakes of relatively large magnitudes as well as warping and tilting of pleistocene and holocene strath terraces analysis of selected morphometric indices valley floor width valley height ratio riverbed gradients stream length gradient index basin elongation ratios and others conducted for the entire region and some chosen test areas in the westernmost part of the outer western ac c ep te d m an u sc r ip t accepted manuscript 24 carpathians proved their usefulness in detecting zones showing tendencies to young surface uplift however in the case of the stream length gradient index sl hack s index a word of caution should be added since the index is extremely sensitive to lithologic contrasts in the bedrock and its applicability to young tectonic analysis of fold and thrust belts appears to be strongly limited dr andrzej piotrowski apiot pgi gov pl szczecinie panstwowy instytut geologiczny szczecin poland and dr klaus reicherter rwth aachen university germany

a long term high latitude record of eocene hydrological change in the greenland region abstract a range of proxy approaches have been used to reconstruct short term changes to earth s hydrological cycle during the early eocene hyperthermals however little is known about the response of earth s hydrological and biogeochemical systems to long term cenozoic cooling which began following the early eocene climatic optimum 53 3 49 4 million years ago ma here we use the molecular distribution and isotopic composition of terrestrial biomarkers preserved in marine sediments of odp site 913 east greenland to develop a long term record of high latitude hydrological change between 50 and 34 ma there is a marked decline in the concentration of conifer derived diterpenoids and angiosperm derived triterpenoids during the eocene as the input of wind blown conifer pollen remains stable during this interval this implies that decreasing di and triterpenoid concentrations reflect declining influence of fluvial inputs and perhaps terrestrial runoff throughout the eocene branched gdgts and bacterial derived hopanes indicate an increased input of soil and kerogen derived organic matter respectively after 38 ma this coincides with evidence for ice rafted debris and suggests input of organic matter via glacial processes this also implies some continental glaciation occurred on east greenland in the middle to late eocene leaf wax hydrogen isotopes extending throughout this section the first such long term record from the paleogene indicate that precipitation 2h was persistently higher than that of modern coastal greenland consistent with warmer ocean source waters and enhanced poleward moisture transport non intuitively however this effect appears to have been smallest during the warmest part of the record and higher 2h values occur in the middle eocene although interpretation of these hydrogen isotope trends is unclear they clearly indicate alongside the changes in biomarker abundances a perturbed hydrological cycle through the eocene in coastal greenland more long term records are required to ascertain if this represents regional or global hydrological reorganisation

late miocene ductile extension and detachment faulting mykonos greece the geometry and style of structural relations at map to microscopic scale on mykonos cyclades aegean sea greece suggests ductile extension and detachment faulting during the late miocene this island is dominated by granitic rocks that have a well developed shallowly dipping mylonitic foliation and a northeast southwest trending mineral elongation lineation kinematic indicators in these rocks exhibit a top to the northeast down dip sense of shear textural relations suggest that conditions during mylonitic deformation were greenschist to amphibolite facies and published k ar geochronology suggests a late miocene age for this deformation event mylonitic rocks lie in the footwall of a low angle fault and fault striae parallel to the elongation lineation suggest kinematic coordination between mylonitic deformation and movement along the fault translation along the fault juxtaposes younger tilted sedimentary rocks of low metamorphic grade upon the once deeper mylonitic rocks the style and geometry of deformational fabrics and map relations on this island are strikingly similar to those observed in metamorphic core complexes of the western united states

metamorphic core complexes of cordilleran type in the cyclades aegean sea greece the islands of ios and naxos in the cycladic archipelago greece contain elongate domes over which a pervasive north to north northeast stretching lineation is warped these islands may be metamorphic core complexes of cordilleran type involving middle crustal rocks drawn upward and outward from underneath the sedimentary basins now 100 km to the south from ca 25 ma onward during uplift the crystalline rocks now exposed on the islands were deformed noncoaxially in the deeper levels of a major shallow dipping ductile shear zone this shear zone may have connected with low angle normal faults in its upper levels because it is probable that its later history involved the metamorphic complexes being dragged out from under a stretching and fracturing upper plate composed mainly of unmetamorphosed sedimentary and ophiolite suite rocks this model can be extended to explain the exhumation of the high pressure low temperature metamorphic rocks on crete which with the cyclades forms a distended paired metamorphic belt separated by an active sedimentary basin

evolution of the lithosphere in the area of the rhine rift system the rhine rift system rrs forms part of the european cenozoic rift system ecris and transects the variscan orogen permo carboniferous troughs and late permian to mesozoic thermal sag basins crustal and lithospheric thicknesses range in the rrs area between 24 36 km and 50 120 km respectively we discuss processes controlling the transformation of the orogenically destabilised variscan lithosphere into an end mesozoic stabilised cratonic lithosphere as well as its renewed destabilisation during the cenozoic development of ecris by end westphalian times the major sutures of the variscan orogen were associated with 45 60 km deep crustal roots during the stephanian early permian regional exhumation of the variscides was controlled by their wrench deformation detachment of subducted lithospheric slabs asthenospheric upwelling and thermal thinning of the mantle lithosphere by late early permian times when asthenospheric temperatures returned to ambient levels lithospheric thicknesses ranged between 40 km and 80 km whilst the thickness of the crust was reduced to 28 35 km in response to its regional erosional and local tectonic unroofing and the interaction of mantle derived melts with its basal parts re equilibration of the lithosphere asthenosphere system governed the subsidence of late permian mesozoic thermal sag basins that covered much of the rrs area by end cretaceous times lithospheric thicknesses had increased to 100 120 km paleocene mantle plumes caused renewed thermal weakening of the lithosphere starting in the late eocene ecris evolved in the pyrenean and alpine foreland by passive rifting under a collision related north directed compressional stress field following end oligocene consolidation of the pyrenees west and northwest directed stresses originating in the alps controlled further development of ecris the rrs remained active until the present whilst the southern branch of ecris aborted in the early miocene extensional strain across ecris amounts to some 7 km plume related thermal thinning of the lithosphere underlies uplift of the rhenish massif and massif central lithospheric folding controlled uplift of the vosges black forest arch

effects of aridity and vegetation on plant wax δd in modern lake sediments we analyzed the deuterium composition of individual plant waxes in lake sediments from 28 watersheds that span a range of precipitation d h vegetation types and climates the apparent isotopic fractionation ea between plant wax n alkanes and precipitation differs with watershed ecosystem type and structure and decreases with increasing regional aridity as measured by enrichment of 2 h and 18 o associated with evaporation of lake waters the most negative ea values represent signatures least affected by aridity these values were 125 5 for tropical evergreen and dry forests 130 for a temperate broadleaf

permeability anisotropy and its relations with porous medium structure 1 the complete permeability tensor of 18 porous rock cores was determined by means of x ray tomography monitoring during the displacement of a salty tracer to study the effect of the pore space geometry on the anisotropy of permeability we compared the three dimensional shape of the invasion front with the x ray porosity maps obtained before injection the samples clean and shale bearing sandstones limestones and volcanic rocks belong to a broad variety of granulometry and pore space geometry their porosity ranges from 12 to 57 and their permeability ranges from 1 5 10 14 to 4 10 12 m2 for sandstones the permeability anisotropy is well correlated with the presence of bedding for volcanic rocks it is clearly related to the orientation of vesicles or cracks however for limestones no evident link between the geometry of the porous network and the permeability anisotropy appears probably because of the influence of the nonconnected porosity that does not contribute to the hydraulic transport this systematic work evidences the ability and the limitations of the tracer method to characterize the anisotropy of permeability in the laboratory in a simple and rapid way

saturation path dependency of p wave velocity and attenuation in sandstone saturated with co2 and brine revealed by simultaneous measurements of waveforms and x ray computed tomography images abstractwe performed a laboratory experiment to measure compressional p wave velocity and its attenuation in low permeability striped sandstone at ultrasonic frequency during drainage co2 injection and imbibition brine injection x ray computed tomography ct images of the rock sample were simultaneously recorded during the injections on the basis of the ct images we calculated the co2 saturation inside a prolate spheroid shaped volume the first fresnel zone that enclosed the wave propagation path the relationship of p wave velocity and that of attenuation to the co2 fraction were then obtained both relationships showed nonuniqueness with remarkable hysteresis in a drainage imbibition cycle to explain the nonunique relationship of p wave velocity to the co2 fraction we investigated the continuous random patchy saturation model by using exponent type autocorrelation the nonunique relationship of velocity to the co2 fraction was explained by the model with a correlation length from an order

late pleistocene holocene slip rate of the zhangye thrust qilian shan china and implications for the active growth of the northeastern tibetan plateau 1 we derive a slip rate for a thrust at the central qilian shan mountain front by combining structural investigations satellite imagery topographic profiling luminescence dating and 10be exposure dating the seismically active zhangye thrust transects late pleistocene alluvial fan deposits and forms a prominent north facing scarp the fault consists of two segments that differ in orientation scarp height and age a series of loess covered terraces records the uplift history of the western thrust segment loess accumulation on all terraces started at 8 5 1 5 kyr and postdates terrace formation gravels from the highest terrace yielded a 10be exposure age of 90 11 kyr which dates the onset of faulting with a displacement of 55 60 m derived from fault scarp profiles this yields a vertical slip rate of 0 64 0 08 mm yr 1 along the eastern thrust segment three 10be ages from the uplifted alluvial fan constrain that faulting started at 31 5 kyr together with a displacement of 25 30 m this leads to a vertical faulting rate of 0 88 0 16 mm yr 1 a dip estimate of 40 to 60 for the fault plane combined with lower and upper limits of 0 6 and 0 9 mm yr 1 for the vertical slip rate gives minimum and maximum horizontal shortening rates of 0 4 and 1 1 mm yr 1 across the zhangye thrust our results are consistent with geologic and gps constraints which suggest that nne directed shortening across the northeastern tibetan plateau is distributed on several active faults with a total shortening rate of 4 to 10 mm yr 1

how sediment promotes narrow rifting application to the gulf of california 1 if the gravitational stress changes related to crustal thinning are large enough to affect the mode of extension then sedimentation should also affect that mode we propose that the weight of sediments reduces the difference in crustal buoyancy forces caused by local crustal thinning allowing a rift to extend more easily in a narrow rift mode we examine the effect of deposition of large amounts of nonlocally derived sediment on extensional style using two dimensional regional scale numerical experiments of extending thick continental crust with varied initial thermal conditions geometries rheological parameters and sedimentation properties depending on initial model conditions the onset of rifting in thick continental crust occurs in the narrow rifting wide rifting or core complex mode with continued extension all cases eventually transition to a narrow rifting mode for a system in wide rift mode moderate to fast sedimentation shortens the time needed to transition to a narrow rift in the gulf of california changes in extensional style correlate with sediment thickness with an earlier transition to narrow rifting in the north versus the south we compare our model results to the extensional history of the gulf of california where sediments may have caused the northern and north central domain of the gulf delfin tiburon and guaymas segments to transition to narrow rifting before the south central domains alarcon segment

forcing of wet phases in southeast africa over the past 17 000 years a continuous record of hydrologic variability for the past 17 000 years at the mouth of the zambezi river shows that hydrologic conditions in southeast africa were controlled by variations in local insolation and migrations of the intertropical convergence zone rather than by indian ocean temperature records of hydroclimatological variability in southern africa since the last glacial maximum have produced a conflicting picture of the relative influences of events in the remote northern hemisphere and the more local indian ocean this paper presents a continuous record of hydrological variability for the past 17 000 years from marine sediment core drilled off the mouth of the zambezi river the record shows that hydrological conditions in the region were influenced by variations in local insolation and migrations of the intertropical convergence zone which were probably driven by events in the northern hemisphere rather than the indian ocean intense debate persists about the climatic mechanisms governing hydrologic changes in tropical and subtropical southeast africa since the last glacial maximum about 20 000 years ago in particular the relative importance of atmospheric and oceanic processes is not firmly established1 2 3 4 5 southward shifts of the intertropical convergence zone itcz driven by high latitude climate changes have been suggested as a primary forcing2 3 whereas other studies infer a predominant influence of indian ocean sea surface temperatures on regional rainfall changes4 5 to address this question a continuous record representing an integrated signal of regional climate variability is required but has until now been missing here we show that remote atmospheric forcing by cold events in the northern high latitudes appears to have been the main driver of hydro climatology in southeast africa during rapid climate changes over the past 17 000 years our results are based on a reconstruction of precipitation and river discharge changes as recorded in a marine sediment core off the mouth of the zambezi river near the southern boundary of the modern seasonal itcz migration indian ocean sea surface temperatures did not exert a primary control over southeast african hydrologic variability instead phases of high precipitation and terrestrial discharge occurred when the itcz was forced southwards during northern hemisphere cold events such as heinrich stadial 1 around 16 000 years ago and the younger dryas around 12 000 years ago or when local summer insolation was high in the late holocene that is during the past 4 000 years

compound specific radiocarbon dating of the varved holocene sedimentary record of saanich inlet canada 1 the radiocarbon contents of various biomarkers extracted from the varve counted sediments of saanich inlet canada were determined to assess their applicability for dating purposes calibrated ages obtained from the marine planktonic archaeal biomarker crenarchaeol compared favorably with varve count ages the same conclusion could be drawn for a more general archaeal biomarker gdgt 0 although this biomarker proved to be less reliable due to its less specific origin the results also lend support to earlier indications that marine crenarchaeota use dissolved inorganic carbon dic as their carbon source the average reservoir age offset r of 430 years determined using the crenarchaeol radiocarbon ages varied by 110 years this may be caused by natural variations in ocean atmosphere mixing or upwelling at the ne pacific coast but variability may also be due to an inconsistency in the marine calibration curve when used at sites with high reservoir ages

climate variability on the yucatan peninsula mexico during the past 3500 years and implications for maya cultural evolution climate variability on the yucatan peninsula during the past 3500 yrs is reconstructed from the measurement of 18o in monospecific ostracods and gastropods in a 6 3 m sediment core from lake punta laguna mexico this late holocene record is divided into three periods based on changes in mean 18o values from 3310 to 178514c yr b p period i low mean 18o values indicate relatively wet conditions i e low evaporation to precipitation ratio e p mean oxygen isotopic values increased 178514c yr b p and the interval between 1785 and 93014c yr b p period ii was distinctly drier than the periods before or after the climate during the latter part of period ii was persistently dry with exceptionally arid events centered at 1171 1019 and 94314c yr b p equivalent to 862 986 and 1051 a d this interval of frequent drought was recorded at several other localities in mexico and central america and coincided with the collapse of classic maya civilization following the last arid event 18o values decreased abruptly at 93014c yr b p beginning of period iii signaling a return to wetter conditions that have generally prevailed to the present with the exception of a dry episode centered at 55914c yr b p 1391 a d the paleoclimatic record from punta laguna provides evidence that multi decadal and millennial scale changes ine poccurred on the yucatan peninsula during the late holocene these wet dry episodes may have influenced cultural evolution in mesoamerica

carbon isotope composition of lake sediments in relation to lake productivity and radiocarbon dating abstract carbon 13 profiles and radiocarbon dates were obtained from two canadian kettle basins having similar geological and hydrological characteristics to develop criteria for evaluating the validity of radiocarbon dates on lake sediment from basins in calcareous terrain radiocarbon dates from a site in alberta show a variable hard water effect related to local hydrological changes during postglacial history of the lake basin whereas radiocarbon dates from the other site in ontario show no noticeable influence of old carbon during its history these differences are mainly related to lake water residence time which has influenced carbon isotopic exchange between atmospheric co2 and dissolved inorganic carbon in lake water 13c values for bulk organic sediment and terrestrial and aquatic macrofossils reveal that the main component of lake sediment at both sites is autocthonous in origin furthermore each site supported different submerged aquatic plant communities that used different sources of carbon for photosynthesis thereby imprinting the organic sediments with a characteristic 13c composition both sites reflect a clear relationship between 13c values and paleoproductivity this study shows the individualistic response of the developing lake system to the hydrology lake biota and local geology and demonstrates the problem of using 13c in lake sediments as a single criterion to recognize the validity of radiocarbon dates of lake sediment without supporting paleoecological information

estimating seismic velocities at ultrasonic frequencies in partially saturated rocks seismic velocities in rocks at ultrasonic frequencies depend not only on the degree of saturation but also on the distribution of the fluid phase at various scales within the pore space two scales of saturation heterogeneity are important 1 saturation differences between thin compliant pores and larger stiffer pores and 2 differences between saturated patches and undersaturated patches at a scale much larger than any pore we propose a formalism for predicting the range of velocities in partially saturated rocks that avoids assuming idealized pore shapes by using measured dry rock velocity versus pressure and dry rock porosity versus pressure the pressure dependence contains all of the necessary information about the distribution of pore compliances for estimating effects of saturation at the finest scales where small amounts of fluid in the thinnest most compliant parts of the pore space stiffen the rock in both compression and shear increasing both p and s wave velocities in approximately th

biogeochemical evidence from ogcp core 2a sediments for environmental changes preceding deposition of tuff ib and climatic transitions in upper bed i of the olduvai basin abstract sediment cores recovered by the olduvai gorge coring project ogcp in 2014 afford the opportunity to examine the coupling of biogeochemical evidence for climatic and environmental change within the context of hominin evolution at this renowned east african locality investigations of elemental total organic carbon toc or corg wt carbon to nitrogen ratio c n molecular source specific biomarkers and isotopic 13corg 2hnc31 compositions of organic matter provide evidence for temporal changes in sedimentary materials derived from terrestrial plants c3 c4 and aquatic producers algae sponges cyanobacteria and in precipitation the 13 kyr record of upper bed i immediately preceding tuff ib extends high resolution stratigraphic profiles of precession scale alternations of wetter and drier conditions to encompass the entire interval from the bed i basalt to tuff ib the second wetter interval designated w2 records local influences on climate and water supply consistent with evidence for discrete sediment sources based its physical properties e g gamma radiation magnetic susceptibility compared with the overall sequence the 13ctoc values for wetter interval w2 reveal two millennial scale 2 5 kyr drier episodes followed by a shift in the dominance of c3 over c4 plants accompanying the transition to a drier climate d3 moreover biogeochemical data for upper bed i show that changes from drier to wetter conditions occur more rapidly 900 yr than wetter to drier transitions 2 6 kyr based on interpolated ages in addition biomarker profiles indicate that aquatic plants primarily algae and macrophytes may have been subject to more profound and faster fluctuations than variations in terrestrial vegetation expressed in terms of the relative proportions of woodland and grassland settings thus environmental and climatic changes not only influenced the availability of resources of food and shelter for hominins within the olduvai region but also led to their variation on centennial to millennial to precessional timescales

atmospheric circulation patterns during late pleistocene climate changes at lake malawi africa abstract the climate of tropical africa transitioned from an interval of pronounced orbitally paced megadroughts to more humid and stable conditions approximately 70 000 years ago scholz et al 2007 the regional atmospheric circulation patterns that accompanied these climatic changes however are unclear due to a paucity of continental paleoclimate records from tropical africa extending into the last interglacial we present a new 140 kyr record of the deuterium hydrogen isotopic ratio of terrestrial leaf waxes d wax from drill cores from lake malawi southeast africa that spans this important climatic transition d wax shifts from highly variable and relatively d depleted to more stable and d enriched around 56 ka contemporary with the onset of more humid conditions in the region moisture source and transport history dominate the d wax signal at lake malawi with local rainfall amount playing a secondary role for much of the paleorecord analysis of modern moisture sources for lake malawi suggests that d depletion of waxes during the megadroughts may have been caused by an enhanced contribution of the drier d depleted air mass currently located in central southern africa to the lake malawi catchment this d depleted air mass is associated with the descending limb of the hadley cell which implies significant changes in the hadley circulation during the megadroughts and related changes in the position of the intertropical convergence zone over africa these findings demonstrate the ability of d wax to serve as an atmospheric tracer when used in conjunction with additional proxy records for moisture balance and elucidate potential mechanisms for pronounced hydrological change in southeast africa during the late pleistocene

on a tectonic mechanism for regional sealevel variations abstract no satisfactory tectonic explanations have yet been offered for the apparent sealevel fluctuations of about 1 cm 1000 years and a magnitude of up to a few hundred meters that have been proposed by vail et al 1 we propose a mechanism that does appear to be able to explain these changes if horizontal stresses of the order of a few kilobars occur in the lithosphere and if changes in these stress fields occur on geological time scales the proposed model is one of an interaction between these stresses and the deflections of the lithosphere caused by sedimentary loading apparent sealevel changes of up to 100 m can be produced at the flanks of the sedimentary basins by this interaction the mechanism is most effective for young margins that are subject to rapid sediment loading by its nature the tectonic model can explain contemporaneous fluctuations in apparent sealevel in neighbouring depositional environments in principle it implies the possibility of regional correlations in different basinal settings

selective preservation of old organic carbon fluvially released from sub arctic soils amplified climate warming in the arctic may cause thaw remobilization of its large soil organic carbon soc pool here we assess the remobilization and preservation of old soc by the watershed integrated radiocarbon signature of molecular soc markers released from northernmost scandinavia the radiocarbon analyses revealed a remarkable fractionation for identical vascular plant markers 420 or 6000 14c years upon settling from surface water to the underlying sediments from this we infer fluvial export of two soc pools a young surface peat component and an old deep mineral soil component the young pool exists as an easily degradable humic suspension while the old pool is matrix protected from degradation and ballasted for preferential settling the two soil types with highest oc in arctic permafrost evidently exhibit different susceptibilities to degradation hence a significant part of the thaw released oc may simply be fluvially relocated to sediments instead of being emitted to the atmosphere

estimating rock porosity and fluid saturation using only seismic velocities evaluation of the fluid content in deep earth reservoirs or fluid contaminants in shallow earth environments has required the use of geophysical imaging methods such as seismic reflection prospecting interpretation of seismic velocities and amplitudes is based on theories of fluid saturated and partially saturated rocks that have been available since the 1950s here we present a new synthesis of the same physical concepts that uses compressional wave velocities together with shear wave velocities in a scheme that is much simpler to understand and apply yet yields detailed information about porosity and fluid saturation magnitudes and spatial distribution the key idea revolves around the fact that the density and the lame elastic parameter are the only two parameters determining seismic velocities that also contain information about fluid saturation at low enough frequencies gassmann s well known equations show that the shear modulus is independent of the fluid saturation level we use these facts to

a new look at old carbon in active margin sediments recent studies suggest that as much as half of the organic carbon oc undergoing burial in the sediments of tectonically active continental margins may be the product of fossil shale weathering these estimates rely on the assumption that vascular plant detritus spends little time sequestered in intermediate reservoirs such as soils freshwater sediments and river deltas and thus only minimally contributes to the extraneously old 14c ages of total organic matter often observed on adjacent shelves here we test this paradigm by measuring the 14c and 13c values of individual higher plant wax fatty acids as well as the 13c values of extractable alkanes isolated from the eel river margin california the isotopic signatures of the long chain fatty acids indicate that vascular plant material has been sequestered for several thousand years before deposition a coupled molecular isotope mass balance used to reassess the sedimentary carbon budget indicates that the fossil component is less abundant than previously estimated with pre aged terrestrial material instead composing a considerable proportion of all organic matter if these findings are characteristic of other continental margins proximal to small mountainous rivers then the importance of petrogenic oc burial in marine sediments may need to be reevaluated 2009 the geological society of america

along strike variations of the slip direction on normal faults insights from three dimensional finite element models normal faults in nature exhibit a systematic variation of the slip direction along strike with pure dip slip at their centres that changes gradually to oblique slip near their tips here we evaluate the variation of the slip direction along normal faults by three dimensional finite element modelling the model results reveal a nearly linear increase of the strike slip component over two thirds of the distance from the fault centre to its tips which results in an increasing obliqueness of the slip vector along strike excluding the fault tips the relationship between lateral slip and fault length can be approximated by a power law function which shows that the strike slip component is proportional to the dip slip and to the fault dip the development of the sinistral and dextral slip components is caused by the orientation of the minimum principal stress which is deflected toward the fault centre in both footwall and hanging wall a comparison with two faults in the central apennines italy shows good agreement between modelled and measured slip vectors the occurrence of converging slip patterns implies that caution is advised when inferring oblique extension regional stress trajectories and palaeostress fields from slip vectors measured away from the fault centre

δd values of individual n alkanes from terrestrial plants along a climatic gradient implications for the sedimentary biomarker record abstract the compound specific hydrogen isotope composition d of sedimentary n alkanes is increasingly used as a palaeoclimate proxy to explore the origin of the hydrogen isotope signal of n alkanes from higher terrestrial plant biomass in sedimentary organic matter of small lakes we have analysed the n alkane composition and d values of 31 plant biomass samples birch betula beech fagus oak quercus alder alnus hornbeam carpinus and myrtle myrtus as well as non stomata containing sphagnum cladonia and moss from 14 sites along a climatic gradient from northern finland to southern italy eleven of the sites were previously investigated for the n alkane d values in adjacent lake sediments and are compared to the leaf wax n alkane d values the distribution of terrestrial n alkanes in lake sediments was not found to be characteristic of the dominant vegetation around the lake evidently n alkane distributions within the same species at different sites were found to be variable these findings complicate the use of certain n alkane distributions in sediments as a palaeoenvironmental indicator d values of plant biomass n alkanes show a significant positive correlation with the precipitation d values biomass n alkane d values are in general less negative than the associated sedimentary n alkanes of terrestrial origin possibly due to the stronger evapotranspiration during the summer when sampling took place this suggests that n alkanes in leaves show seasonal variations and the sedimentary organic matter receives the lighter isotope signal of the autumn when most leaves are incorporated into the sediment the variability of the d values from non stomata containing plants is much higher than for broadleaf trees since stomata can regulate water loss through evapotranspiration the average chain length acl of n alkanes from deciduous tree leaves increases from north to south with increasing acl the hydrogen isotopic fractionation e between source water and n alkanes also increases our results prove that terrestrial n alkane d values record the d value of precipitation modified by the amount of isotope enrichment in the leaf water due to plant anatomy stomata vs no stomata and site specific meteorological conditions such as evapotranspiration relative humidity and soil moisture therefore terrestrial n alkanes in lake sediments can deliver information on changes in these parameters over geological timescales in lake sediments where aquatic n alkanes such as n c 17 record the lake water d value the isotopic difference between terrestrial and aquatic n alkanes could therefore be used to reconstruct changes in evapotranspiration

landscape evolution at the margin of the basin and range streams erode new basins in extensional mountain ranges where tectonic asymmetry facilitates divide migration ranges in the northern basin and range of the united states form a space for time series that illustrates stream incision and divide migration following footwall uplift accelerating basin growth and changes in the amount and direction of volume loss during basin expansion stream erosion exceeds hillslope retreat which elevates summit plateaus

abyssal hills formed by stretching oceanic lithosphere tectonic plates are formed and move apart at mid ocean ridges some portion of this plate separation process can occur by stretching of the crust resulting in a complex pattern of extensional faults abyssal hills the most ubiquitous topographic features on earth1 are thought to be a product of this faulting2 3 here we report the results of a self consistent numerical model of lithospheric formation and stretching that includes spontaneous fault creation in this model an axial valley develops where the fault activity is most concentrated the frozen fault generated topography rafted out of the axial valley is visually and statistically similar to observed abyssal hills formed at many slower spreading ridges faults appear to be replaced by new faults because their offset changes the local stress field we accordingly need no temporal variation in magmatism as required by some previous models4 5 6 to control the spacing or offset of faults our model results suggest instead that the irregularity of abyssal hill relief may result from a self organized critical stress state at spreading centres

the origin of large local uplift in extensional regions large localized uplift is commonly observed in continental regions undergoing extension these observations can be modelled by planar high angle normal faulting of an elastic upper crust overlying an inviscid lower crust isostasy provides the necessary driving force the model quantifies the role of flexural rigidity density variations in the crust and erosion and deposition of sediment

high resolution fault displacement mapping from three dimensional seismic data evidence for dip linkage during fault growth abstract detailed mapping using high resolution three dimensional seismic data has revealed a number of sub horizontal anomalies in the distribution of vertical displacement throw on the planes of growth faults in the gulf of mexico recognition of these anomalies is highly sensitive to the interval at which the fault displacements are sampled because they represent local decreases in throw which are confined to small discrete parts of the fault planes the distribution of the anomalies is inconsistent with model displacement fields of quasi elliptical concentric contours and is therefore incompatible with models of fault growth by uniform slip distribution and radial tip line propagation an alternative model is proposed whereby the evolution of a fault plane is established by the propagation and linkage of precursor fault segments in the dip direction dip linkage overlap and linkage of fault tips in the dip direction results in relay structures that are sub parallel to fault strike and therefore displacement minima that are sub horizontal on normal and thrust faults however since they are orthogonal to the main slip direction on the fault these structures have a low preservation potential and are therefore unlikely to be well resolved on cross sectional seismic profiles

a 4000 year lacustrine record of environmental change in the southern maya lowlands peten guatemala a 4000 yr sediment core record from lake salpeten guatemala provides evidence for maya induced forest clearance and consequent soil erosion between 1700 cal yr b c and 850 cal yr a d radiocarbon ages of wood seeds and charcoal support an age depth model with average errors of 110 cal yr relatively low carbonate 18o values between 1300 and 400 cal yr b c coincide with pollen evidence for forest loss consistent with increased surface and groundwater flow to the lake minimum 18o values between 400 cal yr b c and 150 cal yr a d suggest a high lake level as do 14c dated aquatic gastropods as much as 7 5 m above the present lake stage high lake levels resulted from reduced evaporation to precipitation ratios increased hydrologic input caused by anthropogenic deforestation or both the preclassic abandonment 150 a d and early classic late classic boundary 550 a d are marked by relatively high 18o values indicating reduced lake levels oxygen isotope composition increased further coincident with the terminal classic maya demographic decline between 800 and 900 a d this period of high 18o may have been caused by the greater aridity that has been documented in northern yucatan lakes or by decreased hydrologic input to the lake as a consequence of forest recovery reduced soil erosion after 850 cal yr a d coincided with the terminal classic maya demographic decline and permitted forest recovery and resumption of organic sedimentation

cenozoic postrift domal uplift of north atlantic margins an asthenospheric diapirism model postrift domal uplifts are a distinct feature of the northern north atlantic rifted margins uplifted regions southern norway finnmark svalbard northern united kingdom occur with a typical spacing of 900 km the amount of domal uplift is substantial 1 2 km thermochronological geomorphological and seismic stratigraphic data suggest a coincident neogene onset of uplift postdating north atlantic breakup and predating onset of glaciation the norwegian domes are characterized by strongly negative gravity anomalies and reduced mantle p wave and s wave velocities previous models for uplift around the north atlantic e g glacial erosion intraplate stresses secondary convection fail to explain the above characteristics we present an asthenospheric diapir model based on a rayleigh taylor instability wherein a hot icelandic asthenosphere layer meets cold cratonic lithosphere the generated asthenospheric diapirs and associated partial melting offer a viable explanation for updoming application of this model to the south norwegian dome succesfully explains most of the currently available data

effect of sub core scale heterogeneities on acoustic and electrical properties of a reservoir rock a co2 flooding experiment of brine saturated sandstone in a computed tomography scanner the effect of sub core scale heterogeneity on fluid distribution pattern and the electrical and acoustic properties of a typical reservoir rock was studied by performing drainage and imbibition flooding tests with co2 and brine in a laboratory moderately layered rothbach sandstone was used as a test specimen two core samples were drilled one perpendicular and the other parallel to the layering to allow injection of fluids along and normal to the bedding plane during the test 3d images of fluid distribution and saturation levels were mapped by an industrial x ray ct scanner together with simultaneous measurement of electrical resistivity ultrasonic velocities as well as amplitudes the results showed how the layering and the flooding direction influenced the fluid distribution pattern and the saturation level of the fluids for a given fluid saturation level the measured changes in the acoustic and electrical parameters were affected by both the fluid distribution pattern and the layering orientation relative to the measurement direction the p wave amplitude and the electrical resistivity were more sensitive to small changes in the fluid distribution patterns than the pwave velocity the change in amplitude was the most affected by the orientation of the layering and the resulting fluid distribution patterns in some instances the change due to the fluid distribution pattern was higher than the variation caused by the change in co2 saturation as a result the gassmann relation based on uniform or patchy saturation pattern was not suitable to predict the p wave velocity variation overall the results demonstrate the importance of core imaging to improve our understanding of fluid distribution patterns and the associated effects on measured rock physics properties

bargen continuous gps data across the eastern basin and range province and implications for fault system dynamics we collected data from a transect of continuous global positioning system gps sites across the eastern basin and range province at latitude 39 n from 1997 2000 intersite velocities define a region 350 km wide of broadly distributed strain accumulation at 10 nstr yr 1 on the western margin of the region site egan 10 km north of ely nevada moved at a rate of 3 9 0 2 mm yr 1 to the west relative to site cast which is on the colorado plateau velocities of most sites to the west of ely moved at an average rate of 3 mm yr 1 relative to cast defining an area across central nevada that does not appear to be extending significantly the late quaternary geological velocity field derived using seismic reflection and neotectonic data indicates a maximum velocity of egan with respect to the colorado plateau of 4 mm yr 1 also distributed relatively evenly across the region the geodetic and late quaternary geological velocity fields therefore are consistent but strain release on the sevier desert detachment and the wasatch fault appears to have been anomalously high in the holocene previous models suggesting horizontal displacement rates in the eastern basin and range near 3 mm yr 1 which focused mainly along the wasatch zone and intermountain seismic belt may overestimate the holocene wasatch rate by at least 50 per cent and the quaternary rate by nearly an order of magnitude while ignoring potentially major seismogenic faults further to the west

active deformation and shallow structure of the wagner consag and delfin basins northern gulf of california mexico oblique rifting began synchronously along the length of the gulf of california at 6 ma yet there is no evidence for the existence of oceanic crust or a spreading transform fault system in the northern gulf instead multichannel seismic data show a broad shallow depression 70 200 km marked by active distributed deformation and six 10 km wide segmented basins lacking well defined transform faults we present detailed images of faulting and magmatism based on the high resolution and quality of these data the northern gulf crust contains a dense up to 18 faults in 5 km complex network of mainly oblique normal faults with small offsets dips of 60 80 and strikes of n n30 e faults with seafloor offsets of tens of meters bound the lower and two upper delfin basins these subparallel basins developed along splays from a transtensional zone at the nw end of the ballenas transform fault twelve volcanic knolls were identified and are associated with the strands or horsetails from this zone a structural connection between the two upper delfin basins is evident in the switching of the center of extension along axis sonobuoy refraction data suggest that the basement consists of mixed igneous sedimentary material atypical of mid ocean ridges on the basis of the near surface manifestations of active faulting and magmatism seafloor spreading will likely first occur in the lower delfin basin we suggest the transition to seafloor spreading is delayed by the lack of strain partitioned and focused deformation as a consequence of shear in a broad zone beneath a thick sediment cover

footwall topographic development during continental extension 1 we examine the progressive development of footwall topography associated with a set of active normal faults in the northeastern basin and range province of the western united states fault length and displacement increase monotonically from northeast to southwest in the study area allowing us to track both variations in footwall morphology with increasing displacement and along strike changes in morphology on a single fault we show that patterns of catchment area footwall relief and catchment outlet spacing vary predictably and are related to the growth of the range bounding normal fault array in this semiarid region full parsing of footwall drainage area and removal of antecedent topography do not occur until fault arrays grow beyond two crustal scale segments multiple segment faults with lengths of up to 150 km have footwall relief that is limited to 1000 m in the center of the footwall and that decays to zero at the fault tips over a length scale of 15 km we hypothesize that this relatively uniform footwall relief is erosionally limited and reflects the efficacy of surface processes in removing footwall material in the center of the footwall if the fault array grows by relatively steady propagation of the tips we suggest that the 15 km length scale required to reach uniform relief is related to a timescale of relief generation by the fault tip propagation rate while such propagation rates are poorly known an average rate of 10 mm yr 1 would imply footwall relief generation over a timescale of 1 myr

spatial variations in catchment averaged denudation rates from normal fault footwalls we test the spatial correspondence between rock uplift in active normal fault footwalls in the western usa and catchment averaged denudation rates from cosmogenic radionuclide crn analysis we find that denudation rates vary along strike depending on the fault length and displacement for the 18 km long sweetwater fault foot wall relief is largely inherited from the prefaulting topography and denudation rates are only partly reflective of fault displacement for the 130 km long wassuk fault all inherited topography has been removed by erosion in response to fault displacement denudation rates however show little along strike consistency and no correlation with catchment size or morphology we argue that in the early stages of fault growth crn derived denudation rates reflect inherited prefaulting relief with an overprint of fault controlled erosion in later stages of fault growth rates are decoupled from fault displacement through the impact of stochastic landsliding events and longer term measures of denudation such as low temperature thermochronometry that integrate over multiple earthquakes may provide a better record of spatial variations in rock uplift

correlation of bulk sedimentary and compound specific δ 13 c values indicates minimal pre aging of n alkanes in a small tropical watershed abstract inherent to sedimentary compound specific isotopic proxies of paleoecological and paleoclimate change is the assumption that biomarkers are coeval with the surrounding sedimentary matrix compound specific radiocarbon analyses of lake and nearshore marine sediments have indicated a potential offset between the ages of terrestrial biomarkers and their surrounding sediments that could confound efforts to establish strong chronological control for compound specific isotopic data we conducted high resolution compound specific 13c analyses of n alkanes 13calkane in a well studied sediment core from laguna castilla dominican republic and compared the results to bulk sedimentary 13c 13cbulk fossil pollen and sediment geochemistry to assess potential pre aging of alkanes in the terrestrial environment prior to deposition we found significant positive correlations between 13cbulk values and 13calkane values indicating little or no temporal lag in the response of 13calkane values to vegetation change and thus little or no offset in the age of terrestrially derived compounds and the organic fraction of the sedimentary matrix while this study highlights the need for further research into the variables affecting age offsets between proxy data we propose the comparison of 13cbulk and 13calkane values as a method to assess potential age offsets between compound specific and other proxy datasets particularly in small watersheds with sediment records containing a high proportion of allochthonous organic matter this method is more available to researchers than obtaining numerous compound specific radiocarbon analyses which are costly and not a routine service offered by radiocarbon facilities

the basin and range province origin and tectonic significance the basin and range province is a vast arid tract of regionally corrugated angular topography of high relief in the western cordillera it is characterized by evenly spaced parallel mountain ranges and intervening desert basins fig ure la the range flanks are marked by poorly sorted gravel aprons that slope smoothly basinward interrupted here and there by low fault scarps that paral lel the range front faults and by alluvial fans at the mouths of canyons draining the ranges thermal springs located at or near range bounding faults attest to vigorous hydrothermal circulation within zones of fracture porosity created and maintained by faulting in the southern part of the province especially in southeastern california and southwestern arizona range fronts have been worn back by erosion leaving a thin veneer of gravel on an erosion cut bedrock surface that slopes gently outward the range bounding faults of these mountain blocks are buried at the outer edge of such pediments often at considerble distances from the erosional remnants of the ranges themselves the american physiographer n m fenneman 1928 1931 named the basin and range province and defined its general boundaries as thus circum scribed the province includes some 800 000 km2 of area in eight western states later students pardee 1950 lawrence 1976 reynolds 1979 eaton 1979b have observed that many of the fundamental geological and geo physical characteristics of the province are found well beyond the boundaries drawn by fenneman which were based on physiography alone as a tec tonophysical entity its areal extent is greater than 1 million km2 more than 10 of the area of the united states figure 1 fenneman 1931 subdivided the province into five physiographic sections the largest of which is the great basin see figure 1b it is not as its name implies a single regional depression with a common topographic center but is characterized instead by isolated networks of interior drainage divisible into

estimation of co2 saturation during both co2 drainage and imbibition processes based on both seismic velocity and electrical resistivity measurements summary in order to monitor injected carbon dioxide co2 simultaneous measurements of seismic velocity and electrical resistivity are employed during the drainage co2 injection and imbibition water injection processes of a berea sandstone supercritical co2 10 mpa at 40 o c was injected into a water saturated berea sandstone in the drainage stage and monitored via simultaneous measurements after the injection of supercritical co2 fresh distilled water was injected into the co2 injected sandstone during the imbibition stage electrical resistivity and p wave velocity measurements acquired during the drainage and imbibition stages were employed to evaluate co2 saturations sco2 based on the resistivity index and the gassmann fluid substitution equations respectively comparing estimated values for sco2 saturation against those from volume derived sco2 based on analysis on injected and drained fluid volumes in the drainage process we conclude that gassmann brie and resistivity index are suitable for the evaluation based on p wave velocity and electrical resistivity respectively rt based estimation properly tracks the variation in sco2 even when sco2 is large 0 15 while vp based estimation is sensitive to the variation in sco2 when sco2 is small 0 1 while properly estimating sco2 when sco2 is small 0 1 monitoring the co2 imbibition process confirms residual co2 saturation within the sample

can sedimentary leaf waxes record d h ratios of continental precipitation field model and experimental assessments abstract d h ratios of leaf waxes d wax derived from terrestrial plants and preserved in lake sediments can provide important information on past continental hydrology ideally d wax can be used to reconstruct precipitation d h ratios d p which is a well established paleoclimate proxy however many other factors such as vegetation and relative humidity rh also affect d wax variation how the combination of these factors affects sedimentary d wax is unclear here we use a transect of 32 lake surface sediments across large gradients of precipitation relative humidity and vegetation composition in the southwestern united states to study the natural factors affecting sedimentary d wax d values of c 28 n alkanoic acids show significant correlation with d p values r 2 0 76 with an apparent isotopic enrichment of 99 8 indicating that sedimentary d wax values track overall d p variation along the entire transect leaf waxes produced by plants grown under controlled conditions rh 80 60 40 show a small increase in d h ratios as rh decreases consistent with prediction from the craig gordon model however the isotopic effect of rh on d wax along the natural transect is partially countered by the opposing influence of vegetation changes the correlation between d wax and d p values is significantly higher r 2 0 84 in the drier portions of the transect than in the wetter regions r 2 0 64 this study suggests that d h ratios of sedimentary leaf waxes can be used as a proxy for precipitation d variations with particularly high fidelity in dry regions although more studies in other regions will be important to further test this proxy

controls on the age of vascular plant biomarkers in black sea sediments abstract transfer of organic carbon oc from the terrestrial to the oceanic carbon pool is largely driven by riverine and aeolian transport before transport however terrigenous organic matter can be retained in intermediate terrestrial reservoirs such as soils using compound specific radiocarbon analysis of terrigenous biomarkers their average terrestrial residence time can be evaluated here we show compound specific radiocarbon 14c ages of terrigenous biomarkers and bulk 14c ages accompanied by geochemical proxy data from core top samples collected along transects in front of several river mouths in the black sea 14c ages of long chain n alkanes long chain n fatty acids and total organic carbon toc are highest in front of the river mouths correlating well with bit branched and isoprenoid tetraether indices which indicates contribution of pre aged soil derived terrigenous organic matter the radiocarbon ages decrease further offshore towards locations where organic matter is dominated by marine production and aeolian input potentially contributes terrigenous organic matter average terrestrial residence times of vascular plant biomarkers deduced from n c29 31 alkanes and n c28 30 fatty acids ages from stations directly in front of the river mouths range from 900 70 years to 4400 170 years these average residence times correlate with size and topography in climatically similar catchments whereas the climatic regime appears to control continental carbon turnover times in morphologically similar drainage areas of the black sea catchment along transect data imply petrogenic contribution of n c29 31 alkanes and input via different terrigenous biomarker transport modes i e riverine and aeolian resulting in aged biomarkers at offshore core locations because n c29 31 alkanes show contributions from petrogenic sources n c28 30 fatty acids likely provide better estimates of average terrestrial residence times of vascular plant biomarkers moreover sedimentary n c28 and n c30 fatty acids appear clearly much less influenced by autochthonous sources than n c24 and n c26 fatty acids as indicated by increasing radiocarbon ages with increasing chain length and are thus more representative as vascular plant biomarkers

the provenance of vegetation and environmental signatures encoded in vascular plant biomarkers carried by the ganges brahmaputra rivers organic matter carried by rivers and deposited in continental and marine sediments contains valuable information on past environmental conditions and their impact on the terrestrial biosphere in order to use sedimentary records to reconstruct past environmental conditions on the continents such as vegetation cover and type or precipitation intensity we need to understand the provenance of the organic signatures and how they are transferred and potentially modified by fluvial transport to the sedimentary reservoir in particular we need to understand how environmental conditions are imprinted in the composition of riverine particulate organic carbon here we investigate the stable carbon and hydrogen isotopic signatures of vascular plant leaf wax biomarkers in the modern day ganges and brahmaputra river complex one of the largest fluvial systems on earth the distribution of n alkanes and n alkanoic acids in ganges brahmaputra river sediments suggests that vascular plant inputs are consistently a significant component of the organic carbon pool molecular 13c measurements reveal that c3 vegetation inputs delivered by the himalayan rivers are partly degraded and replaced by mixed c3 c4 vegetation input in the floodplain the hydrogen isotopic composition of long chain c24 n alkanoic acids in combination with their stable c isotopic composition provides constraints on the isotopic composition of the environmental water used by higher plants within the drainage basin calculated compositions compare well with the depleted d isotopic ratios of the river water during the summer monsoon suggesting that h isotopic compositions of long chain alkanoic acids are a valuable proxy for the composition of summer monsoon moisture in the ganges brahmaputra basin detailed studies of the isotopic anatomy of modern river systems are critical for informed interpretation of marine sedimentary records in river influenced continental margins

seismic wave attenuation and dispersion resulting from wave induced flow in porous rocks a review one major cause of elastic wave attenuation in heterogeneous porous media is wave induced flow of the pore fluid between heterogeneities of various scales it is believed that for frequencies below 1 khz the most important cause is the wave induced flow between mesoscopic inhomogeneities which are large compared with the typical individual pore size but small compared to the wavelength various laboratory experiments in some natural porous materials provide evidence for the presence of centimeter scale mesoscopic heterogeneities laboratory and field measurements of seismic attenuation in fluid saturated rocks provide indications of the role of the wave induced flow signatures of wave induced flow include the frequency and saturation dependence of p wave attenuation and its associated velocity dispersion frequency dependent shear wave splitting and attenuation anisotropy during the last four decades numerous models for attenuation and velocity dispersion from wave induced flow have been developed with varying degrees of rigor and complexity these models can be categorized roughly into three groups according to their underlying theoretical framework the first group of models is based on biot s theory of poroelasticity the second group is based on elastodynamic theory where local fluid flow is incorporated through an additional hydrodynamic equation another group of models is derived using the theory of viscoelasticity though all models predict attenuation and velocity dispersion typical for a relaxation process there exist differences that can be related to the type of disorder periodic random space dimension and to the way the local flow is incorporated the differences manifest themselves in different asymptotic scaling laws for attenuation and in different expressions for characteristic frequencies in recent years some theoretical models of wave induced fluid flow have been validated numerically using finite difference finite element and reflectivity algorithms applied to biot s equations of poroelasticity application of theoretical models to real seismic data requires further studies using broadband laboratory and field measurements of attenuation and dispersion for different rocks as well as development of more robust methods for estimating dissipation attributes from field data

a 35 myr north american leaf wax compound specific carbon and hydrogen isotope record implications for c4 grasslands and hydrologic cycle dynamics article i nfo hydrology source region and timing of precipitation are important controls on the climate of the great plains of north america and the composition of terrestrial ecosystems moisture delivered to the great plains varies seasonally and predominately derives from the gulf of mexico atlantic ocean with minor contributions from the pacific ocean and arctic region for this work we evaluate long term relationships for the past 35 million years between north american hydrology climate and floral change using isotopic records and average carbon chain lengths of higher plant n alkanes from gulf of mexico sediments dsdp site 94 we find that carbon isotope values 13 c of n alkanes corrected for variations in the 13 c value of atmospheric co2 provide minor evidence for contributions of c4 plants prior to the middle miocene a sharp spike in c4 input is identified during the middle miocene climatic optimum and the influence of c4 plants steadily increased during the late miocene into the pleistocene consistent with other north american records chain length distributions of n alkanes indicative of the composition of higher plant communities remained remarkably constant from 33 to 4 ma however a trend toward longer chain lengths occurred during the past 4 million years concurrent with an increase in 13 c values indicating increased c4 plant influence and potentially aridity the hydrogen isotope values d of n alkanes are relatively invariant between 33 and 9 ma and then become substantially more negative 75 from 9 to 2 ma changes in the plant community and temperature of precipitation can solely account for the observed variations in d from 33 to 5 ma but cannot account for plio pleistocene d variations and imply substantial changes in the source region of precipitation and seasonality of moisture delivery we posit that hydrological changes were linked to tectonic and oceanographic processes including the shoaling and closure of the panamanian seaway amplification of north atlantic deep water production and an associated increase of meridional winds the southerly movement of the intertropical convergence zone near 4 ma allowed for the development of a near modern pressure storm track system driving increased aridity and changes in seasonality within the north american interior

age discrepancy between molecular biomarkers and calcareous foraminifera isolated from the same horizons of northwest pacific sediments abstract recent observations show that establishment of molecular level radiocarbon stratigraphy is increasingly critical for paleoceanographic studies especially to enable comparable discussion about past ocean and climate changes inferred from multiple proxy records based on lipid biomarkers and calcareous foraminiferal microfossils so far although we have interesting evidence that there are temporal and spatial age offsets between the algal alkenone biomarker used for sst sea surface temperature estimates and planktonic foraminifera in regions with high sedimentation rates less is known about such age offsets in the settings of lower sedimentation in this study to investigate the potential of biomarkers as an alternative dating proxy to foraminifera in a low sedimentation rate setting we measured radiocarbon ages of 17 different lipid biomarkers fatty acids fas n alkanes and alkenones bulk total organic matter toc and foraminifera from two sections 12 15 cm and 21 24 cm depth of a surface sediment core in the northwest pacific the sedimentation rate estimated from the toc ranged from 10 5 cm kyr in the core top to 0 9 cm kyr in the lower part of the core the ages of the fas detected at 12 15 cm depth ranged from 530 yr bp c 18 to 3250 yr bp c 28 the 14 c analysis of the fas could be divided into two groups fas c 16 c 18 derived from marine organisms and those c 24 c 26 c 28 derived from terrestrial higher plants the high molecular weight hmw fas ages were older 2550 yr bp c 24 to 3250 yr bp c 28 than those of the low molecular weight lmw fas 530 yr bp c 18 to 1820 yr bp c 16 at 21 24 cm depth the alkenone ages were 7100 7300 yr younger than those of the planktonic foraminifera in this horizon the alkenone 14 c age 7500 yr bp and the alkenone estimated sst 15 3 c suggest that these alkenones were produced in this region during the holocene the alkenone 14 c age was also in good agreement with those of the lmw fas c 14 ic 15 aic 15 c 16 and c 18 1 derived from marine plankton and bacteria similarly the toc age was 5700 yr younger than that of the planktonic foraminifera these age differences are large compared with those estimated for the horizon at 12 15 cm depth which was characterized by a relatively higher sedimentation rate these trends between ages of alkenones toc and planktonic foraminifera are not comparable to the results from sites with high sedimentation rates such as the benguella upwelling system mollenhauer g eglinton t i ohkouchi n schneider r r muller p j grootes p m et al 2003 asynchronous alkenone and foraminifera records from the benguela upwelling system geochim cosmochim acta 67 2157 2171 or the bermuda rise drift deposit ohkouchi n eglinton t i keigwin l d hayes j m 2002 spatial temporal offsets between proxy records in a sediment drift science 289 1224 1227 which are significantly different sedimentary settings from our site the radiocarbon results from these high sedimentation rate regions suggest that the alkenones are several thousand years older than the coexisting planktonic foraminifera on the other hand the age offsets between alkenones and planktonic foraminifera at our site are larger than those from the other sites and the alkenones are younger than the planktonic foraminifera

normal faulting driven by denudational isostatic rebound fluvial piracy in the guadix baza basin southeast spain promoted erosion of a high volume of sediments during the late quaternary after the former internal drainage of this basin changed to external due to headward erosion by the guadalquivir river as a response to load release this basin underwent uplift which in turn enhanced fluvial incision and erosional processes differential erosion within the guadix baza basin resulted in dissimilar isostatic rebound we numerically model the lithospheric response to sediment unloading and show a total rising of 15 m in the guadix subbasin compared to 2 m in the baza subbasin this differential uplift is likely to have been accommodated along the baza normal fault which has been active throughout the quaternary modeling results suggest that 13 of the total quaternary fault throw directly arises from the differential isostatic readjustment between subbasins this example is one of the first estimates of fault slip partitioning between tectonic and isostatic effects due to unloading driven by river incision

late quaternary behavior of the east african monsoon and the importance of the congo air boundary both atlantic and indian ocean climate dynamics exert influence over tropical african hydroclimate producing complex patterns of convergence and precipitation to isolate the indian ocean influence on african paleohydrology we analyzed the deuterium hydrogen ratio of higher plant leaf waxes delta d wax in a 25 000 year sediment record from lake challa 3 degrees s 38 degrees e in the easternmost area of the african tropics whereas both the seismic record of inferred lake level fluctuations and the branched and isoprenoidal tetraether bit index proxy record changes in hydrology within the challa basin delta d wax as a proxy for the isotopic composition of precipitation delta d p is interpreted as a tracer of large scale atmospheric circulation that integrates the history of the moisture transported to the lake challa area specifically based on modern day isotope rainfall relationships we argue that lake challa delta d wax reflects the intensity of east african monsoon circulation the three hydrological proxy records show generally similar trends for the last 25 000 years but there are important differences between them primarily during the middle holocene we interpret this deviation of delta d wax from local hydrological history as a decoupling of east african monsoon intensity which heavily influences the isotopes of precipitation in east africa today from rainfall amount in the challa basin in combination the hydrological proxy data from lake challa singularly highlight zonal gradients in tropical african climate that occur over a variety of timescales suggesting that the congo air boundary plays a fundamental role in controlling hydroclimate in the african tropics

theoretical derivation of a brie like fluid mixing law prediction of the velocity of acoustic waves in partially saturated rocks is very important in geophysical applications the need to accurately predict acoustic velocities has resulted in a widespread popularity of brie s effective fluid mixing law this empirical model together with gassmann s formula are used routinely in fluid substitution problems in petroleum geophysics and seismic monitoring of carbon capture and storage most attempts to justify brie s model have been focused on interpretation in terms of patchy saturation models and attaching meaning to the brie parameter in terms of the patch size in this paper using a microstructural description of the rock and a parameter relating to capillary pressure we calculate an effective fluid modulus that is very similar to brie s law the fluid mixing law we propose is independent of frequency and has a solid theoretical foundation this proposed law produces analytically harmonic and arithmetic averaging at the endpoints our results indicate that brie like behaviour may not necessarily be related to frequency and patch size dependent phenomena

human impacts climate change and aquatic ecosystem response during the past 2000 yr at lake wandakara uganda analyses of carbon and hydrogen isotope ratios of terrestrial leaf waxes and the carbon and nitrogen abundance ratio and isotopic composition of bulk sediments from lake wandakara a crater lake in western uganda east africa document human and climatic controls on the aquatic system and on the surrounding terrestrial vegetation during the past two millennia our data indicate that wandakara was a relatively stable productive lake surrounded by c3 vegetation from ad 70 to 1000 abrupt changes in the 13c of terrestrial leaf waxes indicate a series of abrupt shifts in the relative abundance of c3 and c4 vegetation caused by a combination of climate change and human activities around wandakara beginning at ad 1000 abrupt shifts in bulk sediment organic geochemistry particularly c n ratios and 15n indicate that human activities at this time caused permanent changes in the limnology of lake wandakara including eutrophication our results suggest that the biogeochemistry of lake wandakara was more sensitive to shifting human impacts than to climate variations during the past millennium highlighting the importance of understanding the intensity of pre colonial human impacts on africa s aquatic ecosystems

laboratory monitoring of p waves in partially saturated sand energy dissipation is observed on seismic data when a wave propagates through a porous medium involving different frequency regimes depending on the nature of rock and fluid types we focus here on the role of partial fluid saturation in unconsolidated porous media looking in particular at p wave phase velocity and attenuation the study consists in running an experiment in a sand filled tank partially saturated with water seismic propagation in the tank is generated in the khz range by hitting a steel ball on a granite plate seismic data are recorded by buried accelerometers and injecting or extracting water controls the partial saturation several imbibition drainage cycles were performed between the water and gas residual saturations a continuous wavelet transform applied on seismic records allowed us to extract the direct p wave at each receiver we observe an hysteresis in phase velocities and inverse quality factors between imbibition and drainage phase velocities and inverse quality factors are then jointly inverted to get a final poro visco elastic model of the partially saturated sand that satisfactorily reproduces the data the model formulation consists in generalizing the biot theory to effective properties of the fluid and medium permeability and bulk modulus in order to properly explain the phase velocity variation as a function of the saturation the strong level of attenuation measured experimentally is further explained by an anelastic effect due to grain to grain sliding adding to biot s losses this study shows that fluid distribution at microscopic scale has strong influence on the attenuation of direct p waves at macroscopic scale and confirms that seismic prospection may be a powerful tool for the characterization of transport phenomena in porous media

an alternative model for the growth of faults conventional growth models suggest that faults become larger due to systematic increases in both maximum displacement and length we propose an alternative growth model where fault lengths are near constant from an early stage and growth is achieved mainly by increase in cumulative displacement the model reconciles the scaling properties of faults and earthquakes and predicts a progressive increase in fault displacement to length ratios as a fault system matures this growth scheme is directly applicable to reactivated fault systems in which fault lengths were inherited from underlying structure and established rapidly the model may also apply to some non reactivated fault systems near constant fault lengths during subsequent growth are attributed to retardation of lateral propagation by interaction between fault tips the model is validated using kinematic constraints from growth strata which are displaced by a system of reactivated normal faults in the timor sea nw australia

long term storage and age biased export of fluvial organic carbon field evidence from west iceland terrestrial organic carbon oc plays an important role in the carbon cycle but questions remain regarding the controls and timescale s over which atmospheric co remains sequestered as particulate oc poc motivated by observations that terrestrial poc is physically stored within soils and other shallow sedimentary deposits we examined the role that sediment storage plays in the terrestrial oc cycle specifically we tested the hypothesis that sediment storage impacts the age of terrestrial poc we focused on the efri haukadalsa river catchment in iceland as it lacks ancient sedimentary bedrock that would otherwise bias radiocarbon based determinations of poc storage duration by supplying pre aged petrogenic poc our radiocarbon measurements of riverine suspended sediments and deposits implicated millennial scale storage times comparison between the sample types suspended and deposits suggested an age offset between transported suspended sediments and stored deposits poc at the time of sampling which is predicted by theory for the sediment age distribution in floodplains we also observed that poc in suspended sediments is younger than the predicted mean storage duration generated from independent geomorphological data which suggested an additional role for oc cycling consistent with this we observed interparticle heterogeneity in the composition of poc by imaging our samples at the microscale using x ray absorption spectroscopy specifically we found that particles within individual samples differed in their sulfur oxidation state which is indicative of multiple origins and or diagenetic histories altogether our results support recent coupled sediment storage and oc cycling models and indicate that the physical drivers of sediment storage are important factors controlling the cadence of carbon cycling

exact expression for the effective acoustics of patchy saturated rocks seismic effects of a partially gas saturated subsurface have been known for many years for example patches of nonuniform saturation occur at the gas oil and gas water contacts in hydrocarbon reservoirs open pore boundary conditions are applied to the quasi static biot equations of poroelasticity to derive an exact analytic expression of the effective bulk modulus for partially saturated media with spherical gas patches larger than the typical pore size the pore fluid and the rock properties can have different values in the central sphere and in the surrounding region an analytic solution prevents loss of accuracy from ill conditioned equations as encountered in the numerical solution for certain input for a sandstone saturated with gas and water we found that the p wave velocity and attenuation in conventional models differ as much as 15 from the exact solution at seismic frequencies this makes the use of present exact theory necessary to describe patchy saturation although more realistic complex patch shapes and distributions were not considered we found that despite earlier corrections the white conventional model does not yield the correct low frequency asymptote for the attenuation