The Experts below are selected from a list of 21156 Experts worldwide ranked by ideXlab platform
Susan L Brantley - One of the best experts on this subject based on the ideXlab platform.
-
Regolith production and transport at the susquehanna shale hills critical zone observatory part 2 insights from meteoric 10 be
Journal of Geophysical Research, 2013Co-Authors: Nicole West, Eric Kirby, Paul R Bierman, Rudy Slingerland, Dylan H Rood, Susan L BrantleyAbstract:[1] Regolith-mantled hillslopes are ubiquitous features of most temperate landscapes, and their morphology reflects the climatically, biologically, and tectonically mediated interplay between Regolith production and downslope transport. Despite intensive research, few studies have quantified both of these mass fluxes in the same field site. Here we present an analysis of 87 meteoric 10Be measurements from Regolith and bedrock within the Susquehanna Shale Hills Critical Zone Observatory (SSHO), in central Pennsylvania. Meteoric 10Be concentrations in bulk Regolith samples (n = 73) decrease with Regolith depth. Comparison of hillslope meteoric 10Be inventories with analyses of rock chip samples (n = 14) from a 24 m bedrock core confirms that >80% of the total inventory is retained in the Regolith. The systematic downslope increase of meteoric 10Be inventories observed at SSHO is consistent with 10Be accumulation in slowly creeping Regolith (~ 0.2 cm yr−1). Regolith flux inferred from meteoric 10Be varies linearly with topographic gradient (determined from high-resolution light detection and ranging-based topography) along the upper portions of hillslopes at SSHO. However, Regolith flux appears to depend on the product of gradient and Regolith depth where Regolith is thick, near the base of hillslopes. Meteoric 10Be inventories at the north and south ridgetops indicate minimum Regolith residence times of 10.5 ± 3.7 and 9.1 ± 2.9 ky, respectively, similar to residence times inferred from U-series isotopes in Ma et al. (2013). The combination of our results with U-series-derived Regolith production rates implies that Regolith production and erosion rates are similar to within a factor of two on SSHO hillcrests.
-
Regolith production and transport in the susquehanna shale hills critical zone observatory part 1 insights from u series isotopes
Journal of Geophysical Research, 2013Co-Authors: Francois Chabaux, Nikki West, Eric Kirby, Susan L BrantleyAbstract:[1] To investigate the timescales of Regolith formation on hillslopes with contrasting topographic aspect, we measured U-series isotopes in Regolith profiles from two hillslopes (north facing versus south facing) within the east-west trending Shale Hills catchment in Pennsylvania. This catchment is developed entirely on the Fe-rich, Silurian Rose Hill gray shale. Hillslopes exhibit a topographic asymmetry: The north-facing hillslope has an average slope gradient of ~20°, slightly steeper than the south-facing hillslope (~15°). The Regolith samples display significant U-series disequilibrium resulting from shale weathering. Based on the U-series data, the rates of Regolith production on the two ridgetops are indistinguishable (40 ± 22 versus 45 ± 12 m/Ma). However, when downslope positions are compared, the Regolith profiles on the south-facing hillslope are characterized by faster Regolith production rates (50 ± 15 to 52 ± 15 m/Ma) and shorter durations of chemical weathering (12 ± 3 to 16 ± 5 ka) than those on the north-facing hillslope (17 ± 14 to 18 ± 13 m/Ma and 39 ± 20 to 43 ± 20 ka). The south-facing hillslope is also characterized by faster chemical weathering rates inferred from major element chemistry, despite lower extents of chemical depletion. These results are consistent with the influence of aspect on Regolith formation at Shale Hills; we hypothesize that aspect affects such variables as temperature, moisture content, and evapotranspiration in the Regolith zone, causing faster chemical weathering and Regolith formation rates on the south-facing side of the catchment. The difference in microclimate between these two hillslopes is inferred to have been especially significant during the periglacial period that occurred at Shale Hills at least ~15 ka before present. At that time, the erosion rates may also have been different from those observed today, perhaps denuding the south-facing hillslope of Regolith but not quite stripping the north-facing hillslope. An analysis of hillslope evolution and response timescales with a linear mass transport model shows that the current landscape at Shale Hills is not in geomorphologic steady state (i.e., so-called dynamic equilibrium) but rather is likely still responding to the climate shift from the Holocene periglacial to the modern, temperate conditions.
-
Regolith production rates calculated with uranium series isotopes at susquehanna shale hills critical zone observatory
Earth and Planetary Science Letters, 2010Co-Authors: Francois Chabaux, Eric Pelt, E Blaes, Susan L BrantleyAbstract:Abstract In the Critical Zone where rocks and life interact, bedrock equilibrates to Earth surface conditions, transforming to Regolith. The factors that control the rates and mechanisms of formation of Regolith, defined here as material that can be augered, are still not fully understood. To quantify Regolith formation rates on shale lithology, we measured uranium-series (U-series) isotopes ( 238 U, 234 U, and 230 Th) in three weathering profiles along a planar hillslope at the Susquehanna/Shale Hills Observatory (SSHO) in central Pennsylvania. All Regolith samples show significant U-series disequilibrium: ( 234 U/ 238 U) and ( 230 Th/ 238 U) activity ratios range from 0.934 to 1.072 and from 0.903 to 1.096, respectively. These values display depth trends that are consistent with fractionation of U-series isotopes during chemical weathering and element transport, i.e., the relative mobility decreases in the order 234 U > 238 U > 230 Th. The activity ratios observed in the Regolith samples are explained by i) loss of U-series isotopes during water–rock interactions and ii) re-deposition of U-series isotopes downslope. Loss of U and Th initiates in the meter-thick zone of “bedrock” that cannot be augered but that nonetheless consists of up to 40% clay/silt/sand inferred to have lost K, Mg, Al, and Fe. Apparent equivalent Regolith production rates calculated with these isotopes for these profiles decrease exponentially from 45 m/Myr to 17 m/Myr, with increasing Regolith thickness from the ridge top to the valley floor. With increasing distance from the ridge top toward the valley, apparent equivalent Regolith residence times increase from 7 kyr to 40 kyr. Given that the SSHO experienced peri-glacial climate ∼ 15 kyr ago and has a catchment-wide averaged erosion rate of ∼ 15 m/Myr as inferred from cosmogenic 10 Be, we conclude that the hillslope retains Regolith formed before the peri-glacial period and is not at geomorphologic steady state. Both chemical weathering reactions of clay minerals and translocation of fine particles/colloids are shown to contribute to mass loss of U and Th from the Regolith, consistent with major element data at SSHO. This research documents a case study where U-series isotopes are used to constrain the time scales of chemical weathering and Regolith production rates. Regolith production rates at the SSHO should be useful as a reference value for future work at other weathering localities.
-
weathering from the soil profile to the watershed what controls the weathering advance rate
Geochimica et Cosmochimica Acta, 2006Co-Authors: Susan L Brantley, Marina Lebedeva, Raymond C Fletcher, Heather L Buss, Joel Moore, Elisabeth M Hausrath, A K Navarre, A F WhiteAbstract:The weathering advance rate for residual, noneroding Regolith is defined as the rate at which the interface between altered Regolith and unaltered parent material propagates downward as the Regolith pile thickens with time. Theoretically, for such a profile developing on infinitely thick parent material, the weathering front reaches a quasistationary state wherein the reaction front propagates downward but the geometry is constant with time.
Eric Kirby - One of the best experts on this subject based on the ideXlab platform.
-
Regolith production and transport at the susquehanna shale hills critical zone observatory part 2 insights from meteoric 10 be
Journal of Geophysical Research, 2013Co-Authors: Nicole West, Eric Kirby, Paul R Bierman, Rudy Slingerland, Dylan H Rood, Susan L BrantleyAbstract:[1] Regolith-mantled hillslopes are ubiquitous features of most temperate landscapes, and their morphology reflects the climatically, biologically, and tectonically mediated interplay between Regolith production and downslope transport. Despite intensive research, few studies have quantified both of these mass fluxes in the same field site. Here we present an analysis of 87 meteoric 10Be measurements from Regolith and bedrock within the Susquehanna Shale Hills Critical Zone Observatory (SSHO), in central Pennsylvania. Meteoric 10Be concentrations in bulk Regolith samples (n = 73) decrease with Regolith depth. Comparison of hillslope meteoric 10Be inventories with analyses of rock chip samples (n = 14) from a 24 m bedrock core confirms that >80% of the total inventory is retained in the Regolith. The systematic downslope increase of meteoric 10Be inventories observed at SSHO is consistent with 10Be accumulation in slowly creeping Regolith (~ 0.2 cm yr−1). Regolith flux inferred from meteoric 10Be varies linearly with topographic gradient (determined from high-resolution light detection and ranging-based topography) along the upper portions of hillslopes at SSHO. However, Regolith flux appears to depend on the product of gradient and Regolith depth where Regolith is thick, near the base of hillslopes. Meteoric 10Be inventories at the north and south ridgetops indicate minimum Regolith residence times of 10.5 ± 3.7 and 9.1 ± 2.9 ky, respectively, similar to residence times inferred from U-series isotopes in Ma et al. (2013). The combination of our results with U-series-derived Regolith production rates implies that Regolith production and erosion rates are similar to within a factor of two on SSHO hillcrests.
-
Regolith production and transport in the susquehanna shale hills critical zone observatory part 1 insights from u series isotopes
Journal of Geophysical Research, 2013Co-Authors: Francois Chabaux, Nikki West, Eric Kirby, Susan L BrantleyAbstract:[1] To investigate the timescales of Regolith formation on hillslopes with contrasting topographic aspect, we measured U-series isotopes in Regolith profiles from two hillslopes (north facing versus south facing) within the east-west trending Shale Hills catchment in Pennsylvania. This catchment is developed entirely on the Fe-rich, Silurian Rose Hill gray shale. Hillslopes exhibit a topographic asymmetry: The north-facing hillslope has an average slope gradient of ~20°, slightly steeper than the south-facing hillslope (~15°). The Regolith samples display significant U-series disequilibrium resulting from shale weathering. Based on the U-series data, the rates of Regolith production on the two ridgetops are indistinguishable (40 ± 22 versus 45 ± 12 m/Ma). However, when downslope positions are compared, the Regolith profiles on the south-facing hillslope are characterized by faster Regolith production rates (50 ± 15 to 52 ± 15 m/Ma) and shorter durations of chemical weathering (12 ± 3 to 16 ± 5 ka) than those on the north-facing hillslope (17 ± 14 to 18 ± 13 m/Ma and 39 ± 20 to 43 ± 20 ka). The south-facing hillslope is also characterized by faster chemical weathering rates inferred from major element chemistry, despite lower extents of chemical depletion. These results are consistent with the influence of aspect on Regolith formation at Shale Hills; we hypothesize that aspect affects such variables as temperature, moisture content, and evapotranspiration in the Regolith zone, causing faster chemical weathering and Regolith formation rates on the south-facing side of the catchment. The difference in microclimate between these two hillslopes is inferred to have been especially significant during the periglacial period that occurred at Shale Hills at least ~15 ka before present. At that time, the erosion rates may also have been different from those observed today, perhaps denuding the south-facing hillslope of Regolith but not quite stripping the north-facing hillslope. An analysis of hillslope evolution and response timescales with a linear mass transport model shows that the current landscape at Shale Hills is not in geomorphologic steady state (i.e., so-called dynamic equilibrium) but rather is likely still responding to the climate shift from the Holocene periglacial to the modern, temperate conditions.
Francois Chabaux - One of the best experts on this subject based on the ideXlab platform.
-
Regolith production and transport in the susquehanna shale hills critical zone observatory part 1 insights from u series isotopes
Journal of Geophysical Research, 2013Co-Authors: Francois Chabaux, Nikki West, Eric Kirby, Susan L BrantleyAbstract:[1] To investigate the timescales of Regolith formation on hillslopes with contrasting topographic aspect, we measured U-series isotopes in Regolith profiles from two hillslopes (north facing versus south facing) within the east-west trending Shale Hills catchment in Pennsylvania. This catchment is developed entirely on the Fe-rich, Silurian Rose Hill gray shale. Hillslopes exhibit a topographic asymmetry: The north-facing hillslope has an average slope gradient of ~20°, slightly steeper than the south-facing hillslope (~15°). The Regolith samples display significant U-series disequilibrium resulting from shale weathering. Based on the U-series data, the rates of Regolith production on the two ridgetops are indistinguishable (40 ± 22 versus 45 ± 12 m/Ma). However, when downslope positions are compared, the Regolith profiles on the south-facing hillslope are characterized by faster Regolith production rates (50 ± 15 to 52 ± 15 m/Ma) and shorter durations of chemical weathering (12 ± 3 to 16 ± 5 ka) than those on the north-facing hillslope (17 ± 14 to 18 ± 13 m/Ma and 39 ± 20 to 43 ± 20 ka). The south-facing hillslope is also characterized by faster chemical weathering rates inferred from major element chemistry, despite lower extents of chemical depletion. These results are consistent with the influence of aspect on Regolith formation at Shale Hills; we hypothesize that aspect affects such variables as temperature, moisture content, and evapotranspiration in the Regolith zone, causing faster chemical weathering and Regolith formation rates on the south-facing side of the catchment. The difference in microclimate between these two hillslopes is inferred to have been especially significant during the periglacial period that occurred at Shale Hills at least ~15 ka before present. At that time, the erosion rates may also have been different from those observed today, perhaps denuding the south-facing hillslope of Regolith but not quite stripping the north-facing hillslope. An analysis of hillslope evolution and response timescales with a linear mass transport model shows that the current landscape at Shale Hills is not in geomorphologic steady state (i.e., so-called dynamic equilibrium) but rather is likely still responding to the climate shift from the Holocene periglacial to the modern, temperate conditions.
-
Regolith production rates calculated with uranium series isotopes at susquehanna shale hills critical zone observatory
Earth and Planetary Science Letters, 2010Co-Authors: Francois Chabaux, Eric Pelt, E Blaes, Susan L BrantleyAbstract:Abstract In the Critical Zone where rocks and life interact, bedrock equilibrates to Earth surface conditions, transforming to Regolith. The factors that control the rates and mechanisms of formation of Regolith, defined here as material that can be augered, are still not fully understood. To quantify Regolith formation rates on shale lithology, we measured uranium-series (U-series) isotopes ( 238 U, 234 U, and 230 Th) in three weathering profiles along a planar hillslope at the Susquehanna/Shale Hills Observatory (SSHO) in central Pennsylvania. All Regolith samples show significant U-series disequilibrium: ( 234 U/ 238 U) and ( 230 Th/ 238 U) activity ratios range from 0.934 to 1.072 and from 0.903 to 1.096, respectively. These values display depth trends that are consistent with fractionation of U-series isotopes during chemical weathering and element transport, i.e., the relative mobility decreases in the order 234 U > 238 U > 230 Th. The activity ratios observed in the Regolith samples are explained by i) loss of U-series isotopes during water–rock interactions and ii) re-deposition of U-series isotopes downslope. Loss of U and Th initiates in the meter-thick zone of “bedrock” that cannot be augered but that nonetheless consists of up to 40% clay/silt/sand inferred to have lost K, Mg, Al, and Fe. Apparent equivalent Regolith production rates calculated with these isotopes for these profiles decrease exponentially from 45 m/Myr to 17 m/Myr, with increasing Regolith thickness from the ridge top to the valley floor. With increasing distance from the ridge top toward the valley, apparent equivalent Regolith residence times increase from 7 kyr to 40 kyr. Given that the SSHO experienced peri-glacial climate ∼ 15 kyr ago and has a catchment-wide averaged erosion rate of ∼ 15 m/Myr as inferred from cosmogenic 10 Be, we conclude that the hillslope retains Regolith formed before the peri-glacial period and is not at geomorphologic steady state. Both chemical weathering reactions of clay minerals and translocation of fine particles/colloids are shown to contribute to mass loss of U and Th from the Regolith, consistent with major element data at SSHO. This research documents a case study where U-series isotopes are used to constrain the time scales of chemical weathering and Regolith production rates. Regolith production rates at the SSHO should be useful as a reference value for future work at other weathering localities.
Bruce Hapke - One of the best experts on this subject based on the ideXlab platform.
-
Bidirectional reflectance spectroscopy 8. The angular width of the opposition effect in Regolith-like media
Icarus, 2021Co-Authors: Bruce HapkeAbstract:Abstract The opposition effect is the sharp, narrow surge observed in the reflectance of a scattering medium near zero phase angle. Numerous observations and experiments have shown that the primary cause of the phenomenon in particulate media is coherent backscattering, in which wavelets traveling in opposite directions along chains of scatterers interfere constructively and generate the peak. A broader opposition surge caused by shadow hiding and preferential escape is also present, but is entangled with the incoherent continuum reflectance on which the coherent peak is superposed, making it difficult to identify and isolate. Theoretical models of media of independent scatterers predict that the angular width and shape of the coherent backscatter peak depend on the wavelength, porosity and particle size. It was hoped that remote measurements of the opposition effect would give information on the latter two quantities in planetary Regoliths. However, observations and laboratory studies of media of large particles in contact with one another find little dependence on any of these quantities. Instead, these studies imply that the opposition effect in Regolith-like media comes from reflection by short chains only a few scatterers long located on the surfaces of the particles of the medium, and that the lengths of these chains are proportional to the wavelength. Since the angular width of the peak is controlled by the ratio of the wavelength to the mean scattering chain length, the width is independent of wavelength. Because the wavelets never enter a particle, low albedo media can exhibit a strong coherent backscatter peak. Opposition effect peaks less than a degree wide on solar system bodies can imply an immature Regolith; peaks several degrees wide imply a mature Regolith.
-
bidirectional reflectance spectroscopy 7 the single particle phase function hockey stick relation
Icarus, 2012Co-Authors: Bruce HapkeAbstract:Abstract The measured volume-average single particle angular scattering functions of a large number of types of particle of interest for planetary Regoliths in the visible-near-IR wavelength region can be represented to a reasonable approximation by two-parameter, double Henyey–Greenstein functions. When the two parameters of this function are plotted against one another they are found to be inversely correlated and lie within a restricted zone shaped like a hockey stick within the parameter space. The centroid of the zone is a curve that can be represented by a simple empirical equation. The wide variety of types of particles used to construct the plot implies that this equation may represent most of the particles found in Regoliths. This means that when modeling the bidirectional reflectance of a Regolith it may be possible to reduce the number of parameters necessary to specify the reflectance, and also to characterize the entire single particle phase function from observations at phase angles less than 90°. Even if the hockey stick relation has a finite width, rather than being a line, it restricts the parameter space that must be searched when fitting data. The curve should also be useful for forward modeling particle phase functions.
-
a quantitative test of the ability of models based on the equation of radiative transfer to predict the bidirectional reflectance of a well characterized medium
Icarus, 2009Co-Authors: Bruce Hapke, Michael K Shepard, R M Nelson, W D Smythe, Jennifer L PiatekAbstract:Predictions of two widely-used Regolith reflectance models, a numerically exact computer code and an approximate analytic equation, based on the equation of radiative transfer were tested against the measured reflectance of a medium of close-packed spheres, whose properties supposedly can be well-characterized. Surprisingly, the approximate analytic model was a better match to the experimental data than the numerically exact computer solution. Other approximate Regolith models were tested briefly with similar results. Discrepancies between the two models and between models and experiment can be explained if the phase functions and albedos of the spheres are not the same as when the particles are isolated. Differences include the absence of the Fraunhoffer diffraction peak, which is an intrinsic assumption of the approximate analytical model but not the exact numerical model, and increased scattering in the mid-range of phase angles, which the approximate analytic model fortuitously describes more accurately than the exact numerical model. These changes may be caused by the close proximity of surrounding particles. If they are taken into account, models based on the radiative transfer equation appear able to quantitatively predict the reflectances of Regoliths and other particulate media. Interparticle perturbations are also predicted to cause a coherent backscatter opposition effect in the backward direction that was observed, but its angular width was found to be much larger than predicted by theories for sparsely-packed media.
-
a model of radiative and conductive energy transfer in planetary Regoliths
Journal of Geophysical Research, 1996Co-Authors: Bruce HapkeAbstract:The thermal regime in planetary Regoliths involves three processes: propagation of visible radiation, propagation of thermal radiation, and thermal conduction. The equations of radiative transfer and heat conduction are formulated for particulate media composed of anisotropically scattering particles. Although the equations are time dependent, only steady state problems are considered in this paper. Using the two-stream approximation, solutions are obtained for two cases: a layer of powder heated from below and an infinitely thick Regolith illuminated by visible radiation. Radiative conductivity, subsurface temperature gradients, and the solid state greenhouse effect all appear intrinsically in the solutions without ad hoc additions. Although the equations are nonlinear, approximate analytic solutions that are accurate to a few percent are obtained. Analytic expressions are given for the temperature distribution, the optical and thermal radiance distributions, the hemispherical albedo, the hemispherical emissivity, and the directional emissivity. Additional applications of the new model to three problems of interest in planetary Regoliths are presented by Hapke (this issue).
Ling Zhang - One of the best experts on this subject based on the ideXlab platform.
-
A story of Regolith told by Lunar Penetrating Radar
Icarus, 2019Co-Authors: Ling Zhang, Zhijun Huo, Zhaofa Zeng, Jianmin Zhang, Ling Huang, Jing Li, Nan HuaiAbstract:Knowledge of the lunar Regolith not only provides important information about lunar geology, but is also critical to quantifying potential resources for lunar exploration and engineering for human outposts. The Lunar Penetrating Radar (LPR) onboard China's Chang'E-3 (CE-3) provides a unique opportunity for mapping the subsurface structure and the near-surface stratigraphic structure of the Regolith. A radar image with high resolution can be produced using a data processing pipeline. The contact interface of the Regolith and the basement rock is explored according to forward simulation results. F-K (Frequency-wavenumber) filtering that highlights the contact surface of the Regolith and the basement rock is carried out. The energy distribution of the LPR data helps to stratify the lunar Regolith. Finally, by combining this with the history of the Moon, regional geology, and particularly the LPR data, we deduce the evolution of the Regolith on the CE-3 landing site.
-
Rock Location and Quantitative Analysis of Regolith at the Chang’e 3 Landing Site Based on Local Similarity Constraint
MDPI AG, 2019Co-Authors: Deli Wang, Ling Zhang, Zhaofa ZengAbstract:Structural analysis of lunar Regolith not only provides important information about lunar geology but also provides a reference for future lunar sample return missions. The Lunar Penetrating Radar (LPR) onboard China’s Chang’E-3 (CE-3) provides a unique opportunity for mapping the subsurface structure and the near-surface stratigraphic structure of the Regolith. The problem of rock positioning and Regolith-basement interface highlighting is meaningful. In this paper, we propose an adaptive rock extraction method based on local similarity constraints to achieve the rock location and quantitative analysis for Regolith. Firstly, a processing pipeline is designed to image the LPR CH-2 A and B data. Secondly, we adopt an f-x EMD (empirical mode decomposition)-based dip filter to extract low-wavenumber components in the two data. Then, we calculate the local similarity spectrum between the filtered CH-2 A and B. After a soft threshold function, we pick the local maximums in the spectrum as the location of each rock. Finally, according to the extracted result, on the one hand, the depth of Regolith is obtained, and on the other hand, the distribution information of the rocks in Regolith, which changes with the path and the depth, is also revealed
-
parameter estimation of lunar Regolith from lunar penetrating radar data
Sensors, 2018Co-Authors: Ling Zhang, Zhijun Huo, Zhaofa Zeng, Ling Huang, Kun Wang, Jianmin ZhangAbstract:Parameter estimation of the lunar Regolith not only provides important information about the composition but is also critical to quantifying potential resources for lunar exploration and engineering for human outposts. The Lunar Penetrating Radar (LPR) onboard China’s Chang’E-3 (CE-3) provides a unique opportunity for mapping the near-surface stratigraphic structure and estimating the parameters of the Regolith. In this paper, the electrical parameters and the iron-titanium content of Regolith are estimated based on the two sets of LPR data. Firstly, it is theoretically verified that the relative dielectric constant can be estimated according to the difference of the reflected time of two receivers from a same target. Secondly, in order to verify the method, a parameter estimation flow is designed. Subsequently, a simple model and a complex model of Regolith are carried out for the method verification. Finally, on the basis of the two sets of LPR data, the electrical parameters and the iron-titanium content of Regolith are estimated. The relative dielectric constant of Regolith at CE-3 landing site is 3.0537 and the content of TiO2 and FeO is 14.0127%. This helps us predict the reserves of resources at the CE-3 landing site and even in the entire Mare Imbrium.
