Time filter

Source Type

Bassi D.,University of Ferrara | Iryu Y.,Nagoya University | Nebelsick J.H.,University of Tbingen
Journal of Coastal Research | Year: 2012

The past environment is often reconstructed by measuring certain proxy data, such as changes in oxygen isotopes, taxonomic assemblages, and taphonomic signatures in a palaeoenvironmental archive (e.g., rhodoliths, corals, invertebrate shells, trees, ice cores, speleothems, etc.). Proxy analysis usually yields a record that has to be compared with present-day analogues to yield meaningful results. This also holds true for the interpretation of the palaeoenvironment of rhodolith deposits. The characteristics of Recent rhodoliths and the environments in which they are formed, thus, need to be known to interpret their fossil counterparts. The comparison of fossil and Recent rhodoliths and their environment is, however, not straightforward because the respective analytical methods applied to them are usually different and often difficult to reconcile. To reduce the uncertainties of this problem and to facilitate direct comparisons, we describe a number of analytical methods applied to fossil rhodoliths that can also be performed on Recent material. The analytical methods introduced here correspond to three different scales of analysis: (1) the outcrop scale as completed in field studies and the study of (2) isolated specimens and (3) thin sections in the laboratory. © 2012, the Coastal Education & Research Foundation (CERF). Source

Schmelzbach C.,University of Potsdam | Schmelzbach C.,Free University of Berlin | Schmelzbach C.,ETH Zurich | Tronicke J.,University of Potsdam | And 2 more authors.
Water Resources Research | Year: 2012

Mapping hydrological parameter distributions in high resolution is essential to understand and simulate groundwater flow and contaminant transport. Of particular interest is surface-based ground-penetrating radar (GPR) reflection imaging in electrically resistive sediments because of the expected close link between the subsurface water content and the dielectric permittivity, which controls GPR wave velocity and reflectivity. Conventional tools like common midpoint (CMP) velocity analysis provide physical parameter models of limited resolution only. We present a novel reflection amplitude inversion workflow for surface-based GPR data capable of resolving the subsurface dielectric permittivity and related water content distribution with markedly improved resolution. Our scheme is an adaptation of a seismic reflection impedance inversion scheme to surface-based GPR data. Key is relative-amplitude-preserving data preconditioning including GPR deconvolution, which results in traces with the source-wavelet distortions and propagation effects largely removed. The subsequent inversion for the underlying dielectric permittivity and water content structure is constrained by in situ dielectric permittivity data obtained by direct-push logging. After demonstrating the potential of our novel scheme on a realistic synthetic data set, we apply it to two 2-D 100 MHz GPR profiles acquired over a shallow sedimentary aquifer resulting in water content images of the shallow (3-7m depth) saturated zone having decimeter resolution.© 2012. American Geophysical Union. All Rights Reserved. Source

Lyson T.R.,Yale University | Lyson T.R.,Marmarth Research Foundation | Joyce W.G.,University of Tbingen | Joyce W.G.,Yale University
Journal of Vertebrate Paleontology | Year: 2010

A fragmentary skull from the Hell Creek Formation (Maastrichtian) of southwestern North Dakota represents a new taxon of baenid turtle named herein Gamerabaena sonsalla. The length of the frontals, jugal contribution to the labial ridge, and convex contact between the vomer and the pterygoids indicate its affinities with the clade Palatobaena, but the new taxon clearly lacks the great posterior expansion of the triturating surface, complete absence of a lingual ridge, subrectangular skull, and wide angle between the maxillae that diagnose Palatobaena spp. A maximum parsimony analysis provides strong support for G. sonsalla as sister taxon to Palatobaena spp. Gamerabaena sonsalla has several morphological features that are intermediate between Plesiobaena antiqua and the morphologically disparate Palatobaena spp., including orbits that are oriented slightly dorsally and moderately expanded posterior triturating surfaces. Our phylogenetic analysis, combined with stratigraphic arguments, indicates that our skull-based taxon G. sonsalla could belong to the shell-based taxon "Baena" hayi. Similarly, the skull taxa Hayemys latifrons and Eubaena cephalica may be synonymous with the shell taxa Thescelus insiliens and "Baena" hatcheri, respectively. © 2010 by the Society of Vertebrate Paleontology. Source

Wohling T.,Lincoln Ventures Ltd | Wohling T.,University of Tbingen | Vrugt J.A.,University of California at Irvine | Vrugt J.A.,University of Amsterdam | Vrugt J.A.,Los Alamos National Laboratory
Water Resources Research | Year: 2011

In the past two decades significant progress has been made toward the application of inverse modeling to estimate the water retention and hydraulic conductivity functions of the vadose zone at different spatial scales. Many of these contributions have focused on estimating only a few soil hydraulic parameters, without recourse to appropriately capturing and addressing spatial variability. The assumption of a homogeneous medium significantly simplifies the complexity of the resulting inverse problem, allowing the use of classical parameter estimation algorithms. Here we present an inverse modeling study with a high degree of vertical complexity that involves calibration of a 25 parameter Richards'-based HYDRUS-1D model using in situ measurements of volumetric water content and pressure head from multiple depths in a heterogeneous vadose zone in New Zealand. We first determine the trade-off in the fitting of both data types using the AMALGAM multiple objective evolutionary search algorithm. Then we adopt a Bayesian framework and derive posterior probability density functions of parameter and model predictive uncertainty using the recently developed differential evolution adaptive metropolis, DREAMZS adaptive Markov chain Monte Carlo scheme. We use four different formulations of the likelihood function each differing in their underlying assumption about the statistical properties of the error residual and data used for calibration. We show that AMALGAM and DREAMZS can solve for the 25 hydraulic parameters describing the water retention and hydraulic conductivity functions of the multilayer heterogeneous vadose zone. Our study clearly highlights that multiple data types are simultaneously required in the likelihood function to result in an accurate soil hydraulic characterization of the vadose zone of interest. Remaining error residuals are most likely caused by model deficiencies that are not encapsulated by the multilayer model and can not be accessed by the statistics and likelihood function used. The utilization of an explicit autoregressive error model of the remaining error residuals does not work well for the water content data with HYDRUS-1D prediction uncertainty bounds that become unrealistically large. Copyright © 2011 by the American Geophysical Union. Source

Pollock D.,University of Tbingen | Pollock D.,ETH Zurich | Pollock D.,CSD Ingenieure AG | Cirpka O.A.,University of Tbingen
Water Resources Research | Year: 2012

We perform a salt tracer experiment, monitored by time-lapse electrical resistivity tomography, in a quasi-two-dimensional sandbox with the aim of determining the hydraulic conductivity distribution in the domain. We use sodium chloride as a tracer, together with cochineal red for visual monitoring. The time series of observed resistance for each electrode configuration is characterized by its temporal moments. We invert the mean arrival time of electrical potential perturbations and a few steady state hydraulic head measurements using the fully coupled hydrogeophysical approach recently introduced by Pollock and Cirpka (2010). This is the first application of the approach to experimental data. The results obtained show a reasonable agreement between the estimated hydraulic conductivity field and the pattern of the actual sandbox filling. Using this estimation, a transient simulation is performed to compute the propagation of the salt tracer plume through the sandbox. The latter is compared to pictures taken during the experiment. These results show an even better agreement, indicating that the lenses of different sand types are not entirely homogeneous and some unexpected preferential flow paths are present. We conclude that temporal moments of potential perturbations obtained during salt tracer tests provide a good basis for inferring the hydraulic conductivity distribution by fully coupled hydrogeophysical inversion. Source

Discover hidden collaborations