Deciphering the diagenetic history of the El Abra Formation of eastern Mexico using reordered clumped isotope temperatures and U-Pb dating

Carbonates form ubiquitously throughout the history of deposition, burial, and uplift of basins. As such, they potentially record the environmental conditions at the time of formation. Carbonate clumped isotopes provide the temperature of precipitation but can be internally reordered if the host rock is exposed to elevated temperatures over geologic time scales. Here, we exploited this kinetic behavior by analyzing multiple generations of cements that capture the range of environments experienced by the El Abra Formation from eastern Mexico. From this, we developed a quantitative diagenetic history for these different phases of cementation. We observed a 70 °C range in clumped isotope temperatures from 64 °C to 134 °C for these cements, which is not compatible with their inferred precipitation environments. This suggests that bond reordering occurred during burial but did not fully reorder all cements to a common apparent temperature. We reconstructed original cement growth temperatures and the isotopic signature of the parent fluids to show that precipitation from a marine pore fluid began at 125 Ma, contemporaneous with deposition, and continued throughout burial to temperatures of at least 138 °C at 42 Ma. We show that precipitation of equant cements, which occluded 90% of the pore space, was coincident with Laramide-related burial to depths greater than 3800 m. A U-Pb age of diagenetic calcite of 77.1 ± 3.6 Ma provides independent support for our estimates of the absolute timing of precipitation of two distinct phases of the paragenesis. This is the first demonstration of the utility of integrating U-Pb age dating with reordered clumped isotope temperatures to provide quantitative constraints on the time-temperature history of cementation. Such information may ultimately lead to advances in our understanding of the formational environments and geological processes that drive diagenesis in carbonates for temperatures below the clumped isotope “blocking temperature.

Locative Media and Sociability:Using Location-Based Social Networks to Coordinate Everyday Life

Foursquare was a mobile social networking application that enabled people to share location with friends in the form of “check-ins.” The visualization of surrounding known social connections as well as unknown others has the potential to impact how people coordinate social encounters and forge new social ties. While many studies have explored mobile phones and sociability, there is a lack of empirical research examining location-based social network’s (LSBNs) from a sociability perspective. Drawing on a dataset of original qualitative research with a range of Foursquare users, the paper examines the application in the context of social coordination and sociability in three ways. First, the paper explores if Foursquare is used to organize certain social encounters, and if so, why. Second, the paper examines the visualization of surrounding social connections and whether this leads to “serendipitous encounters.” Lastly, the paper examines whether the use of Foursquare can produce new social relationships

3/4 discrete optimal transport

International audienceThis paper deals with the 3 4-discrete 2-Wasserstein optimal transport between two measures, where one is supported by a set of segment and the other one is supported by a set of Dirac masses. We select the most suitable optimization procedure that computes the optimal transport and provide numerical examples of approximation of cloud data by segments

Differentiation and regularity of semi-discrete optimal transport with respect to the parameters of the discrete measure

International audienceThis paper aims at determining under which conditions the semi-discrete optimal transport is twice dierentiable with respect to the parameters of the discrete measure and exhibits numerical applications. The discussion focuses on minimal conditions on the background measure to ensure dierentiability. We provide numerical illustrations in stippling and blue noise problems

Approximation of curves with piecewise constant or piecewise linear functions

In this paper we compute the Hausdorff distance between sets of continuous curves and sets of piecewise constant or linear discretizations. These sets are Sobolev balls given by the continuous or discrete L p-norm of the derivatives. We detail the suitable discretization or smoothing procedure which are preservative in the sense of these norms. Finally we exhibit the link between Eulerian numbers and the uniformly space knots B-spline used for smoothing

Optimal Transport Approximation of 2-Dimensional Measures

International audienceWe propose a fast and scalable algorithm to project a given density on a set of structured measures defined over a compact 2D domain. The measures can be discrete or supported on curves for instance. The proposed principle and algorithm are a natural generalization of previous results revolving around the generation of blue-noise point distributions, such as Lloyd's algorithm or more advanced techniques based on power diagrams. We analyze the convergence properties and propose new approaches to accelerate the generation of point distributions. We also design new algorithms to project curves onto spaces of curves with bounded length and curvature or speed and acceleration. We illustrate the algorithm's interest through applications in advanced sampling theory, non-photorealistic rendering and path planning

Approches variationnelles pour le stippling : distances L 2 ou transport optimal ?

International audienceLe stippling est un problème qui a beaucoup progressé dernièrement grâce à l'introduction de méthodes variationnelles. On s'intéresse ici à deux types de formulations. L'une repose sur une distance L 2 entre mesures et fait appel à des outils d'analyse harmonique appliquée. L'autre repose sur la distance de Wasserstein et fait appel à des outils de géométrie algorithmique. Différentes méthodes de résolution et de discrétisation sont comparées et nous présentons leurs atouts et leurs limitations. Abstract-Stippling is a problem that recently found elegant and efficient solutions thanks to the introduction of variational methods. The aim of this paper is to compare two state-of-the-art approaches: one is based on the minimization of an L 2 norm (which links to applied harmonic analysis), while the other is based on the Wasserstein distance (which links to computational geometry)