No abstract

International audienceTo better understand the recent motion of the Pacific plate relative to the Rivera plate and to better define the limitations of the existing Rivera–Pacific plate motion models for accurately predicting this motion, total-field magnetic data, multibeam bathymetric data and sidescan sonar images were collected during the BART and FAMEX campaigns of the N/O L'Atalante conducted in April and May 2002 in the area surrounding the Moctezuma Spreading Segment of the East Pacific Rise, located offshore of Manzanillo, Mexico, at 106°16′W, between 17.8°N and 18.5°N. Among the main results are: (1) the principle transform displacement zone of the Rivera Transform is narrow and well defined east of 107o15′W and these azimuths should be used preferentially when deriving new plate motion models, and (2) spreading rates along the Moctezuma Spreading Segment should not be used in plate motion studies as either seafloor spreading has been accommodated at more than one location since the initiation of seafloor spreading in the area of the Moctezuma Spreading Segment, or this spreading center is not a Rivera–Pacific plate boundary as has been previously assumed. Comparison of observed transform azimuths with those predicted by the best-fit poles of six previous models of Rivera–Pacific relative motion indicate that, in the study area, a significant systematic bias is present in the predictions of Rivera–Pacific motion. Although the exact source of this bias remains unclear, this bias indicates the need to derive a new Rivera–Pacific relative plate motion model

The paleoclimatic variability of northern Mexico since the Late Wisconsinan is determined from sedimentological, geochemical, and stratigraphic studies of the lacustrine sequence of Laguna Babícora (29.4°N, 107.7°W; elevation 2100 m asl). Chronological control is based on 13 radiocarbon dates (6 from this study and 7 previously reported) from four stratigraphic profiles that cover a range from 16 342 to 2800 BP. Two major periods of increased humidity are recognized by lake-level variation during the Late Wisconsinan and early Holocene. The Late Wisconsinan humid period may be related to jet stream migration to southerly latitudes and the influence of the mobile polar high. This period has been identified in the sedimentary record of El Diablo profile with a radiocarbon date of 16 342 ± 201 BP. The early Holocene humid period is recorded in El Diablo (10 976 ± 115 BP) and Cano profiles (9614 ± 130 BP). It is interpreted as a result of the Younger Dryas climatic anomaly characterized by a temperature decrease and cold paleoclimatic conditions similar to those for the Late Wisconsinan. The early Holocene was followed by an overall gradual drying that reached a maximum around 6000 BP, during the middle Holocene. For the late Holocene evidence of widespread erosion, sedimentation changes, flooded surfaces, and paleosoils indicates that Laguna Babícora was subjected to short-term climatic changes.Résumé : Les variations paléoclimatiques qui ont affecté la partie septentrionale du Mexique du Wisconsinien tardif à nos jours ont été déterminées à partir des études sédimentologique, géochimique et stratigraphique de la séquence lacustre de Laguna Babícora (29,4°N, 107,7°O, élévation 2100 m au dessus du niveau marin). La chronologie des événements se base sur 13 datations au 14 C (6 étudiées ci-dessous et 7 ayant été reportées auparavant). Ceux-ci s'échelonnent entre 16 342 et 2800 ans avant le Present. Deux grandes périodes marquées par une recrudescence de l'humidité ont été identifiée : celle du Wisconsinien tardif et celle de l'Holocène précoce. La première peut être liée à la migration du courant-jet vers les latitudes méridionales et à l'influence des anti-cyclones mobiles polaires, provoquant une augmentation de l'humidité effective et des niveaux lacustres élevés, comme l'ont révélé les données sédimentologiques du profil stratigraphique El Diablo d'un âge de 16 342 ± 201 ans avant le Présent. La période humide de l'Holocène précoce mise en évidence par les profils El Diablo (10 976 ± 115 ans avant le Présent) et Cano (9614 ± 130 ans avant le Présent) résulterait de l'anomalie climatique du Dryas Récent, caractérisée par la chute de température et des conditions climatiques froides similaires au modèle climatique en vigueur pendant le Wisconsinien tardif. À la période de l'Holocène précoce succéda une vague de sécheresse progressive qui atteignit son apogée vers 6000 ans avant le Présent, au cours de l'Holocène moyen. Les témoignages d'une érosion étendue, un changement dans la sédimentation, les surfaces inondées ...

We consider a series of hydrogeophysical techniques that provide a multiscale investigation of the water content in the vadose zone and of the perched aquifer at the experimental site of ''La Soutte'' in the Vosges Mountains (France). It is located in a catchment area where several springs and streams occur along fractured volcanic and weathered plutonic rocks. The site is the object of a long-term study that uses both continuous and repeated measurements to monitor hydrogeological processes. The main results from AMT and DC resistivity techniques allow the determination of a high-resolution 3D resistivity model over a large range of depths (from 10 0 to 10 3 m). We discuss their use and propose a hydrogeological model (porosity, water conductivity and water content). We also use MRS and GPR for a detailed investigation of the shallow part of the catchment that consists of soil and weathered rocks of highly varying thickness (0 to 15 m). MRS is used to map the thickness and total water volume content by unit surface of the saturated weathered zone. It also yields estimates of the vadose zone thickness through the depth to the top of the saturated zone. Moreover, we show results from GPR CMP measurements that yield estimates of the water content and porosity in the shallowest layer (0-30 cm) by simple interpretation of the ground direct wave.

This article presents the results of a ground penetrating radar (GPR) and Electrical Resistivity Tomography (ERT) investigation carried out in the atrium of the Cathedral of Puebla to shed new light on the location of the original temple known as the "Old Cathedral". Historians who endeavor to reconstruct the past of this historical monument propose two hypotheses. To verify whether the foundations are located on the northwest or northeast side of the current cathedral, a GPR study was conducted with 200 and 400 MHz antennas. The study was completed with an ERT survey. The remains of the old cathedral were located and identified in the northwestern part of the atrium. Further anomalies related to subsurface structures and consistent with the ephemeral existence of a smaller temple, the "Sagrario", were detected. The GPR proved to be the most suitable method to investigate without causing damage suspected subsurface remains, thus protecting cultural heritage.