Abstract Geophysical electrical resistivity tomography (ERT) is a promising measurement technique for non-intrusive monitoring of an engineered barrier system (EBS) during the operational phase of geological disposal of high-level radioactive waste. Electrical resistivity is sensitive to water content and temperature, which are the key variables characterizing the response of the EBS. In order to assess the technology readiness level of the ERT technique for EBS operational monitoring, a field demonstrator has been developed at the underground research laboratory (URL) in Tournemire (France) within the project ‘Modern 2020’. Preliminary ERT surveys were carried out in January and November 2017 to establish the background resistivity of the experimental area and assess the quality of electrode installation and survey protocols. Results of the surveys confirmed that the resistivity of the host rock in the demonstrator area is quite homogenous and lower than 100 Ωm in accordance with independent measurements carried out in previous campaigns. In addition, the lesson learned from the blank tests allowed identifying key requirements for effective ERT measurements. These include the need for a 3D electrode configuration, bespoke measurement protocols designed on the basis of the sensitivity analysis of the geometric factor and the collection of reciprocal data for enhanced data quality control.

ABSTRACT Lower Mesozoic clastic rocks that unconformably overlie Paleozoic rocks within the Northern Sierra terrane provide clues regarding the evolution of the terrane during a 60 m.y. interval spanning the late Carnian through Bajocian. New detrital-zircon data provide fresh insights into the ages and provenance of these clastic rocks, together with new inferences about the Mesozoic tectonic evolution of the terrane. Previous studies have shown that from the late Carnian to the Sinemurian (~40 m.y.), a 1-km-thick section of subaerial to shallow-marine clastic arc-derived sediment accumulated and shallow-marine carbonate was deposited. At the base of this section, detrital-zircon results suggest the Northern Sierra terrane was located near a source area, possibly the El Paso terrane, containing Permian igneous rocks ranging in age from 270 to 254 Ma. By the earliest Jurassic, the detrital-zircon data suggest the Northern Sierra terrane was located near a source containing latest Triassic–earliest Jurassic igneous rocks spanning 209–186 Ma. The source of this material may have been the Happy Creek volcanic complex of the Black Rock terrane. A deep-marine, anoxic basin developed within the Northern Sierra terrane ca. 187–168 Ma. Approximately 3.5 km of distal turbidites were deposited in this basin. Previously reported geochemical characteristics of these turbidites link the Northern Sierra terrane with arc rock of the Black Rock terrane during this interval, except for a short time in the late Toarcian, when the terrane received an influx of quartz-rich sediment, likely derived from Mesozoic erg deposits now exposed on the Colorado Plateau. Clastic deposition within the Northern Sierra terrane ended in the Bajocian. Eruption of proximal-facies, mafic volcanic rocks and intrusion of hypabyssal rock and 168–163 Ma plutons reflect development of a magmatic arc within the terrane. These igneous rocks represent the first unequivocal evidence that the Northern Sierra terrane was located within a convergent-margin arc during the Triassic and Jurassic. Because detrital-zircon data from Lower Mesozoic strata within the Northern Sierra terrane indicate that it was depositionally linked with differing source areas through time early in the Mesozoic, the terrane may have been mobile along the western margin of Laurentia. There is little evidence from sediment within the Lower Mesozoic section of the terrane that can clearly be tied to the craton or the continental-margin Triassic arc prior to the late Toarcian. The absence of Upper Triassic or Lower Jurassic plutonic rocks within the terrane prior to the mid-Bajocian is also consistent with some form of isolation from the continental-margin arc system. While new detrital-zircon results place the Northern Sierra terrane proximal to the western margin of Laurentia in the late Toarcian, the current location of the terrane likely reflects Early Cretaceous offset along the Mojave–Snow Lake fault.

ABSTRACT Upper Triassic and Lower to Middle Jurassic strata in the Plomosas uplift of central Chihuahua accumulated in backarc and rift settings, respectively. The succession, as much as ~3250 m thick, consists of four stratigraphic units. The Cerro El Carrizalillo Formation (Carnian–Norian), a volcanic-lithic shallow-marine succession deposited in the (newly named) El Carrizalillo backarc basin, is characterized by predominantly Triassic detrital zircon ages. The overlying Plomosas Formation consists of three members: (1) the Cerro de Enmedio Member (Hettangian–Toarcian), a succession of conglomerate, siltstone, and shallow-marine carbonate strata deposited during the onset of extension in Chihuahua; (2) the Cerro Nevado Ignimbrite Member (176 ± 1 Ma; late Toarcian), a widespread ash-flow tuff; and (3) La Sofía Member (Aalenian–Callovian?), consisting of alluvial-fan conglomerate, fluvial sandstone, tidal sandstone and siltstone, and delta-plain red beds characterized by rapid facies changes, lithic compositions, and diverse Proterozoic, Paleozoic, and Triassic detrital zircon ages characteristic of a rift-basin setting. The extensional basin in which the Cerro de Enmedio and La Sofía members accumulated is termed the Plomosas basin. Improved age control provided by U-Pb maximum depositional ages from detrital zircon and U-Pb zircon analyses of the ignimbrite indicates that the Cerro El Carrizalillo Formation is partly correlative with the Chinle Formation of the Colorado Plateau, and the Plomosas Formation is equivalent to eolianites of the Glen Canyon and San Rafael Groups of the Colorado Plateau. Detrital zircon ages and sandstone textures are consistent with both proximal and distal sediment sources along the Laurentia-Gondwana suture and adjoining Grenville basement of Laurentia, including sources in northern Mexico and the composite Appalachian orogen. Although the depositional setting of the Cerro El Carrizalillo Formation was not connected to fluvial systems of the Chinle Formation, subsequent eolian transport of voluminous sediment to the overlying Cerro de Enmedio and La Sofía members from the Colorado Plateau ergs is suggested by the composition and texture of some sandstone, thick siltstone accumulations, and detrital zircon characteristics that broadly resemble those of the Colorado Plateau eolianites. Thick siltstone in the upper part of La Sofía Member is interpreted as deflated fine-grained sediment that was transported downwind from a time-equivalent erg to accumulate in shallow-marine and coastal-plain settings of the Plomosas basin.

Abstract The North German Basin yields enormous geothermal resources of more than 13 000 EJ (exajoule: 1 EJ = 1 × 10 18 J) heat in place bound to Paleozoic petrothermal and Mesozoic hydrothermal reservoirs. So far, these resources are only exploited at a few localities. Thus, geothermal energy is considered an underutilized energy resource. Despite long-term experi