ALBERT

Description: Auf Bol'shoy Lyakhovsky, die südlichste der Neusibirischen Inseln, wurden fünf Bohrkerne mit einer Gesamtlänge von 52 m gewonnen. Sie erfassen Permafrostböden aus dem Holozän bis zurück ins Prä-Eem (ca. 200 Tausend Jahre vor heute). Die z.Zt. laufenden geowissenschaftlichen Analysen der Kerne beinhalten sedimentologische, geophysikalische, biogeochemische und mikrobiologische Techniken. Hauptziel des Projektes ist es, die aktuelle natürliche Produktion von Treibhausgasen in Permafrostböden zu bewerten, um eine künftige Treibhausgasproduktion in einer wärmer werdenden Arktis besser abzuschätzen. Die heutigen Raten der Treibhausgasproduktion werden dabei mit Signalen des Abbaus organischer Substanz in den zurückliegenden zwei Glazial-Interglazial-Zyklen in Beziehung gesetzt. Diese Studie ist Teil des deutsch-russischen Gemeinschaftsprojektes CARBOPERM, das mehr als 50 Wissenschaftler aus verschiedenen Instituten in Deutschland und Russland verbindet. Das 3-Jahres-Projekt widmet sich dem besseren Verständnis der Bildung, Umwandlung und Freisetzung von organischem Kohlenstoff in nordsibirischen Permafrostlandschaften.

Description: This contribution is presenting a multidisciplinary investigation of heterogeneities in a clay rock formation, based on seismic tomography, logging and core analysis, as a reconnaissance study for a diffusion experiment. Diffusion experiments in clay rock formations provide crucial experimental data on diffusive transport of radionuclides (RN) in extremely low hydraulic conductivity media. Previous diffusion experiments, conducted, for example, in the Mont Terri underground rock laboratory within the relatively homogeneous shaly facies of Opalinus Clay, and modelling studies of these experiments have demonstrated that the clay rock could sufficiently well be described as a homogeneous anisotropic medium. For other lithofacies, characterized by larger heterogeneity, such simplification may be unsuitable, and the description of heterogeneity over a range of scales will be important. The sandy facies of the Opalinus Clay exhibits a significantly more pronounced heterogeneity compared to the shaly facies, and a combined characterization and RN diffusion study has been initiated to investigate various approaches of heterogeneity characterization and subsequent diffusion in a heterogeneous environment. As an initial step, two inclined exploratory boreholes have been drilled to access the margins of the experiment location. These boreholes have been used to acquire a cross-hole tomographic seismic data set. Optical, natural gamma and backscattering logging were applied and rock cores were analysed. The integrated results of these investigations allowed the identification of an anomalous brighter layer within the investigated area of the sandy facies of approximately 1 m thickness and with its upper bound at roughly 10 m depth within the inclined exploratory wells. Mineralogical analyses revealed only slight variations throughout the rock cores and indicated that the anomalous layer exhibited a slightly higher quartz content, and locally significantly higher calcite contents, accompanied by a lower content of clay minerals. The anomalous layer was characterized by reduced natural gamma emissions, due to the lower clay content, and increased neutron backscattering likely indicating an increased porosity. Seismic P-wave velocities, derived from anisotropic tomography, exhibited a maximal gradient near the top of this layer. The transition from the overlaying darker rock matrix into this layer has been identified as an appropriate location for the setup of a tracer diffusion experiment in a heterogeneous environment.