A.M. Casas Sainz

Evolution of experimental thrust wedges accreted from along-strike tapered, silicone-floored multilayers

The possible effect of pre-deformational, along-strike sedimentary tapers on the structural architecture of thrust wedges accreted above viscous materials has been commonly underestimated or neglected. We illustrate results of an experimental programme specifically designed to study the impact of this parameter on thrust wedge evolution using sandbox analogue modelling. Two series of experiments were performed: the first series was designed to investigate the sensitivity of wedge growth to the along-strike sedimentary taper variability; the second was designed to investigate the sensitivity of a growing along-strike tapered wedge to the convergence rate. Our experimental results indicate that even gentle pre-deformational along-strike thickness variations in foredeep clastic sequences overlying viscous materials, such as evaporites or overpressured shales, can produce dramatic changes in the first-order structural architecture and kinematic evolution of accreting thrust wedges.

Magnetometry and ground-penetrating radar surveys applied to tracing potential collectors of mining-derived pollutants in coastal sediments (Piscinas Bay, Montevecchio mining area, SW Sardinia)

Abstract Dispersion of pollutants from mining areas can result in risks to human health. The dynamic interaction of geological processes can generate complex situations that favor enrichment in toxic elements by sedimentary and diagenetic mechanisms. In order to explore the distribution of iron-rich minerals in coastal and river sediments, a geophysical campaign was performed along the outlet of the Piscinas and Naracauli Rivers that drain two abandoned mining areas in SW Sardinia. Both rivers flow into the Mediterranean Sea, a bay where fluvial, marine, and eolian processes interact. The geophysical campaign comprised magnetometry and ground-penetrating radar surveys. Magnetic properties were controlled by means of magnetic susceptibility measurements along the beach and dune areas, through sampling of surface sediments, natural outcrops and trenches, and considering different grain size intervals. Results indicate enrichment in ferromagnetic minerals at the leeside of dunes and berms. Sedimentological interpretation is supported by means of ground-penetrating radar. Due to both sedimentary and diagenetic processes, the 100- to 300-μm fraction of fine sands exhibits high susceptibility. Implied tenors of toxic elements in the magnetite may represent a serious hazard to environmental and health security. The results inferred from magnetic anomalies support the applicability of the geophysical approach in order to locate high concentrations of iron-rich particles both at surface and below ground and the usefulness of joint evaluation of magnetic susceptibility and ground-penetrating radar in order to characterize the sedimentary and geomorphology-controlled magnetite distribution.