Fossilized silica diagenetic fronts: Implications for palaeoceanographic evolution across the Falkland/Malvinas plateau

Abstract

A set of newly collected 2D seismic reflection data allows the mapping of two distinct cross-cutting reflectors across the Falkland/Malvinas Plateau. Reflector XR-F/MB in the Falkland/Malvinas Basin appears as a bottom simulating reflector that mimics the geometry of the present seafloor, whereas reflector XR-F/MT in the Falkland/Malvinas Trough is a non-bottom simulating reflector that mimics a shallower reflector representing the Early-Middle Miocene unconformity. The discordant geometry of these two reflectors with respect to the host-stratigraphy is argued to be associated with Opal-A to Opal-CT diagenesis, which is primarily a function of temperature. However, the estimated temperature at the present depth for reflector XR-F/MB lies below the minimum temperature for the onset of silica diagenesis. Based on their geometry and seismic characteristics, the two reflectors are interpreted to be fossilized silica diagenetic fronts, formed under palaeo-thermal conditions different from today. We hypothesize that the erosional action of intensified deep and bottom water masses subsequent to Antarctic glaciations during the Early-Middle Miocene may have driven the fossilization of the diagenetic front in the study area. It is estimated that erosion of a minimum of 270 m of overburden would account for the temperature drop driving the fossilization of the silica diagenetic fron.