Submarine landslides have been documented in many deep-water systems. Mass wasting processes and related emplacement of mass-transport deposits (MTDs) may reset the bathymetry of the seafloor through creation of erosional and depositional relief. MTD-related seafloor bathymetry may influence the dispersal patterns of subsequent sediment gravity flows, through reflection, deflecting, or ponding over a relatively small length scales (<1 km), and may thus exert major control on the architecture and internal heterogeneity of associated turbidites. The principal aim of this thesis is to better constrain the links between MTD-related seafloor bathymetry and facies variability in subsequent deposits.
Two case studies of MTD-influenced deep-water systems are presented: the subsurface Britannia Sandstone Fm. (Lower Cretaceous, UK North Sea) and the outcropping Marnoso-arenacea Fm. (Miocene, Central Italy). These studies document i) the different scales of seafloor rugosity created by the emplacement of MTDs and ii) the predictability of the effects of such bathymetry upon sandstone facies distribution and termination geometries. An original structural restoration exercise in the Britannia Sandstone Formation enabled construction of maps of the palaeobathymetry developed after each of four major mass transport events. Morphological features such as deep troughs provide pathways for the emplacement of relatively sandy, high net-to-gross deposits, whereas subtle rugosity produced hybrid event bed-prone deposits with marginal clay-rich banded facies adjacent to confining slopes. Field data from the Casaglia MTD enable the recognition of three different scales of rugosity on the upper MTD surface, the smallest of which effectively represents inter-well scale in the subsurface. Overlying sandstone deposits show evidence of flow deflection, confinement and ponding, with the latter resulting in thick mud caps and a taken net-to-gross.
The study emphasises that reservoir heterogeneity in sandstone deposits overlying MTDs is controlled by the shape, depth and size of the morphological features associated with the MTD, together with their elevation above the seafloor bathymetry in relationship to the thickness and direction of the depositing flows.
