Abstract
AbstractThe term base‐of‐scarp is proposed for those submarine deposits controlled by a fault and physically disconnected from their more proximal counterpart located on the footwall, although genetically linked to it. These systems differ from conventional fault‐controlled deltas, such as shoal‐ and Gilbert‐type, because they are entirely subaqueous and lack equilibrium morphology—a steady state in which the system grows in size without altering its shape. We present field examples of fault‐controlled deposits from the Crati Basin and the Messina Strait (southern Italy) consisting of stratigraphic clastic wedges that thin towards and onlap onto the active margin with primary inclined bedding. Beds are composed of immature coarse‐grained gravels and sand, lack structures representative of wave‐action and reflect gravity‐driven processes such as debris flow, debris fall and high‐density turbidity currents. These deposits represent the unsteady‐state phase in which the system grows reducing its slope angle leading to conditions under which the unsteady state may eventually turn into a Gilbert‐type or shoal‐water system. A diagram for fault‐controlled base‐of‐scarp (B), Gilbert (G) and shoal‐water (S) deposits is presented, including their steady‐ and unsteady states, and the conceptual conditions under which a base‐of‐scarp system might evolve into Gilbert‐type or shoal‐water systems and vice versa.
Highlights
Fault-controlled systems have long been studied to improve the understanding and prediction of sandand gravel-body architectures in analogous subsurface systems (Colella, 1998a; Ethridge and Wescott, 1984; Lewis et al, 2015). Such fault-controlled deposits are important in basin analysis because they provide a record of tectonic events and base level changes that operated during basin evolution (Hardy et al, 1994; Gobo et al, 2015)
The proposed unsteady-state is characterised by the evolution in morphology and internal geometry during basin filling (Prior and Bornhold, 1988) gradually reducing its slope angle (Nemec, 1990), eventually aggrading close to the base level and potentially evolving into either a shoal-water or Gilbert-type delta system with morphologies that grow in steady-state conditions
The Crati Basin hosts well-known examples of fault-controlled shoal-water and Gilbert-type deltas (Colella, 1988b), and in the present study we focus on facies variations and vertical evolution of the lower portion of the EarlyMiddle Pleistocene Civita section (Fig. 3A)
Summary
Fault-controlled systems have long been studied to improve the understanding and prediction of sandand gravel-body architectures in analogous subsurface systems (Colella, 1998a; Ethridge and Wescott, 1984; Lewis et al, 2015). Such fault-controlled deposits are important in basin analysis because they provide a record of tectonic events and base level changes that operated during basin evolution (Hardy et al, 1994; Gobo et al, 2015). The proposed unsteady-state (i.e. base-of-scarp deposit) is characterised by the evolution in morphology and internal geometry during basin filling (Prior and Bornhold, 1988) gradually reducing its slope angle (Nemec, 1990), eventually aggrading close to the base level and potentially evolving into either a shoal-water or Gilbert-type delta system with morphologies that grow in steady-state conditions
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