Architecture and evolution of the Finale channel system, the Numidian Flysch Formation of Sicily; insights from a hierarchical approach

Large scale channel systems are commonly imaged using seismic data and classified hierarchically. Where exposed at outcrop, similar scale ancient channel systems provide an opportunity to investigate subseismic scale architectures, produced for example through short duration autocyclic processes, and assess how they contribute to larger seismic scale architectures. In this study, a seismic scale slope-confined channel system from the Numidian Flysch Formation of northern Sicily is described using a hierarchical classification scheme. The channel system is 5.7 km wide and is organised within 3 hierarchical levels, comprising; 2 channel complex sets, 16 channel complexes, and >30 channel elements. channel complexes are mappable bodies and reach 500 m wide and 90 m thick.Slope confined sinuous channel complexes contain stacked channel elements which show a progression of incision and bypass to fill with massive sandstones interspersed with graded turbidite deposits. Flows are interpreted to predominantly deposit during quasi-steady flow conditions although flow non-uniformity produced beds with complex grading patterns. Lateral expansion of channel elements produced terracing within the complex margin and had the capacity to alter flow rheology through incorporation of large mud volumes. Sinuosity of channel element thalwegs and offset stacking produced asymmetric channel complexes with heterogeneous internal architectures and lithofacies distributions.Both channel complexes and channel elements thicken with younging indicating increased entrenchment through allocyclic forcing. The frequency distribution of channel-element thicknesses also shows a positive skew centred around 12 m as with published data global datasets. We question whether this distribution similarity may result from a fundamental process at the channel-element scale such as substrate armouring through coarse grained sedimentary deposits exceeding the capacity limits of transiting flows. The use of a hierarchical classification scheme therefore highlights the importance of subseismic scale processes on mappable architectures. The quantification of specific hierarchical elements also allows the role of allocyclic forcing to be investigated in an area of complex palaeogeography.

► A seismic-scale upper slope-confined channel system is described.
► Depositing flows are dominantly waxing to steady but can be nonuniform.
►  Element scale sinuosity and offset stacking produces asymmetric complexes.
► Allocyclic forcing increased slope erosion and flow confinement with younging.
► Element thickness distributions suggest a fundamental limit upon channel thickness.