Ander Martinez-Donate , Euan Soutter , Ian Kane, Miquel Poyatos-Moré, David Hodgson, Ashley J. M. Ayckbourne, William J. Taylor, Max Bouwmeester, Stephen S. Flint

Tectonic deformation and associated submarine slope failures modify seafloor relief, influencing sediment dispersal patterns and the resulting depositional architecture of deep-water systems. The exhumed Middle Eocene strata of the Banastón deep-water system in the Aínsa depocentre, Spain, allow the interplay between submarine slope confined systems, mass flow deposits, and syn-depositional compressional tectonics to be investigated. This study focuses on the Banastón II sub-unit, interpreted as low-sinuosity and narrow (2-3 km wide) channel-belt deposits confined laterally by opposing tectonically induced, fine-grained slopes. The studied succession (111 m-thick) is exposed along a 1.5 km long depositional dip-orientated (SE-NW) outcrop belt and documented here using facies analysis and physical correlation of 10 measured sections. Results show a stratigraphic evolution in which the channel axes migrated to the southwest, away from a growing structure in the northeastern part of the Aínsa depocentre. Uplift of the active margin promoted breaching of channel walls and confining slopes, with mass failures and the development of sand-rich crevasse scour-fills and crevasse lobes. We show that crevasse deposits form an important component of the overbank succession. These crevasse lobes are characterised by structureless thick and medium beds that form < 5 m thick packages in proximal parts and thin abruptly over 1 km into structured thin beds similar to the heterolithic dominated overbank deposits. Although development of crevasse lobes has been observed in multiple deep-water systems in ancient and modern systems, this study documents, for the first time, crevasse lobe development on the active compressional margins of a foreland basin rather than in the opposing and more stable and gentle margin. We discuss the mechanism for the formation of these crevasse deposits, which exploited the accommodation generated by the submarine landslides derived from the tectonically-active compressional margin.