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Depositional and erosional bedforms can be used to reconstruct sedimentary processes and aid palaeoenvironmental interpretations. Using exhumed deep-marine strata in the Eocene Aínsa Basin, Spain, we document a 3-dimensional package of dunes, a rarely identified bedform in deep-marine environments. Our analysis shows that the dunes have curvilinear crests in planform, with smaller superimposed oblique dunes and ripples across the stoss sides. Beds containing these dunes have two main internal divisions: a lower inversely-graded (fine-to-coarse sandstone) and predominantly structureless division, and an upper coarse-grained sandstone division with well-developed cross-stratification, which is scoured and mantled with mudclasts and coarse-grains on the stoss-side. The rugose remnant relief of the bedforms controls the location of subsequent bedforms. Following recently reported direct measurements of natural turbidity currents, we interpret the basal division as recording deposition from the dense basal head of a high-velocity turbidity current, followed by the development of dunes beneath the more sustained but relatively high-velocity and unsteady flow body that reworked the initial sandy deposit into downstream migrating dunes and scours. These dune-forming beds have been identified in different deep-water environments in the Aínsa Basin stratigraphy, including channel overbank and channel mouth settings and scour-fills. These locations suggest that the dunes were intimately tied to high-velocity flows that bypassed through channel axes before expanding and depositing in less confined channel overbank or channel mouth settings. Preservation of these dunes in the Aínsa Basin was likely enhanced by tectonically-forced lateral migration of channels, which prevented cannibalisation of bypass-dominated zones, in combination with high aggradation rates due to confinement. Where identified these dune-like bedforms are considered diagnostic of substantial sediment bypass downslope to deep-water basins. This article has a related Corrigendum

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 deposits of low-sinuosity and narrow (2-3 km wide) channel-belts confined laterally by tectonically-controlled, fine-grained slopes. The studied succession (111 m-thick) is exposed along a 1.5 km long SE-NW trending depositional dip section and is documented here by 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 this structure promoted the breaching of confining channel walls and slope material 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 overbank succession. These crevasse lobes are characterized by structureless thick and medium beds that form < 5 m thick packages in proximal parts and thin abruptly over 1 km across strike (NE) and along downdip (NW) into structured thin beds, similar to the heterolithic dominated overbank deposits. Although the 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 margin of a foreland basin rather than on the opposing, more stable and gentler inactive margin. We discuss the mechanism for forming these crevasse deposits, which exploited the accommodation generated by submarine landslides derived from the tectonically-active compressional margin.