A tectonically-induced Eocene sedimentary mélange in the West Ligurian Alps, Italy

• Published in: Tectonophysics Vol. 568-569; pp. 200 - 214
• Main Authors: Perotti, E., Bertok, C., d'Atri, A., Martire, L., Piana, F., Catanzariti, R.
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 28.09.2012
• Subjects: Basins; Breccia; Chaos theory; Debris flow; Formations; Mud; Olistostromes; Rock; Sands; Tectonics; Transtensive syndepositional tectonics; Ventimiglia Flysch; Italy, Alps Mts; Olistostromes; Debris flow; Transtensive syndepositional tectonics; Ventimiglia Flysch
• ISSN: 0040-1951; 1879-3266
• DOI: 10.1016/j.tecto.2011.09.005

The southern Alpine Foreland basin succession (Late Eocene–Early Oligocene?) lies over the Mesozoic condensed carbonate succession of the Provençal Dauphinois Domain, ends with a chaotic complex, and is overthrust by more internal Alpine units (San Remo–Monte Saccarello Ligurian unit) emplaced in Late Oligocene–Early Miocene times. The chaotic complex consists of debris flow paraconglomerates, breccias, and megablocks, up to km-sized. Despite the post-Eocene Alpine tectonics overprint, particularly intense in its uppermost part, the sedimentary origin of the chaotic complex is proved by the interbedding of paraconglomerates and breccias with fine-grained turbidites. Megablocks consist both of formations buried below the chaotic deposits (Mesozoic Provençal Dauphinois succession, Eocene Alpine Foreland basin succession) both of exotic units (Ligurian Helminthoides Flysch). Paraconglomerate and breccia clasts were sourced by the penecontemporaneous turbidite sands and muds as well as the same lithologies as megablocks. All these features suggest the activity of early Alpine Eocene strike-slip or transtensive fault systems that juxtaposed and exhumed the Helminthoides Flysch unit and the Provençal Dauphinois succession. Submarine ridges were generated and favored rock fall phenomena that involved both small, mm- to dm-sized, clasts and huge slabs detached from the main rock masses. These morphostructural highs were flanked by oversteepened slopes affected by failures that gave rise to debris flows, involving hemipelagic muds and turbidite sands and lithified fragments of older formations, which resulted in strongly polygenic paraconglomerates. The studied mélange is thus fully due to sedimentary processes that were, however, completely controlled by early Alpine tectonics.