Depositional processes on oceanic island shelves – Evidence from storm‐generated Neogene deposits from the mid‐North Atlantic

Abstract

Oceanic islandssuch as the Azores in the mid-North Atlanticare periodically exposed to large storms that often remobilize and transport marine sediments along coastlines, and into deeper environments. Such disruptive events create depositsdenominated tempestiteswhose characteristics by storm events is the main process of sediment deposition acting on steep and narrow shelves subjected to high-energetic environments, such as the insular shelves of open-sea volcanic islands.

The Palaeontological Heritage of Santa Maria Island (Azores: NE Atlantic): a Re-evaluation of Geosites in GeoPark Azores and Their Use in Geotourism

“…The first represents a tempestite, seldom described from an oceanic island, which provides invaluable information on the processes of sediment remobilization, transport and deposition taking place on insular shelves during and after major storms. Moreover, this particular tempestite at Ponta do Castelo was overlain by a contemporary coastal lava delta, which enables the inference of the precise water depth of the geosite at the time of deposition, a very rare condition worldwide (Meireles et al 2013). Pedra-que-pica was considered of international importance because it is probably the most extensive fossiliferous, multispecific coquina ever reported in the literature from volcanic oceanic islands.…”

“…Ponta do Castelo portrays a set of specific conditions which allowed the preservation of a shelf tempestite deposit for which its precise water depth could be inferred and additionally provides a good proxy for island uplift or subsidence reconstructions; Pedra-que-pica is probably the most extensive fossiliferous, multispecific coquina from the shelf ever reported in the literature of any of the ∼20,000 known volcanic oceanic islands in the world. For instance, whereas the fossil fauna found at Pedra-que-pica is predominantly allochthonous and transported from shallower depths that found at Ponta do Castelo is a mixture of allochthonous and autochthonous elements (Meireles et al 2013 (Ávila et al 2002, 2010Kirby et al 2007; Habermann 2010). Furthermore, they represent distinct marine palaeoenvironments (lower shore intertidal in Prainha versus inner to middle-shelf environment in Figueiral).…”

“…Thus, recent work has consistently produced general cross sections of the overall sequences and detailed composite columnar sections for each outcrop, displaying the most relevant body fossils and trace fossils, the internal sedimentary structures, and the contacts between volcanic and sedimentary units. This was done for the Late Miocene-Early Pliocene outcrops of Pedra-que-pica (Kirby et al 2007;Habermann 2011), Cré (Janssen et al 2008), Figueiral (Habermann 2010), Pedreira do Campo (Habermann 2010), Ponta do Castelo (Meireles et al 2013), as well as the Pleistocene deposits of Prainha and Lagoinhas (Callapez and Soares 2000;Ávila et al 2002, 2010Amen et al 2005) and Vinha Velha (Ávila et al 2015). Work is also being carried out to provide a formal geological description for many other fossiliferous outcrops (e.g.…”

Coastal evolution on volcanic oceanic islands: A complex interplay between volcanism, erosion, sedimentation, sea-level change and biogenic production

“…The resulting sediment dynamics, with strong cross-and along-shore currents, means that sediments constantly shift along and across the shelf. In fact, in all these settings, sediments (especially fine ones like small gravel, sand or silt) tend to have a short residence time nearshore since high storm waves effectively remove coastal sediments and transport them offshore (Tsutsui et al, 1987;Quartau et al, 2012;Romine and Fletcher, 2013;Meireles et al, 2013). These sediments are typically deposited further offshore to form clinoform bodies on the deeper parts of the shelf (Chiocci and Romagnoli, 2004;Quartau et al, 2012).…”

Intense hurricane transports sand onshore: Example from the Pliocene Malbusca section on Santa Maria Island (Azores, Portugal)

“…Moreover, observations by Meireles et al (2013) on Pliocene deposits at nearby Ponta do Castelo also report significant sediment transport by storms down to depths of -55 m.…”