Imprints of volcanic, erosional, depositional, tectonic and mass-wasting processes in the morphology of Santa Maria insular shelf (Azores)

Neogene marine sediments and biota encapsulated between lava flows on Santa Maria Island (Azores, north‐east Atlantic): An interplay between sedimentary, erosional and volcanic processes

“…Typically, the Cruziana ichnofacies in high energy shores extend from the lower shoreface to lower offshore (Pemberton et al , 2001). However, on insular shelves and sediment‐stripped submarine slopes, as in the case of Santa Maria Island (see Ricchi et al , 2018, 2020), a deeper environment (just below storm‐wave base) cannot be excluded as the explanation for the impoverished ichnoassemblages, because the limited habitats can be colonized by export of trace makers from shallower zones along with the sediments.…”

“…A high‐resolution bathymetric and seismic reflection survey demonstrates the occurrences of sedimentary wedges around Santa Maria Island (Ricchi et al , 2018, 2020). These sediments are interpreted to be sourced from the erosion of the island but also from a diverse accumulation of remains of heterozoan organisms that live on the shelf.…”

“…Probably, this palaeotopography corresponds to a flooded marine terrace much like that at the outer shelf of Santa Maria Island today ( Fig. 12; Ricchi et al, 2018Ricchi et al, , 2020.…”

“…These well‐preserved and easily accessible outcrops are exposed along the southern, eastern and northern coasts of the island, offering a unique insight into the geometry, composition and structural characteristics of lava deltas of different types, as well as the palaeoenvironments recorded by marine sediments intercalated between volcanic sequences, and the associated biota. In addition, owing to a recent very high‐resolution bathymetrical survey and detailed geomorphological analysis of its insular shelf (Ricchi et al , 2018, 2020), Santa Maria also provides modern analogues for sedimentary deposits, from which much can be learned about sediment transport on volcanic islands (see also Meireles et al , 2013; Johnson et al , 2017).…”

“…Oceanic islands are generally subjected to high‐energy wave regimes, a condition that, in addition to the effects posed by glacio‐eustatic sea‐level changes and the typically narrow shelves of these islands, makes the preservation of marine fossiliferous deposits difficult (Ávila et al , 2008, 2018; Quartau et al , 2012; Ramalho et al , 2013; Ricchi et al , 2020). Effectively, accumulations of island coastal sediments normally correspond to small perched beaches, with such materials easily remobilized and transported offshore during storms to form deeper‐water shelf clinoforms (Quartau et al , 2012; Meireles et al , 2013; Ramalho et al , 2013), particularly in non‐tropical settings that lack fringing reefs and early diagenetic cementation of carbonate sediments.…”