Marine terrace development on reefless volcanic islands: New insights from high-resolution marine geophysical data offshore Santa Maria Island (Azores Archipelago)

Abstract

Five sets of submerged marine terraces have been recognized at different depth on Santa Maria's insular shelf. The possible correlation between the formation of raised and submerged terraces with relative sea-level changes have been investigated. The presently raised marine terraces were probably formed from ~3.5 Ma to ~1 Ma, whilst submerged terraces were formed from ~1 Ma to the Last Glacial Maximum. A better estimation of the uplift trend for Santa Maria island has been proposed. The formation and preservation of marine terraces is discussed according to a number of interacting factors.

Towards a ‘Sea‐Level Sensitive’ dynamic model: impact of island ontogeny and glacio‐eustasy on global patterns of marine island biogeography

“…(A) Southern shores of Santa Maria Island (Azores), showing the bathymetry offshore Prainha fossiliferous outcrop (Ricchi et al ., ). The black line indicates the location of the transect shown in B depicting the bottom topography from the intertidal down to 250 m depth.…”

Pliocene and Late Pleistocene actinopterygian fishes from Santa Maria Island, Azores (NE Atlantic Ocean): palaeoecological and palaeobiogeographical implications

“…This stage lasted until 3.5 Ma, when the subsidence trend was reversed and the island's volcanic edifice initiated an uplift trend continuing to the present day. Initially, a rate of 59 m Ma -1 occurred during 3.50-2.15 Ma, and then a slower rate of 42 m Ma -1 between 2.15 Ma and the present (Ricchi et al 2018). This uplift trend, coupled with Pleistocene glacio-eustatic sea-level fluctuations, produced a staircase of ten subaerial and five submerged marine terraces, the former particularly evident across the island's western sector at elevations ranging from 7-11 to 210-230 m (Ramalho et al 2017), and the latter on the shelf all around the island at depths ranging between 40-50 and 120-140 m below sea level (Ricchi et al 2018).…”

“…It is the oldest island of the Azores Archipelago and first rose above sea level at c. 6 Ma, initially by Surtseyan activity (the Cabrestantes Formation) and then by subaerial, monogenetic volcanism associated with the Porto Formation. High rates of magma production formed a shield volcano (the Anjos volcanic complex, dating from 5.8 to 5.3 Ma), which substantially increased the area of the Santa Maria protoisland, as attested by the present-day insular shelf (Ricchi et al 2018). Although the entire volcanic edifice has likely undergone subsidence since extrusion of the first lavas of the submarine edifice, a prolonged subsidence rate of c. 100 m Ma -1 lasted from 5.3 Ma until 3.5 Ma (Ramalho et al 2017).…”

Recent geospatial dynamics of Terceira (Azores, Portugal) and the theoretical implications for the biogeography of active volcanic islands

“…During sea level low-stands, the islands in the Azores were larger than they are today, whereas during sea level high-stands surface areas in the Azores were smaller (Rijsdijk et al 2014, Norder et al 2018). The differences in size are generated by exposure during glacial periods of the insular shelves that surround the islands and span from the present-day coastline to ~-130 m (Quartau et al, 2010(Quartau et al, , 2015a, and on some islands, (e.g., Flores, Graciosa or Santa Maria) it can exceed the subaerial area (Ávila et al 2010, Quartau et al 2015b, Ricchi et al 2018). The global curve of mean sea level (MSL) change shows the rate of sea level variation on a global scale, but sea level varied differently across the planet, with large deviations from the mean nearby continents (Milne andMitrovica 2008, Simaiaikis et al 2017).…”

“…Our aim is to quantify how volcanic processes affect surface areas of islands over longer time scales and how that relates to climatic drivers of area and distance changes. Owing to increasing radiometric dating of volcanogenic rocks, crucial insights into their spatiotemporal dynamics can be obtained (e.g., Ramalho et al 2013, Clague and Cherod 2014, Ricchi et al 2018, thus linking the long-term geological dynamism of volcanic islands to bio-evolutionary processes. Such integrative island studies gave rise to the General Dynamic Model (GDM) of oceanic island biogeography (Whittaker et al 2008), which states that present-day patterns of endemic richness can be explained by the dynamic geological life cycle of volcanic oceanic islands over millions of years (see also : Ziegler 2002, Stuessy 2007, Whittaker et al 2008, Borges and Hortal 2009, Warren et al 2015, Borregaard et al 2017, Ávila 2018a, Lim and Marshall 2018.…”