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Marine terrace development on reefless volcanic islands: New insights from high-resolution marine geophysical data offshore Santa Maria Island (Azores Archipelago)
Ist Teil von
Marine geology, 2018-12, Vol.406, p.42-56
Ort / Verlag
Elsevier B.V
Erscheinungsjahr
2018
Link zum Volltext
Quelle
Elsevier ScienceDirect Journals Complete
Beschreibungen/Notizen
Submerged marine terraces are relict coastal erosional landforms now underwater due to rising sea level and/or land subsidence. Using as case study the shelf around Santa Maria Island (North Atlantic Ocean), we intend to advance our knowledge on the formation and preservation of these features on reefless volcanic islands. Santa Maria is an ideal place to study their combined generation, since it displays a sequence of subaerial and submerged marine terraces (the latter not studied before), distributed between 7/230 m in elevation, and −40/−140 m in depth, respectively. Based on some geological constraints, we investigated a possible correlation between the formation of the different terraces with known sea-level changes. Our results suggest that the spatial distribution of marine terraces at Santa Maria depends on the complex interplay between glacio-eustatic sea-level fluctuations, the island's vertical motion trends, the morphology of the shelf, and the intensity of marine erosion. Subaerial terraces probably developed from ~3.5 Ma to ~1 Ma following a fortuitous conjugation of optimal exposure to energetic waves and a suitable arrangement/lithology of the stratigraphic units promoting easier erosion. Their preservation was likely promoted by the uplift trend the island experienced in the last 3.5 Ma, which was rapid enough to prevent their destruction by subsequent highstands. The submerged terraces, presumably all younger than ~1 Ma, were largely influenced by shelf gradient, leading to more developed and preserved terraces in wider and low-gradient sectors. Displacement by active faults also conditioned the formation and further development of both subaerial and submerged terraces, with tectonic activity documented for the 0.693 Ma–2.7 Ma period.
•Five sets of submerged marine terraces have been recognized at different depth on Santa Maria’s insular shelf.•The possible correlation between the terrace formation and relative sea-level changes has been investigated.•The marine terraces were probably formed from ~3.5 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.