Rhodoliths from the Cape Verde Archipelago: insights into climate change and megatsunami sediment dynamics

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Coralline red algae (Rhodophyta) are common carbonate producers throughout the Cenozoic time, especially in non-reefal environments, such as the Cape Verde Islands. Unlike most other algae, corallines are also capable of forming unattached nodules lying on soft or hard grounds, known as rhodoliths. These rhodoliths are reworked by wave and storm action into other environments offshore, or even onshore onto the beach, where they can form remarkable accumulations. On the Cape Verde Islands, such rhodolith accumulations along the coastline are known from at least three time intervals, namely (1) the interglacial MIS5e (ca. 120.000 years before present), (2) the last glacial period at ca. 73.000 years b.p., as well as (3) present-day beach deposits. A crucial interval for the formation of these accumulations is the second mentioned, because it is related to tsunami deposits formed by a flank collapse of Fogo volcano, one of the Cape Verde Islands. Rhodoliths from these three intervals as well as the associated marine terraces and tsunami deposits will be studied in the proposed project. The central aim is to use the younger geological record of Cape Verde to improve our scientific understanding of rhodolith beds and their species composition in a non-reefal tropical island shelf environment, both during a glacial and an interglacial period. The project also aims to investigate rhodolith transport and deposition during tsunami events, as a complementary, non-overlapping component of ongoing tsunami research. First of all, we will study the sedimentological background of rhodolith formation in the field and take representative samples that will be analyzed in the lab. We will make petrographic thin sections that allow the identification of algal taxa and associated biota, as well as the study of growth-forms, taphonomy, and the microfacies analysis of associated sediments. With this knowledge, we can reconstruct the formation of the rhodolith bodies as well as the associated tsunami deposits.