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

珊瑚红藻(红藻)在整个新生代都是常见的碳酸盐生产者，特别是在非珊瑚礁环境中，如佛得角群岛。与大多数其他藻类不同的是，珊瑚还能够在软或硬的地面上形成独立的结节，即所谓的红柱藻。这些红石在海浪和风暴的作用下被改造成其他近海环境，甚至岸上的海滩，在那里它们可以形成显著的堆积。在佛得角群岛，沿海岸线的这种红石堆积至少可从三个时间间隔获知，即(1)间冰期MIS5E(距今约120.000年)，(2)约73.000年前的最后一次冰期，以及(3)今天的海滩沉积。这些堆积形成的关键时间间隔是第二个，因为它与佛得角群岛之一的福戈火山侧向坍塌形成的海啸沉积有关。在拟议的项目中，将研究这三个区间的红柱石以及相关的海洋阶地和海啸沉积物。中心目的是利用佛得角较年轻的地质记录，提高我们对冰期和间冰期非珊瑚礁热带岛屿陆架环境中的红柱石床及其物种组成的科学了解。该项目还旨在调查海啸事件期间红柱石的运输和沉积，作为正在进行的海啸研究的一个互不重叠的组成部分。首先，我们将在野外研究红柱石建造的沉积学背景，并采集具有代表性的样品，在实验室进行分析。我们将制作岩石学薄片，以便识别藻类和相关生物群，以及研究生长形式、挖掘和相关沉积物的微相分析。有了这些知识，我们可以重建罗多里斯体的形成以及相关的海啸沉积物。

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.