Basalt sea stack and related facies from the Middle Pleistocene on Sal Island (Cabo Verde Archipelago, NE Atlantic Ocean)

Johnson, Markes E., Uchman, Alfred, Ramalho, Ricardo S., Martín-González, Esther, Martins, Gustavo M., Hipólito, Ana, Marques, Sandra, Ávila, Gonçalo C., Madeira, Patrícia, Doukani, Mohamed Amine and Ávila, Sérgio P. 2025. Basalt sea stack and related facies from the Middle Pleistocene on Sal Island (Cabo Verde Archipelago, NE Atlantic Ocean). Facies 71 (4) , 20. 10.1007/s10347-025-00710-8

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Abstract

A former sea stack formed by basalt occurs at Ponta Manuel Lopes on the north coast of Sal Island in the Cabo Verde Archipelago. Reduced by wave erosion prior to coastal uplift, the dimensions may be partially reconstructed as a rectangular-shaped block 45 m long, by 20 m wide and 7 m high. The long axis sits parallel to a Mid-Pleistocene terrace elevated as much as 15 m above present sea level. Contrasting facies are preserved on two flanks. The smaller western face is joined laterally by a massive limestone deposit dominated by the coral Siderastrea radians with hundreds of dome-shaped to pillar-shaped colonies preserved largely in growth position. Other corals within the same fringing facies include Porites porites, Madracis cf. pharensis, and Favia cf. gravida. The carbonate matrix in the coral beds also includes abundant sea urchin spines. A separate lithofacies that extends across the inner, long axis of the block consists of calcarenites and calcirudite with angular basalt fragments that decrease in size and abundance from the wall. These deposits dip 35º to the south to merge with the adjacent Pleistocene terrace. The eastern half of the basalt block was truncated by marine erosion, which allows access to steeply dipping beds banked against the former surface. That deposit includes rare oyster debris. Other mollusks are common in flat-lying limestone on the adjacent marine terrace. Although fossil corals are abundant throughout the Cabo Verde, Canary and Madeira archipelagos, in situ fossil coral-reef structures are uncommon and the island shelves around those groups historically lack the protection of fringing or barrier reefs.

Item Type:	Article
Date Type:	Published Online
Schools:	Schools > Earth and Environmental Sciences
Publisher:	Springer
ISSN:	0172-9179
Date of Acceptance:	3 August 2025
Last Modified:	10 Sep 2025 10:01
URI:	https://orca.cardiff.ac.uk/id/eprint/181021

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