Tracers of uplift and subsidence in the Cape Verde Archipelago
electronic supplement
Ramalho*, R.; Helffrich, G.; Schmidt, D.; Vance, D.
Department of Earth Sciences, University of Bristol, Wills Memorial Building
Bristol, BS8 1RJ, UK
*Corresponding author: [email protected].
1 Introduction
This an electronic supplement of the paper ”Tracers of uplift and subsidence in the Cape Verde
Archipelago”. The objective of this supplement is to provide more detailed information on the volcanostratigraphy of some of the Cape Verde islands mentioned in the main text, and a detailed description of key palaeo-markers of relative sea-level height used to track the history of vertical movements affecting those islands.
2 Palaeo-markers of sea-level in the Cape Verde islands
2.1 Sal
Sal’s volcanostratigraphy comprises (Silva et al. 1990; Torres et al. 2002a): Ancient Eruptive
Complex; Principal Eruptive Formation; Ponta do Altar-Baleia Complex; Conglomerate Brec-
1 cia; Ribeira da Fragata Formation; Serra Negra Eruptive Formation; Monte Grande-Pedra
Lume Formation; and Quaternary Sediments (see Figure S1, and Table 1 in the main text).
2.1.1 The Ancient Eruptive Complex
The Ancient Eruptive Complex constitutes the basement unit and is profoundly eroded and weathered. It occurs mainly in the central part of the island where it reaches the maximum elevation of ∼ 60 m asl. Silva et al. (1990) and Torres et al. (2002b) describe the Ancient
Eruptive Complex as a complex sequence of formations mostly comprising hydrovolcanic prod- ucts of effusive and explosive nature. The whole unit is intensively intruded by dykes - up to 95% of the outcropping area - and small plutonic bodies, a condition that in conjunction with the advanced state of weathering exhibited by its products is an obstacle for solid event reconstructions.
The oldest products seem to comprise weathered basaltic pillow-lavas, pillow-breccias and hyaloclastites (Torres et al. 2002a) probably extruded in the Late Oligocene as the 25.6±2.2 Ma
K-Ar age suggests (Torres et al. 2002b). Volcanic breccias of trachytic, trachyphonolitic and basaltic nature occur in association with the previous lithologies (Silva et al. 1990; Torres et al.
2002a), also exhibiting a typical hydroclastic texture (often with glassy matrix) and supporting a submarine environment for the origin of the Ancient Eruptive Complex (Torres et al. 2002a).
In their study, (Torres et al. 2002a) state that the final effusions of the Ancient Eruptive
Complex correspond to ’small and scarce’ fissural subaerial flows with plugs, dykes and flows of phonolites. These outcrops, though, probably belong to the younger Principal Eruptive
Formation, due to their apparent discordance with the submarine volcanic products attributed to the Ancient Eruptive Complex. The complexity and weathering of the Ancient Eruptive
Complex unfortunately prevent conclusive event reconstructions based on field observations.
Silva et al. (1990) noted the presence of small outcrops of dolomitic limestone apparently within the ancient submarine lavas, near Espargos. These sediments occur in a discontinuous
2 23º00’W 22º56’W 22º52’W 22º48’W 16º52’N 16º52’N Ponta Norte Sal N Baía de Fiúra
Monte Grande (406 m) 0 2 4 km
16º48’N 16º48’N Quaternary sediments (Q) Baleia Monte Grande-Pedra Lume Pedra Lume Fm (MG-PL) extrusives EspargosEspargos Palmeira calc Serra Negra Formation (SN) extrusives 16º44’N 16º44’N Ribª de Fragata Formation (RF) Ribª do Lizardo (not shown) Conglomerate-Breccia Deposit (CB) Rabo de Junco (not shown)
Ponta do Altar-Baleia Complex (PAB) extrusives 16º40’N 16º40’N Serra Negra Principal Eruptive Formation (EP) extrusives plutonic rocks (formerly CEA) Ribª de phonolites (formerly CEA) Fragata Algodoeiro Ancient Eruptive Complex (CEA) plutonic rocks predominant 16º36’N Santa Maria pelagic carbonates (calc) 16º36’N polygenetic breccia pillow-lavas &