ALBERT

Description: By mapping the vertical and lateral distribution of reefal facies on the west and south coast of Barbados we have produced a revised model of reef development for the Last Interglaciation. We find that reef architecture around Barbados has significant complexity including evidence for wave exposure-related variations in reef geometry and at least 3 stages of reef development that were controlled by variations in sea level. During the main stage of development, an Acropora palmata-dominated reef-crest aggraded ∼22 m in response to a minimum sea-level rise of 20 m. During stage 2, a sea cave was cut 3–4 m above the fossil reef-crest, possibly indicating that reef growth was terminated before sea level reached the highstand. Similar sequences elsewhere in the Caribbean indicate that this early reef demise may not be a local phenomenon: several reefs apparently stopped growing between +2 and +4 m and only in sheltered areas did they reach the highstand at +6 m, as recorded by intertidal notches. This pattern of reef demise has previously been related to rapid sea-level rise at the end of the interglacial, but stratigraphic data are equivocal. The final stage of reef development on Barbados occurred when sea level began to fall. This fall was rapid, leaving a thin but widespread veneer of reef-crest deposits over the proximal reef-front, and discontinuous intertidal and shallow subtidal deposits capping the distal reef-front. Although further dating is required to differentiate these three stages, our only reliable U–Th TIMS date indicates that almost 50% of the exposed reef had accreted by 129 ka, giving an estimate of 15 ka for the main aggradational stage. Furthermore, reports of relict reef-crests buried beneath these exposed deposits indicate that our revised model is incomplete and that earlier stages of reef growth occurred during the Last Interglaciation. These earlier stages imply that sea-level was at an ‘interglacial level’ for as long as 20 ka — supporting the Devils Hole record of interglacial duration. Unfortunately, these estimates could not be verified directly because most of our U–Th data show major stratigraphic age reversals attributed to diagenesis. This pattern is also evident in all other well-dated reefal units in the Caribbean and leads us to conclude that only diagenetically screened, precise, stratigraphically consistent coral dates can be used to directly estimate the duration of the Last Interglaciation.

Description: Les Cephalopodes qui font l'objet de cette petite note furent recueillis au cours de la Campagne de la Calypso dans le golfe de Guinee, pendant les mois de mai a juillet 1956. Les recoltes proviennent de dragages, de chalutages et de peches planctoniques au large du continent africain, du Senegal au Gabon, et de dragages, de plongees et de peches a pied autour des iles S. Tome, Principe et Annobon. Le but principal de la campagne etait l'etude de la faune littorale des iles, et les conditions de travail dans cette region expliquent que les Cephalopodes captures soient peu nombreux. Je me fais un devoir de remercier M. le Professeur L. FAGE et M. J. FoREST d'avoir bien voulu me confier l'etude de ce materiel.