Palaeoecology of Quaternary Shorelines and Sea-Level Change in Mallorca

Abstract

descriptive, and merely attempted to fit the shorelines into the classic Tyrrhenian framework of Deperet (1918). This placed the shorelines in the last interglacial period, and related their formation to periods of high eustatic sea levels. The interglacial origin of the shorelines was supported by the presence of the thermophilous gastropod Strombus latus {-bubonious), which is today found living in West Africa. A Tyrrhenian I 'transgressive complex' was recognized by Butzer and Cuerda (1962) at heights between +4 m and +34 m; two stages of the Tyrrhenian II were identified with shorelines at +10.5 m, +12.5 m and +2 m to 9 m; and Tyrrhenian III deposits were found at +0.5 m to +2.8 m. The fauna associated with the shorelines is similar to that reported from many other areas of the Mediterranean, with a rich Strombus fauna characterizing the Tyrrhenian II shoreline. Following this initial stratigraphic analysis, 15 Thorium/Uranium (Th/U) dates were obtained for shell material in the shorelines (Stearns and Thurber, 1965). The dates fell into three basic age ranges which tended to support the threefold division of the Tyrrhenian, but the spread of dates also indicated that the sequence of marine and terrestrial deposits was far more complex than was originally thought. Six major marine transgressions were eventually recognized in the Mallorcan sequence (Table I). Each marine hemicycle was identified by a beach overlain by a palaeosol, and the terrestrial hemicycle was equated with a silt/aeolianite complex followed by a pedocal. A useful review of the Mallorcan literature is presented in the Quaternary Research Association field guide for the island (Crabtree et al, 1978). The guide also contains location maps and sections of all the key sites. Most of the sites were visited in the present study, and their molluscan fauna was sampled. Methods Samples of the fossil molluscan fauna were collected from each site over a set time period of one hour. This method provides comparability with abundance data obtained for modern live and dead molluscan assemblages in the Mediterranean (Richards, 1982; in press). Thus each site could be matched with a modern analogue with a known relationship to sea level, allowing the position of the contemporaneous sea level to be established to within ?0.5 m or better.