Review of evidence for late Tertiary shorelines occurring on South Atlantic coasts

Recognition of (late) Tertiary shorelines on continental coasts is becoming increasingly common. It is argued that the elevations of such features are central to their approximate dating and the demonstration of contemporaneity with similar features elsewhere. South Atlantic coasts have not had a long history of investigation, yet there exist many diffuse observations, in both time and space, which are here drawn together into a preliminary synthesis and the case for widespread occurrences of late Tertiary shorelines in the region reviewed. This allows comparison with other areas from which Tertiary shorelines are known, the Atlantic seaboards of the Southeastern United States and Northwest Europe, for example.The coasts of oceanic islands are probably the best places to examine the legacy of late Cenozoic sea-level changes. It is suggested that, since many of the cliffed shores of these islands appear to be the result of a rapid emergence, coastal features predating this event might be preserved on the cliff-tops. Possible late Tertiary shorelines from South Atlantic islands are described, as are those which have been positively dated to this period, in the Eastern Canary Islands, for instance. Sedimentary and morphological indicators of Tertiary high sea-levels are described from Antarctic coasts. South American and African Atlantic continental margins. Evidence from the latter two areas is most suspect, owing to their generally more complex Quaternary tectonic histories. A summary of the evidence for Tertiary shorelines on South Atlantic coasts is tabulated.Methods which have been or could be used to date late Tertiary shorelines are described. Minimum age can be deduced from that of deposits resting on an erosional surface, maximum age from that of the youngest formation across which a surface is cut. More precise age can be estimated where a marine surface is sandwiched between datable non-marine formations or where periods of tectonic activity (responsible for differential surface deformation) can be dated. Elevations of surfaces can be used to estimate ages. Problems in both recognising and dating Tertiary shorelines are discussed. Recognition of their origin is made more difficult by their degraded state and, if they occur within a Quaternary erosional sequence, their antiquity may not be realised.It is suggested that fluctuations in the Antarctic ice sheet during the late Tertiary induced substantial glacio-eustatic changes of sea-level which may have been most marked in adjacent areas. This is considered to be the mechanism through which late Tertiary shorelines in the area were formed yet, considering the paucity of the morphological and sedimentary data, these should not be used as the basis for a eustatic chronology.