Coastal terraces and Holocene sea-level changes along the Patagonian Atlantic coast

The results of morphological, pedostratigraphical, and geochronological studies of marine terraces along the Patagonian Atlantic coast are reported in this work. There is evidence for the preservation of up to three Last Interglacial, and at least three Penultimate Interglacial beach ridge systems as well as several levels of Holocene beach ridges. Towards the interior, these beach ridges are frequently bordered by elevated beach deposits from the Middle and Early Pleistocene / Late Pliocene (Schellmann, 1998a, b). The various Holocene shorelines are due to different stages of relative sea-level lowering since the Middle Holocene transgression maximum. The relative sea-level seemed to decline continuously during the Middle and Late Holocene. However, this decline may have been interrupted by a significant high tide water level rise in the early Late Holocene (around 2,700 C-14 BP; not calibrated). The equivalent sea-level changes cannot be accurately quantified through raised beach ridge systems since their altitudes mainly depend on wave extension and therefore on storm frequency and strength. The elevation of fluvial terraces at the mouths of dry valleys with periodic runoff ('Canadones') is a better indicator for sea-level reconstruction. Dry valleys are adjusted to the present high tide water level, while terrace surfaces are adjusted to a high tide water level (hTw) at the time of their formation. Beach deposits are intertwined with fluvial sediments near the coast. These marine insertions often contain articulated shells, which allow for a numeric dating of modern and fossil hTw. "Fluvio-littoral" terraces were dated near Camarones and suggest a 5 +/- 1 m increase of the hTw during the Holocene transgression maximum (about 6,600 C-14 years ago). Sea-level declined to about 3 +/- 1 m above the present hTw about 5,800 C-14 years ago.