Redating of the To’aga site (Ofu Island, Manu’a) and a revised chronology for the Lapita to Polynesian Plainware transition in Tonga and Samoa

Radiocarbon dating Pacific archaeological sites is fraught with difficulties. Often situated in coastal beach ridges or sand dunes, sites exhibit horizontal and vertical disturbances, while datable materials such as wood charcoal are typically highly degraded, or derived from old trees or drift wood and bone collagen rarely survives in the tropical conditions. Shell, therefore, is the most logical material for dating Pacific sites since it is resistant to alteration, can be sampled to ensure only the last few seasons of growth are represented and is often closely tied to human economic activities. However, shell radiocarbon (14C) dating has been plagued by interpretive problems largely due to our limited knowledge of the 14C cycle in near shore marine and estuarine environments. Consequently, shell dates are typically ignored in regional chronometric evaluations and often avoided for dating altogether. Recent advances in our understanding of the source of shell 14C content as well as the development of the first South Pacific Gyre model of changing marine 14C over time, combined with Bayesian statistical modelling, have now provided us with insight into the value of these shell radiocarbon dates, enabling a revision of the age of the To’aga site on Ofu Island, an early occupation site associated with the initial Polynesian Plainware period in Samoa, the earliest use of which is now dated to between 2782 and 2667 cal BP.

New geochemical data on fossil wood from the Albian of the Dolomites (Southern Alps, Italy)

Information is provided about organic-matter bearing sediments and fossil drift-wood from the Puez area (Col de Puez, Southern Alps) near Wolkenstein (S. Tyrol, Italy). The locality is located on the Trento Plateau which represents a submarine high during the Lower Cretaceous. Its terpenoid hydrocarbon composition indicates that the wood fragment derived from a conifer belonging to the family Podocarpaceae or Araucariaceae. Intense degradation of OM argues for lengthier drifting. Long-term drifting is also indicated by the infestation of the bivalve Teredo (“shipworm”). The finding of a fossil tree trunk sheds some light on the early Lower Cretaceous tectonic history of the Trento Plateau and the Dolomites.

Observations on aquatic Macrophyte Dynamics In the Reservoir Of The Balbina Hydroelectric Powerplant, Amazonas State, Brazil

Between 1991 and 1995 aquatic macrophyte composition was observed in the lower part of the reservoir of the hydroelectric power plant of Balbina (Amazonas, Brazil). After closure of the dam in 1987, vegetation cover - mostly Eichhornia crassipes - was high, but was not quantified. After 1990 it declined rapidly with a characteristic succession pattern: Eichhornia ® Vincularia + Cyperaceae ® Salvinia. The Cyperaceae, and many other less dominant species, were mostly associated with drift wood, produced by the decomposing, emergent forest. Comparison of the chemical data of the Uatumã river before the construction of the dam (1983) with those of later years (1989 - 1995) suggests that the succession was the result of a relatively mild and short period of eutrophication, followed by declining nutrient levels. Annual variation of water levels, followed by aquatic and terrestrial decomposition of the marginal vegetation, may allow for the maintenance of relatively productive vegetation belts along the shore lines of islands and inundated stream valleys.