Contribuição dos sedimentos e ictiólitos para a identificação do ambiente de formação do Sambaqui do Moa (Saquarema-RJ)

Abstract

The Moa’s shellmound is an archaeological site located in Itaúna, Saquarema coastline from the State of Rio de Janeiro. Three moments of occupation were recognized this site: stratum 3 corresponding to the beginning of the occupation of this site basis; 2, intermediate, points to a more intense occupation with great concentration of mollusks, fish bones and human burials; and 1, the most superficial, related to the last occupation. To identify the environmental conditions of development from Moa’s shellmound, sediment samples and zooarchaeological material were collected in these three strata. The zooarchaeological material is represented by microscopic fish remains (ichthyoliths), composed by microteeth with different morphologies: canines, incisors and molars. The sediments according to XRD analyzes are composed by quartz and kaolinite, calcite, aragonite and fluorapatite. The latter is the main mineral of zooarchaeological material, while calcite and aragonite reflect the remains of shells contained there, abundant in this site. The mineralogical analyses were confirmed by chemical analysis, in which high levels of P2O5, CaO and FB (H2O, CO2), account for the fluorapatite, calcite and aragonite. Chemical modifications variations of the C and P in microteeth suggest that these experienced mineralization, an initial fossilization process, post-deposition. The data of stable isotopes 13C and 15N allowed defining the source of organic matter from Moa’s shellmound as marine/brackish, where the vegetation is represented, predominantly, for C3 plants by type of rainforest. The 87Sr/86Sr ratios in ichthyoliths confirm that the environment surrounding the shellmound as estuary. The tooth morphology allowed us to recognize five families previously not recorded for the site, as Labridae, Serranidae, Ariidae, Erythrinidae and Characidae, which confirm the estuarine environment. The age of the Moa’s shellmound by radiocarbon from the sediments showed disruption of stratum 2, causing a reversal of aged strata which can be explained by processes of formation and/or changes in the rivers changed the geological and geomorphological settings area. Another explanation could be human interference, due to the large number of burials (over 30), has upset the order of the moments of occupation from Moa’s shellmound, and possible erosion. The Moa’s shellmound is therefore installed in an area of marine-estuarine transition.