Macrofossil analysis of a composite 19m long sediment core from Rano Raraku Lake (Easter Island) wasrelated to litho-sedimentary and geochemical features of the sediment. Strong stratigraphical patterns are shown by indirect gradient analyses of the data. The good correspondence between the stratigraphical patterns derived from macrofossil (Correspondence Analysis) and sedimentary and geochemical data (Principal Component Analysis) shows that macrofossil associations provide sound palaeolimnological information in conjunction with sedimentary data. The main taphonomic factors influencing the macrofossil assemblages are run-off from the catchment, the littoral plant belt, and the depositional environment within the basin. Five main stages during the last 34,000 calibrated years BP (calyrBP) are characterised from the lithological, geochemical, and macrofossil data. From 34 to 14.6calkyrBP (last glacial period) the sediments were largely derived from the catchment, indicating a high energy lake environment with much erosion and run-off bringing abundant plant trichomes, lichens, and mosses into the centre of Raraku Lake. During the early Holocene the infilling of the lake basin and warmer conditions favoured the growth of a littoral plant belt that obstructed terrigenous input. Cladoceran remains and Solanaceae seeds are indicative of reduced run-off and higher values of N and organic C indicate increased aquatic and catchment productivity. From 8.7 to 4.5calkyrBP a swamp occupied the entire basin. The increase of Cyperaceae seeds reflects this swamp development and, with oribatid mites and coleopteran remains, indicates a peaty environment and more anoxic conditions in Raraku. At around 4.5calkyrBP dry conditions prevented peat growth and there is a sedimentary hiatus. About 800calyrBP, peat deposition resumed. Finally, in the last few centuries, a small lake formed within the surrounding swamp. Evidence of human activity is recorded in these uppermost sediments.
Bibliographical noteFunding Information:
This research was funded by the Spanish Ministry of Science and Education through the projects LAVOLTER ( CGL2004-00683/BTE ), GEOBILA ( CGL2007-60932/BTE ) and CONSOLIDER GRACCIE ( CSD2007-00067 ) and an undergraduate grant (BES-2008-002938 to N. Cañellas-Boltà). We are grateful to CONAF (Chile) and the Riroroko family for the facilities provided on Easter Island. We are also grateful to Bas van Geel, Geoffrey Lemdahl, Oliver Heiri, Emily Coffey, Garland Upchurch, Frode Ødegaard, Robert Anderson, Charles O'Brien, Torstein Solhøy, Fred Stauffer, Heinrich Schatz, Alice Telka, and members of the PALEOLIM mailing list who responded to the first author's request, for their help in the identification of and comments about the macrofossils found. This is publication nr. A 376 from the Bjerknes Centre for Climate Research.
Copyright 2012 Elsevier B.V., All rights reserved.
- Last glacial period
- Rapa Nui
- Sedimentary facies