Holocene vegetational and coastal environmental changes from the Lago Crispim record in northeastern Para State, eastern Amazonia

Vegetational and coastal environmental changes have been interpreted from a 600 cm long and 7640 C-14 yr B.P, old sediment core from Lago Crispim loca ted in the northeastern Part State in northern Brazil. The radiocarbon date d sediment core was studied by multi-element geochemistry, pollen and charc oal analysis. Holocene Atlantic sea-level rise caused an elevation of local water table, which allowed the formation of organic deposits in a probably former inter- dune valley. Dense, diverse and tall Amazon rain forest, and some restinga (coastal vegetation) covered the study area at the beginning of the record at 7640 C-14 yr B.P. Mangrove vegetation developed along rivers close to th e core site at that time. Subsequent decrease in less mangrove vegetation n ear the study site indicates a sea-level regression, beginning since around 7000 C-14 yr B.P. Lower sea-levels probably favoured the formation of a lo cal Mauritia/Mauritiella palm swamp at 6620 C-14 yr B.P. Oscillations of hi gher and lower sea-level stands probably changed the size of the local palm swamp area several times between 6620 and 3630 C-14 yr B.P. Sea-level tran sgression at around 3630 C-14 yr B.P., caused marked coastal environmental changes: the development of mangroves near the site, the replacement of the local palm swamp by a Cyperaceae swamp, the substitution of the surroundin g former Amazon rain forest and some restinga vegetation mainly by salt mar shes. High amount carbonised particles suggest a strong human impact by bur ning on the coastal ecosystems during this late Holocene period. Highest concentrations of NaCl and also Ca, Mg and K in the upper sediment core indicate that the Atlantic was close during the late Holocene period. The core site, which is today 500 m from the coastline and only 1-2 m above modern sea-level, was apparently never reached by marine excursions during the Holocene. Less representation of mangrove since ca. 1840 C-14 yr B.P., may be related due to a slightly lower sea-level or to human impact in the study region. The modern shallow lake seems to be formed recently by road construction, f orming an artificial dam. (C) 2001 Elsevier Science B.V. All rights reserve d.