Abstract:
This paper presents a summary of a palynological study carried out for the Ocean Drilling Program, Leg 155. The study focused on the composition and distribution of organic matter in sediments of the Amazon Fan during the Pleistocene glacial/interglacial sequences. Samples from holes 940A, 944A, and 946A showed that glacial lowstand deposits are characterized by large concentrations of a palynological assemblage composed of Andean and tropical lowland taxa, minor amounts of reworked Paleozoic, Cretaceous, and Tertiary taxa, and large volumes of organic debris (e.g. wood, vessels, epidermis, cuticles). In general, these intervals do not contain many taxa diagnostic for the lowland savannah's. In all the studied sites, there is an increase of ferns, fern allies, reworked reworked and corroded palynomorphs, and fungal spores at the time of the last glacial episode. Interglacial highstand deposits are characterized by low concentrations of the terrigenous palynological assemblage and a predominance of marine microfossils. Although no marked differences exist in the composition of the organic matter along the fan, there is a decrease in the concentration of palynomorphs from proximal to distal sites. No compositional difference between the levees and the debris flow was observed. The palynological sequences in the Amazon deep sea fan give no indication of major vegetational changes in the lowlands. If extensive savannah vegetation existed in Amazonia during the Pleistocene glacial intervals, as claimed in the refugia theory, they were either obliterated or not recorded in the sediments of the Amazon Fan.