Phytoliths and seeds in fluvial island paleoenviroment reconstruction (interaction with pollen analysis)

We tested the use of phytoliths and seeds as bioindicators in the paleoenvironmental reconstruction of fluvial islands and compared the results with those of facies and pollen analyses. The studied material was taken from a 215 cm core drilled in Mutum Island. The study included a) the quantification and identification of phytoliths and seeds, b) the determination of the distribution of biological material in the island sediment and sedimentary facies, c) the determination of organic material contents, and d) a chronological analysis with three ¹⁴C dates. This study also determined the distribution of seeds and phytoliths over the sedimentary environment succession. We identified the following distributions of seeds and phytoliths over the paleoenvironmental hydrach succession. 1) Channel paleoenvironment (eupotamic stage): the sediment was deposited under lotic flow conditions, with the occurrence of Podostemaceae phytoliths and a predominance of Poliygonaceae seeds. 2) Blind channel paleoenvironment (parapotamic stage): this environment, which occurred 725–935 cal yrs BP., demonstrated an increase in the quantity of Podostemaceae phytoliths and seed quantity alternations. 3) Lake paleoenvironment (paleopotamic stage): a change from the blind channel to lake environment occurred at 631–797 cal yrs BP. An increase in the phytolith concentration was associated with a saddle morphology peak and general decrease in seeds, except for over the 110-100 cm interval, with a high occurrence of Cecropiaceae and Lentibulariaceae seeds. 4) Present swamp environment (paleopotamic to terrestrial stage): the present environment was settled approximately 300 cal yrs BP. (uncertainties range) with phytoliths. The seed assemblage in the sediment resembles the current vegetation on the island. The variation in the types of phytoliths and seeds from the base to the top of the sedimentary column reflect changes in the vegetation with changes in the environmental conditions and the great potential for these structures to be paleoindicators in fluvial systems. The seed and phytolith data were compared with the pollen analysis results.