Microscopic organic matter particles in late Holocene riparian sediments near the Cauca River, Colombia

Abstract

We conducted a palynofacies analysis on late Holocene fluvio-palustrine sediments from a succession that outcrops as a terrace proximal to the Cauca River, Colombia, in northern South America. The succession is composed of laminated clay, organic-rich laminae, sand beds and buried soils. These buried soils range in thickness from 2 to 16 cm and are composed of silty clay with varying degrees of root bioturbation and have a gray-green-bluish color. They could classify as Entisols and in this article we refer to them as paleosols. Samples from each of these sediment types (except sand), and samples from two modern-analog environments, also on the proximal part of the Cauca River, i.e. sediment from a seasonally flooded pond and the upper-most layer of a modern soil, were analyzed for organic matter content. Prior to selection of an organic matter extraction method, four protocols were tested on the modern pond sediment sample. A modified protocol involving flotation with ZnCl2 proved to be the best method for these sediment types. We produced an atlas of the main taxa and their relative proportions found in this study and propose this method as an excellent approach to environmental reconstruction of fluvial environments. Very little work has been done on fluvio-palustrine palynofacies in the Neotropics.