Holocene evolution of Itapeva Lake, Rio Grande do Sul, Brazil: Palynomorphs C org, N, and S records

Abstract

Holocene coastal environmental changes are interpreted from a 590 cm long core taken from Itapeva Lake in the northern coastal plain, Rio Grande do Sul, Brazil. The sediment core is radiocarbon dated at 211 cm depth (6460±40 yr B.P.) and studied by geochemistry and palynomorph analyses. The Pleistocene–Holocene boundary is predicted at the top of a glauconitic sand layer at 330 cm depth. On the basis of C org, N, S, and palynomorph data, it is possible to distinguish four zones related to the Holocene transgression–regression cycle, as well as proxies for the salinity trends and organic matter source. The start of Zone 1 represents the oldest Holocene sedimentary record in the core. Palynomorphs reveal a marsh environment with a freshwater influence. In Zone 2, Operculoclinium centrocarpum and high S values indicate brackish water and reflect a Holocene sea-level rise related to the postglacial marine transgression. The high amount of Cyperaceae pollen grains and a significant C org increase in Zone 3 indicate a typical marsh environment with episodes of marine water that reflect a regression phase. Salvinia natans (L) All. and Cyperaceae pollen grains are the most significant palynomorphs in Zone 4, which characterizes a freshwater marsh.