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

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 I represents the oldest Holocene sedimentary record in the core. Palynomorphs reveal a marsh environment with a freshwater influence. In Zone 2, Opereuloclinium centrocarpum and high S values indicate brackish water and reflect a Holocene sea-level rise related to the post-facial 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 charterizes a freshwater marsh. (c) 2005 Elsevier Ltd. All rights reserved.