Behaviour and taphonomic loss in foraminiferal assemblages of mangrove swamps of French Guiana

Abstract

Fifty-three surface sediment samples were collected in January 1999, July 2000 and December 2000 on mud flats and in mangrove swamps of French Guiana. Sampling stations were selected to provide information on different environmental conditions, on the mud flats and in the mangrove forest. Thirteen samples were also collected at a depth of about 8–12 cm in the sediment. Additional samples were collected from three long cores in the channel of the Kaw River. The main parameter controlling the distribution of recent foraminiferal assemblages is the seasonally variable relative influence of coastal water of reduced salinity and low pH, low-Ca river water. Areas under the influence of coastal water are dominated by calcareous species, mainly Ammonia tepida and Cribroelphidium spp., even in mangrove swamps during the dry season. River water influences almost all the study area during the rainy season and leads to the dominance of agglutinated species, with the nature of the assemblages depending on local environmental characteristics. On the mud flats, tests are typically well preserved in the 10 cm below the surface that is the most important taphonomically active zone for foraminifera. However, owing to intense bioturbation, the taphonomic processes in the mangrove swamp may result in the total destruction of the microfauna, including agglutinated tests. This study shows that the preservation of thanatocoenoses in mangrove swamp environments of French Guiana only occurs in exceptional circumstances. When they are preserved, the remaining assemblages, even if modified by taphonomic processes, give valuable information for paleoenvironmental reconstructions in this environment.