High-resolution last deglaciation record from the Congo fan reveals significance of mangrove pollen and biomarkers as indicators of shelf transgression

High abundances of mangrove pollen have been associated with transgressive cycles oil tropical margins, but the detailed relations between systems tracts and the taphonomy of the pollen are unclear. We report here the occurrence and high abundance of Rhizophora pollen, in association with taraxerol, a Rhizophora-sourced biomarker, from a high-resolution Congo fail core covering the last deglaciation. All age model based on 14 C dates enables the temporal changes in taraxerol content and the percentage frequencies and flux (pollen grains (pg) cm(-2) (10(3) yr)(-1)) of mangrove pollen to be compared quantitatively with the lateral rate of transgression across the flooding Surface (derived from glacio-hydro-isostatic model output and the bathymetry of the margin). Rhizophora pollen concentrations and taraxerol content of the sediment are very strongly positively correlated with the lateral rate of transgression and indicate, independently of any sequence stratigraphic context, that mangrove pollen spikes are associated with the transgressive systems tract rather than the highstand systems tract or maximum flooding surface. Lower-resolution longer-term records from this margin indicate an association between taraxerol concentrations and transgressive rather than regressive phases. The flux of these materials to the Congo fail is interpreted as a function of the erosion of flooded mangrove swamp on the shelf and, less importantly, changing extent of mangrove habitat, during sea-level rise. Congo River palaeoflood events also result in reworking of mangrove pollen and supply to the far, but this mechanism is subdominant. Rhizophora pollen has been underestimated in many palynological studies undertaken oil cores from the African margin because of inappropriate sieve mesh size used during laboratory preparation. (c) 2005 University of Washington. All rights reserved.