Geochemical, mineralogical, and palynological records from a Holocene sediment core 12.7 m long from Lake Silvana, southeastern Brazil, served to identify the source of detrital sediments within catchment soils. The lake basin was first flooded in the early Holocene (9400 14C yr B.P.), when a gibbsite-rich B soil horizon started to accumulate. Four distinct hydrologic phases are consistent with vegetational changes indicated by pollen data. Phases of slope instability (colluviation) and low lake level correspond to pollen-free intervals and point to a severe retreat of the vegetation cover. The rapid sedimentation of slope-wash sediments alternating with alluvial sediments appears to have formed a tributary fan 7.8 m thick that dammed the Lake Silvana Basin 8500 14C yr B.P., probably as a response to a drastic increase in precipitation rates.

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