Tropical rain-forest history from the Colombian Pacific area: a 4200-year pollen record from Laguna Jotaordo

Pollen analysis of a 5 m long core from Lake Jotaordo, located in northern 'Chocobiogeographic area' (5 degreesN, 76 degrees 42 W) along the Pacific c oast of Colombia, shows the environmental history of the rain forest during the last 4200 years. Time control has been based on 6 AMS C-14 dates rangi ng from 4230 to 365 C-14 yr BP. The period of 4230 to 4053 C-14 yr BP shows sandy deposits and river influence and represents at that time the initial phase of the lake. The composition of the rain forest was different compar ed to the last 1400 years. Pioneer taxa belonging to Cecropia, Melastomatac eae/Combretaceae and Moraceae/Urticaceae dominated the forest. A 30 cm thic k organic rich clay from 440 to 410 cm core depth spans a period of 2600 ye ars (from 4050 to 1450 C-14 yr BP), pointing to a hiatus in the sediment re cord, possibly caused by riverine erosion of previously deposited sediments . During the last 1400 years rain forest is characterized by Mauritiella, E uterpe/Geonoma, Iriartea, Pachira aquatica and Malpighiaceae. Floral compos ition of the rain forest is not constant. Abiotic dynamics caused changes i n the drainage system. The presence of human settlements during the last 10 00 yrs is evidenced by Zea mays and possibly also by the increase of palms.