An environmental reconstruction of the sediment infill of the Bogotá basin (Colombia) during the last 3 million years from abiotic and biotic proxies

Basin infill started with accumulation in a fluvio-lacustrine environment between 586 and 530 m below the present-day sediment surface of the basin. In the 530- to 325-m interval (c. 3-1.5 Ma), the basin contained mainly shallow water and swamps, in combination with some fluvial activity. The 325-5-m interval (1.5-0.028 Ma) shows almost uninterrupted lacustrine paleoenvironmental conditions. The uppermost 5 m reflect a fluvial paleoenvironment deposited by the Bogotá River and its tributaries. The downcore changing ratio between shallow water aquatics (Myriophyllum, Ludwigia, Polygonum, Cyperaceae) and aquatics of deeper water (Isoëtes) is indicative of lake level changes. Isoëtes as an indicator of high water levels is not consistent with fluvial and fluvio-lacustrine depositional regimes. Several lithological discontinuities, evidenced by the sharp transition from swamp deposits to fluvio-lacustrine and fluvial deposits, are present in the core, in the interval from 530 to 325 m in particular. It is plausible that swamp deposits have been eroded during episodes during which the water table quickly raised or during events of sudden coarse fluvial input into the basin.