Uplift, subsidence, and volcanism in the southern Neiva Basin, Colombia, Part 1: Influence on fluvial deposition in the Miocene Honda Formation

Abstract

In the southern Neiva Basin, four large-scale sedimentary sequences are recognized in the deposits of the Miocene Honda Formation on the basis of maximum clast diameter, fluvial channel/overbank deposit ratio, thickness of the overbank and channel sequences, and lithology of the sandstones. These sequences can be related to tectonic activity of the Central Cordillera and the Garzón Massif, to volcanism, and to the rate of basin subsidence. They may be interpreted in terms of different alluvial fan systems and volcanic aprons that prograded onto a broad plain during periods of active uplift or volcanism and braided and meandering river systems that developed during the intervening periods of greater volcanic and tectonic quiescence. The lower two sequences were deposited under relatively quiet tectonic conditions, following the major and final phase of thrust faulting of the Central Cordillera. During deposition of these sequences, sediment loading let to subsidence of the basin. The depositional processes of these sequences, furthermore, were influenced by activity of the Central Cordillera volcanic arc. Radiometric age determinations on two tuff beds located some 300 meters above the base of the formation in the lowermost sequence gave ages of 15.8 ± 0.6 and 14.3 ± 0.5 Ma, respectively. Conglomerates of the third sequence record pronounced uplift of the source area, i.e., the Central Cordillera. Deposition of this sequence very probably coincided with uplift of the Garzón Massif, the southermost extension of the Eastern Cordillera, which took place at about 12 Ma. Uplift of both cordilleras led to rapid subsidence of the basin. The upper sequence was deposited under conditions of waning tectonic activity.