Identificación de los máximos eventos de inundación marina miocenos y su uso en la correlación y análisis de la cuenca de antepaís de los llanos orientales, Colombia

Abstract

Maximum marine flooding events constitute regional chronostratigraphic correlative surfaces in foreland basins dominated by continental sedimentary fill, such as in the Colombian Llanos Basin. Despite of the importance of these surfaces for the hydrocarbon prospectivity, yet their lateral extent, duration, and basin evolution implications remain unknown. Analysis of sequence stratigraphy using outcrops, wells, seismic and palynological data, allowed the identification of two marine flooding events in the early and middle Miocene, and a third flooding event in the Oligocene, along with two sequence boundaries. The two Miocene flooding surfaces are synchronous and cover entirely this forelandbasin accumulation system. The early Miocene surface is recorded by muddy deposits of the informal member C2 of the Carbonera Formation, whereas the middle Eocene surface is recorded by the muddy deposits of the Leon Formation. Also, sequence boundaries were identified at the middle and top of the Carbonera Formation. Thickness maps of early and middle Miocene for the entire Llanos Basin document the location of depocenters adjacent to the deformation front, which delineate thicker areas involving significant loading and more burial for the Cretaceous and Paleogene petroleum source rocks. However, more distally into the Llanos basin, thickness trends vary between the early and middle Miocene, revealing thickness increases towards the north during the early Miocene, and then increasing towards the south during middle Miocene. Accumulation rates of the middle Miocene (108 m/my) is more than twice than the calculated for the Early Miocene (47 m/my), this strong increase represented in total subsidence is associated with an increase in shortening of the eastern flank of the Cordillera Oriental, intra-basinal uplifts related to the Vaupes arch and a global rise in the sea level, which favored the continuous sediment supply and the generation of accommodation space without affecting the continuous muddy accumulation during marine flooding events.