2008 Joint Meeting of The Geological Society of America, Soil Science Society of America, American Society of Agronomy, Crop Science Society of America, Gulf Coast Association of Geological Societies with the Gulf Coast Section of SEPM

Paper No. 1
Presentation Time: 1:35 PM

Lithospheric Flexure and Related Base-Level Stratigraphic Cycles In the Putumayo Foreland Basin, Colombia

LONDONO, John, Shell, 200 North Dairy Ashford, Off 7584, Houston, TX 77079 and LORENZO, Juan, Dept of Geology and Geophysics, Louisiana State University, E235 Howe Russell Kniffen, Louisiana State University, Baton Rouge, LA 70803, J.Londono@shell.com

In continental forelands basins the response of the underlying elastic lithosphere via flexure to tectonic and sedimentary loads ultimately controls base-level related sedimentary-cycles in upstream fluvial-deposits, in addition to the regional geometry of the basin. Seismic and well data from the Putumayo basin in Colombia suggest a testable model showing how the nature, amount, distribution and timing of loading produce a variable, but identifiable, set of seismo-stratigraphic architecture related to each flexural event.

Four chronostratigraphic units from the basin, reduced to decompacted-thickness profiles, are forward-modeled to reproduce the successive deflections throughout the evolution of the basin. Tectonic-related deflections are then calculated as the residual flexure of the first-order compensation due to sediments. Results suggest that most of subsidence in the basin is caused by sediment loading (~75% of the total) and subsidence rate varies between 60 to 140 m/m.y. Additionally, the elastic thickness of the crust in the area (~ 25 to 35 km) did not change during basin history.

Seismic-reflector geometry can be indicative of the dominant subsidence regime. Hinterland-onlap shifts, for example, probably reflect changes in the subsidence rate near to the thrust belt due to tectonic loading, while continuous foreland-onlap probably reflects subsidence due mostly to sediment loading. However, forebulges, which are developed individually for each loading event, and their characteristic flanking pinch-outs, are not recognizable in the Putumayo seismic data.