Past Amazon Basin fluvial systems, insight into the Cenozoic sequences using seismic geomorphology (Marañón Basin, Peru)

Abstract

This study of the seismic geomorphology of riverine deposits describes and discusses the spatial resolution at which we can detect fluvial features and how the subsequently collected data can help with our understanding of ancient fluvial reservoirs. For this assessment we use three dimensional seismic reflection data, borehole data from ancient deposits in the Marañón foredeep basin of Peru, as well as digital elevation and satellite imagery data from the present day fluvial systems of the Amazonian Basin in the same area of Peru. Based on seismic stratigraphic principles on amplitude display we test parameters to highlight the details of the internal structure of horizons interpreted on continuous wavelets. Seismic attributes such as amplitude, phase, sweetness and spectral decomposition techniques have been successfully applied to make a framework of seismic stratigraphic surfaces that highlight the internal architecture and morphologic details of the studied intervals. This work confirms the presence of a Cenozoic fluvial system in Peru with straight, meandering and anastomosing channels. The observed fluvial features are associated with narrow to medium sized channels (10–∼700 m). Evolution of parameters such as sinuosity allows the variation of load in the identified channel features to be constrained. Cenozoic Marañón Basin rivers/streams size and shape are comparable to those observed in the present-day fluvial Amazon Basin. The fluvial dynamics in the study area are identified to be at least present since the deposition of the Pozo-Chambira Formation (Eocene-Oligocene) in the Marañón Basin.