--> Abstract: Contrasting Submarine Fans off the Amazon and Magdalena Rivers, by C. Pirmez, R. D. Flood, and G. Ercilla; #90933 (1998).

Datapages, Inc.Print this page

Abstract: Contrasting Submarine Fans off the Amazon and Magdalena Rivers

Pirmez, Carlos - Columbia University; R. D. Flood - State Univ. of New York; G. Ercilla - Institute de Ciencias del Mar, CSIC

The Amazon and Magdalena submarine fans are the two largest modem turbidite systems of the South American continent. Both river systems drain the Andes Mountains and major fan development occurred after the Miocene. Despite the contrasting margin setting - a passive margin for the Amazon and an oblique convergent margin for the Magdalena - both fans show overall similar morphologic characteristics, with the development of large channel-levee complexes and meandering channel systems. During the Pleistocene, fan construction in both systems resulted from the lateral switching of fan depocenters, but while a relatively long-lived canyon on the Amazon led to autocyclic channel avulsion to occur within the fan; margin tectonics affected the position of the Magdalena River with consequent formation of several smaller canyon-channel systems along the margin.

During the Late Pleistocene and Holocene these fans were the locus of large scale mass-wasting, triggered by mud diapirism and instability of rapidly deposited channel-levee systems. Partial reactivation of older channel systems occurred on the Magdalena Fan, while mass-wasting was coeval with the final stages of channel-levee development on the Amazon Fan. The last sea level rise shut down turbidity current activity on the meandering channels of both fan systems, but recent tectonic activity on the lower Magdalena Basin led to switching of the river and the onset of large scale slumping and turbidity current activity off the present river mouth. The Holocene Magdalena system negotiates the irregular basin and ridge topography of the accretionary prism, outpouring large scale mass flows on the abyssal plain.

AAPG Search and Discovery Article #90933©1998 ABGP/AAPG International Conference and Exhibition, Rio de Janeiro, Brazil