ABSTRACT: Tectonics and Sedimentation in a Failed Rift System: Marajo Basin, Northern Brazil

LARA, MARIA ESTER, and GREGOR P. EBERLI, University of Miami, Miami, FL

The Marajo Basin is a Mesozoic failed rift system located at the mouth of the Amazon River. Although affected by two rifting phases, the Marajo Basin never developed into an oceanic basin, probably as a consequence of its peripheral location in relation to the locus of the main extension.

Geophysical and well data released by Texaco document that the Marajo Basin consists of three subbasins. Their thick sedimentary columns include a Paleozoic prerift sequence, early and late synrift sections of Mesozoic clastics, and Cenomanian to Cenozoic postrift sediments. The early rift phase is characterized by normal growth faults whose orientations define the arcuate architecture of the Marajo Basin: they trend northwest to southeast in the central Limoeiro and southern Cameta subbasins, and southwest to northeast in the northern Mexiana subbasin. Individual grabens are separated by SW-NE-trending strike-slip faults. The second phase of rifting occurred between Barremian and Cenomanian times, producing new normal faults and strike-slip faults. The late synrift sedimentation was ontrolled by a northward-flowing axial river, indicating a northward tilt of the basins. Post-rift sedimentation was characterized by the deposition of fluviodeltaic to marginal marine clastics.

The first rift phase seems to be related to the southern propagation of the North Atlantic opening, from Late Triassic to Early Jurassic. The second extensional episode is probably associated with the transform opening of the Equatorial Atlantic, during the Early Cretaceous. We speculate that the development of transform faults during this second episode terminated the connection between the Marajo Basin and the North Atlantic, preventing further opening.

AAPG Search and Discovery Article #91012©1992 AAPG Annual Meeting, Calgary, Alberta, Canada, June 22-25, 1992 (2009)