Uppermost Jurassic and Cretaceous 2nd Order Sequence Boundaries in Brazilian Marginal Basins: Correlations with some Andean Basins and Implications
PEREIRA, MARCIO J.
Based on seismic and wells data throughout the uppermost Jurassic and
Cretaceous sections of the Brazilian marginal basins and three Andean basins
(Neuquen, Western/Eastern Peru and Ecuador), twelve major 2nd order depositional
sequence boundaries were identified in either siliciclastic and carbonate
sections. Biostratigraphic
data, few radiometric dating in volcanic flows, and
the conspicuous recurrence of the sequence boundaries and maximum transgressions
suggest a quasi-synchronism among the boundaries, been them either in rift or
post rift stages, or either in continental or marine sections.
Based on this regional study in the South American Plate, the important
question "tectonics versus eustasy" comes up for discussion again. The sequence
boundaries seem to have age
and time span controlled by major global eustatic
falls, but in phase with relatively short episodes of increasing compression
(e.g., ending of a widespread rifting phase, subduction blocking or collision)
in several areas of the world. The enhanced intraplate stresses resulting from
these episodes had remarkable effects in the origin of the studied sequence
boundaries. Renewed deformations in major crustal discontinuities and arches in
the South American Plate took place strongly affecting the source areas, borders
and depocenters of its marginal and interior basins. In Brazilian marginal
basins, predictive regional trends of systems tract and lithofacies (type and
volume) are remarkable when we consider the tectonics as the main control on
erosion and resedimentation processes.