Max A. Torres¹

(1) Repsol - YPF, Denver, CO

ABSTRACT: Sequence Stratigraphy of Recent Shallow Marine Upper Cretaceous - Tertiary Discoveries and Exploration Potential of the Magallanes Basin, Argentina

A series of important (>15MMBO) recent stratigraphic discoveries in the marine dominated Lower Magallanes (Maastrichtian - Late Eocene) formation motivated a regional sequence stratigraphic comprehensive study in order to establish new reservoir and exploration concepts for the underexplored Magallanes basin. The sediments of the studied unit were deposited under a flexure-loading regime in a narrow foredeep and are represented largely by a progradational eustatically controlled clastic wedges with downlapping geometries to the north and east. Third order marine unconformity-bounded foreland-type sequences were identified seismically and in well logs. Main discontinuities and depositional cycles were dated biostratigraphically and found to be in agreement with current global sea level charts. Adjacent detailed geological surface sections correlated with the seismic and well data improved considerably the facies descriptions of the units. Main producing and potential reservoirs are related to sand prone forced regressions and transgressive system tracts in shore and inner shelf bodies. Enhanced sand content forced regression facies are present due to differential subsidence patterns as a result of progressive flexural loading. System tracts and facies maps were constructed to define sand fairways to orient the future search for strat traps in the Lower Magallanes formation.

New geochem data indicated mature intervals in Upper Cretaceous shales upgrading the exploration potential of a large western area of the basin as proved by rich gas tests in the Cerro Cazador formation (Maastrichtian - Campanian) marine reservoirs.

AAPG Search and Discovery Article #90906©2001 AAPG Annual Convention, Denver, Colorado