ALEMAN, ANTENOR M., and ROBERT M. MARKSTEINER, Amoco Production Company, Houston, TX

ABSTRACT: Mesozoic and Cenozoic Tectonic Evolution of the Maranon Basin in Southeastern Colombia, Eastern Ecuador and Northeastern Peru

The Late Triassic to Early Jurassic in the Maranon was characterized by tectonic quiescence and carbonate shelf deposition. During Middle to Late Jurassic, a northeast-southwest extensional event occurred which is documented by the presence of northwest oriented grabens filled with red beds and volcaniclastic rocks. Cretaceous deposition commenced during the Aptian and continued to the Early Campanian within the vast South America Cretaceous Seaway (SACS) that extended from Venezuela to Central Peru. These strata comprised of shallow marine clastics sourced from the Brazilian and Guyana cratons to the east.

Retreat of the SACS resulted from the Late Cretaceous (Peruvian) phase of the Andean Orogeny. Deposition became largely continental with sediments derived from the west. The deformation was contemporaneous with oblique collision and accretion of an allochthonous terrain present in Colombia and Ecuador, as well as uplift of the Putumayo, Napo, Cutucu and Cenepa (PNCC) Mountains, westward erosion of the Napo/Chonta Formations, widespread deposition of red beds, volcanic activity in the foreland and the subtle inversion of half grabens.

The Middle Eocene (Inca) phase of the Andean Orogeny, correlated to a relative increase in convergence rates along the western margin of South America (SA). This orogeny was characterized by the development of folds and reverse faults within a narrow and elongated belt, the reactivation of the PNCC Uplifts, the deposition of varicolored fluviatile deposits, the renewed inversion of half grabens, and volcanic activity close to the hinterland.

The three main pulses of the Late Miocene to Pliocene (Quechua) phase of the Andean Orogeny correlate with high rates of convergence along the SA margin. This orogenic phase was characterized by thick fluviatile deposition, reactivation of the PNCC Uplifts, eastward propagation of the fold and thrust belt, renewed inversion of the half grabens and alkaline volcanism in the foreland.

AAPG Search and Discovery Article #90988©1993 AAPG/SVG International Congress and Exhibition, Caracas, Venezuela, March 14-17, 1993.