Abstract: Cretaceous Sequence Stratigraphy of the Maranon-Oriente-Putumayo Basins, Northeastern Peru, Eastern Ecuador and Southeastern Colombia

Dave Valasek, Antenor M. Aleman, Robert Marksteiner

The Cretaceous of the Maranon, Oriente, and Putumayo (MOP) Basins were deposited in a tectonic setting varying from a passive margin in southeastern Colombia and eastern Ecuador to a retro-arc setting in northeastern Peru. Transgression took place from northwest to southeast. Cretaceous deposition was diachronous across the basin in an epeiric sea. Accommodation was greater in the Maranon than the Oriente and Putumayo basins.

The oldest Cretaceous strata consist of aggradational braided fluvial deposits formations above a regional sequence boundary. They consist of aggradational high frequency genetic sequences with complex lateral small-scale sequence boundary relationships. Local small-scale progradational deltaic deposits are present in stratigraphically higher positions. Several high frequency amalgamated incised valleys cap fluvial deposits. All valley deposits are truncated by a transgressive surface of erosion overlain by marine mudstones and shelf palimpsest deposits below the Albian maximum flooding surface. These valley deposits are overlain by five genetic sequences. A genetic cycle begins with thin aggradational deposits capped by a condensed interval. Shaly limestones are deposited during tran gression until resumed clastic influx during progradation terminates the limestone deposition. Small-scale valleys were incised and filled after maximum progradation.

The Peruvian phase of the Andean Orogeny ended marine deposition in the MOP basin as indicated by the Vivian Formation which is only present in the Maranon Basin. This unit consists of two genetic sequences made up of valley-fill deposits with both present in the east and one to the west. Unlike the Napo valley-fill deposits the Vivian Formation consists entirely of aggradational terrestrial fluvial deposits.

AAPG Search and Discovery Article #90951©1996 AAPG International Conference and Exhibition, Caracas, Venezuela