Early Maastrichtian to Early Paleocene accretion of a subduction complex to the west side of the Colombian Central Cordillera produced both the extinction of a Cretaceous extensional basin and the beginning of a foreland basin that dominates the Tertiary of the Colombia basin. The Maastrichtian-Paleocene sedimentary succession is characterized by a major shift of depositional systems from marine to coastal plain and continental environments that is closely related to the reorganization of the basin. This succession is bounded both at base and top by regional unconformities. The lower unconformity is related to the accretion of the subduction complex in the early Maastrichtian and onset of the transition extensional to foreland basin. The accretion of the Western Cordillera and the regional uplift of the Central Cordillera produced the Late Paleocene-Eocene unconformity at the top. Deposits above this unconformity record the growth of a foreland basin during the later Tertiary. The sandstone composition of the Maastrichtian-Paleocene succession changes progressively upsection from quartzarenite to litharenite, indicating the uplift of Precambrian Quetame and Santander-Floresta massifs, as well as local uplifts in the Central Cordillera. Some structures bounding these massifs coincide with older faults dating from the extensional phase of the basin. These uplifts segmented the formerly continuous Cretaceous extensional basin into two depositional sub-basins, the eastern and the western basins. In the western basin the thickness increases northward, whereas the eastern is more condensed, decreasing in thickness eastward. Maximum subsidence was reached in an elongate depocenter located between the Quetame and Floresta massifs, and its axis was parallel to older north-south normal faults. The basin transition also produced a regional change in the polarity of the shoreline and associated coastal-fluvial deposits from east-west during the Late Cretaceous, to south-north in the late Maastrichtian.

AAPG Search and Discovery Article #90928©1999 AAPG Annual Convention, San Antonio, Texas