1New Mexico State University
2University of Florida
Abstract: Maastrichtian-Paleocene Basin Evolution of Northwestern South America: The Transition from a Mature Extensional Basin to Foreland Basin
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