that separates the basement from the first sequences indicates the approximate time
rifting began.
First sequence The first sequence was deposited in the
Jurassic during the
rifting which caused the initial formation of the basin. This
Jurassic formation is called the
Girón Formation which consists of siltstones and rhyolitic tuffs. During this period, the basin also experienced granitic plutonism along its western margins. The
Jurassic-
Cretaceous angular unconformity, separating the first and second sequence, is representative of the post-rift boundary.
Second sequence The middle sequence represents the formations deposited throughout the
Cretaceous and
Early Paleocene. The oldest formations in this sequence are the
Tambor and
Los Santos Formations. The conglomerates and sandstones indicate a continental to fluvial
depositional environment. In the
Early Cretaceous, sea level began to rise and formed a shallow marine environment with siltstone and shale deposits of the
Cumbre Formation. Sea level continued to rise throughout the
Middle Cretaceous when the
Tablazo and Salto limestones and Simití shales were deposited. The
La Luna Formation represents a
maximum flooding surface with deep marine deposits of limestone, chert, and shale. Sea level then began to fall, returning the environment to shallow marine with deposition of the Umir Formation of shales and sandstones. Finally, the
Paleocene saw the deposition of the
Lisama Formation, consisting of deltaic mudstones and sandstones. This entire middle sequence indicates a marine megacycle consisting of five transgressive-regressive cycles. The angular unconformity between the second and third sequences is a result of erosion from the accretion of the
Western Ranges.
Third sequence The final sequence represents deposition from the
Early Tertiary to present day. Within this sequence, there are three subsequences that are the result of deformation and uplift of the Central and Eastern Ranges. The first subsequence consists of the
Chorro Group with the
La Paz and
Esmeraldas Formations and the
Chuspas Group with the
Mugrosa and
Colorado Formations, all deposited during the
Eocene to
Oligocene. These groups consist of fluvial sandstones, mudstones, siltstones, and shales, and are a result of erosion in the
Central Ranges. The second subsequence is the
Miocene Real Group, consisting of fluvial sandstones and conglomerates. Similar to the Real Group, the final subsequence is the
Pliocene Mesa Formation, which is composed of sandstones and conglomerates deposited due to the
Eastern Ranges uplift. The uppermost sedimentary rocks of the basin are
Pleistocene alluvial fan deposits, overlain by Holocene sediments of the Magdalena River. == Petroleum resources ==