Colombia Sinu Offshore Basin Tectonic Evolution, Depositional Models, and Impact of the Panama Arc-South America Collision

Abstract

The Anadarko and EcoPetrol partnership recently drilled several deepwater exploratory wells in the Sinu Offshore Basin in SW Caribbean between Panama and Colombia, including Kronos-1, Calasu-1, Purple Angel-1 (PA-1), and Gorgon-1 wells based on large 3D seismic data. Interpretation of well results and 3D seismic data allows a first close look of tectonic and depositional evolutionary histories in the basin located between the Panama Arc and Sinu Fold Belt, and provides direct understanding and evidence on timing and impact of the Panama Arc collision with the South America Plate. The Sinu Offshore Basin may be subdivided into the Sinu Basin and Cartagena Basin separated by a volcanic basement high (Figure 1, 2a). The Sinu Basin is adjacent to the Northern Panama Deformed Belt (NPDB) and west of the Sinu Fold Belt. The Sinu Fold Belt is the SW extension of the Southern Caribbean Deformed Belt (SCDB). Formation of the Sinu Fold Belt and rapid uplift of the Central-Eastern Cordilleras have been widely attributed to collision between the Panama Arc and the South America Plate. Timing of the collision ranges from Oligocene-Middle Miocene to late Miocene-Pliocene according to onshore rock records and biological interchange analyses between Panama and South America. However, direct evidence is absent from the offshore Sinu Basin, between NPDB and the Sinu Fold Belt. This work fills the gap with a collision occurring at latest Miocene-earliest Pliocene (6-5 Ma) based on well results and 3D seismic data in the Sinu Basin area. In addition to addressing collision timing between the Panama Arc and the South America Plate, impact of the collision on basin tectonic and depositional evolutions is studied. The main deposition of the Sinu Basin is divided into three stages (Figure 2a): (1) Miocene open basin with amalgamated meandering channel complexes followed by collisional faulting; (2) Early Pliocene post-collision closed foredeep basin with flexural normal faulting; and (3) post-collision closed basin dominated by mass transport complexes and bottom current sequences with progradation and aggradation accompanied by drastic fold belt thrusting events. Depositional models for various periods of the basin history are proposed. Regional correlation and synthesis indicate that the basin sits on the Caribbean oceanic crust with volcanic basement overlain by Cretaceous-Tertiary sediments. A volcanic basement high, probably part of the Caribbean Large Igneous Province, has a 1.5 km deep hole at the top (Figure 2a) with circular volcanic/lava flows surrounding the high. During Cretaceous-Paleogene, the area received predominantly open marine deposition of likely shale and condensed sediments or carbonates with the late Cretaceous being characterized by polygonal faulting. However, there was little tectonic deformation except some Late Cretaceous or older faults trending perpendicular to the coast, which might link to the pre-Andean orogeny. The Miocene Sinu and Cartagena basins remained open, but started to receive a large amount of sand deposition in large scale amalgamated meandering channel complexes, especially during Late Miocene. However, sediments may have been sourced from different drainage basins. The Cartagena Basin Miocene sedimentation appears to have a W-SW transport direction sourced from a drainage system occupying the northern part of Colombia, while the Sinu Basin Miocene deposition appears to have a NW-NNW transport direction sourced from a proto-Cauca River system with a Western-Central Cordillera affinity. In the Sinu Basin, several amalgamated meandering channel complexes of Messinian-Tortonian age developed. The largest one spans over 15km in width with numerous channels crosscutting each other (Figure 2b). Thick amalgamated channel sands with high net to gross ratios and of a Western and Central Cordillera affinity were penetrated by several wells across a broad area in offshore Colombia. This demonstrates that a large amount of Upper Miocene sediments were transported onto a relatively flat basin from onshore Colombia. Therefore, the Sinu Fold Belt was not a large scale feature forming a major barrier for sediment transport from onshore Colombia into the Sinu Basin at this time. Structural deformation of the Miocene section from collision did not occur until latest Miocene. The Sinu Basin Stage (1) deposition of Miocene open basin amalgamated channel complexes ended as a result of the Panama Arc-South America collision during latest Miocene-earliest Pliocene (6-5 Ma) and is marked by drastic faulting deformation (Figure 2c, 2d), followed by significantly different deposition styles. Meanwhile, open basin deposition continued in the Cartagena Basin with amalgamated meandering channels and basin floor fans during the Pliocene-Pleistocene. The collision formed a series of NNE-striking normal faults with grabens, half grabens, slumps, en echelon faults, transpressional faults, and as well as thrust and reverse faults (Figure 2e), which fit into a classic strain ellipse. A regional unconformity was formed by collisional deformation and erosion, which appears as a strong, regional trough to peak seismic reflection extending over 100s of kilometers. Sinu Basin Stage (2) deposition evolved into a closed foredeep basin during Early Pliocene above the regional unconformity. The foredeep basin is adjacent to NPDB and areally restricted. However, part of the foredeep basin might have been overridden by later northward thrusting of NPDB. The foredeep basin thins quickly towards the volcanic basement high. The foredeep underwent basin fill, erosion, and backfill. Many normal faults formed within the foredeep basin section are probably due to forebulge flexural bending. The end of Stage (2) is marked with another regional unconformity, and a sharp change of basin deposition into Stage (3) of fast progradation and aggradation during the Pliocene-Pleistocene. Stage (3) deposition in the Sinu Basin remains a closed basin dominated by numerous mass transport complexes (MTC) with multiple sequences of bottom current contourites mixed with turbidity deposition. Some apparent progradational packages formed by bottom current reworking. The large number of MTCs generally formed in a NNW direction coming from the Sinu Fold Belt, and no MTCs are from the Panama Arc side of the basin. Large scale MTCs tend to correlate with dramatic fold belt thrusting. Depositional rate is high, averaging in 1,000-2,000 m/my, which might result from collapses, slumps, and erosional reworking of thrusted folds or fault scarps. This stage was accompanied by multiple episodes of drastic thrusting of the Sinu Fold Belt and NPDB, thus the size of the Sinu Basin probably shrunk significantly due to thrusting of the two fold belts. During Stage (3) evolution, the Sinu Basin underwent compressions from both fold belts, i.e. from south to north from NPDB and from east to west from the Sinu Fold Belt. Low angle stratal deformation is commonly observed. A classic model of basin floor fan with amalgamated meandering channel complexes applies to the Sinu Basin Miocene open basin deposition. For the Pliocene-Pleistocene closed basin, a mixture of the following models is proposed: (1) line sourced slope fan apron, (2) point sourced slope fans/lobes, (3) mass transport complexes from fold/fault scarp failures, and (4) contourites trends from bottom current reworking. The Panama Arc-South America collision not only resulted in formation of the Sinu Fold Belt and large uplifting of the Cordilleras, but also changed onshore drainage patterns and sediment supply as evidenced from well results, 3D seismic data, and onshore drainage study. Prior to the collision, a large proto-Cauca river system might have drained from the Western and Central Cordilleras into the Sinu Basin with progradational deltas, while a proto-Magdalena river system flowed south then east from the present day middle-upper Magdalena valley regions. Since the collision, the proto-Magdalena River switched direction and flowed north into the Caribbean Sea forming the Magdalena Fan, meanwhile the Cauca River changed course to merge into the northern Magdalena River. As a final note, the latest Miocene-earliest Pliocene (6-5 Ma) collision timing is based on data from the present day Sinu Basin area. Evidences for older timing might have been wiped out by large-scale thrustings of the Sinu Fold Belt and NPDB during Pliocene-Pleistocene.

AAPG Datapages/Search and Discovery Article #90330©2018 AAPG Hedberg: Geology of Middle America – the Gulf of Mexico, Yucatan, Caribbean, Grenada and Tobago Basins and Their Margins “Integration of the geology of the area from the southern onshore of North America to the northern onshore of South America”, Siguenza, Guadalajara, Spain, July 2-5, 2018