Miocene strike-slip tectonics as a controller of the connections between the Northern Andes hinterland and the Pebas system

The Neogene tectonic and landscape evolution of the Northern Andes mountain belts, and its role as a bridge or barrier for different species, played a key role in the evolution of highly diverse ecosystems, such as the Amazonian, Andean, Pacific, and Caribbean regions. A major difference between the tectonic evolution of the Northern Andes and the southern Andean provinces is a first-order control of strike-slip tectonics on the Miocene sedimentation and deformation patterns. Therefore, strike-slip deformation influenced the evolution of tropical landscapes and ecosystems in the Northern Andes. These landscape controls on ecosystem evolution were especially important during The Middle to Late Miocene rise of the Northern and Central Andes, which formed the Amazonian basin and terminated a large wetland known as the Pebas system. Depending on the species, the Andes and the Pebas system acted as barriers or bridges that facilitated species migration or isolation; these processes were critical for the high diversity observed in the Amazon basin (the highest on Earth) and other regions of northern South America.

The limited rock exposures in Western Amazonia have limited the understanding of the Pebas system. However, in the Colombian Andes, the Magdalena hinterland basin preserves a record of former foreland deposits that were associated with the Pebas system, which presents an opportunity for understanding the northwestern Pebas system, its connections with other regions, and its response to Miocene strike-slip tectonics.

The Magdalena hinterland basin is located between the Central and the Eastern cordilleras in the Northern Andes. This sedimentary basin contains an ample Miocene record, which includes Lower Miocene fine-grained strata, and Middle Miocene to Pliocene coarsening-up strata. These sedimentary successions have been correlated with similar clastic strata in the Pacific and Amazonian regions, however, the connections between these sedimentary systems and the configuration of the drainage system are still unclear. This study presents a source-to-sink dataset that includes low-temperature thermochronology from the Central Cordillera in Colombia detrital U-Pb zircon ages, and sandstone petrography, in the adjacent Magdalena Basin.

Based on our results and previously published data, we constructed a model of the Miocene to Pliocene palaeogeographical configuration of the Northern Andes, and the Pebas System in western Amazonia. This model includes playa and permanent lake systems at ~17.5 Ma in the Northern Andes hinterland basins. Lacustrine sedimentation may be related to a marine incursion into NW South America and the Pebas system, facilitated by land connections between these regions. The appearance of Eocene to Miocene volcanic sources in the eastern Colombian basins after ~16 Ma suggests the development of fluvial passages, which connected the Pacific with the Amazonian Pebas system and the Caribbean region. These passages were synchronous with Miocene exhumation and topographic growth (~16–10 Ma) in the Central Cordillera and the transition from lacustrine to fluvial deposition in the Northern Andes. Middle to Late Miocene strike-slip deformation likely explains the synchronous along-strike fragmentation and exhumation in the Central Cordillera, controlling the opening and closure of short-lived trans-Andean passages.