NEW THERMOTECTONIC AND PALEO-ENVIRONMENTAL CONSTRAINTS FROM THE WESTERN CORDILLERA AND ASSOCIATED SEDIMENTARY BASINS (NORTHERN ANDES, COLOMBIA): THE BIRTH OF A MAJOR OROGRAPHIC BARRIER AND THE CHOCO BIO-GEOGRAPHIC REGION?

The Chocó Bio-geographic Region (CBR) is one of the wettest, most bio-diverse geographic provinces on Earth. Its Oligo-Miocene geologic/environmental evolution was highly influenced by geodynamic and climatic/environmental process around the equatorial circum-Pacific and circum-Caribbean, several of which are still a matter of important debate: Panama-Chocó Block docking, emergence of the Panamanian Isthmus, re-accommodation of oceanic/atmospheric circulation, topographic build-up of the Western Cordillera (WCo) and development of a major orographic barrier, facial changes in sedimentary basins. These processes lead to important transformations in continental and marine environments. Understanding the paleo-geographic progression of the WCo and associated basins (morphotectonic pulses, basin development, ocean/atmospheric circulation and climate, flora/fauna dispersion evolution, etc.) is key to grasping CBR’s evolution. We present new thermo/geo-chronology data that allows identifying significant Neogene pulses of uplift/exhumation in crystalline massifs within the WCo. In addition, we track sediment sourcing-routing-accumulation in associated basins at the WCo western margin (San Juan Basin/Juanchaco-Ladrilleros section) where we identify environmental and climatic responses such as changes in sedimentary facies (fine to coarse grained), changes in marine microfossil communities and sedimentation rates, variations in pollen net amount and diversity. Some of these changes are interpreted as the result of increased precipitation and growth of the fluvial network produced by the establishment of a sufficiently high WCo (onset of strong orographic effect) that lead to the modern CBR.

Our diverse, multi-proxy dataset indicates significant uplift of the WCo starting at ~16 Ma (sustained until ~5 Ma), a morphotectonic event that disrupted atmospheric moisture advection from the Pacific pool into South America, triggering major changes in regional environmental processes. This pulse of uplift may have ignited the development of Chocó-Like conditions: orographic precipitation, hyperpluvial system, major fluvial networks, great biodiversity, reduction in sea surface salinity, etc.