STRATIGRAPHY, PETROGRAPHY AND PROVENANCE MULTI-METHOD ANALYSIS OF THE GUINEALES FORMATION, NORTHERN OF THE COLOMBIAN WESTERN CORDILLERA

Abstract

The Guineales Formation is located in the northern area of the Cordillera Occidental, to the West of the town of Dabeiba (Antioquia). It crops out as a N-S band, 30 km long and 2-3 km wide, forming a monocline structure that strikes N 10-23° W and dips 53- 70° E. It is composed by coarse polimyctic conglomerates with interbedded sandstones. The stratigraphic analysis of the sequence established a total thickness of 2199.26 m in the Dabeiba – Mutata road between the Choromandó and Guineales creeks. The sandstone layers were classified as lithic wackes and lithic arenites; the provenance analysis of the clasts in the conglomerates showed several cycles of deposition marked by the prevalence of volcanic or sedimentary clasts. The source for the volcanic clast were the Basaltos de El Botón (Upper Miocene), Diabasas de San José de Urama (Jurassic - Lower Cretaceous limit), and Complejo Santa Cecilia – La Equis formations (Lower Eocene), whereas the source for the sedimentary clasts were Sedimentitas de Las Cruces and Litoarenitas, Limolitas y Lodolitas de Urrao formations. The U-Pb geochronology zircons found in the matrix of the conglomerates, shows groups of zircons with ages ranging from Miocene (10.5 Ma) to Proterozoic (1509-1599 Ma), the most representative being the range in age that corresponds to Middle Triassic ( 206.5 to 287 Ma); this age is consistent with metamorphic zircons that come from the Triassic basement of the Cordillera Central. The depositional event represents uplifting, erosion and accumulation in a continental environment where rivers flowed from east to west in the collision area between the block and Cañasgordas and Chocó- Panama blocks, and could be related to the Andean orogeny occurred in the Pliocene. Based on stratigraphic relationships, provenance analysis of the clasts and detrital zircons geochronology, it is possible to conclude that the accumulation age of Guineales Formation is later than 9 Ma (Upper Miocene).