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 Volume 1 Chapter 5

Chapter 5

Precambrian Records of the Llanos Orientales Basin, Colombia


Citation is suggested as: 

Dueñas–Jiménez, H. & Montalvo–Jónsson, J. 2019. Precambrian records of the Llanos Orientales Basin, Colombia. In: Gómez, J. & Mateus–Zabala, D. (editors), The Geology of Colombia, Volume 1 Proterozoic – Paleozoic. Servicio Geológico Colombiano, Publicaciones Geológicas Especiales 35, p. 127–149. Bogotá.


In the Llanos Orientales Basin of Colombia, below thick Tertiary and Cretaceous strata, Paleozoic sedimentary sequences are present, which yield good, diverse and well–preserved assemblages of palynomorphs. In the northeastern part of the basin in the Arauca Graben, after crossing the unconformity at the base of the Cretaceous sequence, oil wells face the presence of Cambrian and Precambrian (Ediacaran – Cryogenian) sediments deposited in low latitudes under shallow marine settings that yield abundant, diverse, poorly preserved and dark–colored sphaeromorph acritarch assemblages. 

In the Chiguiro–1, La Coral–1 and Pato–1 wells drilled in 1985, the presence of Ediacaran palynomorphs was observed for the first time in Colombia. This discovery can be considered to be the oldest sediment dated by paleontological methods reported in Colombia. Twenty–six years later, analysis of samples from the Chilacoa–1S, Coralito–1S, Torodoi–1X and Vaco–1X wells confirmed the presence of Ediacaran sediments in the Llanos Orientales Basin. All these wells are located in the Arauca Graben, which is a northeast tectonic depression that extends north, reaching Venezuelan territory. 

In the Arauquita–1—Torodoi–1X seismic transect it is possible to observe the presence of a general pinch–out of Tertiary and Cretaceous stratigraphic units towards the east. Under the basal Cretaceous unconformity, all of the stratigraphic units have suffered a great tectonic activity that divides the Arauca Graben into narrow blocks. In those narrow blocks, it is possible to observe the presence of a not yet drilled stratigraphic sequence with a thickness of several thousand feet that could involve pre–Ediacaran sediments. The detailed palynological analysis of those sediments could aid in the interpretation of the evolution of life during early times.

Keywords:   acritarchs, Cryogenian,   Ediacaran,   Llanos  Orientales Basin, Arauca Graben.