REMARKABLE ALLUVIAL TERRACES AT THE BEGINNING OF THE MIDDLE MAGDALENA RIVER VALLEY, COLOMBIA: FAR FROM RHETORIC, CLOSER TO REALITY

Very high terraces with rounded fragment gravel size of igneous rocks between argillaceous matrix as geological curiosities were observed in the broad geological information of the Middle Magdalena River Valley; this information was gathered in an investigation of basic data collection across the channel in scale 1: 25.000 and 1: 10,000 in specific sectors. It was conducted for pre-feasibility analysis of a multipurpose project.

The two main terraces, near town named Guataquí, Cundinamarca have approximately 10 m and 20 m high above the level of recent alluvial deposits, and are composed for well-rounded gravels poor selected, dated as Holocene united to Lower Cretaceous rocks.

The conformation of these terraces occurs by sediments coming from the tributary rivers called “Seco and “Opia” at the South; also “Totare”, “Venadillo”, “Recio”, and “Lagunillas” rivers in the North. All of them located on the west side of the Middle Magdalena River Valley. During rain stages the Magdalena River’s bed grow up can dammed tributaries reducing energy from their flows sediment material by gravity.

Seismic methods and drilling several wells had determined thicknesses of alluvial deposits between 20 m and 48 m underground, which is indicated irregular geometric shapes on the basis of these terraces; it would be logical because of the erosion processes that were exposed after the Laramie orogeny's phenomena that affected Cretaceous marine and Tertiary continental deposits.

The future step as scientific research will be searched for government commitment to protect these wonderful phenomena and geological heritage of the harmful action of artisanal or trade miners.