The Siamaná Formation (Spanish: Formación Siamaná, E3s) is a fossiliferous geological formation of the Cocinetas Basin in the northernmost department of La Guajira.

The Siamaná Formation dates to the Paleogene period; Middle to Late Oligocene epoch, corresponding to the Deseadan in the SALMA classification.

The formation was defined by Renz in 1960 and named after the village of Siamaná.

[1] The Siamaná Formation consists of conglomerates and thick carbonates.

The age has been estimated to be Middle to Late Oligocene, corresponding to the Deseadan in the SALMA classification.