Umir Formation: Organic geochemical and stratigraphic assessment as cosource for Middle Magdalena basin oil, Colombia

A detailed geochemical and stratigraphic study conducted on a sedimentary sequence of the Upper Cretaceous Umir Formation, in a section outcropping on the eastern flank of Middle Magdalena basin (MMB), Colombia, identifies this formation as a new hydrocarbon source rock, not previously considered as a source for MMB oil.The Umir Formation is composed of coal, coaly shale, claystone, siltstone, and sandstone. Based on Rock-Eval data, the coal and coaly shale show good potential for oil generation. Certain biomarkers are characteristic of the depositional environment of the Umir Formation and related oil and contrast it with the La Luna Formation and related oil. For example, biomarkers of the Umir Formation show pristane/phytane ratios greater than 1; predominance of C29 steranes; low oleanane/hopane ratios (