f Distinguishing Petroleum Source Rock Acmes Across Northern South America: Application to Evaluate the Potential of the Albian to Maastrichtian Guyana Basin

This chronostratigraphic study focuses on distinguishing the unique intervals (acmes) of Cretaceous deposition, to evaluate their lateral variation from the Magdalena Basin (Colombia) to the areas of recent petroleum discoveries in the Guyana Basin and Demerara Plateau.

The current focus on lithostratigraphic formations, lumping entire depositional intervals, has led to confusion surrounding even one of the most referenced source rocks in the Southern Caribbean, the La Luna Formation.

The focus on this formation can lead to unintentionally disregarding other potential source acmes including the underlying Machiques Member of the Apon Formation in the Western Maracaibo basin, which is widely correlated to the first Oceanic Anoxic Event (OAE-1a), has a thickness of 30 meters, and an average of 1–1.5 wt.% TOC1. Additionally, while La Luna is one of many productive source rocks in the southwestern Mérida Andes, its productivity seems to be replaced by the La Morita Sandstone and slightly younger Navay Formation (corrected TOC 2.59 wt.%; 185 m thickness)2,3 in the neighboring Barinas-Apure Basin without a published explanation for the latter.

We constructed a chronostratigraphic column through Colombia to offshore Suriname by the combination and rationalization of multiple local stratigraphic columns, well log data, and paleoenvironmental information.

This integrated approach allows for a time-equivalent correlation of units to one another throughout the Caribbean and the ability to describe type localities of individual source rock deposition acmes. Using this methodology, the identification of numerous productivity acmes both younger and older than Cenomanian-Turonian (e.g. 85, 87 and 101) throughout northern South America as far as the Demerara Plateau, has allowed for an extrapolation of potential source rocks into current exploration areas of the Guyana Basin. This extrapolation has increased our understanding of source rock potential, correlation to OAE events, and continuity of lithologic units throughout the Guyana Basin. The upper acmes of the Demerara Rise condensed section can be correlated with lithostratigraphic units (Canje Formation) on the Guyana-Suriname shelf but are replaced by time-equivalent basin turbidite deposits in the deep basin. This methodology has also revealed the upper Albian as a potential source rock in basinal areas unaffected by the mid-Albian unconformity. Lastly, this identification of organic-rich acme timings provides the foundation for more accurate Ultimate Expellable Potential (UEP) modeling in future work.