The open marine, fluvio-deltaic and lagoonal claystones, limestones and conglomerates preserve fossils dating back to the Early Miocene period.

[3] The type locality designated by Popov is a small outcrop located 1.2 to 3.0 kilometres (0.75 to 1.86 mi) east of Trinidad, on the highway linking Trinidad and Banao.

The youngest lithostratigraphic unit overlain by Lagunitas is the Oligocene Las Cuevas Formation in the type section.

Lagunitas is in turn overlain by the Middle Miocene Güines Formation and younger sediments.

[4] Partial temporal and lithological equivalents of the Lagunitas Formation situated elsewhere in Cuba include the Arabos, Paso Real, Rosario and Magantilla Formations.