The Sierra de Huaco exposes the western flank of the Bermejo foreland basin of central western Argentina. The exposed 5,400-m section is well dated (14-2.3 Ma) and consists of synorogenic continental strata. Petrographic data combined with decompaction techniques provide first-order estimates of the absolute age of cementation of the sandstones. This information can be used to interpret petroleum migration paths and reservoir potential.

Three diagenetic zones have been recognized, each characterized by a dominant cementing material within a distinct framework texture. These textures reflect varying degrees of compaction and framework-grain replacement prior to cementation. The intergrain volume in the sandstones increases upward in a nonlinear, nonexponential fashion and is interpreted to reflect the porosity at the time of cementation. The lowest 550 m of strata exhibits abundant compaction features, low intergrain volume (~10%), and is cemented by analcime. The overlying 900 m exhibits little evidence of compaction, relatively high intergrain volume (up to 33%), and is cemented by gypsum. The remaining 4,000 m exhibits abundant evidence of framework-grain replacement by calcite, has very high intergrain volume (up o 40%), and is cemented by calcite.

The diagenetic histories of the three zones were genetically linked to thrusting in the adjacent Precordillera, changes in depositional environment, and subsurface fluid flow. The depth at which cementation occurred in each zone is constrained by comparison of observed intergrain volume to predicted volumes (for uncemented sands) at any given burial depth. First-order estimates of the absolute age of cementation in each zone were made possible by comparing these relationships with a curve of accumulation history of the decompacted strata. The lowest zone compacted with little interstitial cement for as long as 11 m.y. after deposition. The middle zone was cemented within 3 m.y. after deposition. The upper zone experienced framework-grain replacement by calcite at very shallow depths w thin 2 m.y. and experienced little compaction.