Origin and Organization of Mass-Transported Carbonate Debris in the Lower Cretaceous (Albian) Tamabra Formation, Poza Rica Field Area, Mexico

R.G. Loucks¹, Charles Kerans², Xavier Janson², and Alfredo Marhx^3
1 Bureau of Economic Geology, Jackson School of Geosciences,The University of Texas at Austin, Austin, TX
² The University of Texas at Austin, Austin, TX
³ Pemex Exploración y Producción, Poza Rica, Veracruz, Mexico

Carbonates in the Poza Rica field are mass-transport deposits formed by gravity flow and suspension processes in a deepwater basinal setting (as great as 1000 m) in front of a by-pass margin associated with the shallow-water Tuxpan platform. Reefal and grain-rich debris formed on the platform. The carbonate debris wedge extends more than 20 km into the basin.

The internal architecture of the debris wedge shows an orderly pattern of depositional units that reflects control of relative sea-level changes on availability of source material. Debris and mud flows composed of platform and slope carbonate mud, sand, and clasts were generally deposited during sea-level lowstands and transgressions or during early highstands when the platform was rapidly aggrading, whereas hyperconcentrated to concentrated density-flow and turbidite deposits composed of carbonate sand and lesser mud were generally deposited when the platform was flooded and shedding during highstands of sea level. The lower section of the debris wedge is predominately debris- and mud-flow deposits totaling more than 300 ft thick, whereas the middle to upper section is composed mainly of hyperconcentrated to concentrated density-flow deposits totaling more than 300 ft thick. The uppermost section changes from debris flows updip to hyperconcentrated to concentrated density flows downdip.

The field is approximately 30 km long and 5 km wide, covering an area of 150 km2. With ~5 billion barrels of original oil in place, it is the largest deepwater carbonate gravity-flow reservoir in the world. The major reservoir rocks are grainstones, grain-dominated packstones, and grain-dominated matrix breccias.