ABSTRACT

In northern Louisiana, the Terryville Formation of the Cotton Valley Group is composed of four thick progradational sandstone members. These sandstones lie stratigraphically between the underlying marine shales of the Bossier Formation and the overlying limestone of the Knowles Formation. Extending updip from the two youngest sandstone members of the Terryville Formation are at least 14 distinct sandstone tongues with blanket geometry. These blanket sandstones thin updip and eventually pinch out into the time-equivalent shales of the Hico Formation.

The blanket sandstones can be divided into two groups based on thickness and extent. Sandstones of Group I are generally less than 70 feet (21 m) thick and extend across most of northern Louisiana. In Group II, sandstones are rarely greater than 30 feet (9 m) thick and are far less extensive, commonly occurring in isolated pods. Sandstones of both types are stacked vertically and are distributed across northern Louisiana in an elongate, arcuate belt.

The Terryville sediments were delivered to a slowly subsiding shelf by two major marine-dominated delta systems. Marine processes spread the sediments across the shelf, forming the thick sandstone members. The blanket sandstones were produced when minor marine transgressions resulting from eustatic sea level rise or subsidence caused the transportation of sediments northward from the area of massive sand accumulation. Local topographic relief on the shelf apparently had little effect on the distribution of the blanket sandstones, although overall deposition of the Cotton Valley Group was influenced by several local structures.