Named as uppermost member in the Eagle Ford Formation for the Maribel schoolhouse about 5 mi east of the county courthouse in Sherman, Grayson Co, TX in the South Oklahoma folded belt province. Composite stratotype described in vicinity of Sherman, TX. Occurs in outcrop and subsurface in northern Collin and Grayson Cos, TX in the South Oklahoma folded belt province and in Fannin Co, TX in the Ouachita tectonic belt province. Formerly called Lake Crockett Shale Member (McNulty, 1954), herein abandoned. Is a north- and east-thinning tongue of Eagle Ford lithosome of Grayson and Collin Cos; loses identity southward as the underlying Bells Sandstone Member grades laterally into shale; and loses identity eastward as it and the overlying Ector tongue of Austin lithosome change facies. Consists of as much as 21 ft of medium- to dark-gray, laminated shale with silty and (or) jarositic partings. Overlies Bells Sandstone Member with sharp contact. Assigned a late Turonian age on the basis of ammonites and stratigraphic position dating.

Source: GNU records (USGS DDS-6; Denver GNULEX).