Name applied to the upper 300 to 400 ft of the Cotton Valley Group. Named for the Knowles Field, Lincoln Parish, LA in the Arkla basin. Is one of four formations assigned to the Cotton Valley in LA. Type section is in the California Co., T. C. Colvin No. 1 in SE NW sec 14, T19N, R4W between 8,240 and 8,550 ft depths. Overlies Hico Shale (new) of Cotton Valley. Underlies Hosston Formation. Known only in the subsurface. Cross sections. Consists of thin regionally persistent dark-gray argillaceous limestone interbedded with dark-gray shale. Base placed at base of 100-ft thick limestone--called informally the B limestone. Top of formation is a persistent 30-ft thick gray shale. Grades northward into the Schuler Formation, upper formation of the Cotton Valley near the LA-AR border. Known as far south as present drilling [i.e. northern LA]. Late Jurassic age. Deposited in an open lagoon. [Authors do not identify nomenclature that was applied to these rocks in papers published prior to 1964.]

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