Excerpt from Arkansas Geological Survey web page (emphasis added is my own):
The Sligo Formation is in the upper Coahuila Series of the Lower Cretaceous period and underlies the Pine Island black shale section of the Trinity group and above the Hosston sands and shales. The Sligo Formation is in conformable contact with the overlying Pine Island, but is time-transgressive on the Hosston Formation as indicated by the dark shallow water marine sediments overlying the nonmarine Hosston sediments. The Sligo in the "Ark-La-Tex" region is composed primarily of gray to brown shales, limy shales and limestones, locally containing lentils of dark gray oolitic argillaceous fossiliferous and sandy limestones and light to dark gray and brown fossiliferous shales. The thickness of the Sligo is less than 100 ft in south Arkansas and greater than 500 ft in central Louisiana.
The type locality of the Sligo Formation is the Sligo field in Bossier Parish, Louisiana. Production from the Sligo is generally referred to as the Pettet Limestone, a term that refers to a productive, porous, pelletal-ooid limestone. The Pettet porosity zones of the Sligo formation have accounted for a major portion of the gas production and a considerable portion of the oil production in the North Louisiana, Arkansas and East Texas areas. Production is obtained from anticlines, fault traps and stratigraphic porosity traps. Of these the stratigraphic trap is by far the most important from the standpoint of accumulated production.
Here is a link to a recent Pettet Lime (Sligo) unit application in Webster Parish.
Last Sligo completion in Bear Creek Field. It's a horizontal El Paso well.
COMPLETED 8-16-08; GAS; SLIGO; 1536 MCFD; 5 BCD; 14/64 CHOKE; 51 GVTY; 1200FP; 1300 CP; PERFS 6974-10,750' MD; 6501-6589' TVD