BROWNSTOWN MARL/FORMATION

Age: Late Cretaceous Period, Gulfian Series
Distribution: Gulf Coastal Plain in southwest Arkansas in parts of Clark, Pike, Hempstead, Howard, Sevier and Little River Counties; Texas, Oklahoma, (Louisiana?)
Geology: The Brownstown Marl is composed of clay marls, thin (sometimes sandy) limestones, sandy marls, and some fine-grained sands. Glauconite and some phosphatic material may be associated with the various lithologies. Color is quite variable, depending on the degree of weathering, iron content, and other factors, yielding tan, brown, blue, green, red, yellow, gray, or any color combination and hue. Near the base of the unit, beds of thin hard limestone exist that contain poorly preserved fossils. The marls in the formation are often highly fossiliferous. The most common fossils are oysters and other bivalves, some cephalopods, and occasional echinoderms, fish material, and annelids. The Brownstown Marl rests unconformably on underlying formations. The formation is about 250 feet thick in Howard County, but thins both to the east and west.
Original reference: R. T. Hill, 1888, Arkansas Geological Survey Annual Report 1888, v. 2, p. 72, 86-87, 188; 1894, Geological Society of America Bulletin, v. 5, p. 302.
Type locality: Named after Brownstown, Sevier County, Arkansas