Petrology of Buckner Member of Haynesville Formation in Adjacent Parts of Texas, Louisiana, and Arkansas: ABSTRACT

Abstract

The Buckner Member of the Haynesville Formation is an evaporitic mudstone unit of Late Jurassic age that is present only in the subsurface around the margin of the Gulf Coast embayment. It has been divided informally into two parts, lower and upper. The most common rock types in the Buckner are nodular anhydritic mudstone and nodular anhydrite. The nodules consist of swirls of lathy anhydrite in a matrix of blocky to anhedral crystals. The mudstone matrix consists of a red or gray non-laminated or poorly laminated mixture of silt and clay minerals. The clay minerals are mostly illite and chlorite. The next most common rock type is light gray crypto- to micrograined laminated anhydrite that is largely confined to the lower part. This type contains scattered minute rounded dolomite grains, clay mineral grains, and fine-grained sand and silt. Some less common rock types in the Buckner are oolitic and detrital limestone, oolitic-micritic and detrital-micritic limestone, rock salt, micrograined dolomite, and medium-grained dolomite. > The member was deposited around the margin of the Gulf Coast embayment in linear basins. Contemporaneously growing salt-cored anticlines along the seaward margin caused restricted circulation with the open sea. The lower part was deposited mainly in standing bodies of water and the upper part was deposited on a tidal mud flat that was, from time to time, flooded by both marine and non-marine water. The sea generally was regressing during deposition of the Buckner. Micrograined anhydrite is associated with rock salt and is considered to be primary. Nodular anhydrite is associated with brackish-water fossils and was probably deposited as gypsum. End_of_Article - Last_Page 461------------