IDENTIFICATION OF HIGH FREQUENCY CYCLICITY IN THE MISSISSIPPIAN (OSAGEAN) BENTONVILLE FORMATION, NORTHWESTERN ARKANSAS

Formerly known as the Burlington-Keokuk, the Bentonville Formation comprises the uppermost Osagean section in Arkansas, Missouri, Kansas, and Oklahoma. Facies interpretation infers that the Bentonville is composed of shallow water, high energy sand shoals prograding to the south and west. The formation shows an overall shoaling upward succession comprised of chert and crinoidal limestones capped locally by cross-bedded oolitic sand.

The Bentonville represents a portion of one 3^rd order eustatic sea level rise and fall of approximately 1-10 million years. Higher frequency 4^th and 5^th order cyclicity on the order of 40,000 to 400,000 years is seen superimposed on the overall 3^rd order sequence in the formation. Higher frequency cycles are generally meters in thickness, and show a repeatable facies succession of chert, crinoidal packstone, and coarsening upward crinoidal grainstone. The cherts present in the Bentonville are interpreted to have replaced more mud-rich or finer-grained intervals at the base of each individual 4^th and 5^th order cycle. Outcrop investigation and thin section analysis show the cherts as being highly fractured and containing minor to abundant amounts of micro- to nano-scale porosity, while packstone to grainstone facies are extensively cemented and void of porosity.

Repetition of cyclic facies successions creates a complex vertical sequence of potential permeable and impermeable units that could play a large role in controlling fluid migration and storage. Interpretation of the Bentonville Formation in a detailed sequence stratigraphic framework can help to understand the vertical heterogeneity as well as lateral variability in the unit. This can lead to more constrained predictions during subsurface analysis and exploration.