Throughout much of the Benton uplift, the lower member of the Arkansas Novaculite can be subdivided into five lithostratigraphic units: (1) a basal chert-and-shale subdivision consisting of alternating beds of chert and green shale, (2) a calcareous subdivision made up of massive novaculite containing disseminated carbonate grains, (3) a translucent novaculite subdivision consisting of thick beds of noncalcareous translucent novaculite separated by thin layers of green shale, (4) a unit of massive white novaculite, and (5) an uppermost subdivision of chert breccia.

In most exposures, the four lower subdivisions include layers showing fine, parallel, laminated couplets. These couplets are of two types. The chert-and-shale and translucent novaculite subdivisions contain terrigenous couplets defined by thin chert layers enriched in terrigenous detritus alternating with thicker layers of nearly pure chert. Calcareous couplets in the calcareous and massive novaculite subdivisions are defined by alternating carbonate-rich and carbonate-poor laminations. The couplets are composed of three grain populations. The chert represents recrystallized and cemented biogenic particles, mainly sponge spicules and radiolarian tests. Both couplet types contain disseminated quartz silt and very fine-grained sand interpreted to be wind-blown detritus. Terrigenous coup ets also include clay and fine silt transported in suspension by ocean-surface currents and originating on a shallow-marine to subaerial shelf on the north. Calcareous couplets contain silt to fine-grained-sand-sized carbonate rhombohedra probably representing aeolian and aqueously transported carbonate material.

The couplets are interpreted to be varves. The terrigenous varves formed within a narrow zone of sedimentologic overlap between a northern shale and black-chert facies and a southern biogenic-silica facies. Within this overlap area, seasonal influxes of terrigenous detritus from the north, possibly related to seasonal storms or runoff, alternated with periods of nonterrigenous silica sedimentation to form the varve couplets. Terrigenous varves formed when the Ouachita basin was exchanging surface waters with adjacent seas and surface-water circulation was well developed.

Sequences of calcareous varves are regionally extensive and formed under more restricted conditions when there was less intrabasinal circulation; detritus from the north was not spread so far to the south. Supratidal and evaporitic flats developed around the basin margins may have served as sources for the carbonate material in the varves.

Varve counts suggest that the lower four subdivisions of the lower member of the Arkansas Novaculite, 120 m thick at Caddo Gap, were deposited in about 100,000 years. The possibility of significant unconformities within the Arkansas Novaculite, especially at the top of the lower member, must be considered.