Sedimentary deposits within the upper 40-100 ft of the Dakota Formation exposed in Russell County, Kansas, record deposition in an environmentally diverse deltaic setting developed during the initial stages of the Greenhorn marine cyclothem. The lower two thirds or more of the Dakota (200-300 ft thick in central Kansas) consists predominately of nonmarine kaolinitic mudstone and discontinuous channel sandstone lenses; however, the upper part contains a complex of fluvial-deltaic, delta-plain and marginal-marine lithofacies, which grade upward into the shallow-water marine Graneros Shale. Such lithofacies have been mapped in detail and can be differentiated according to macroinvertebrate and trace-fossil assemblages, sedimentary body geometry and lateral depositional relat ons, sedimentary structures, and petrology.

The sedimentary complex in Russell County is dominated by an elongate fluvial-deltaic channel sandstone which changes within 30 mi from a highly meandering, trough-shaped fluvial sandstone body containing freshwater mollusks to a tabular-wedge shaped, delta-front sandstone body containing freshwater to brackish-water macroinvertebrates and a variety of trace fossil types. Kaolinitic floodplain deposits containing abundant plant fossils most commonly are laterally associated with channel sandstones; however, within the upper 20-30 ft of the formation, freshwater lignitic coal-swamp facies and freshwater to brackish-water sideritic clay-ironstone swamp facies are common. Locally, laminated to highly burrowed delta-marine and strandline marine sandstones are present. These contain a dive se association of marine macroinvertebrates and an abundance of trace fossil types. The deltaic facies grade upward into the fossiliferous, glauconite-rich marine sandstone and montmorillonitic shale of the Graneros.

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