PALEOENVIRONMENTAL INTERPRETATION OF THE FLAT ROCK CHURCH PALEOBOTANICAL SITE, BENTON COUNTY, MISSISSIPPI

The Flat Rock Church (or Hurley’s Schoolhouse) paleobotanical site in southeastern Benton County, Mississippi, has been known since before the American Civil War, although after 1933 it became covered with vegetation and, due to excessive collecting, essentially barren of fossil material. Recent road work has again exposed this classic outcrop. The exposure consists of a well-zoned paleosol succession developed at the top of the Porters Creek Formation (Midway Group, Paleocene), although the age of pedogenesis itself is uncertain and could range from Late Paleocene to Early Eocene. The paleosol consists of a kaolin-rich zone developed from the Porters Creek, overlain by argillaceous sand with redoximorphic color mottling and vertical to subvertical, branching root molds and casts, and capped by a high-chroma, hematite-rich claystone (ironstone). This thin ironstone contains the fossil leaves (more than 25 species) and wood that made the site noteworthy. The fossil leaves are preserved as impressions with minute details of venation preserved by iron oxide replacement of the organic material. The leaves are often large, nearly all smooth margined, some with drip tips, and stacked in mats that can be several centimeters thick. These features are all characteristic of tropical rainforest floors and suggest that during soil formation this area was covered by a dense upland coastal plain rainforest, distinguished from the coastal marshes represented by the lignite deposits scattered through the Naheola and much of the Wilcox Group (Late Paleocene to Early Eocene) section. Kaolinization associated with pedogenesis is consistent with leaching by organic acids under high precipitation/evaporation ratios characteristic of rainforest soils. Preliminary field inspections and literature review suggest this buried soil is present over several square kilometers, with bauxite noted at this interval east of the Flat Rock Church site. Although the Meridian Sand (Claiborne Group, Middle Eocene) overlies the paleosol at Flat Rock Church, in other exposures the fine-grained, glauconitic sand of the Naheola overlies the kaolinized Porters Creek. As this is not a regional unconformity, local structure and topography may have influenced the preservation of the paleosol.