NEW OCCURRENCES OF PTERIDOSPERMATOPHYTE DRIFTWOOD IN THE MISSISSIPPIAN SUBSYSTEM (OSAGEAN SERIES) OF SOUTHWESTERN MISSOURI

Occurrences of waterlogged driftwood have been documented from different time periods and depositional settings at several localities around the world. Pteridospermatophyta (extinct seed ferns) range from late Devonian to Paleogene periods. Two specimens, provisionally identified as pteridospermatophytes, collected several years ago recently were reported from surficial float derived from the Mississippian Elsey Formation in northeastern Greene County between the towns of Fair Grove and Strafford. Another float specimen from either the Elsey or Reeds Spring Formation was found in a stream bed in eastern Lawrence County, west of Springfield. These occurrences follow a 2010 published report of discovery of several pteridosperm fragments from chert residuum in an area mapped as Elsey Formation in southeastern Greene County, just east of Springfield. Previous investigators have noted the occurrences of fossil pteridosperms in the Reeds Spring Formation near Crane in northern Stone County. Another specimen from northern Stone County, slightly longer than four meters, was reported from the upper part of the Burlington Limestone.

Both the Reeds Spring and Elsey formations are composed of mixed lime mudstone to wackestone and chert and are interpreted to have been deposited in a fully marine, mid-shelf setting. The Reeds Spring in its type area is overlain by the Elsey Formation. The Reeds Spring typically has nodules and anastomosing masses of chert, whereas chert in the Elsey Formation typically is lenticular to bedded. In places the stratigraphic units are not distinguishable from one another, but in extreme southwestern Missouri, the units are identified by color. The Reeds Spring is composed of dark chert and medium gray lime mudstone. The Elsey has white chert with dark brown-gray lime mudstone and includes tripolitic chert in the uppermost part. Both units are regarded as facies of the Burlington Limestone. Collectively, these somewhat rare pteridospermatophyte specimens represent post-mortem dispersal and subsequent deposition of fossil pteridospermatophytes as waterlogged driftwood across the southern margin of Laurentia.