PETRIFIED WOOD FROM THE INGLEFIELD SANDSTONE OF THE PATOKA FORMATION (UPPER PENNSYLVANIAN) IN VANDERBURGH COUNTY, SOUTHWEST INDIANA

Upper Pennsylvanian rocks in southwest Indiana dip 1 to 2 degrees to the west on the eastern margin of the Illinois Basin. The Patoka Formation overlies the West Franklin Limestone of the Shelburn Formation and is capped by the Carthage Limestone of the Bond Formation. The lowermost part of the Patoka is subdivided into the Ditney Coal and overlying Inglefield Sandstone. The Inglefield Sandstone consists of tan to gray, thin to thick bedded, trough cross-stratified, fine- to medium-grained sublithic to quartz arenite. The Inglefield is typically 5 to 10 m thick, with localized 20 to 25 m thick deposits in Vanderburgh and Posey Counties, Indiana. The thick sandstone deposits are interpreted as incised paleovalleys that formed during lowstand systems tracts and subsequently filled during early stages of transgression.

Eight samples of petrified wood were collected from the Inglefield Sandstone west of Evansville in Vanderburgh County, Indiana. Tangential and transverse thin sections were prepared from silicified and hematite replaced specimens. Transverse sections exhibit uniseriate rays with one to twelve cells high. Most cells are circular in shape, while others are angular or distorted. This distortion is most likely caused by compaction. Tangential sections show narrow rays in contrast to broad tracheids. There are no growth rings present in any of the specimens. Four specimens are identified as Dadoxylon, two specimens are Cordaites, and two specimen are coniferous.

Episodic regression of continental seas due to periodic Gondwana glaciation in the Late Pennsylvanian resulted in repeated exposure of depositional systems across the Illinois Basin. The association of Cordaitalean and coniferous petrified wood from the Inglefield Sandstone is consistent with dry lowland vegetation that accumulated during a lowstand systems tract. Because of the decreased preservation potential of lowstand deposits, this study provides additional insights into the xerophytic floras of the Late Pennsylvanian (Kasimovian) of North America.