Early Pennsylvanian paleotopography and depositional environments, Rock Island County, Illinois /

Porostrobus nathorstii (Leary & Mickle) emend. and its spores from the Namurian of Illinois, USA

“…Cones were found in sediments completely filled channels eroded in a nearly level limestone surface (Leary 1981). Isolated S. praetextus megaspores are concentrated in the highly fissile black shale at the top of the sequence.…”

“…The mesophile (i.e. upland) flora described by Havlena (1970) was present only as fragments whereas preservation of the plants in the Rock Island is excellent (Leary & Trask 1985).…”

“…14, T.17 N., R.2 W., Milan Quadrangle). Specimens were collected from sediments that fill a channel eroded in Devonian Cedar Valley Limestone (Leary 1981). The channel is 6 m deep, 8 to 30 m wide, steep-sided, and flat-bottomed.…”

“…The presence of a permanent body of water in the channels apparently permitted the growth on the drier sites in Rock Island of genera (e.g. Lepidodendron Sternberg and Mesocalamites Hirmer) common to coal swamp (Leary & Trask 1985).…”

“…Based on the associated flora, the Porostrobus-bearing plants probably grew in area adjacent to channels. Leary & Trask (1985) interpreted plant assemblage of the Rock Island County as upland flora. This term has been used to designate distinctive nonswamp floras.…”