Print this pageThe Influence of Climate on Pennsylvanian Incised Valley Fills
FELDMAN, HOWARD, R. M. JOECKEL, ALLEN W. ARCHER, and EVAN K. FRANSEEN
Relative changes in climate during the Pennsylvanian dramatically influenced the nature of sequence boundaries (sb) and sediment infill of associated incised valleys in the Midcontinent. Evidence includes the abundance of coals in incised valley fills, fossil plant assemblages, and provenance of valley-fill sediment. A study of 8 depositional sequences along an outcrop transect from southern Kansas to western Iowa reveals 2 distinct types of sequence boundaries.
Wet climates produce sequence boundaries with large incised valleys infilled with fluvial sandstone to estuarine mudstone. These valley fills contain abundant coals, and allogenic sandstone indicating extensive drainage networks. An example of this type, the Tonganoxie incised valley of the Douglas Group, is approximately 41 m deep, 11 km wide, and at least 240 km long. It is infilled with fluvial conglomerate and sandstone through estuarine mudstone. In addition, coals are common at the sb and within the valley fill indicating high paleowater tables.Drier climates produce sequence boundaries with incised valleys that are narrower and shallower, typically a few hundred meters wide and up to 10 m deep. Coals are absent and plant assemblages are dominated by conifers. Examples include the Captain Creek Ls. and Stanton Ls. incised valleys. These valleys are typically infilled with a lower limestone conglomerate, locally derived from adjacent valley walls, followed by a thin upper estuarine mudstone to siltstone facies. The interfluve paleosol in the Stanton Ls., an Aridisol, confirms that the sb formed in a dry climate.
Our study provides a model by which incised valley systems can be interpreted both in terms of sea level history and climate. * Present address: Exxon Production Research, PO Box 2189, Houston TX