AAPG Bulletin; June 2007; v. 91; no. 6;
p. 809-821; DOI: 10.1306/11060606022
© 2007 American Association of Petroleum Geologists (AAPG)
Paleovalley fills: Trunk vs. tributary
Erik P. Kvale1 and
Allen W. Archer2
1 Indiana Geological Survey, 611 North Walnut Grove, Bloomington, Indiana, 47405; present address: Devon Energy Corporation, Exploration, Central Division, 20 North Broadway, Oklahoma City, Oklahoma 73102; Erik.Kvale{at}dvn.com
2 Department of Geology, Kansas State University, Manhattan, Kansas 66506
Erik received his M.S. degree (1982) and his Ph.D. (1986) in geology at Iowa State University. Hired by the Indiana Geological Survey in 1987, his research has largely been field based and spans fluvial, marine, and carbonate depositional systems. He has published numerous articles on the sedimentology of the Carboniferous of the Illinois Basin and the Jurassic and Cretaceous of northern Wyoming. He is also a former director of the Iowa State University Geology Field Station in Shell, Wyoming, and is currently employed by Devon Energy Corporation in Oklahoma City, Oklahoma.
Allen acquired his M.A. degree (1979) and his Ph.D. (1983) from Indiana University. His research has focused on tidal rhythmites, paleontology, and sedimentology, with a recent emphasis on the tidal-fluvial sedimentology of the Amazon River. Other ongoing projects involve study of fluvio estuarine transitions in modern hypertidal systems, including Cook Inlet in Alaska, the Atlantic Ocean estuaries in southern Patagonia, and southwestern Ungava Bay in Quebec, Canada. The tidal range in these systems exceeds 10 m (33 ft). All these modern analogs are providing useful models for the delineation of large-scale, paleofluvial systems formed during the Carboniferous in the eastern United States. He is currently an associate professor in the Department of Geology at Kansas State University in Manhattan, Kansas. He has been a member of the faculty since 1989.
A late Mississippian–early Pennsylvanian eustatic sea level drop resulted in a complex lowstand drainage network being eroded across the Illinois Basin in the eastern United States. This drainage system was filled during the early part of the Pennsylvanian. Distinct differences can be recognized between the trunk and tributary paleovalley fills. Fills preserved within the trunk systems tend to be fluvially dominated and consist of bed-load deposits of coarse- to medium-grained sandstone and conglomerate. Conversely, the incised valleys of tributary systems tend to be filled with dark mudstone, thinly interbedded sandstones, and mudstones and siltstones. These finer grained facies exhibit marine influences manifested by tidal rhythmites, certain traces fossils, and macro- and microfauna. Examples of tributary and trunk systems, separated by no more than 7 km (4.3 mi) along strike, exhibit these styles of highly contrasting fills.
Useful analogs for understanding this Pennsylvanian system include the Quaternary glacial sluiceways present in the lower Ohio, White, and Wabash river valleys of Indiana (United States) and the modern Amazon River (Brazil). Both the Amazon River and the Quaternary rivers of Indiana have (or had) trunk rivers that are (were) dominated by large quantities of bed load relative to their tributaries. The trunk valley systems of these analogs aggraded much more rapidly than their tributary valleys, which evolved into lakes because depositional rates along the trunk are (were) so high that the mouths of the tributaries have been dammed by bed-load deposits. These Holocene systems illustrate that sediment yields can significantly influence the nature of fill successions within incised valleys independent of rates of sea level changes or proximity to highstand coastlines.
Copyright © 2009 by American Association of Petroleum Geologists (AAPG)
