Valley Alluviation in Southwestern Wisconsin∗

Abstract

Meander erosional banks of fifth and sixth order southwestern Wisconsin streams having drainage areas of twenty square miles (30 km2) or less frequently reveal three distinct sedimentary sequences. The basal unit of coarse textured debris is thought to represent bed load sediment of a prior channel active near the terminus of a mid-Holocene drought about 6,000 years B. P. A silty clay series over the coarse layer is interpreted to have been derived by vertical accretion on a paleo floodplain during a climatic shift toward more humid conditions of the late Holocene. Distinctly laminated silt loam sediments produced by vertical accretion extend from the middle series to the current surface, and mainly result from increased flooding related to modern land use practices. The recent man-induced change in channel morphology is analogous to natural adjustments produced by Holocene climatic fluctuation, and suggests that temporal aspects of channel and floodplain evolution may be described by a step function model. KEY WORDS: Biogeomorphic response, Climatic change, Floodplain, Holocene, Valley alluviation, Wisconsin.HE morphology of stream channels and T floodplains is controlled by the physical environment of the contributing drainage basin. Maintenance or change of an established system of alluvial morphology is highly regulated by the rates of surface runoff and sediment yield. The purpose of this study is to analyze the fluvial adjustments that have occurred in response to known or presumed changes in surface runoff and sediment yield.The study area is restricted to southwestern Wisconsin valleys of fifth and sixth order having drainage areas of twenty square miles (30 km2) or less. Meander erosional banks of the fifth and sixth order streams frequently reveal three distinct sedimentary sequences : basal coarse gravel overlain by silty clay in turn overlain by recent alluvium. I will attempt to demonstrate that the lower and intermediate series are products of channel and floodplain response to

South Atlantic continental margins of Africa: A comparison of the tectonic vs climate interplay on the evolution of equatorial west Africa and SW Africa margins

“…8). It is argued that during icehouse conditions, high frequency alternate glacial / interglacial periods expressed by alternate wet / wetter climates is the major parameter in bedrock erosion (Knox, 1972). Analyses of alterites in Equatorial Africa indicate long term evolution from tropical climate during the late Cretaceous and Paleocene, toward more humid equatorial climate during Neogene (Tardy and Roquin, 1998), culminating in the Congo catchment during the Quaternary, with annual precipitation of 1600 mm.…”

Drainage basin responses to climate change

“…Thus it is reasonable to expect that even larger Holocene-scale climatic variations should have a significant impact on patterns of erosion and sedimentation within drainage basins. This seems to be borne out by studies of Holocene alluvial stratigraphy and palcoclimate [e.g., Knox, 1972Knox, , 1984Brakenridge, 1980;Blum and Valastro, 1989].…”

“…Traditionally, efforts to understand the connection between climate change and drainage basin response have been historical in nature, focusing on the Quaternary record of landscape change [e.g., Vita-Finzi, 1969;Knox, 1972Knox, , 1983Knox, , 1984Brakenridge, 1980;Smith, 1982 The goal of this study is to model the response of a "typical" midlatitude watershed to changes in runoff and in surface resistance to erosion by running water. We do not consider the full range of drainage basin types, with varying relief, processes, and other factors, but instead restrict the analysis to the case of moderate-relief, threshold-dominated basins.…”

Dependence of Gully Networks on Faults and Lineaments Networks, Case Study from Hronska Pahorkatina Hill Land

“…A different point of view was presented by Knox [25]. According to his work, at long-time scale, gully development was a complex response to a set of driving factors, including tectonic movements.…”