6 Getting a Better Handle on the “Dirt” Covering the Bedrock—Mapping and Dating of Surficial Deposits

Monday, 11 May 2009
1:00 PM - 5:00 PM

ARROYO CUT AND FILL RECORD FROM KANAB CREEK IN SOUTHERN UTAH

Paper number: 6-2
Program: Theme Sessions
Time: 1:00 PM – 1:20 PM

Authors

Abstract

In the late 1880's, many river systems in the southwestern US incised and formed deep arroyos. This arroyo cutting event left many historical settlements perched well above their water source. Kanab Creek is an excellent example of a mature arroyo, and has incised 30- 40 meters into its alluvium leaving behind fluvial terraces and thick basin-fill sediments. This research is testing the hypothesis that cycles of incision and aggradation may be linked to changes in regional climate. River deposits were mapped at the 1:12000 scale for spatial reference, and stratigraphic columns of exposed terrace and basin fill sediments were described and interpreted. As a method for age control, quartz sand grains were analyzed using Optically Stimulated Luminescence (OSL) dating.

Preliminary OSL and previous radiocarbon results suggest at least 5-6 cycles of fluvial cutting and filling over the last 25k years. These 5-6 cycles are recorded in the fine-grained basin and terrace fill deposits, strath terraces, and as cut-fill relationships. One major aggradational period along Kanab Creek occurred between 14-7ka, coinciding with the Pleistocene-Holocene transition. Initial results suggest that Kanab Creek is a dynamic fluvial system, and comparison of this alluvial record to regional paleoclimate records may relate arroyo cut and fill processes to changes in sediment supply, regional precipitation regime, and flood frequency.