Date of Award:

2013

Document Type:

Thesis

Degree Name:

Master of Science (MS)

Department:

Geology

Advisor/Chair:

Tammy M. Rittenour

Abstract

This study examines middle to late Holocene episodes of arroyo incision and aggradation in the Kitchen Corral Wash (KCW), a tributary of the Paria River in southern Utah. Arroyos are entrenched channels in valley-fill alluvium, and are capable of capturing decadal- to centennial-scale fluctuations in watershed hydrology as evidenced by the Holocene cut-fill stratigraphy recorded within near-vertical arroyo-channel walls. KCW has experienced both historic (ca. 1880-1920 AD) and prehistoric (Holocene) episodes of arroyo cutting and filling. The near-synchronous timing of arroyo cut-fill events between the Paria River and regional drainages over the last - 1 have led some researchers to argue that arroyo development is climatically driven. However, the influence of allogenic (climate-related) or autogenic (geomorphic threshold) forcings on arroyo dynamics are less clear. Uncertainty in influence of the controlling mechanisms of arroyo cutting and filling is partly due to the limited or poorly dated alluvial chronologies. This study tests the applicability of AMS radiocarbon and optically stimulated luminescence (OSL) dating to reconstruct alluvial chronologies in dryland fluvial systems, such as the KCW arroyo. Results from 12 arroyo-wall study sites in KCW indicate that 24 of the 39 analyzed AMS radiocarbon sample s and preliminary results from 12 of the 14 OSL sample s returned strati graphically consistent ages. Applying a combination of these two dating techniques allowed for increased sampling opportunities and cross-checking of ages to determine aberrant age results. By using detailed stratigraphic panels, sedimentologic descriptions, and the age control from AMS radiocarbon and OSL dating, this study produces a new chronostratigraphy that suggests at least five arroyo cut-fill cycles during the middle to late Holocene with periods of aggradation at: - 4.3 5 - 3 .4 ka (Qfl ), - 3 .2 - 2.25 ka (Qf2), - 2. 15 - 1 .45 ka (Qf3), - 1.3 - 0.8 ka (Qf4), - 0. 7- 0.12 ka (Qf5), and an older period of aggradation from - 7 .3 - 4.85 ka identified in an earlier stud y. This newly developed KCW cut-fill chronostratigraphy is compared to regional alluvial and paleoclimate records to test hypotheses regarding allogenic or autogenic forcings. Regional alluvial chronologies do not show coherent patterns of arroyo cut -fill dynamics, but instead appear to be affected by both allogenic and autogenic influences.

Included in

Geology Commons

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