Sediment supply, base level, braiding, and bedrock river terrace formation: Arroyo Seco, California, USA

Research Article| July 01, 2013 Sediment supply, base level, braiding, and bedrock river terrace formation: Arroyo Seco, California, USA Noah J. Finnegan; Noah J. Finnegan † 1Department of Earth and Planetary Sciences, University of California, Santa Cruz, California 95064, USA †E-mail: nfinnega@ucsc.edu Search for other works by this author on: GSW Google Scholar Greg Balco Greg Balco 2Berkeley Geochronology Center, 2455 Ridge Road, Berkeley, California 94709, USA Search for other works by this author on: GSW Google Scholar Author and Article Information Noah J. Finnegan † 1Department of Earth and Planetary Sciences, University of California, Santa Cruz, California 95064, USA Greg Balco 2Berkeley Geochronology Center, 2455 Ridge Road, Berkeley, California 94709, USA †E-mail: nfinnega@ucsc.edu Publisher: Geological Society of America Received: 10 May 2012 Revision Received: 08 Sep 2012 Accepted: 11 Nov 2012 First Online: 08 Mar 2017 Online ISSN: 1943-2674 Print ISSN: 0016-7606 © 2013 Geological Society of America GSA Bulletin (2013) 125 (7-8): 1114–1124. https://doi.org/10.1130/B30727.1 Article history Received: 10 May 2012 Revision Received: 08 Sep 2012 Accepted: 11 Nov 2012 First Online: 08 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn Email Permissions Search Site Citation Noah J. Finnegan, Greg Balco; Sediment supply, base level, braiding, and bedrock river terrace formation: Arroyo Seco, California, USA. GSA Bulletin 2013;; 125 (7-8): 1114–1124. doi: https://doi.org/10.1130/B30727.1 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGSA Bulletin Search Advanced Search Abstract In many settings, rivers alternate between carving wide valley bottoms (straths) and cutting narrow gorges over time, thereby creating longitudinally continuous paired bedrock strath terraces along valleys. Strath terraces are used ubiquitously in geomorphology and tectonics; however, how and why they form remain poorly understood. Here, we focus on Arroyo Seco in the central California Coast Ranges, where we test hypotheses for strath planation and subsequent strath terrace formation. Several lines of evidence indicate that strath planation is triggered by braiding in bedrock channels. In particular, hydraulic modeling reveals that the width of Arroyo Seco's most recently formed terrace is comparable to the width of currently braided channel reaches. Additionally, a comparison of currently braided reaches to abandoned bedrock meander cutoffs shows that braided channels have valleys that are several times wider than single-thread meandering bedrock channel reaches. Lastly, in locations where the modern channel is currently braided, terraces are poorly preserved, suggesting that evidence for past episodes of braiding, in the form of paired strath terraces, is apparently largely destroyed by subsequent episodes of braiding. Field observations combined with mapping of terrace levels using an objective light detection and ranging (LiDAR)–based terrace identification algorithm reveal that temporal variation in tectonic uplift rate, sea level, and/or alluvial cover along the river cannot explain strath planation and subsequent terrace formation in Arroyo Seco. Rather, our results provide evidence that aggradation and degradation of alluvial sediments downstream of the Reliz Canyon fault result in impulsive base-level forcing of Arroyo Seco's bedrock channel. Strath abandonment and terrace formation apparently occur as incision into downstream alluvial sediments propagates upstream into bedrock. Braiding and planation of straths, in contrast, occur during intervals of low vertical incision rate associated with downstream aggradation or immediately following pulses of vertical lowering triggered by downstream incision of alluvial sediments. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.