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UNIVERSITY of CALIFORNIA Santa Barbara the Geomorphic Transition

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UNIVERSITY of CALIFORNIA Santa Barbara the Geomorphic Transition UNIVERSITY OF CALIFORNIA Santa Barbara The Geomorphic Transition between the Santa Barbara and Ventura Fold Belts near Rincon Point, California A Thesis submitted in partial satisfaction of the requirements for the degree Master of Science in Earth Science by Shelby Marie Fredrickson Committee in Charge: Professor Edward A. Keller, Chair Professor Alexander Simms Professor Phillip Gans June 2016 The thesis of Shelby Marie Fredrickson is approved. _____________________________________________ Alexander Simms _____________________________________________ Phillip Gans _____________________________________________ Edward A. Keller, Committee Chair June 2016 The Geomorphic Transition between the Santa Barbara and Ventura Fold Belts near Rincon Point, California Copyright © 2016 by Shelby Marie Fredrickson iii ACKNOWLEDGMENTS Thank you to Ed Keller for introducing me to tectonic geomorphology and giving me the opportunity to do local research. Thanks to the Earth Research Institute for a 2015 summer fellowship and to the family of Carolyn Edwards Murphy and Christine Edwards for the 2015 Field Studies Fellowship. Thank you to Neal Driscoll for access to seismic data. Special thanks to Alexander Neely for providing the knickpoint data for the study area. Many thanks to Jonathan Harvey, Aaron Bufe, and Eric Schoettle for their expertise with GIS, Matlab, TopoToolbox, and Geomorphtools. Thank you to Doug Burbank for lending me the laser rangefinder and for thought-provoking discussions. Thank you to Laura Reynolds for discussions on shoreface deposits. Many thanks to my committee members for insightful comments. This material is based upon work supported by the National Science Foundation under Grant Nos. EAR-1358514, 1358554, 1358401, 1358443, and 1101100 (EarthScope National Office). Any opinions, findings, and conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the National Science Foundation. Thanks to the EarthScope program for its support. Thanks to Tammy Rittenour, Joel Pederson, Michelle Nelson, and Carlie Ideker for optically stimulated luminescence expertise. iv The Geomorphic Transition between the Santa Barbara and Ventura Fold Belts near Rincon Point, California ABSTRACT The Santa Barbara and Ventura fold belts have very different uplift rates based on marine terrace data: ~1-2 m/ky and ~6-8 m/ky, respectively. The onshore transition between these fold belts occurs at Rincon Creek, near Carpinteria, where the first emergent marine terrace rises from below sea level to nearly 200 m elevation over less than 10 km. A statistical comparison of normalized stream steepness values in weak rocks supports higher uplift rates east of Rincon Creek within the field area. Optically stimulated luminescence dating of the first emergent marine terrace between Carpinteria and Rincon Creek yields ages ranging from ~18-40 ka including error. The most reliable of these ages yield an average age of 32.81 ± 6.06 ka. This age is younger than previous dates of ~45 ka on the Punta Gorda terrace east of Rincon Creek but within the range of ages collected on MIS 3 terraces in Santa Barbara. These ages suggest the Carpinteria Bluffs marine terrace is continuous with the Punta Gorda terrace. Based on the age of 32.81 ± 6.06 ka and a local sea level curve, uplift rates on the Carpinteria Bluffs marine terrace are 1.8 ± 0.6 m/ky near Tar Pit Park and 3.2 ± 1.1 m/ky near the Carpinteria Bluffs Nature Preserve. Because the terrace is tilted toward the west, there is an east-west gradient in uplift rates from ~0 m/ky where the wave- cut platform emerges from below sea level at Carpinteria Beach to ~4-5 m/ky near La Conchita. The age and vertical offset of marine terrace deposits indicate minimum vertical slip rates of 0.06 m/ky and 0.20 m/ky on the Railroad fault and Carpinteria fault, respectively. v Digital topographic analysis indicates Rincon Point is a geomorphic boundary between the subsiding Carpinteria basin and the uplifting Rincon Mountain. This geomorphic boundary may coincide with a proposed tear fault, but it is most likely influenced by the position of the Red Mountain fault, which takes a left turn offshore of Rincon Point. The profile of the Carpinteria Bluffs marine terrace can be interpreted as either vertically offset or kinked across Rincon Creek. The former supports the presence of a tear fault with an east- side-up sense of slip, but the latter discounts the tear fault in favor of uplift by the Red Mountain fault. Alluvial cover, brush, and private property have hindered discovery of convincing tear fault outcrops. A subaqueous delta at Rincon Point may conceal a bedrock ridge that coincides with the trend of the proposed tear fault, but no direct evidence for a structural origin of Rincon Point is available. vi TABLE OF CONTENTS ACKNOWLEDGMENTS .....................................................................................................iv ABSTRACT ...........................................................................................................................v LIST OF FIGURES ...............................................................................................................ix LIST OF TABLES .................................................................................................................ix INTRODUCTION .................................................................................................................1 BACKGROUND ...................................................................................................................2 Geologic Setting.....................................................................................................................2 Previous Work .......................................................................................................................5 Marine Terraces.........................................................................................................5 Rock Strength .............................................................................................................7 Fault and Fold Growth ..............................................................................................8 Drainage Rearrangement ..........................................................................................9 Rincon Creek Anticline ..............................................................................................11 Study Area .............................................................................................................................11 METHODS ............................................................................................................................14 Digital Topographic Analysis ................................................................................................14 Measuring the Elevation of the Carpinteria Bluffs Wave-cut Platform ................................14 Chronology: Optically Stimulated Luminescence (OSL) ......................................................15 Concept ......................................................................................................................15 Sampling ....................................................................................................................15 Processing ..................................................................................................................16 Slip Rates ...............................................................................................................................17 Calculating Uplift Rate of the Carpinteria Bluffs Marine Terrace ........................................18 Calculating Propagation Rate of the Rincon Creek Anticline ...............................................20 Stream Profile Analysis .........................................................................................................20 Stream Steepness ........................................................................................................20 Knickpoints ................................................................................................................23 RESULTS ..............................................................................................................................24 Tear Fault ...............................................................................................................................24 Shepard Mesa Fault................................................................................................................25 Carpinteria Bluffs Marine Terrace .........................................................................................27 Tar Seeps and Marine Terrace Shoreface Deposits ..................................................27 Elevation of the Carpinteria Bluffs Marine Terrace..................................................30 Chronology of the Carpinteria Bluffs Marine Terrace ..............................................35 Uplift Rate of the Carpinteria Bluffs Marine Terrace ...............................................40 Slip Rates on the Carpinteria and Railroad faults ..................................................................41 Rincon Creek Anticline..........................................................................................................46 Chronology of the Rincon Creek Anticline Paleochannel .........................................50 Uplift Rate of the Rincon Creek Anticline..................................................................51
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