Title: Chronostratigraphy of talus flatirons and piedmont alluvium along the Book Cliffs, Utah – Testing models of dryland escarpment evolution

Abstract

Research on the evolution of dryland escarpments and what drives and controls their erosional retreat have been limited by a lack of chronologically constrained records. Prior investigations of escarpments in the southwestern U.S. and globally garner two endmember conceptual models -- one focused on bottom-up baselevel drivers and autogenic variations in piedmont and toeslope erosion processes, the other focused on the role of climate as a top-down forcing mechanism on sediment production and transport from cliffs. In this work, we test these conceptual models along a section of the Book Cliffs in central Utah, where climate has varied strongly and baselevel has fallen significantly over the late Quaternary. Four generations of talus flatirons and piedmont terraces are preserved in the study area we date them by optically stimulated luminescence and 10Be-exposure techniques. OSL depositional ages cluster into four generations of deposits with mean ages and mean standard errors of 117.8 ± 6.7 ka, 83.4 ± 3.3 ka, 52.4 ± 1.8 ka, and 5.6 ± 0.3 ka. 10Be-exposure results from talus boulders protruding from flatirons confirm that the youngest generation of talus is Holocene, with recent rock-fall boulders still being received on the landform top. Older flatiron generations produce incoherent, minimummore » exposure ages reflecting an increasing dominance of in situ boulder weathering and a steady-state denudation rate of ~45 mm/ky after tens of thousands of years. Based on the chronostratgraphy and correlation of talus and piedmont deposits, we interpret climate as the primary control on escarpment evolution. Depositional ages do not correspond to glacial epochs as historically presumed, but instead to episodes of intermediate and unstable or variable Pleistocene climate during Marine Isotope Stage-3 and 5 a/b. Results support the significance of high climate variability at millennial timescales in driving both sediment production by mass wasting from the cliff as well as sediment storage and reworking along the piedmont. In contrast, wetter climates of glacial epochs apparently caused greater erosion and sediment transport to trunk drainages. Our chronology also reveals a systematic decrease in deposit age with increasing distance up the piedmont from the regional baselevel of the Price River, consistent with transient fluvial incision and terrace abandonment. The Book Cliffs record notably does not correlate with similarly constrained records in Spain or the contrasting record from the Negev, yet they all share the feature of enhanced talus deposition and cliff retreat corresponding to climate instability rather than in response to steady glacial-climate conditions. Thus, we outline a model of escarpment evolution and retreat governed largely by top-down climate-forcing of sediment production and transport during climate variability, with local changes in baselevel and erosional processes on the piedmont being a modifying, secondary factor.« less

Authors:

McCarroll, Nicholas R.  ^[1];

• Search DOE PAGES for author "McCarroll, Nicholas R."
• Search DOE PAGES for ORCID "0000-0001-6817-497X"

Pederson, Joel L. ^[2]; Hidy, Alan J.  ^[3];

• Search DOE PAGES for author "Hidy, Alan J."
• Search DOE PAGES for ORCID "0000-0003-2916-1425"

Rittenour, Tammy M. ^[2]

---

+ Show Author Affiliations

1. Utah State Univ., Logan, UT (United States); Kansas State Univ., Manhattan, KS (United States)
2. Utah State Univ., Logan, UT (United States)
3. Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)

Publication Date:

Mon Nov 22 00:00:00 EST 2021

Research Org.:

Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)

Sponsoring Org.:

USDOE National Nuclear Security Administration (NNSA); USDOE Laboratory Directed Research and Development (LDRD) Program

OSTI Identifier:

1834481

Report Number(s):

LLNL-JRNL-815462
Journal ID: ISSN 0277-3791; 1024642

Grant/Contract Number:  

AC52-07NA27344; 19-LW-036

Resource Type:

Accepted Manuscript

Journal Name:

Quaternary Science Reviews

Additional Journal Information:

Journal Volume: 274; Journal Issue: na; Journal ID: ISSN 0277-3791

Publisher:

Elsevier

Country of Publication:

United States

Language:

English

Subject:

58 GEOSCIENCES; Dryland; Escarpment; Talus flatiron; Luminescence; Cosmogenic; Book cliffs