Detrital signals of coastal erosion and fluvial sediment supply during glacio-eustatic sea-level rise, Southern California, USA

G.R Sharman,J.A Covault,Z.T Sickmann,M.A Malkowski,D.F Stockli,S.A Johnstone

doi:10.1130/g49430.1

G.R Sharman, J.A Covault + Show 4 more

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https://doi.org/10.1130/g49430.1

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Abstract

AbstractCoastal erosion, including sea-cliff retreat, represents both an important component of some sediment budgets and a significant threat to coastal communities in the face of rising sea level. Despite the importance of predicting future rates of coastal erosion, few prehistoric constraints exist on the relative importance of sediment supplied by coastal erosion versus rivers with respect to past sea-level change. We used detrital zircon U-Pb geochronology as a provenance tracer of river and deep-sea fan deposits from the Southern California Borderland (United States) to estimate relative sediment contributions from rivers and coastal erosion from late Pleistocene to present. Mixture modeling of submarine canyon and fan samples indicates that detrital zircon was dominantly (55%–86%) supplied from coastal erosion during latest Pleistocene (ca. 13 ka) sea-level rise, with lesser contributions from rivers, on the basis of unique U-Pb age modes relative to local Peninsular Ranges bedrock sources. However, sediment that was deposited when sea level was stable at its highest and lowest points since the Last Glacial Maximum was dominantly supplied by rivers, suggesting decreased coastal erosion during periods of sea-level stability. We find that relative sediment supply from coastal erosion is strongly dependent on climate state, corroborating predictions of enhanced coastal erosion during future sea-level rise.

Highlights

A majority of the world’s coastlines are net erosive with retreating sea cliffs (Young and Carilli, 2019)
We considered two explanations for the anomalous result from the single Oceanside fan sample (Fig. 2): (1) local derivation from submarine erosion of the proximal Oceanside shelf and/or canyon, or (2) sediment supplied from coastal erosion (Fig. 3)
We used detrital zircon (DZ) as a sediment tracer to reveal that rivers supplied the bulk of sediment to deepsea fans in the Southern California Borderland during periods of stable sea level

Summary

Introduction

A majority of the world’s coastlines are net erosive with retreating sea cliffs (Young and Carilli, 2019). Rates of coastal erosion are predicted to increase with global sea-level rise in the coming century (Hackney et al, 2013; Limber et al, 2018; Mentaschi et al, 2018), likely exacerbating the consequences of sea-cliff retreat and coastal gullying along heavily populated coastlines, such as in Southern California, where residential and industrial cliff-top developments are widespread (Young and Ashford, 2006). Limber et al (2018) estimated rates of cliff retreat increasing twofold or greater over the coming century in Southern California. We used detrital zircon (DZ) as a sediment tracer to track the relative contributions from rivers and coastal erosion to deep-sea fans in the Southern California Borderland over the past 40 k.y

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Discussion

Conclusion