Sea Levels And Marine Terraces: The Importance Of Glacio-Hydro-Isostastic Adjustment In Determining Vertical Tectonic Motion Across The Pacific Coast Of North America

Abstract

Differences in marine terrace elevations across the Pacific Coast of North America have long been assumed to be a result of differences in the rates of tectonic motion. However, other processes such as glacio- isostatic adjustment (GIA) lead to regional variations in sea levels. In this study, we compile the elevations of marine isotope stages (MIS) 5a (∼84 ka) and 5c (∼106 ka) terraces across the Pacific Coast of North America and compare these regional variations in elevation to predictions of GIA. These predictions are generally consistent with the observed trends in the elevations of both terraces and show that GIA creates up to 20 m of coeval variation in local sea levels along the central Pacific Coast (between 20¬∞N and 45¬∞N) of North America during MIS 5c and MIS 5a but less, ∼4 m, during MIS5e (119-129 ka). Ignoring GIA leads to overestimating uplift rates by an average of 35% but up to 70% across the Pacific Coast of North America. An understanding of regional variations in GIA-corrected sea levels allows the identification of areas with mistaken age assignments and/or time dependent changes in uplift rates.

AAPG Datapages/Search and Discovery Article #90215 © 2015 Pacific Section AAPG Convention, Oxnard, California, May 3-6, 2015