Dr. Muhs et al., URANIUM-SERIES AGES OF MARINE TERRACE CORALS FROM THE PACIFIC COAST OF NORTH-AMERICA AND IMPLICATIONS FOR LAST-INTERGLACIAL SEA-LEVEL HISTORY, Quaternary research, 42(1), 1994, pp. 72-87
Few of the marine terraces along the Pacific coast of North America ha
ve been dated using uranium-series techniques. Ten terrace sequences f
rom southern Oregon to southern Baja California Sur have yielded fossi
l corals in quantities suitable for U-series dating by alpha spectrome
try. U-series-dated terraces representing the approximately 80,000 yr
sea-level high stand are identified in five areas (Bandon, Oregon; Poi
nt Arena, San Nicolas Island, and Point Loma, California; and Punta Ba
nda, Baja California); terraces representing the approximately 125,000
yr sea-level high stand are identified in eight areas (Cayucos, San L
uis Obispo Bay, San Nicolas Island, San Clemente Island, and Point Lom
a, California; Punta Banda and Isla Guadalupe, Baja California; and Ca
bo Pulmo, Baja California Sur). On San Nicolas Island, Point Loma, and
Punta Banda, both the approximately 80,000 and the approximately 125,
000 yr terraces are dated. Terraces that may represent the approximate
ly 105,000 sea-level high stand are rarely preserved and none has yiel
ded corals for U-series dating. Similarity of coral ages from midlatit
ude, erosional marine terraces with coral ages from emergent, construc
tional reefs on tropical coastlines suggests a common forcing mechanis
m, namely glacioeustatically controlled fluctuations in sea level supe
rimposed on steady tectonic uplift. The low marine terrace dated at ap
proximately 125,000 yr on Isla Guadalupe, Baja California, presumed to
be tectonically stable, supports evidence from other localities for a
+6-m sea level at that time. Data from the Pacific Coast and a compil
ation of data from other coasts indicate that sea levels at approximat
ely 80,000 and approximately 105,000 yr may have been closer to presen
t sea level (within a few meters) than previous studies have suggested
. (C) 1994 University of Washington.