New, high-precision U-series ages of solitary corals (Balanophyllia elegans) coupled with molluscan faunal data from marine terraces on the Pacific Coast of NorthAmerica yield information about the timing and warmth of the last interglacial sea-level highstand. Balanophyllia elegans takes up U in isotopic equilibrium with seawater during growth and shortly after death. Corals from the second terrace on San Clemente Island (offshore southern California), the third terrace on Punta Banda (on the Pacific Coast of northern Baja California), and the Discovery Point Formation on Isla de Guadalupe (in the Pacific Ocean offshore Baja California) date to the peak of the last interglacial period and have U-series ages ranging from ca. 123 to 114 ka. The first terrace on Punta Banda has corals with ages ranging from ca. 83 to 80 ka, which corresponds to a sea-level highstand formed in the late last interglacial period. U-series analyses of corals from the Cayucos terrace (central California) and the Nestor terrace at Point Loma (southern California) show that these fossils have evidence of open-system history, similar to what has been reported by other workers for the same localities. Nevertheless, a model of continuous, secondary U and Th uptake shows that two ages of corals are likely present at these localities, representing the ca. 105 and ca. 120 ka sea-level highstands reported elsewhere. . ing the peak of the last interglacial period at ca. 120 ka.

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New high-precision thermal ionization mass-spectrometric (TIMS) U-series ages of solitary corals (Balanophyllia elegans) from several marine terrace localities along the California and southern Oregon coasts date to the 80,000 yr BP high stand of sea, correlative with marine isotope substage 5a, late in the last interglacial complex. Ages of multiple corals from localities north of Point An˜o Nuevo (central California) and San Nicolas Island (southern California) suggest that this high sea stand could have lasted at least 8000 yr, from 84,000 to 76,000 yr BP. These ages overlap with those from marine deposits on tectonically stable Bermuda and tectonically emergent Barbados. Higher-elevation terraces at two California localities, in the Palos Verdes Hills and on San Nicolas Island, have corals with ages that range mostly from 121,000 to 116,000 yr BP, correlative with marine isotope substage 5e. These ages are similar to those reported for other terraces in southern California but are younger than some ages reported from Hawaii, Barbados and the Bahamas.Marine terrace faunas are excellent proxies for nearshore marine paleotemperatures during past high sea stands. Terraces on the Palos Verdes Hills and San Nicolas Island dated to the 120,000 yr BP high sea stand have dominantly zoogeographically ''neutral'' species in exposed coastal localities, indicating nearshore waters similar to those of today. In contrast, 80,000 yr BP, exposed coastal localities typically have molluscan faunas characterized by numerous extralimital northern species and a lack of extralimital southern species. These fossil assemblages are indicative of nearshore water temperatures that were cooler than modern temperatures at 80,000 yr BP. Waters at least as warm as today's at 120,000 yr BP and cooler than present at 80,000 yr BP are in excellent agreement with marine alkenone records and coastal vegetation records derived from pollen data, from both southern and northern California. Decreased insolation or increased upwelling seem inadequate to explain the cool waters off the Pacific Coast from southern Oregon to southern California at 80,000 yr BP. We propose that a stronger California Current (or at least one with a greater component of subarctic waters) may explain cooler-than-modern coastal waters during the 80,000 yr BP high sea stand. r

Few of the marine terraces along the Pacific coast of North America have been dated using uranium-series techniques. Ten terrace sequences from southern Oregon to southern Baja California Sur have yielded fossil corals in quantities suitable for U-series dating by alpha spectrometry. U-series-dated terraces representing the ∼80,000 yr sea-level high stand are identified in five areas (Bandon, Oregon; Point Arena, San Nicolas Island, and Point Loma, California; and Punta Banda, Baja California); terraces representing the ∼125,000 yr sea-level high stand are identified in eight areas (Cayucos, San Luis Obispo Bay, San Nicolas Island, San Clemente Island, and Point Loma, California; Punta Bands and Isla Guadalupe, Baja California; and Cabo Pulmo, Baja California Sur). On San Nicolas Island, Point Loma, and Punta Bands, both the ∼80,000 and the ∼125,000 yr terraces are dated. Terraces that may represent the ∼105,000 sea-level high stand are rarely preserved and none has yielded corals for U-series dating. Similarity of coral ages from midlatitude, erosional marine terraces with coral ages from emergent, constructional reefs on tropical coastlines suggests a common forcing mechanism, namely glacioeustatically controlled fluctuations in sea level superimposed on steady tectonic uplift. The low marine terrace dated at ∼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 compilation of data from other coasts indicate that sea levels at ∼80,000 and ∼105,000 yr may have been closer to present sea level (within a few meters) than previous studies have suggested.

assignments can be evaluated by comparison with radiochemical age assignments and late Pleistocene temperature histories inferred from one or more paleoclimatic records. The kinetic model ages can also be evaluated within the constraints of both eustatic sea-level and isotopic ice-volume records. Age assignments for many of the late Pleistocene localities investigated in this work are in the range of 100,000 to 140,000 years and these localities are correlated with the early part of Stage 5 of the marine isotopic record (Shackleton and Opdyke, 1973). These age assignments are, in all cases, consistent with the radiometric age assignments for" the calibration localities. Samples from high terraces on San Nicolas Island, Palos Verdes Hills, and San Joaquin Hills, and from the San Pedro Sand have kinetic model ages of between 350,000 and 550,000 years and appear correlative with all or part of Stages 9 and II of the marine isotopic record. Three low terrace localities in southern California have yielded samples with ages in the range 200,000 to 250,000 years (correlative with Stage 7 of the marine isotopic record), though previous interpretations of these localities had implied correlation with localities that are sho~~to be younger. Some of these older samples may have been reworked into younger deposits. Localities with late Stage 5 (80,000 to 100,000 yrs.) ages are found at Santa Cruz, California and on Point Loma, San Diego, California (the Bird Rock Terrace). Both radiometric and geologic information are consistent with these age assignments. Samples from Cape Blanco, Oregon, appear to be either lateor post-Stage 5 in age; samples from Goleta, California are definitely post-Stage 5 in age, and appear to be approximately 40,000 years in age. iii Several of these age assignments permit revisions in the interpretation of pre-existing paleoecologic data. In addition, long-term average uplift rates for each dated locality can be estimated: most of the Stage 5 localities reported herein have apparent uplift rates between .1 and .3 meters/lOOO yrs. Uplift rates of .15 to .75 meters/IOOO yrs. are inferred from the results for San Nicolas Island and the Palos Verdes Hills. Quite. rapid uplift rates of 1.5 to 2.75 meters/IOOO yrs. for Goleta and Cape Blanco are also inferred from our results.