59 Quaternary Geology/Geomorphology I

Monday, 28 October 2002
8:00 AM - 12:00 PM

A COOL EASTERN PACIFIC OCEAN AT THE CLOSE OF THE LAST INTERGLACIAL PERIOD, ~80,000 YR BP

Paper number: 59-4
Program: Technical Sessions
Time: 8:45 AM – 9:00 AM

Authors

Abstract

New high-precision (TIMS) U-series ages of solitary corals from eight marine terrace localities along the U.S. Pacific Coast date to the ~80,000 yr B.P. high stand of sea, late in the last interglacial complex. Activity ratios for Th isotopes are high (88-600; most >200), indicating little inherited daughter Th. Except for Pt. Arena, initial U-isotopic ratios indicate that the ages are very reliable. The span of ages from two localities with multiple corals (see below) suggests that the high sea stand lasted at least 4,000 yr (Green Oaks Creek, n=10) and could have lasted as long as 10,000 yr (San Nicolas Island, n=8). All localities have molluscan faunas that contain several extralimital northern species and lack extralimital southern species. In addition, two localities have molluscan oxygen isotope compositions significantly heavier than modern specimens, indicating water temperatures 1.5 to 3.5°C cooler than present. The combined U-series, faunal and oxygen isotope data suggest a major high sea stand at ~80,000 yr B.P., with cooler-than-modern marine waters, probably heightened by a strengthened California Current

LOCALITY

AGE (ka)

INITIAL 234U/238U

Coquille Point, OR

78.6 ± 0.5

1.1427 ± 0.0018

Point Arena, CA

82.8 ± 0.8

1.1145 ± 0.0041

Green Oaks Crk., CA (youngest)

77.3 ± 0.3

1.1488 ± 0.0020

Green Oaks Crk., CA (oldest)

81.2 ± 0.7

1.1486 ± 0.0025

Point Año Nuevo, CA

75.8 ± 0.4

1.1391 ± 0.0023

Point Santa Cruz, CA

71.5 ± 0.4

1.1511 ± 0.0022

San Nicolas Island, CA (youngest)

76.1 ± 0.4

1.1427 ± 0.0023

San Nicolas Island, CA (oldest)

86.6 ± 0.8

1.1501 ± 0.0026

Palos Verdes Hills, CA

82.7 ± 0.9

1.1541 ± 0.0018

San Pedro, CA

78.5 ± 0.5

1.1437 ± 0.0027