ABSTRACT: Sr-Isotopic Variation in the Quaternary: The Record from Glacial and Interglacial Marine Terraces

K. R. Ludwig, D. R. Muhs, K. R. Simmons, B. J. Szabo, J. G. Moore

We report high-precision Sr isotope of aragonitic fossils from Pleistocene marine terraces, which formed during both glacial and interglacial periods, to (1) constrain the marine Sr-isotope trend for the late Quaternary, and (2) test the long-term marine Sr-isotope trend for reversals related to glacial-interglacial transitions. Analyses of multiple samples of mollusks from each of 15 interglacial terraces on San Nicolas Island, San Clemente Island, and the Palos Verdes Hills (California) define a marine Sr-isotope trend (assigning terrace ages based on an assumption of constant long-term uplift rates calculated from the height of dated 120-Ka terraces) that is generally similar to the trend defined by the data of recent workers for DSDP samples. Data for three U-series d ted interglacial terraces on the East Coast of the United States plot close to the California trend, as do data for 14 coral samples of 0-750 Ka age (dated by mass-spectrometric ²³⁴U/²³⁸U) from submerged, glacial-stage reefs off Hawaii. As a whole, our data indicate an approximately linear increase of approximately 0.05 ^pmil in ⁸⁷Sr/⁸⁶Sr over the last 800 k.y., confirm the presence of a subtle (^sim0.01 ^pmil) reversal between approximately 900 and 600 Ka, and resolve a previously unrecognized reversal of approximately 0.02 ^pmil between approximately 1400 and 1200 Ka. In addition, the lack of obvious fine structure in samples younger than 800 ka indicates that the amplitude of any short-period oscillations (<100 k.y.) in the marine ^{87 /SUP>Sr/86Sr trend for the Late Quaternary is probably less than approximately 0.02 ^pmil.}

AAPG Search and Discovery Article #91003©1990 AAPG Annual Convention, San Francisco, California, June 3-6, 1990