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This study tests and improves on previously published early and middle Miocene 87 Sr/ 86 Sr marine correlations, presents Sr isotopic age correlations for this interval using the new timescale of Cande and Kent 1992, and evaluates Sr isotopic changes against an inferred glacioeustatic proxy. We generated a latest Oligocene to early late Miocene 87 Sr/ 86 Sr isotope record from Ocean Drilling Program (ODP) Hole 747A; this site provides an excellent magnetostratigraphic record during most of this interval for independent age estimates, very good foraminiferal preservation, and excellent core recovery. Comparisons of new 87 Sr/ 86 Sr data from Hole 747A with previously published data from Deep Sea Drilling Project (DSDP) Sites 608 Miller et al. , 1991a and 588 Hodell et al. , 1991 yield the following results: (1) confirmation and refinement of the early Miocene Sr isotope changes, (2) improved definition of the timing of the changes in slope of 87 Sr/ 86 Sr near 15.4 Ma and 22.8 Ma, (3) improved Sr isotopic age resolution for the middle Miocene with resolution as good as ±0.7 m.y., and (4) identification of an inflection in the Sr isotope record at 28.0 Ma based on the combined records from DSDP Site 522 Miller et al. , 1988 and ODP Hole 747A. We have been unable to determine the cause of middle Miocene offset between Site 588 and Hole 747A data, although we believe it may be attributed to problems in the age assignments for Hole 588A for the interval ∼14‐11 Ma and Site 747 for the interval 11–8 Ma. Because Hole 747A results provide a better chronology than Site 588 for most of the Miocene and a better middle Miocene Sr isotope record than Site 608, we propose that Hole 747A serves as the best reference section for Miocene 87 Sr/ 86 Sr variations from ca. 23 to 11 Ma. Using 87 Sr/ 86 Sr data from Sites 522, 608, and 747A, we relate late Eocene to early Miocene inflections in the 87 Sr/ 86 Sr isotope record to oxygen isotope increases and decreases inferred to represent glacioeustatic events. The decreases (deglaciations) observed in the δ 18 O record apparently lead the 87 Sr/ 86 Sr inflections by 1 to 1.5 m.y.
Oslick et al. (Wed,) studied this question.