Orbitally-tuned Sr isotope chemostratigraphy for the late middle to late Miocene

Abstract

We present a Sr chemostratigraphic reference section for the late middle to late Miocene (14-5 Ma) from Ocean Drilling Program site 926 on the Ceara Rise. This site combines a precise, orbitally tuned timescale with a high sedimentation rate (15 m/m.y.), continuous deposition, and excellent biostratigraphic control. The Sr isotope curve is based on measurements of cleaned, planktonic foraminifera at 100-200 kyr sample intervals and it illustrates periods of rapid change in 87Sr/86Sr alternating with periods of little change. Chemostratigraphically-defined ages for these intervals can be determined within +/-0.8 m.y. and +/-1.6 m.y. respectively. There is excellent correlation with the published curve for site 588 [Hodell and Woodruff, 1994]; however the curve for site 747 [Oslick et al., 1994] exhibits less structure, which may be due to small errors in age estimates related to slow sedimentation rates, high-latitude fauna and an interval of complicated magnetics. Late Miocene data compare favorably with data from site 758 [Farrell et al., 1995].