Eustasy and sea water Sr composition: application to high-resolution Sr-isotope stratigraphy of Miocene shallow-water carbonates

Oceanic ⁸⁷Sr/⁸⁶Sr‐isotope ratios are strongly influenced by rates of silicate weathering and therefore linked not only to glaciation but also to sea‐level change. The present study combines analysis of sequence stratigraphy and basin architecture with Sr‐isotope stratigraphy in Miocene shallow‐water sediments in southern Portugal and Crete (Greece). The common method is to use smoothed global sea water Sr‐isotope reference curves but here a different approach is chosen. Instead, measured Sr‐isotope curves are correlated with unsmoothed reference curves by identification of similar fluctuations in the order of several 100 kyr. Transgressive intervals are characterized by increasing Sr‐isotope ratios interpreted as corresponding to intensified silicate weathering as a consequence of deglaciation, while lowstand deposits have low Sr‐isotope ratios. Comparison of Sr‐isotope curves and sedimentary sequences in the studied basins with independent global δ¹⁸O data and data on global sea‐level might suggest a general relationship, supporting a connection to global climate change. Because of these relationships, the method presented herein has a high potential for use in high‐resolution age dating and is also applicable in shallow‐water sediments.