High-resolution stable isotope records from the Upper Cretaceous rocks of Italy and Spain: Glacial episodes in a greenhouse planet?

High-resolution delta(13)C and delta(18)O records from upper Albian to lowe r Santonian pelagic carbonates of the Contessa Quarry section in Italy exhi bit large positive oxygen isotopic excursions of similar to 1 parts per tho usand in the lower Cenomanian and upper Turonian-Coniacian strata, Within t he uncertainties of biostratigraphic correlation, these positive excursions appear to correspond to times of large sealevel regressions in global sequ ence stratigraphic sea-level curves. Several lines of evidence suggest that the major delta(18)O excursions in Contessa reflect episodes of global coo ling and not differential diagenesis, Numerical models of oxygen isotope ex change during diagenesis show that a high contrast in the degree of alterat ion would be required to produce these signals as artifacts of diagenesis, and lithological data provide no evidence for such large contrasts in the d egree of alteration. Furthermore, although precise correlation with a secti on in the south of Spain is hampered by stratigraphic complexities, the gen eral sequence of major positive delta(18)O excursions is reproduced. It is unlikely that differential diagenesis would produce similar artifacts in mu ltiple sites. One explanation for the link between episodes of global cooli ng and sea-level falls is that global cooling events led to polar ice-sheet accumulation, lowering sea level. Although ice-free conditions have been i nferred from evidence for a much warmer climate in Late Cretaceous time, ou r results suggest that the relationship between continental high-latitude i ce sheets and overall climatic warmth warrants further examination.