Strontium isotope stratigraphy in the Late Cretaceous: Numerical calibration of the Sr isotope curve and intercontinental correlation for the campanian

Abstract

The white Chalk exposed in quarries at Lägerdorf and Kronsmoor, northwestern Germany, provides a standard section for the European Upper Cretaceous. The 87Sr/86Sr values of nannofossil chalk and belemnite calcite increase upward through 330 m of section, from ≤0.70746 in the Upper Santonian to ≥0.70777 in the Lower Maastrichtian. The data define three linear trends separated by major points of inflection at stratigraphic heights in the section of 162 m (75.5 Ma) in the Upper Campanian Galerites vulgaris zone and at −6 m (82.9 Ma), just above the base of the Campanian in the Inoceramus lingua/Gonioteuthis quadrata zone. The temporal rate of change of 87Sr/86Sr was constant through each of the linear segments of our isotope “curve” when viewed at the resolution of our average sampling interval (0.15 m.y.). Fine structure, if real, may record brief (<100 kyr) excursions of 87Sr/86Sr from values expected from the overall trends. In Lägerdorf, the boundary between the Santonian and Campanian stages, taken here as the level of first occurrence of the belemnite Gonioteuthis granulataquadrata, has an 87Sr/86Sr of 0.707473±5. This is within error of the values of 0.707457±16 for this boundary in the U.S. western interior (base of the Scaphites leei III zone) and 0.707479±9 for this boundary in the English Chalk (top of the Marsupites testudinarius zone). In Kronsmoor, the boundary between the Campanian and Maastrichtian stages, taken here as the level of first occurrence of the belemnite Belemnella lanceolata, has an 87Sr/86Sr of 0.707723±4. This is within error of the values of 0.707725±20 for this boundary in the U.S. western interior (base of the Baculites eliasi zone) and 0.707728±5 for this boundary in the English Chalk (defined as in Germany).