Belemnitellid cephalopods from the Maastrichtian stratotype area (southeast Netherlands) are shown to be comparatively well preserved. Although partial diagenetic alteration has been observed, micromilling techniques have permitted the extraction of pristine belemnite calcite, suitable for the reconstruction of strontium (Sr), oxygen (O) and carbon (C) isotope variation of Maastrichtian seawater. A distinct Sr isotope pattern in the Maastricht record can be matched stratigraphically with records from Hemmoor (northern Germany), El Kef (Tunisia) and ODP site 690 (Maud Rise, Antarctica), leading to a new chemostratigraphical age model for the Maastrichtian stratotype section. Our data improve currently applied strontium isotope stratigraphical reference curves by revealing an Sr isotope inflection pattern near the lower/upper Maastrichtian boundary that is a potentially diagnostic feature for intra-Maastrichtian stratigraphical correlation between distant sections. Belemnites further show significant stratigraphical oxygen isotope variation through the Maastrichtian. We interpret this variation to have resulted from palaeoceanographic reorganisations in the Atlantic Ocean during this time interval.

The Indian subcontinent is widely considered to be the birthplace of whales (Cetacea), and the middle Eocene Harudi Formation of Kutch has long been known to be a major source of early whales. The Kutch cetaceans are of critical importance in understanding the evolutionary transition of whales from land to sea. Strontium isotope analysis of marine biogenic carbonates from the Harudi Formation was conducted to obtain a numerical age of the whale-bearing strata. Although the measured 87Sr/86Sr ratios (0.707742 to 0.707764) correspond to two distinct age clusters of 46–47.5 Ma or 41–42.5 Ma, we prefer the latter, late Lutetian, age cluster.