Astronomical pacing of flint beds in the European chalk sea (type-Maastrichtian, Upper Cretaceous)

Upper Cretaceous chalk deposits, commonly containing flint nodules and bands, are found all over north-west Europe. The question still stands, however, how these flints are formed and whether the pacing of these often rhythmically distributed flint beds can be astronomically controlled. To address this question, we investigated a Maastrichtian chalk succession near Hallembaye (BE) in the type-area around Maastricht (NL). The Hallembaye section is characterized by a gradual change in lithology varying from greyish chalk with rare occurrences of flint nodules towards more pure, whitish chalk with clearly expressed flint bands. Micro X-Ray Fluorescence measurements were carried out on powdered chalk samples to determine their elemental composition. ‘Flint Scores (FS)’ were attributed to quantify the distribution of flints in function of the stratigraphic height. Using an integrated stratigraphic approach, we performed a cyclostratigraphic study to evaluate a potential astronomical imprint. The Ti/Al signal, a diagenesis-resistant proxy reflecting changes in the composition of detrital influx or the provenance thereof, reveals short-scale fluctuations superimposed on a gradually decreasing trend. Time-series and spectral analyses of the Ti/Al signal reveal a dominant 40 kyr obliquity component with its 173 kyr modulation, as well as a weaker precession–eccentricity signal. Analysis of the FS equally suggests an astronomical pacing of the flint layers. We tune the FS record to the stable 173 kyr and 405 kyr astronomical cycles to construct a high-resolution age model in absolute time, complementary to a floating 40 kyr obliquity time scale. The exact mechanisms of the flint formation and its astronomical pacing remains subject of further research but seem most likely to be linked to changes in clay content. Possibly, variations in the influx of detrital material could have influenced local redox conditions as well as the paleoproductivity in the water column.