Flint formation and astronomical pacing in the Maastrichtian chalk of northwestern Europe

Abstract

In Upper Cretaceous chalk sequences, the widespread occurrence of flint, as well as a possible astronomical pacing of their often-encountered rhythmic distribution, remains poorly constrained. The Campanian-Maastrichtian Hallembaye chalk succession (Maastrichtian type area, northeast Belgium) is characterized by the gradual evolution from no flint bands at its base to the regular presence of well-developed flint bands at its top. Here, the Hallembaye section is investigated to gain more insights into the underlying processes behind flint inception. A relationship is found between the amount of detrital material (i.e., clays) present in the chalk and flints, and the extent of silicification and flint development. Several astronomical cycles are identified within the succession using both a lithology-based flint proxy and high-resolution μXRF-based element data from chalk samples. A combined imprint of precession and obliquity is documented in the chalk Ti/Al profile. The flint bands display a predominant obliquity imprint with an increasing contribution of precession and eccentricity up-section. Two consistent stratigraphically integrated astronomical age models are preferred. The first model is a floating age model that is based on the minimal tuning of the short obliquity cycle in the Ti/Al signal. The second model is a numerical age model that is based on flint occurrences, tuned to a combined tuning target consisting of both the inclination and long eccentricity metronomes. Temporal variations in the hydrological cycle and consequent changes in eolian, fluvial and dissolved Si input to the European Basin appear astronomically controlled. In addition, flint nodules and bands are paced by Milankovitch timescales, reflecting astronomical control on the Si cycle and paleoenvironmental conditions governing conditions favorable towards flint formation.