Calcareous dinocysts from the Geulhemmerberg KIT boundary section (Limburg, SE Netherlands)

Abstract

Calcareous dinoflagellate cyst (calcdinocyst) associations from the Cretaceous/Tertiary (K/T) boundary section of the Geulhemmerberg comprise 31 morphotypes in total. In addition, two incertae sedis organisms, morphologically related to the genus Bonetocardiella, occur. In the uppermost Maastrichtian and lowermost Danian, the quantitatively dominant calcdinocysts are Pithonelloideae, nearly exclusively Pithonella sphaerica, accompanied by up to 1.4% Bonetocardiella spp. In the uppermost Maastrichtian, Pithonella and Bonetocardiella make up the entire association. They are joined by Obliquipithonelloideae and Orthopithonelloideae in the lowermost Danian. Most calcdinocyst species (22 of the 31, species) appear to survive the IIT boundary event(s), while eight species first appear above the boundary. The distribution of the Obliquipithonelloideae and Orthopithonelloideae is related to the lithofacies. With up to 18 species, the diversity is highest in the clay layers, notably in the A, B, C and E clays. In these layers, the number of orthopithonelloids increases in comparison to the obliquipithonelloids. The cyclic diversity distribution of calcdinocyst morphotypes may possibly be attributed to sea-level changes, with maxima correlating to the diversity maxima as found in the A, B, C and E clays.