J. de Coninck, and J. Smit. 1982. “Marine Organic-Walled Microfossils at the Cretaceous Tertiary Boundary in the Barranco Del Gredero (S.E. Spain)”. Netherlands Journal of Geosciences, January, 173-78. https://njgjournal.nl/index.php/njg/article/view/13491.