	Authors	Year	Title
	Becker	1988	Ammonoids from the Devonian-Carboniferous Boundary in the Hasselbach Valley (Northern Rhenish Slate Mountains). Courier Forschungsinstitut Senckenberg, 100: 193-213, fig.1-6, pl.1-2; Frankfurt a.M.
	Becker	1996	New faunal records and holostratigraphic correlation of the Hasselbachtal D/C-Boundary Auxiliary Stratotype (Germany). Annales Société géologique de Belgique 117 (1994): 19-45, 5 fig., 3 tabl., 3 pls., Bruxelles.