Jc. Gutierrezmarco et P. Storch, GRAPTOLITE BIOSTRATIGRAPHY OF THE LOWER SILURIAN (LLANDOVERY) SHELF DEPOSITS OF THE WESTERN IBERIAN CORDILLERA, SPAIN, Geological Magazine, 135(1), 1998, pp. 71-92
Eight Lower Silurian graptolite biozones (triangulatus, convolutus, li
nnaei, turriculatus, crispus, griestoniensis, tullbergi and spiralis)
and three subzones (runcinatus-gemmatus, palmeus and hispanicus) have
been recognized in the Sierra Menera, Nevera, and Tremedal massifs in
the Castilian Branch of the Iberian Cordillera (Western Iberian Cordil
lera). Early Silurian, Rhuddanian low-diversity normalograptid faunas
are also present and these, together with the rich graptolite faunas o
f the Aeronian triangulatus and convolutus biozones, come from black,
shaly intercalations within the quartzose sandstones of the upper part
of the Los Puertos Quartzite. Telychian graptolite biozones have been
recognized in the succeeding black-shale sequence of the Badenas Form
ation. Diachroneity of the transition from sandstones to black shales
is dated by graptolites. It ranges from about the base to at least the
top of the linnaei Biozone. We suggest that the Lower Silurian black
shales of the Western Iberian Cordillera were deposited in a shallow,
shelf environment, not much deeper than that of presumably storm-influ
enced sandstones of the Los Puertos Quartzite.