Some of the best outcrops of Iberia to study the
Ediacaran-Cambrian boundary are located in the Ossa-
Morena Zone. In the Crato-Campo Maior region (SW
Iberia, Portugal), this stratigraphic boundary is marked
by an angular unconformity (Gonçalves, 1971). The
Ediacaran sedimentary rocks of the Série Negra Group
(maximum depositional age of c. 545 Ma; Linnemann
et al., 2008) are overlain by Early Cambrian strata. A
folded foliation has been recognized in the Ediacaran
metagreywackes, metapelites, black metachert, marbles
and metabasic rocks (Pereira & Silva, 2002).
This deformation event is previous to the intrusion of
c. 526-525 Ma granitic rocks (Barquete and Barreiros
plutons; Pereira et al., 2011; Sánchez-García et al.,
2013), and is not represented in the unconformable
overlying Early Cambrian strata including sandstone
(maximum depositional age of c. 532 Ma; Pereira et al.,
2011). At the base of the lower Cambrian stratigraphic
section there is the Freixo-Segóvia volcanosedimentary
complex consisting of felsic tuff interbedded with
conglo-merate and rhyolitic-dacitic lava flow (Pereira
et al., 2006). The conglomerate is composed of pebbles
of volcanic rock (basalt, rhyolite, dacite and mafic and felsic tuff), granitic rocks, chert, quartzite, arkosic sandstone,
greywacke and shale in a tuffaceous sandy matrix.
This volcano-sedimentary complex is overlain by a
sequence of sandstone and shale passing vertically to
limestone beds which have been attributed to the lower
Cambrian (Pereira et al., 2006) (see Fig. 12). An ongoing
research project intends to date the volcanic rocks
of the volcano-sedimentary complex using U-Pb zircon
geochronology. The absolute dates determined from
these volcanic rocks will provide the time framework for the calibration of the existing stratigraphic scheme
based on regional correlation
