Spain has some of the
most extensive and fossiliferous Palaleozoic outcrops from Europe and
echinoderm faunas are important in terms of their systematics, palaeobiology
and palaeogeography. The field work will review some of the most remarkable
Palaeozoic localities from North Spain (Fig. 1)
and will be divided in two different but related geologic and geographic areas.
Figure 1.
DAYS 1 and 2
Iberian Chains
The Iberian Cordillera forms a NW-SE striking
intraplate fold belt, placed in NE Spain, and separates the Ebro Basin from the
Tajo and Duero basins. These basins are filled up by continental Cenozoic sediments.
Its highest mountains rarely rise more than 2000 m and it presents a more
simple structure than the neighbouring Alpinic Chains as the Pyrenees and the
Betic Cordillera. Its Hercynian basement, made out by Palaeozoic rocks and more
scarce Precambrian rocks, crops out in two main areas: the Iberian Chains in
the north, forming part of what is known as the Aragonian Branch of the
Cordillera, and the Hesperian Chains in the south, made up by several scattered
massifs in its Castilian Branch. A Neogene intramountain graben, the Calatayud-Teruel Basin, separates
the Eastern and Western Iberian Chains. The Western Iberian Chain is mainly
composed of Cambrian and Lower Ordovician strata, while the Eastern Iberian
Chains displays a much more complete succession, with rocks ranging in age from
the late Precambrian to the Permian.
During the field work we will visit outcrops in the East Iberian Chains
from the Cambrian up to the Devonian.
Figure 2.
Day 1. The Cambrian of
Purujosa
Purujosa is a very small village (Fig. 2) located in the North most part of the
East Iberian Chains. In this area Cambrian rocks are common, fossiliferous and
well exposed. Echinoderms are relatively common in some stratigraphic levels
from the Mansilla and Murero Formations (middle Cambrian). These two formations
were deposited in off shore conditions and echinoderms use to be preserved as
natural molds and rarely calcite skeletons. The main goal of this day will be
the visit and discussion of Cambrian echinoderm communities. We plan to spend
time sampling (Fig. 3) and looking at two
different communities, some having only low diversity of cinctans and
eocrinoids, and other representing one of the highest Cambrian worldwide
diversity, including several blastozoans groups (gogiids, lichenoidids,
eocystitids), cinctans, isorophid edrioasteroids and stylophorans
(cothurnocystids and ceratocystids) (Fig. 4).
Figura 3.
Figure 4.
Day 2.
Ordovician-Silurian-Devonian of Eastern Iberian Chains
In the surroundings of
Fombuena, Luesma and Santa Cruz de Nogueras villages, placed in the
south part of the Iberian Chains Palaeozoic rocks are well exposed and
echinoderms appear in different formations. The aim of the days will be a tour
visiting those localities. The upper Ordovician rocks (Fombuena Formation and
Cystoid limestone) contain two different assemblages deposited in different
environments, low vs high energy (Fig. 5).
Faunal contain include blastozoans (diploporids, rhombiferans, coronoids),
crinoids, asterozoans and solutes. The Silurian outcrops (Badenas Formation)
contain almost monospecific levels of the crinoid Dimerocrinites aragonensis (Fig. 6)
and rare ophiuroids that occur
transported in off shore environments. Finally we will visit the early
Devonian Santa Cruz Formation that has few crinoids.
Figure 5.
Figure 6.
DAYS 4 and 5
Cantabrian Zone
The
Cantabrian Zone outcrops in Asturias, León and Palencia provinces.
Geologically, it represents the most external belt of the Variscan Iberian
Massif in the northwestern Iberian Peninsula and it is mainly composed of
sedimentary rocks. In this Zone, the Palaeozoic sequence rests on a dominantly
Precambrian succession, cropping out in its western boundary but hardly exposed
within the Cantabrian Zone itself. According to the relationships with the
Variscan orogeny, the Palaeozoic succession is usually divided into a
pre-orogenic, and a syn- (and post-) orogenic sequence.
The
pre-orogenic sequence displays a wedge shape, thinning out towards the East,
from where the sediments derived. Stratigraphically, this sequence is
characterized by an incomplete, thin Cambrian-Ordovician sedimentary sequence,
a Siluro-Devonian succession of variable thickness and a well-developed marine
Carboniferous sequence. In a broad sense, it consists of an alternation of
marine carbonate and siliciclastic formations laid down in some shallow water
stable shelf environments. During the Devonian up to seven reefal episodes have
been recorded in this Zone.
The
syn-orogenic sequence comprises several clastic wedges of Upper Carboniferous
age, which represent the fillings of topographic depressions formed at the
front of the thrust sheets. These sediments were supplied from the growing
mountain chain that was being intensively eroded in more internal zones.
From a
tectonic point of view, the Cantabrian Zone is featured by the occurrence of a
thin-skinned deformation, represented by a large number of thrusts and folds
and by the lacking of metamorphism evidences.
Day 4. Cambrian-Ordovician-Devonian of south Cantabrian Zone (León
Province)
The fourth day, after one day travelling, we are visiting
different Palaeozoic outcrops with echinoderm fossils from the south part of
Cantabrian Zone, around the locality of Colle and the Luna Valley. Some of
these localities are equivalent in age to those visited in the Iberian Chains
but they have a significant different fauna due to different palaeocological and
palaeobiogeographic conditions. Cambrian outcrops will show us different
communities from soft (Oville Formation) and firm substrates (Láncara
Formation) (Fig. 7). Faunas will include
cinctans, stylophorans and eocrinoids; including the oldest holdfast attached
to firm grounds (Fig. 8). A short stop in
the upper Ordovician will allow us to visit one of the few outcrops from the
Cantabrian Zone yielding a diverse fauna of crinoids and blastozoans. Lastly we
will visit the classic locality of Colle; a Lower Devonian succession in the
Valporquero Formation yielding the oldest diversified blastoid (Fig. 9) fauna from the world. Crinoids in this
locality are also very abundant and well preserved.
Figure 8.
Figure 9.
Day 5. The Arnao Reef
(Asturias Province)
The Devonian Arnao Reef, laying in the clefs of the
North Cantabrian coast (Fig. 10), around the
area of the village of Castrillón is one of the most spectacular fossil
localities from Spain and every year students from different universities visit
the area. The Devonian rocks belong to the Aguión Formation and are equivalent
in age from those of Colle. The action of recent see waves and tides in this
area have eroded have eroded beautiful bed planes that preserve different
echinoderm holdfasts in situ (Fig. 11). The
aim of the day will be spending the day looking at different parts of the
outcrop and specially focus on different communities of pelmatozoans from hard
ground and soft substrates. Althrought crinoids (Fig.
12) and blastoids are the most abundant groups; there are also
subsidiary edrioasteroids and echinoids.
Figure 10.
Figure 11.
Figure 12.
