in Jurassic and Cretaceous Stratigraphy

Earth Science Frontiers, Vol. 17, Special Issue, Aug. 2010 ISSN 1005-2321
366
The Triassic of the Iberian Micro-Plate: The Early Mesozoic
Pre-Jurassic Tethys Hinge
A. Márquez-Aliaga
Geology Dpt. and ICBiBE, University of Valencia.E- 46100 Burjassot, Valencia, Spain (E-mail: Ana.Marquez@uv.es)
The Triassic represents the short (51.4 my) transi-
tion between the end of Palaeozoic life and the ascent
of Mesozoic life. It is important for me to point out
that in my opinion; this recovery is also the time when
the modern life on Earth began. It was a time when the
huge continent of Pangaea still existed, a land mass
that was altering global climate and ocean circulation.
During the Permian-Triassic transition, one of the most
important climatic and biological crises of Earth history
took place. As a result of extinctions, almost 95% of
marine species disappeared; amongst them whole
groups like trilobites and fusulinids. Others lost the
greater part of their representatives like the brachio-
pods. Goniatites were replaced by ceratites, tabulates
and rugosa by scleractinia. The benthonic fauna,
dominated in the Palaeozoic by brachiopods, sessile
crinoids, echinoderms and bryozoans, consists in the
Triassic mostly of bivalves. The Triassic is also a time
when the survivors of the P/T extinction event spread
and newly colonized the environments lost to low sea
levels. The most important floral and faunal renewal of
phanerozoic times occurred in a relatively short time.
Alberti (1864) was the first to formally describe
and name “Trias” the well-differentiated trilogy of
clastic, carbonatic and evaporitic formations that
followed the underlying Permian “Dias” of Zechstein
and Rothliegendes between the North Sea and the Alps.
At base, red conglomerates, sandstones and clays form
the “Buntsandstein”, followed by the characteristic
carbonate formations with marine fauna of the Mu-
schelkalk, while the upper unit is a series of evaporites,
clays, marls and sandstone, the Keuper. These facies-
units have no chronostratigraphic meaning. Similar
facies-units are present in the Triassic of Spain. After
painstaking investigations, these units were correlated
with the Alpine Triassic, where the Middle and Late
Triassic stages were defined and biostratigraphic zones
established using first ammonoids and later also
conodonts (Virgili, 2008).
During the Triassic, the Iberian micro-plate was
between two large landmasses: Laurasia to the north
and Gondwana to the south, as illustrated by Stampfli
et al. (2001). Simultaneously two processes that
directly affected the Iberian Peninsula began: the
complex evolution of the Tethys and the opening of
the Atlantic. Therefore, knowledge of the palaeon-
tology of the Iberian Peninsula, located on the western
end of Tethys, plays an important role in understanding
of Triassic-Jurassic palaeogeographic developments.
The palaeontology of the Triassic of Spain counts
a limited number of authors. This is due to the very
scarce fossil record and their bad preservation in
general that renders it is very difficult to reach any
taxonomic determination. Schmidt (1935) was first in
studying the marine fauna of the Muschelkalk of the
Central-Eastern area of Spain, comparing it with the
Muschelkalk of the Germanic Basin. To Virgili (1958),
we owe a first faunal synthesis (mainly of molluscs)
and most important, the unraveling of the stratigraphic
succession that with more than one carbonatic and
evaporitic units, and thus counting more than the
original trilogy, had in the early days been erroneously
interpreted as tectonic repetitions. Márquez-Aliaga
(1985) and Ros (2009) gave a modern revision of the
Triassic bivalves, Goy (1995) and Perez Valera (2005)
of the ammonoids. Hirsch (1966) found the first
conodonts, studied further by Budurov et al (1993) and
most recently Plasencia (2009). Márquez (1994) in-
vestigated foraminifera. All members of the Spanish
Working Group of the IGCP 506 have improved this
research line.
The first marine transgression is that of the
Spanish lower Muschelkalk facies (Márquez-Aliaga
and Martínez, 1996) that took place in Anisian times.
In the Iberian Ranges, the “Serra-Association” con-
tains the bivalves Hoernesia socialis, Myophoria
vulgaris, Unionites fassaensis, and Neoschizodus
laevigatus, forming an assemblage, similar to that of
the upper Muschelkalk facies of the German basin. In
the Catalonian Coastal Ranges, this Spanish lower
Muschelkalk facies yields the conodonts Paragon-
dolella bulgarica, P. hanbulogi, P. bifurcata, Neogon-
dolella constricta, N. cornuta, N. excentrica and N.
basisymmetrica. These represent the P. bulgarica and
N. constricta zones and indicate middle-upper
Pelsonian to upper Illyrian ages (Márquez-Aliaga et al.
2000), in good correlation with the Bulgarian assem-
blage of the Tethys.
The second marine transgression is that of the
Spanish upper Muschelkalk facies that took place in
Ladinian times. The bivalve assemblage have Tethyan
nektonic elements as Daonella and Bositra, the
bentonic and cosmopolitan “Enantiostreon” difforme,
Pseudocorbula gregaria, Bakevellia costata, and
numerically abundant “Spanish” Pseudoplacunopsis
teruelensis, P. flabellum, Gervillia joleaudi and Costa-
toria kiliani. The conodonts Pseudofurnishius
murcianus and Sephardiella mungoensis (Plasencia,