Publication: Sedimentary evolution of the continental Early–Middle Triassic Cañizar Formation
(Central Spain): Implications for life recovery after the Permian–Triassic crisis
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Publication Date
2012
Authors
López Gómez, José
Galán Abellán, Ana Belén
Horra del Barco, Raúl de la
Arche, Alfredo
Bourquin, Sylvie
Marzo Carpio, Mariano
Durand, Marc
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Elsevier
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Abstract
The Permian–Triassic transition (P–T) was marked by important geochemical perturbations and the largest
known life crisis. Consequences of this event, as oxygen-depleted conditions and the unusual behavior of
the carbon cycle, were prolonged during the Early Triassic interval delaying the recovery of life in both terrestrial
and marine ecosystems. Studies on Lower Triassic sediments of continental origin, as in the case of
Western Europe, are especially problematic due to the scarcity of fossils and absence of precise dating. The
Cañizar Fm. is an Early–Middle Triassic unit of continental origin of the SE Iberian Ranges, E Spain. A detailed
sedimentary study of this unit allows a shedding of light on some unresolved problems of the continental deposits
of this age.
The top of this unit is dated as early Anisian by means of a pollen association, while the age of its base is here
estimated as late Smithian or Smithian–Spathian transition. Different facies associations and architectural elements
have been defined in this unit. In the western and central parts of the basin, this unit shows sedimentary
characteristics of fluvial deposits with locally intercalated aeolian sediments, while in the eastern part
there is an alternation of both aeolian and fluvial deposits. Sedimentary structures also indicate changes in
the climate conditions, mainly from arid to semiarid. Two marked arid periods when well-preserved aeolian
sediments developed during early–middle Spathian and Spathian–Anisian transition. They alternated with
two semiarid but more humid periods during the late Spathian and early Anisian. These conditions basically
correspond with the general arid and very arid conditions described for central–western European plate during
the same period of time. The Ateca–Montalbán High, in the northern border of the study basin, must have
represented an important topographic barrier in the western Tethys separating aeolian dominated areas to
the N and NE from fluvial dominated areas to the south.
The Cañizar Fm. has been subdivided into six members (A–F) separated by seven (1–7) major bounding
surfaces (MBS). These surfaces are well recognized laterally over hundred of km and they represent
104–105 My. MBS-5 is considered to be of late Spathian age and it is a clear indication of tectonic activity,
represented by a mild unconformity. This event represents a change in the sedimentary characteristics
(reactivation) of the unit and from here to the top of the unit are found the first signals of biotic recovery,
represented by tetrapod footprints, plants, roots and bioturbation. All of these characteristics and the estimated
age represented by the MBS-5 event permit this surface to be related to the coeval Hardegsen unconformity
of Central–Western Europe. These first signals of biotic recovery can thus be related to an
increased oxygen supply due to the new created paleogeographical corridors in the context of this tectonic
activity. These biotic signals occurred 5 My after the Permian–Triassic limit crisis; a similar delay as occurred
in other coeval and neighboring basins.