Publication: Paleoecological and paleoenvironmental changes during the continental Middle–Late
Permian transition at the SE Iberian Ranges, Spain
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Publication Date
2012
Authors
Horra del Barco, Raúl de la
Galán Abellán, Ana Belén
López Gómez, José
Sheldon, N.D.
Luque del Villar, Francisco Javier
Arche, Alfredo
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Elsevier, B.V.
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Abstract
The Middle and Late Permian are characterized by a pair of mass-extinction events that are recorded in both
marine and continental environments. Here, we present the first continental western peri-Tethyan record of
an extinction event located in the Middle–Late interval. In the SE Iberian Ranges, Central Spain, the transition
between the Lower and Middle subunits of the Middle Permian Alcotas Formation indicates a significant paleoclimatic
change from arid and semiarid conditions towards more humid conditions. Coincident with the
onset of humid conditions there were changes in the sedimentology, mineralogy, and geochemistry that indicate
significant environmental changes including a shift in weathering intensity and a change of fluvial
style from braided to meandering systems. Near the top of the Middle Subunit, a local biotic crisis is recorded
by palynomorph assemblages. Following this crisis, there is a total absence of coal beds, plant remains, and
microflora that defines a barren zone in the uppermost part of the Alcotas Formation which is recorded
throughout the basin. The barren zone is accompanied by a shift back to braided stream systems, but not
by a return to carbonate-bearing paleosols indicative of arid or semi-arid conditions. This combination of features
is consistent with other Middle–Late continental basins related with mass extinctions, so the barren
zone is interpreted as the extinction interval. The regional character of the extinction interval and its proximity
with the Middle–Late Permian transition could be related with the global mid-Capitanian biotic turnover
described in this period of time in other marine basins. However, the common difficulties of dating with precision
non-marine rocks make this relationship difficult to probe in the Iberian Basin and in other Middle–
Late Permian basins. Further work, including high resolution carbon-isotope analyses and complete studies
of the magnetostratigraphy, should be desirable in order to obtain a better age constraint and to produce
reliable comparisons with marine sections.