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Unconformity bounded paleofloras in the Carboniferous-Permian transition at the Henarejos Basin, SE Iberian Ranges (Spain)

AuthorsHorra, Raúl de la ; Borruel, Violeta ; Insua Arévalo, Miguel; López-Gómez, José ; Barrenechea, J. F.
Issue Date10-Oct-2017
Citation33rd International Meeting of Sedimentology (2017)
16ème Congrès Français de Sédimentologie (2017)
AbstractThe precise definition of the Carboniferous-Permian boundary based on paleoflora in Western Europe is still controversial. The kind of flora in the continental basins is influenced by its paleolatitudinal location, but it is also climatically controlled and, therefore, its biostratigraphic range is not accurate. As an example, in the Autun Basin, South France, a vertical alternation between grey strata with Stephanian B-C (Carboniferous) macrofloras and red rocks with Autunian (Permian) macrofloras has been described. The coeval existence of late Carboniferous and early Permian floras was explained as an alternation of hygrophyte and xerophyte associations, which were climatically controlled. In the SE Iberian Ranges, the Minas de Henarejos anticline is a key location to analyze the Carboniferous-Permian transition and its relation with the end of the Variscan compressive deformation and the onset of Mesozoic extension. Recent coal mining works have exposed high quality outcrops, which allowed a new detailed stratigraphic study, with a thorough identification of unconformities, and the characterization of the tectonic activity affecting the region. The outcroping stratigraphic formations begin with Silurian quartzites and shales. Unconformably, there is a Stephanian B-C grey succession of siltstones, sandstones, conglomerates, breccias, and coal levels, here described as the Minas unit. A new unconformity separates those facies from the overlying unit, composed by white conglomerates with undifferentiated macroflora remains. Another clear unconformity separates the white conglomerates unit from a thick succession of red conglomerates and fluviatile rocks of middle-late Permian age. The uppermost formations are constituted by Triassic rocks in the classic germanic facies. All those formations draw a regional NNW-SSE anticline structure related to the Alpine orogeny with the Silurian in the core and the Triassic in the limbs. Nevertheless, the Paleozoic outcropping formations are affected by compressional and extensional structures resulting from a complex interaction between different Variscan and Alpine phases of deformation. The Stephanian B-C Minas unit is affected by WNWESE thrusts, reverse faults and folds. These compressional structures do not cross the white conglomerate unit. Moreover, the deposition of the Permian alluvial units was controlled by a N120° extensional tectonic regime, as demonstrated by the presence of syn-sedimentary accommodation faults. These faults are even affecting the previous compressive structures. Although the Autun Basin shows a coexistence of hygrophyte and xerophyte floras in the Carboniferous Permian transition, this does not happen in the SE Iberian Ranges, as each paleoflora is separated by unconformities and different tectonic settings. Moreover, when the Minas unit occurs over any of the conglomerate units, this is due to the reverse faults and thrusts of the Alpine compressional phase. New paleontological or other kind of evidences should be required in order to solve the uncertainties of the Carboniferous-Permian Boundary in Western Europe, but the combination of new stratigraphic and tectonic detailed studies in other basins could be an important tool to do so.
DescriptionTrabajo presentado en el 33rd International Meeting of Sedimentology y 16ème Congrès Français de Sédimentologie (2017), celebrado en Toulouse (Francia), del 10 al 12 de octubre de 2017
Appears in Collections:(IGEO) Comunicaciones congresos
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