The present study focuses on the diversity and paleovegetational significance of the floristic record of the Late Permian continental Alcotas Formation, in five sections of the southeastern Iberian Ranges, central Spain. This unit, of Upper Tatarian or Lower Lopingian (Upper Permian) age, can be subdivided into three parts, represented by sediments originating from sandy and gravely braided, high-sinuosity, and sandy-braided fluvial systems developed in wide floodplains, from bottom to top respectively. Five zones, referred to as A to D, have been differentiated after correlation of the four studied sections, based on sedimentary and stratigraphical criteria. The study of megaremains recovered from the levels placed within each zone indicates changes in both biodiversity and population density. The oldest assemblage comprises impressions of leafy shoots and caules of gymnosperms. The poor preservation of some megaremains hinders their classification. A significant increase in diversity and population density is evident in the next and younger association, which shows reproductive structures and remains of leaves, trunks, and indeterminate caules of sphenopsids, cordaitales, and conifers. The next assemblage is dominated by conifers. The specimens collected mainly correspond to silicified trunk fragments, highly carbonized. A total absence of fossilised plant and trunk remains is the main characteristic of the upper part of the Alcotas Fm. The occurrence of these fossil floras is significant, due to the paucity of the fossil record of megafloras of identical or similar geological age, which has made it difficult to acquire knowledge on the development of flora and vegetation in the Upper Permian of Europe. The evolution of the biodiversity of the megafloras allows us to infer paleoecological changes for a time interval close to the end-Guadalupian biotic crisis.
La présente étude est focalisée sur la diversité et la signification paléovégétale de l’enregistrement floristique du Permien terminal de la formation continentale Alcotas, dans quatre coupes de la chaîne Ibérique sud-orientale, en Espagne centrale. Cette unité, d’âge Tatarien supérieur à Lopingien inférieur (Permien supérieur), peut être divisée en trois parties, représentées par des sédiments issus de systèmes fluviatiles à bras multiples sableux et graveleux de grande sinuosité, et sableux développés dans de vastes plaines inondées, de la base vers le haut, respectivement. Cinq zones, dénommées de A à D, ont été différenciées après corrélation des données des quatre coupes étudiées, sur la base de critères sédimentaires et stratigraphiques. L’étude des mégarestes des niveaux localisés au sein de chaque zone indique des changements, à la fois dans la biodiversité et la diversité de population. Le plus ancien assemblage comporte des impressions de pousses de feuilles et de coiffes de gymnospermes. La mauvaise conservation de certains mégarestes empêche toute classification. Une augmentation significative de la diversité et de la densité de population est évidente dans l’association suivante, plus jeune, qui montre des structures de reproduction et de restes de feuilles, troncs et coiffes indéterminées de sphénopsides, cordaïtales et conifères. L’assemblage suivant est dominé par les conifères. Les échantillons récoltés correspondent principalement à des fragments de troncs silicifiés, très carbonisés. Une totale absence de restes fossiles de troncs et de végétaux caractérise la partie supérieure de la formation d’Alcotas. La présence de ces flores fossiles est importante, en raison de la pauvreté de l’enregistrement fossile de mégaflores d’âges géologiques identiques ou similaires. Cela a, pour une large part, rendu difficile l’acquisition de connaissances sur le développement de la flore et de la végétation au Permien supérieur en Europe. L’évolution de la biodiversité des mégaflores permet de rapporter les changements paléoécologiques à un intervalle de temps proche de la crise biotique de la fin du Guadalupien.
The end-Permian extinction is the largest of all times. An estimated 57% of all the families and 95% of all species of marine animals became extinct. Some recent researches suggest a relatively sudden, possible catastrophic event, perhaps of duration 50,000 years or less
The present study focuses on the diversity and palaeovegetational significance of the flora and microflora record of the Late Permian in the SE Iberian Ranges, central Spain (
The Late Permian sedimentary succession in the Iberian Ranges, southeastern Spain, shows a very interesting plant and palynostratigraphic record. This succession is represented in this area by the Boniches Conglomerates and the Alcotas Siltstones and Sandstones Formations, from base to top respectively. Different palynological assemblages found in these units indicate a Thuringian (Upper Permian) age
The Iberian Basin was an intracratonic basin during the Mesozoic and experienced several extensional periods during the Mesozoic and Cenozoic
As the rest of the Permian-Triassic basins in the Iberia microplate, the Iberian Basin started its development under an extensional tectonic regime, with several synrift–postrift phases that prolonged during almost 100 Myr, from the Early Permian to Late Triassic–Early Jurassic
Ordovician and Silurian slates and quartzites of very low-grade metamorphism forming kilometre-size structures with NW–SE trend represent the Hercynian basement of the Iberian Basin where the Early Permian sediments were deposited
The Iberian and the Ebro Basins were separated during the Permian and Early Triassic by a narrow and longitudinal Palaeozoic high, the so-called Ateca-Montalbán High. On the other hand, to the southwest, another ill-defined Palaeozoic high, the so-called Serranía de Cuenca High, separated the Iberian Basin from the Cuenca–Valencia Basin (
Small and isolated extensional basins were present in the Iberian Basin during the beginning of the Late Permian. Later on, a new subsidence regime allowed the connection between most of these small basins; during the Early Triassic, it had exceeded most of the highs that were separating them. During this mature phase, other different basins of the Iberian microplate, which was located close to the equatorial eastern part of Pangea
A closer look at the Permian sedimentary record in the SE Iberian Ranges reveals a much more complex facies and large thickness variations due to differential rates of extension during the synsedimentary extensional tectonics
The Alcotas Formation consists of red siltstones and sandstones, with minor presence of conglomerate lenses. In the study area, it lies apparently conformably on the Boniches Formation or unconformably on the Hercynian basement, and it is unconformably overlain by the Cañizar Formation, although other possible contacts also occur in neighbouring areas
Detailed studies on the petrological composition of the Alcotas Formation are found in López-Gómez
Five detailed sections have been used for the study of the plant assemblages of the Alcotas Formation in this work (
The Alcotas Formation can be subdivided into three different units, referred to as 1 to 3 from base to top, respectively
Unit 2 ranges from 45 to 55 m. It marks a clear change in lithofacies and fluvial style, where conglomerates disappear and sandstones represent almost 70% of the total lithology. They normally show single-storey sandstone bodies with tabular geometries and abundant lateral accretion surfaces littered by comminuted plant remains. Scarce large silicified trunks and wood fragments also appear at the base of some of the sandstone bodies
Unit 3 reaches 45 m in thickness. A new drastic change is noticed with respect to the previous unit. It now consists of red siltstones (about 85%), which contain lenticular pink sandstone bodies up to 25 m wide and 1.5 m thick. No carbonate palaeosoil or macro- or microflora has been found up to now in this unit. Fining-upwards sequences with planar cross-stratification at their base constitute most of the sandstone bodies. This unit is interpreted as the development of distal very low energy braided fluvial systems within extensive floodplains.
As described previously, detailed sedimentological analysis of the differentiated zones has been recently described by Arche and López-Gómez
Outcrops in zone A are scarce, and the number of megaremains per level is correlatively low. Specimens recovered from the fossiliferous levels of Talayuelas and Montan sections mainly correspond to cordaitalean (
The uppermost part of the Chelva section presents levels with tiny poorly preserved fragments of leaves.
A significant increase in diversity and population density is evident in this zone, which shows reproductive structures and remains of leaves, trunks, and indeterminate axes of sphenopsids (
The collected material includes leave remains and scales (
The palaeovegetation could be interpreted as a forest with an undercanopy of sphenopsids.
This zone shows a great decrease in the number of megaremains, and the scarce specimens collected mainly correspond to silicified conifer trunk fragments, some of them being highly carbonized.
In this zone, the number of fossiliferous levels and plant megaremains that correspond to silicified trunks and vegetative shoots of conifers (Majonicaceae) decreases (
The total absence of plant megaremains is the main characteristic of the upper part of the Alcotas Fm. (zone F).
In general terms, the evolution of palaeovegetation coincides with that obtained through palynological studies
The occurrence of fossil plant remains recovered from the Alcotas Formation is significant, due to the paucity of the fossil record of megafloras of identical or similar ages in western Europe, which has made it difficult to acquire knowledge on the development of flora and vegetation in the Upper Permian of Europe.
In general terms, and due to the dominance of coniferous remains, the vegetation fits in well with Alpine Permian floras, but we have observed significant changes in the biodiversity and population density within each outcrop and defined zone. The patterns of changes and vegetation dynamics are similar to those described after the study of the palynological assemblages of the Alcotas Formation. The observed changes with respect to zone A are an increase of the megaremain levels, of the biodiversity, and of the population density in zone B, followed by a general decrease of these features in zone C. A new increase happened in zone D, and a significant decrease occurred in zone E, ushering in the lack of plant remains noticed in zone F. This pattern allows us to infer paleoecological changes for a time interval close to the biotic crisis of the end-Guadalupian.
The authors want to thank Jean Broutin for helping us with his comments during the development of this paper. We also thank Modesto Escudero for preparing some of the photographs. Financial support for this paper was obtained from project CGL 2005-01520/BTE.
Present-day geographical location of the studied area with superimposed studied sections: (1) Landete (2) Talayuelas, (3) Chelva, (4) Montan.
Fig. 1. Localisation géographique actuelle de la zone étudiée avec superposition des coupes étudiées : (1) Landete (2) Talayuelas, (3) Chelva, (4) Montan.
Permian–Lower Triassic stratigraphic scheme of Iberia, western and central Europe, and southern Urals, with the assay of their possible unit equivalence accepted by the Sub-commission of Permian Stratigraphy. Based on López-Gómez et al., 2005
Fig. 2. Schéma stratigraphique au Permien et Trias inférieur de l’Espagne, de l’Europe centrale et occidentale et du Sud de l’Oural, avec essai d’équivalence possible des unités, acceptée par la sous-commission de stratigraphie du Permien. D’après
Studied stratigraphic sections and location of the fossil macroflora samples. See
Fig. 3. Coupes stratigraphiques étudiées et localisation des échantillons de macroflore fossile. Voir la
Distal part of a Cordaitalean axis. Scale bar: 1 cm.
Fig. 4. Partie distale de l’axe d’une cordaïtale. Barre d’échelle : 1 cm.
Fragments of medullar moulds of sphenopsids stems. Scale bar: 5 cm.
Fig. 5. Fragments de moules de moelle de tige d’une sphénopside.
Leaves and scales. Scale bar: 1 cm.
Fig. 6. Feuilles et écailles. Barre d’échelle : 1 cm.
Conifer axis and shoot. Scale bar: 5 cm.
Fig. 7. Axe et pousse de conifère. Barre d’échelle : 5 cm.