José López-Gómez

ORIGIN OF THE PERMIAN-TRIASSIC IBERIAN BASIN, CENTRAL-EASTERN SPAIN

Abstract The Iberian Basin was an intracratonic rift basin in central-eastern Spain developed since Early Permian times. The basin boundary faults were normal, listric faults controlling an asymmetric extension propagating northeast with time. Hercynian or older lineaments controlled the orientation of the Iberian Basin and extension was accommodated basically in the hanging wall block by the formation of secondary grabens and a central high. The basin was related with the coeval Ebro, Catalan and Cuenca-Mancha Basins and their connections are discussed. Subsidence curves show that the Early Permian-Early Jurassic period of extension can be subdivided into three rifting episodes and a flexural one. Extension factor increases from 1.17 in the northwest to 1.29 near the Mediterranean coast. The increasing extension rate was accommodated by transfer faults trending NNE-SSW, more important in the Levante area. The rift evolution is intermittent and seems to reflect distinct stress fields. The collapse of the late Hercynian orogen and related increased heat flux, extension and rifting is the most probable origin of the Iberian Basin and related basins. The origin of the Catalan and the Valencia-Prebetic Basins is related to the southwards migration of the Hesse-Burgundy Rift along the eastern margin of the Iberian Microplate.

Post-Variscan (end Carboniferous-Early Permian) basin evolution in Western and Central Europe

Abstract The Variscan orogeny, resulting from the collision of Laurussia with Gondwana to form the supercontinent of Pangaea, was followed by a period of crustal instability and re-equilibration throughout Western and Central Europe. An extensive and significant phase of Permo-Carboniferous magmatism led to the extrusion of thick volcanic successions across the region (e.g. NE German Basin, NW part of the Polish Basin, Oslo Rift, northern Spain). Coeval transtensional activity led to the formation of more than 70 rift basins across the region. The various basins differ in terms of their form and infill according to their position relative to the Variscan orogen (i.e. internide or externide location) and to the controls that acted on basin development (e.g. basement structure configuration). This paper provides an overview of a variety of basin types, to more fully explore the controls upon the tectonomagmatic-sedimentary evolution of these important basins.

Temporal and spatial variations in tectonic subsidence in the Iberian Basin (eastern Spain): inferences from automated forward modelling of high-resolution stratigraphy (Permian–Mesozoic)

By subsidence analysis on eighteen surface sections and 6 wells, which cover large part of the Iberian Basin (E Spain) and which are marked by high-resolution stratigraphy of the Permian, Triassic, Jurassic and Cretaceous, we quantify the complex Permian and Mesozoic tectonic subsidence history of the basin. Backstripping analysis of the available high resolution and high surface density of the database allows to quantify spatial and temporal patterns of tectonically driven subsidence to a much higher degree than previous studies. The sections and wells have also been forward modelled with a new ‘automated’ modelling technique, with unlimited number of stretching phases, in order to quantify variations in timing and magnitude of rifting. It is demonstrated that the tectonic subsidence history in the Iberian Basin is characterized by pulsating periods of stretching intermitted by periods of relative tectonic quiescence and thermal subsidence. The number of stretching phases appears to be much larger than found by earlier studies, showing a close match with stretching phases found in other parts of the Iberian Peninsula and allowing a clear correlation with discrete phases in the opening of the Tethys and Atlantic.

Pollen and spores from the Permian and Triassic sediments of the Southeastern Iberian ranges, Cueva de Hierro (Cuenca) to Chelva-Manzanera (Valencia-Teruel) region, Spain

Abstract Assemblages of 27 pollen and spores have been recovered and studied from Permian and Triassic sediments of the Southeastern Iberian Ranges. The different assemblages are of Thuringian, Anisian, Ladinian and Carnian ages and were recovered from different levels of the Buntsandstein, Muschelkak and Keuper facies. The time range and the biostratigraphic problems of some assemblages are discussed.

Sequence stratigraphic analysis and paleogeographic interpretation of the Buntsandstein and Muschelkalk facies (Permo-Triassic) in the SE Iberian Range, E Spain

Abstract The Iberian Ranges is an Alpine structure trending NW-SE in Central Spain. They first appeared as small, intracratonic basins in the Early Permian, and experienced different periods of extensional tectonics during the Mesozoic and Cenozoic controlled by ancient (Hercynian or older) fracture systems and at least two periods of compressive, inversion tectonics. The Permian and Triassic of the SE Iberian Ranges are of “Germanic Type”. Within the prevailing Buntsandstein and Muschelkalk facies, eight formations are recognized. Pollen and spore assemblages and some ammonoid horizons allow for age-assessments ranging from Thuringian (Late Permian) to Carnian (Late Triassic). Two phases of sedimentation can be distinguished during the early extensional period. The first phase (rift phase) led to the development of the lower Buntsandstein Facies, bounded by two angular unconformities and subdivided into two depositional sequences (DS-1 and DS-2); the lower one is dominated by alluvial fans deposited in half-grabens and the upper one by sandy braided rivers in more symmetrical grabens. The second phase (thermal or flexural subsidence phase) led to the deposition of the uppermost Buntsanstein (Rot) and Muschelkalk Facies, mostly shallow marine carbonates, subdivided into two depositional sequences (DS-3 and DS-4) with well developed lowstand, transgressive and highstand systems tracts (LST, TST and HST) intervals. The criteria for separating systems tracts and the interplay of tectonics, eustatism and rate of sedimentation are discussed. DS-3 and DS-4 broadly correspond to 2.1 and 2.2 third order cycles,but their limits are about 3–4 m.y. younger; this may be explained by local tectonic factors.

The siliciclastic Permian-Triassic deposits in Central and Northeastern Iberian Peninsula (Iberian, Ebro and Catalan Basins): a proposal for correlation

The siliciclastic deposits of the Iberian, Ebro and Catalan Basins have been described for more than a century, but facies similarities and a lack of biostratigaphic data have difficulted the correlation of the local stratigraphic units in a general framework up to now. Combining pollen and spores data, the identification of the regional unconformities and hiatuses and the quantitative analysis of the subsidence by backstripping methods, a new correlation scheme for these facies is proposed.

Evidence of precessional and eccentricity orbital cycles in a Tithonian source rock: The mid-outer carbonate ramp of the Vaca Muerta Formation, northern Neuquen Basin, Argentina

Basin to mid-ramp cyclic facies of the Tithonian Vaca Muerta Formation are exposed in the Loncoche Creek section of the Neuquen Basin, Mendoza province, Argentina. This unit is characterized by a decimeter-scale rhythmic alternation of marls, shales and limestones and extends from the lower Tithonian to the upper Berriasian. Cyclostratigraphic studies based on a detailed facies analysis allowed the identification of cyclic patterns with frequencies within the Milankovitch band. According to biostratigraphic data, the dominant cycle in the studied section has a period of 20 k.y., which correlates with the Earths axis precession element. Spectral analysis based on a series of compacted and decompacted cycle thickness identified a subordinate frequency of about 90 to 120 k.y., which we interpret as the modulation of the precessional cycle caused by the Earths orbital eccentricity. The strength of the precession signal, together with the absence of a well-defined cyclicity attributable to the obliquity orbital cycle (i.e., 40 k.y.), is in agreement with previous data from the Northern Hemisphere.

Palaeogeographical significance of clay mineral assemblages in the Permian and Triassic sediments of the SE Iberian Ranges, eastern Spain

The evolution of the palaeogeography of the SE Iberian Basin during the Permian and Triassic represents a general evolution from continental to marine environments. It has been recently studied from the sedimentological, stratigraphical, tectonic and palaeontological points of view. In spite of these results, many aspects of this palaeogeography are still a matter of discussion. In this study, clay mineralogy analysis complements previous studies representing a new aspect for understanding the evolution of the sedimentary environment and the palaeogeography of the Iberian Basin during the periods in question and thus of the palaeogeography and the location of the major high areas in the westernmost border of the Tethys sea. In spite of late diagenetic transformations the original clay mineral associations of the Permian-Triassic sediments of the SE Iberian Ranges can be reconstructed. Seventy-seven samples of siliciclastic and carbonate sediments of these ages have been studied (SEM and XRD), revealing six new aspects that help to precise the palaeogeographical interpretation of the area: (1) Two major mineral assemblages have been found: illite+ kaolinite +pyrophyllite in the continental facies and illite + chlorite + vermiculite + mixed-layer clays in the marine facies. (2) The Mg-rich clay minerals are here considered to be of marine origin. (3) Active phases of basin boundary faults are marked in the sediments by the presence of pyrophyllite, derived directly from the Palaeozoic metamorphic basement. (4) Unconformities separating major depositional sequences also separate formations with different clay mineralogy. (5) Different groups of clay minerals can be separated clearly coinciding with the different palaeogeographical stages also distinguished in the westernmost border of the Tethys sea. (6) The clay mineral associations back up the data of a previous hypothesis of a humid climate for the end of the Permian in the study area just prior to the first incursion of the Tethys sea.

The evolution of the Middle Triassic (Muschelkalk) carbonate ramp in the SE Iberian Ranges, eastern Spain: sequence stratigraphy, dolomitization processes and dynamic controls

Abstract The Upper Permian—Triassic strata of the SE Iberian Ranges, eastern Spain, display the classic Germanic-type facies of Buntsandstein, Muschelkalk and Keuper. The Muschelkalk is represented by two carbonate units with a siliciclastic-evaporitic unit in between. Their ages range from Anisian to basal Carnian (Middle Triassic to base of the Upper Triassic). The carbonate units represent ramps that evolved during the early thermal subsidence period which succeeded the first rift phase. Seven facies have been distinguished, representing shoals, tidal flats, organic buildups and lagoons, as well as a karst horizon in the lower carbonatic unit. Most of the carbonates were dolomitised. Three processes of dolomitization are invoked: mixing waters, penecontemporaneous seepage refluxion, and deep burial. The top of the Buntsandstein and the Muschelkalk facies are subdivided into two depositional sequences, including lowstand, transgressive and highstand systems tracts, with superimposed tectonic and eustatic controls.

New ichnites from the Middle Triassic of the Iberian Ranges (Spain): paleoenvironmental and paleogeographical implications

The Iberian Basin or its present-day expression, the Iberian Ranges, was refilled with red bed sediments of alluvial origin during the late Olenekian–Anisian period represented by the Cañizar (Olenekian–Anisian) and Eslida (Anisian) Formations, both commonly known as Buntsandstein facies. In the late part of the Anisian, the Tethys Sea reached the eastern side of the Iberian microplate, represented by the shallow marine facies of the Landete and Cañete Formations, also called Muschelkalk facies. The ichnites studied in this paper belong to the Anisian continental-marine transition in the SE Iberian Ranges. The Cañizar Formation shows the oldest Triassic footprints found in the Iberian Peninsula, consisting in swimming, uncomplete lacertoid three digit Rhynchosauroides traces with possibly resting (cubichnia) and furrowing (pascichnia) Cruziana/Rusophycus due to large triopsids. Specimens from Lacertoïd and Crocodiloïd groups have been collected in the Eslida Formation. Rhynchosauroides sp. is the most representative ichnospecies of the first group, while in the Crocodiloïd group, the presence of Chirotherium barthii Kaup 1835 and Isochirotherium cf coureli (Demathieu 1970) are distinctive. In the Landete Formation specimens are found from Crocodiloïd and Dinosauroïd groups. Brachychirotherium gallicum Willruth 1917, Brachychirotherium sp. and Chirotherium sp. are characteristic of the first one, and ‘Coelurosaurichnus’ perriauxi and cf Paratrisauropus latus as the most representative of the second group. Some of the specimens described here present ancestors in the Early Triassic and have been described in the Triassic of North America, Italy and France. Possible paleogeographical connections with faunas of SE France can be inferred. Based on different sedimentary structures and plant remains, the footprints are related to fluvial systems within huge flood plains, playa and shallow marine environments, with alternating dry and wet periods. The vertical ichnites distribution during the Anisian shows that the fauna modification was weak at a high clade level. In the Triassic of the Iberian microplate, there are no findings of traces prior to the Anisian, and the footprint content for the Middle Triassic is less diversified than in other neighbouring regions. By comparison with other western Pangea areas, there was a later appearance of the forms after the end-Permian mass extinction event in the studied area.