Alfredo Arche

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.

Chapter 31 - Permian and Triassic rift basins of the Iberian Peninsula

Abstract The Iberian Peninsula is a good example of late Hercynian structures that influenced Mesozoic sedimentation. Complex graben systems, evolving along the fracture systems during late Hercynian movements were filled by hundreds of meters of red beds during the Permian and Triassic, the final stages of Hercynian movements were accompanied by several magmatic events. This paper deals with some well studied areas of the Iberian Peninsula (Cantabrian Mountains, Pyrenees, Catalo-nian ranges, Central System margins, Iberian ranges and southern margin of the Iberian massif) where basin evolution and tectonic activity are clearly related. A model for the evolution of the Iberian ranges is proposed based in Alvaro et al. (1979) with three distinct periods: (1) a compressive regime related to late Hercynian movements and the formation of Pangea, which occurred from the Late Carboniferous to Early Permian (Autunian); (2) a less-well-defined period when Saxonian facies were deposited; and (3) a distensive regime resulting in rift-basin development and Buntsandstein sedimentation, followed by marine sediments as the Tethys Sea encroached on the margins of the Iberian massif. This third period lasted from the Late Permian (Thuringian) to, at least, the Early Jurassic.

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.

Subantarctic macrotidal flats, cheniers and beaches in San Sebastian Bay, Tierra Del Fuego, Argentina

Abstract San Sebastian Bay is a large, semicircular coastal embayment situated on the Atlantic coast of Tierra del Fuego, Argentina. It is a high-energy, subantarctic environment with a tidal range of 10.4 m, influenced by large waves of Atlantic and local origin and swept by constant, strong westerly winds. A 17 km long gravel spit protects the Northern part of the Bay giving rise to a gradient in sedimentary processes. From south to north, are seven distinct sedimentary environments. Coastal sedimentation started at least 5200 years before present (BP) and a rapid progradation related to a relative sea-level drop has infilled about 6 kilometres of the Bay with a sedimentary sequence 10–11 m thick. 14-C dating of unabraded shells in the Chenier ridges of the relict part of the complex allows for a precise reconstruction of the stages of the progradation, that has slowed from 2.35 m/year at 5000 years BP to 0.6 m/year at present. The possible causes of the sea-level drop are discussed.

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.

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.

Some considerations on the initiation of the present SE Ebro river drainage system: post- or pre-Messinian?

The timing and process leading to the opening of the continental Ebro Basin to the Mediterranean is a fundamental issue in the creation of the present-day drainage network of NE Iberia, yet there is no general consensus. The opening has been dated by different authors as middle Miocene to early Pliocene whilst river piracy or lake overspilling have been invoked as the geomorphic processes. Using a multiple approach to constrain the time and plausible process leading to this event, that include estimates of the age and volume of the correlative marine sediments, paleoaltitudinal reconstructions, estimates of the maximum lake level in the interior Ebro basin and rates of fluvial incision in basement rocks; it is concluded that the Ebro basin was tapped by a steep, mountain river on the E flank of the Catalan Coastal Ranges in pre-Messinian times, probably in the middle-late Tortonian. [RESUMEN] El momento de la apertura de la Cuenca del Ebro hacia el Mediterraneo y el proceso que la indujo representan aspectos clave en el desarrollo de la red de drenaje actual del NE de Iberia, aunque todavia no existe un consenso generalizado sobre los mismos. El momento de la apertura ha sido datado por diferentes autores desde el Mioceno medio al Plioceno inferior, mientras que una captura fluvial o el derrame del lago interior han sido propuestos como procesos geomorficos generadores. En este articulo hemos usado una tecnica multiple para precisar el momento y el proceso mas verosimil que condujo a la apertura, que incluye estimacion de la edad y el volumen de los sedimentos marinos correlativos al evento, reconstruccion paleoaltitudinal de las Cadenas Costero-Catalanas en dicho momento, estimacion del nivel maximo del lago interior de la Cuenca del Ebro en dicho momento y la tasa aproximada de incision del paleo-Ebro durante su periodo inicial en el basamento. Nuestra conclusion es que la Cuenca continental lacustre del Ebro fue capturada por un rio corto y de elevada pendiente de la ladera Este de las Cadenas Costero-Catalanas antes del Messiniense, probablemente en el Tortoniense medio-superior