Juan J. Villalaín

Age and Date for Early Arrival of the Acheulian in Europe (Barranc de la Boella, la Canonja, Spain)

The first arrivals of hominin populations into Eurasia during the Early Pleistocene are currently considered to have occurred as short and poorly dated biological dispersions. Questions as to the tempo and mode of these early prehistoric settlements have given rise to debates concerning the taxonomic significance of the lithic assemblages, as trace fossils, and the geographical distribution of the technological traditions found in the Lower Palaeolithic record. Here, we report on the Barranc de la Boella site which has yielded a lithic assemblage dating to ∼1 million years ago that includes large cutting tools (LCT). We argue that distinct technological traditions coexisted in the Iberian archaeological repertoires of the late Early Pleistocene age in a similar way to the earliest sub-Saharan African artefact assemblages. These differences between stone tool assemblages may be attributed to the different chronologies of hominin dispersal events. The archaeological record of Barranc de la Boella completes the geographical distribution of LCT assemblages across southern Eurasia during the EMPT (Early-Middle Pleistocene Transition, circa 942 to 641 kyr). Up to now, chronology of the earliest European LCT assemblages is based on the abundant Palaeolithic record found in terrace river sequences which have been dated to the end of the EMPT and later. However, the findings at Barranc de la Boella suggest that early LCT lithic assemblages appeared in the SW of Europe during earlier hominin dispersal episodes before the definitive colonization of temperate Eurasia took place.

Characterizing the Mesozoic extension direction in the northern Iberian plate margin by anisotropy of magnetic susceptibility (AMS)

We present the results of anisotropy of magnetic susceptibility (AMS) analyses carried out on weakly deformed Triassic red beds, Jurassic and Lower Cretaceous limestones, sandstones and shales from several northern Iberian Mesozoic basins located near the northern Iberian plate margin (Santander, Cabuérniga and Polientes basins in the western part of the Basque–Cantabrian basin, and Bilbao and Aralar basins in the central–eastern part; Cameros basin in the northernmost part of the Iberian chain). A well-defined magnetic lineation of tectonic origin is found at most of the sampled sites, and is interpreted as the stretching direction resulting from the extensional deformation characterizing this period. During the Mesozoic, the northern margin of the Iberian plate underwent two rifting stages, the Triassic and Late Jurassic–Early Cretaceous (Kimmeridgian–Albian) rifting events. Both the Triassic and the period of the Late Jurassic–Early Cretaceous rifting event with maximum subsidence rates (i.e. until the Barremian) are characterized by a NE–SW extensional direction in the main subsidence areas. This indicates that NW–SE master faults controlled basin subsidence and sedimentation through these periods in the northern Iberia plate margin basins. Conversely, during Jurassic and Aptian times a lower activity of NW–SE faults, together with more important extension along a NW–SE direction can be inferred from AMS analysis. This study indicates the power of AMS analysis in basin analysis and geodynamic reconstructions even in subsequently inverted basins.

Widespread Cretaceous inversion event in northern Spain: evidence from subsurface and palaeomagnetic data

Abstract: In this paper we present geological evidence of a mid-Cretaceous inversion event in the Polientes basin (northern Iberian plate) based on geological data. Analysis of seismic profiles across the basin indicates that this tectonic event resulted in the uplift of the basin depocentre and the formation of an upright gentle anticline before Cenomanian times. The presence of a pre-Alpine, syntectonic remagnetization in the Jurassic and Lower Cretaceous rocks of the Polientes basin allows us to define the geometry of the basin at the time between this early inversion event and the main Alpine compressional period. The early inversion in the Polientes basin is consistent with a transpressional tectonic setting, contemporaneous with the left-lateral strike-slip movement of Iberia with respect to Europe. This study shows the successful use of two approaches to unravel the geodynamic scenario of the northern Iberian plate during the Cretaceous, which was later obliterated during the Tertiary Pyrenean orogeny.

The Neogene remagnetization in the western Betics: a brief comment on the reliability of palaeomagnetic directions

Abstract Recent palaeomagnetic investigations in the western Subbetics have shown the existence of a widespread pervasive magnetic overprint of Neogene age in Upper Jurassic rocks. This remagnetization is coeval with the folding deformation in the area. We describe three examples in which the fold test result indicates that the remagnetization is pre-folding, post-folding and synfolding. An evaluation of the consequences of an incorrect interpretation of the remagnetization is presented. Heterogeneous rotational patterns can be explained as a consequence of incorrect evaluation of the timing between folding and overprint acquisition.

Widespread Cretaceous secondary magnetization in the High Atlas (Morocco). A common origin for the Cretaceous remagnetizations in the western Tethys

In this paper, we present the first palaeomagnetic data (51 sites) for Mesozoic (Lower–Middle Jurassic) sediments of the Moroccan Central High Atlas and address the study of a widespread remagnetization. The remagnetization is characterized by a very stable component with systematic normal polarity, carried by magnetite. The relationship between the magnetic properties and location within the basin suggests that the acquisition of the remagnetization is controlled by basin geometry. Fold-tests indicate that the overprint acquisition is syn-folding in some structures but clearly predates the Tertiary compressional stage. Using the small circle intersection method we have calculated the remagnetization direction (D = 336.4°, I = 29.2°). Comparison with the global apparent polar wander path indicates that the remagnetization was acquired during the Late Cretaceous (probably Cenomanian). Considering both the basinal confinement of remagnetization and the connection with other remagnetization events in the western Tethys, we propose a scenario explaining widespread remagnetizations in the region, concerning both basin-scale conditions mainly related to sediment thickness and a regional-scale thermal event acting as catalyst of remagnetizations in those sedimentary basins that satisfy the basin-scale conditions.

Reconstruction of inverted sedimentary basins from syn-tectonic remagnetizations. A methodological proposal

Abstract Syn-tectonic remagnetizations related to burial processes that occurred during their extensional stage are frequently recognized in inverted sedimentary basins. The incremental fold test is the main analytical tool used to detect these syn-tectonic remagnetizations. However this test gives spurious results when asymmetrical folding occurs (i.e. both limbs were not tilted simultaneously at the same rate). Asymmetrical folding is very common in sedimentary basins, especially at their margins, during the basinal stage and subsequent tectonic inversion. To correctly analyse syn-tectonic remagnetizations in these scenarios, we propose a method to restore palaeomagnetic vectors, which allows determining the tilting of beds at the remagnetization stage and therefore gives some hints on the geometry of sedimentary basins and/or folds at the overprint acquisition time. In this paper we consider the analysis of syn-tectonic remagnetization directions for basin reconstruction in two end-member basin models (i.e. syncline vs roll-over geometry). Finally, we compare the results obtained with several northern Iberian examples (Cameros basin in the Iberian Chain, Cabuérniga and Polientes Basin in the Pyrenées), formed during the Mesozoic as extensional basins and subsequently inverted during the Cenozoic compression. From these examples we propose generalizations for the application of syn-tectonic remagnetizations to constrain the geometry of sedimentary basins.

Interpretation of gravimetric and magnetic anomalies in the Cameros Basin (North Spain): combination of deep and shallow sources

Outstanding potential field anomalies (gravimetric and magnetic) in the Cameros Basin (N Spain) follow a WNW-ESE trend, parallel to the geological structures resulting from Mesozoic extension and Tertiary basin inversion. The positive Bouguer gravity anomaly (15 mGal) is interpreted as the result of a strong contrast between the density of Tertiary rocks of the foreland basin and the Paleozoic and Mesozoic rocks, combined with crustal thickening in the Iberian Chain with respect to the Ebro Basin. The dipolar magnetic anomaly, slightly shifted to the south with respect to the relative maximum of the Bouguer anomaly, can be interpreted as related to volcanic rocks within the basement, which are linked to Triassic rifting as witnessed by outcrops of basalts along the basin margins. An exhaustive analysis of rock properties (density, magnetic susceptibility and remanence) and basin geometry from other sources (seismic reflection profiles) allow to constrain variations in crustal thickness and the location of large-scale basement faults.

pySCu: a new python code for analyzing remagnetizations directions by means of Small Circle utilities

Abstract The Small Circle (SC) methods are founded upon two main starting hypotheses: (i) the analyzed sites were remagnetized contemporarily, acquiring the same paleomagnetic direction. (ii) The deviation of the acquired paleomagnetic signal from its original direction is only due to tilting around the bedding strike and therefore the remagnetization direction must be located on a small circle (SC) whose axis is the strike of bedding and contains the in situ paleomagnetic direction. Therefore, if we analyze several sites (with different bedding strikes) their SCs will intersect in the remagnetization direction. The SC methods have two applications: (1) the Small Circle Intersection (SCI) method is capable of providing adequate approximations to the expected paleomagnetic direction when dealing with synfolding remagnetizations. By comparing the SCI direction with that predicted from an apparent polar wander path, the (re)magnetization can be dated. (2) Once the remagnetization direction is known, the attitude of the beds (at each site) can be restored to the moment of the acquisition of the remagnetization, showing a palinspastic reconstructuion of the structure. Some caveats are necessary under more complex tectonic scenarios, in which SC-based methods can lead to erroneous interpretations. However, the graphical output of the methods tries to avoid ‘black-box’ effects and can minimize misleading interpretations or even help, for example, to identify local or regional vertical axis rotations. In any case, the methods must be used with caution and always considering the knowledge of the tectonic frame. In this paper, some utilities for SCs analysis are automatized by means of a new Python code and a new technique for defining the uncertainty of the solution is proposed. With pySCu the SCs methods can be easily and quickly applied, obtaining firstly a set of text files containing all calculated information and subsequently generating a graphical output on the fly.

Palaeomagnetic and AMS study of the Tarfaya coastal basin, Morocco: an early Turonian palaeopole for the African plate

Abstract An early Turonian (c. 93 Ma) anoxic, cyclic marine deposition is registered in the unfolded outcrops from the Tarfaya coastal basin, where very high sedimentation rates enable the investigation of past geomagnetic field record at high temporal resolution. One hundred and fourteen samples have been sampled along a 10.5 m vertical profile (c. 200–500 ka) of orbital-scale forced sedimentation. Rock magnetic investigations reveal mineralogy principally controlled by diamagnetic and paramagnetic behaviour, along with very low concentrations of low-coercivity ferromagnetic material which is probably magnetite. A well-defined magnetic fabric can be seen with the minimum susceptibility axis perpendicular to the foliation plane, and magnetic lineation compatible with NW African palaeostress since sedimentation times and/or the palaeocurrent associated with upwelling system deposition. Magnetic signature has the potential for performing reliability checks of reversed tiny wiggles, which were found in four samples not considered for the tectonic analysis. Alternating field demagnetization shows a single, stable, low-coercivity directional component. The new palaeopole (N=88; PLat=64.3°, PLon=256.3°, A95=2.5°; K=38.7), obtained after moderate (f=0.8) inclination flattening correction, is the first early Turonian palaeopole for the NW African Craton. It can contribute to the 90 Ma-centred sliding window of the different proposed synthetic Apparent Polar Wander Paths.

Integration of surface and subsurface data, paleomagnetism and analogue modelling to reconstruct the extensional geometry of the Cameros basin (N Spain)

Los braquiopodos retzidinos son una fraccion menor de las faunas devonicas de la CordilleraCantabrica (Norte de Espana). Aparte de un par de formas raras, impublicadas, del Praguiense delDominio Palentino y del Emsiense inferior del Astur-Leones, proximas al genero Rhynchospirina, ellinaje alcanzo su maximo de diversidad en la parte superior del Emsiense, con dos especies del generoRetzia, R. adrieni y R. cf. prominula, Cooperispira subferita y, quizas, una forma impublicada dePlectospira. El grupo no es conocido en el resto del Devonico y reaparece en el Pensilvaniense con algunasformas del genero Hustedia. En este trabajo se propone un nuevo taxon de la Familia Retziidae,Argovejia n.gen., de la parte final del Emsiense superior de Asturias y Leon, constituido por su especietipo,A. talenti n.sp. y, quizas, por las formas del Emsiense superior del Macizo Armoricano (Francia)Retzia haidingeri var. armoricana y Retzia haidingeri var. dichotoma.The Ronda Depression is filled by Neogene sediments on the boundary between Subbeticreliefs, with NE-SW structural trends, and the frontal Subbetic Chaotic Complexes. The folding stylein the Subbetic Units of Western Betics is strongly controlled by the rheology of the rocks: thick andmassive beds of Jurassic limestones over Triassic marls and gypsum with plastic behaviour. Main deformationstructures in the sedimentary infill of the Ronda depression are simultaneous box folds withNNE-SSW and WNW-ESE trends that only affect its southwestern part. This distribution of folds isa consequence of the inherited fold trend that affected the basement during Early Burdigalian age.