La Cerdanya Research Articles

Mapping the Late Miocene Pyrenean Forests of the La Cerdanya Basin, Spain

The Late Miocene palaeofloras of the La Cerdanya Basin represent a unique look into the Pyrenean Miocene forested areas of the Iberian Peninsula at a time when the European warm and humid climate was experiencing progressive cooling and aridification. Macrofossils (leaves, seeds, fruits and cones) and miospores from several outcrops revealed the composition and abundances of the different plant species present in the area during the Tortonian and early Messinian geological stages (ca. 11.1–5.7 Ma). These fossils were found in the sediment deposits of an ancient lake system situated in the southwestern part of the basin. Previous studies indicated the presence of highly diversified mixed mesophytic forests with broadleaved evergreen and deciduous trees and conifers. However, the spatial structure and distribution of these forest types remains unknown. In the present work, the biomization method was used to infer the different late Miocene vegetation types from the basin. The extent of these vegetation types was calculated using a methodology for mapping vegetation units from fossil and biome data. While previous attempts at mapping Miocene vegetation units had a broad geographical scale, the present work aimed to map the extent of the vegetation units at a small scale, recreating local and specific vegetation changes in an abrupt basin. Results showed similarly high scores between for four biome types, which represent the different types of vegetation that coexisted in the basin during the Tortonian and the early Messinian: warm-temperate evergreen broadleaf and mixed woodlands (WTEM biome), temperate deciduous forests (TEDE) and cool conifer forests (COMX and COEG). Their extent was depicted in two vegetation maps, which account for differences in palaeoaltitude and palaeoclimate. These forests occupied different vegetation belts, which shifted upwards and downwards with climatic variations and the progressive uplift of the Pyrenees during the late Miocene. Azonal riparian forests and wetland vegetation occupied the more humid areas in the centre of the basin. Nonetheless, dry conditions during the early Messinian and decrease in the lake area degraded the wetland environments, which were partially replaced by broadleaved evergreen mixed woodlands.

Neolithic livestock practices in high mountain areas: A multi-proxy study of pastoral enclosures of Molleres II (Eastern Pyrenees)

This paper presents the results of the archaeological and palaeoenvironmental investigation carried out at Molleres II site located at 2.425 m a.s.l. in the area of Puigpedrós-Malniu (Meranges, La Cerdanya, Eastern Pyrenees). A high-resolution multi-proxy research is proposed combining landscape archaeology, soil micromorphology, anthracology, biomolecular analysis, and radiocarbon dating. This work allowed us to characterize the site's functionality, providing new insight into the occupation dynamics of high mountain spaces starting from the Neolithic onwards. Based on this research Molleres II has been interpreted as a complex and wide open-air site built up by the end of the Middle Neolithic (3636–2701 cal. BC) and consisting of large enclosures entirely dedicated to seasonal animal husbandry and located at an exceptionally high altitude. These unique settings make the site a primer for this period and in the Eastern Pyrenees, revealing the considerable intensity of the animal presence since the Prehistory in these uplands.Following the Neolithic, a second phase of more intense occupation likely occurred during Middle Ages (1179–1434 cal. AD). However, the animal presence in this mountain sector had never been exhausted, even in other historical periods. Palaeoenvironmental data also suggest that such intense and long-term animal presence and possibly fire use could be at the origin of stable grassland-dominated environments and open landscapes maintained almost continuously until nowadays.

Destination management amid COVID-19: a case study in La Cerdanya, Spain

ABSTRACT This study, following the initial stage of the grounded theory development process, investigates how the COVID-19 influences the tourism practice and management in La Cerdanya, Spain. Empirical data were obtained from a field trip in October 2020 and were inductively analysed to provide pertinent insights. The results show that the current destination planning and management should focus on the local tourism market and destination image rather than seeking for one-size-fits-all solutions, and the existing challenges should be addressed by meeting future tourism trends and strengthening collaborations. Based on the high volume of the political and social-cultural complexities revealed in this study, the implications for ensuing research and practices are presented.

CLAMP-based palaeoclimatic analysis of the late Miocene (Tortonian) flora from La Cerdanya Basin of Catalonia, Spain, and an estimation of the palaeoaltitude of the eastern Pyrenees

We analyse the late Miocene (early Tortonian) climate of the La Cerdanya Basin (Catalonia, Spain) using the Climate Leaf Analysis Multivariate Program (CLAMP) based on an assemblage comprising twenty-nine dicot leaf taxa. Results show a mean annual temperature of 11.4 ± 2.1 °C. The coldest mean monthly temperature was 1.8 ± 3.4 °C while the warmest was 21.6 ± 2.5 °C. Growing season was 6.8 ± 1.1 months in duration. Precipitation during this period was 1082 ± 317 mm, reaching 661 ± 38 mm in the three wettest consecutive months, while in the three driest months it was 194 ± 229 mm. These results indicate a permanently humid temperate climate, with warm and wet summers. Compared with published palaeoclimatic results obtained using the Coexistence Approach method, our CLAMP analysis indicates lower temperatures and higher rainfall during the driest month. The climatic parameters are consistent with the occurrence of a temperate mixed evergreen and broadleaf deciduous fossil assemblage in the late Miocene of the La Cerdanya Basin. The assemblage contains more taxa in common with coeval localities from northern and central Europe than with Mediterranean sites; its closest modern analogue is with the montane flora from Honshu Island (Japan). Palaeoaltitudinal estimation using the terrestrial lapse rate method suggests that the La Cerdanya Basin was positioned at 1100–1550 m during early Tortonian times. These results challenge previous palynological and isotopic studies that inferred a palaeoaltitude of c. 600 m in early Tortonian-Messinian times.

Climate Emergency Adaptation and Sustainable Management Strategies in Rural and Agricultural Landscapes

This paper discusses the way in which climate emergency-related strategies and the concepts of climate adaptation, sustainability and governance are being introduced into rural and agricultural landscapes. To investigate environmental impacts on climate change, it uses examples from the ‘Landscape Observatory’ (Catalonia) and the ‘Room for the River’ (the Netherlands) landscape programmes. Noordwaard is the largest rural project of the Room for the River programme, dealing with agricultural land, farming and nature reserves at a strategic scale. It demonstrates the potential and significance of addressing the sea rising water levels by creating landscape climate adaptation projects by introducing the ideas of landscape, low carbon, ecosystem services and governance as vital aspects of rural infrastructure, which underpin the ways in which agricultural land and water are managed. The Landscape Observatory has had a significant impact on the development of landscape policies in Catalonia and has been influential in a global level. Focusing on Lluçanès and the establishment of a Landscape Charter protecting the agricultural land and examining the natural area of La Cerdanya in Pyrenees, the research extracts best practices in policy and legislation as well as participatory methods on climate and landscape awareness. This research concludes that a communication strategy strongly supported by policies, legislation and governance structures, in conjunction with a wider understanding of the role of landscape, results in significantly improved responses to deal with the challenges of the climate crisis in rural and agricultural areas.

Deciphering the Sardic (Ordovician) and Variscan deformations in the Eastern Pyrenees, SW Europe

Detailed geological mapping of the La Cerdanya area (Canigó unit, Eastern Pyrenees) provides new data characterizing the different structural styles exhibited by Cambrian–Lower Ordovician (Jujols Group) and Upper Ordovician successions. Their unconformable contact, related to the Sardic Phase, ranges from 0° (paraconformity) to 90° (angular discordance). The Jujols Group rocks topped by the unconformity are affected by Sardic foliation-free open folds. The pre-Sardic succession, the Sardic Unconformity and the lower part of the post-Sardic succession (Rabassa Conglomerate and Cava formations) are cut and offset by several Late Ordovician NNE–SSW-trending synsedimentary extensional faults associated with hydrothermal activity, which dramatically affected the thickness of the lower part of the Upper Ordovician succession. We relate (1) the Mid-Ordovician Sardic uplift and erosion, and (2) a Mid- to Late-Ordovician upward propagating extensional fault system bounding the outline of half-grabens, subsequently infilled by alluvial deposits, to a thermal doming event (about 475–450 Ma) that led to the uplift and stretching of the Ordovician lithosphere. Thermal doming may be caused by mafic magma underplating and responsible for the coeval calc-alkaline magmatic activity broadly developed in the Eastern Pyrenees. We discuss the similarities between the Mid-Ordovician Sardic Unconformity and other Early Paleozoic unconformities described in neighbouring areas. Finally, we suggest a geodynamic scenario in which a regional-scale thermal event was related to the opening of the Rheic Ocean that led to the drift of Avalonia from the SW European margin of Gondwana.

New palaeobotanical data from Carboniferous Culm deposits constrain the age of the Variscan deformation in the eastern Pyrenees

The pre-Variscan rocks of the Pyrenees exhibit a polyphase deformation linked to the Variscan crustal shortening and a low-pressure–high-temperature metamorphism. However, there is scarce chronostratigraphic evidence of this Variscan deformation. In the Pyrenean low-grade metamorphic domains, maximum ages have been provided by the synorogenic Carboniferous Culm deposits. In medium- to high-grade metamorphic areas, the Variscan regional metamorphism or intrusive magmatic bodies constrain the age of the main Variscan deformation structures. However, these data usually provide a minimum age. Here, we present new palaeobotanical records that assign a Namurian age to the base of the Culm deposits of la Cerdanya in the eastern Pyrenees. This dating is based on the co-occurrence of the sphenopsids Archaeocalamites radiatus , Mesocalamites cistiiformis and the seed of Cardiocarpus sp. The plant remains were found in sandstone facies produced by high-density turbidity flows of a deep-sea fan system. The new biostratigraphic information constrains the age of the Carboniferous Culm succession in the eastern Pyrenees.

Late Miocene vegetation and climate of the La Cerdanya Basin (eastern Pyrenees, Spain)

The Tortonian and early Messinian levels of the La Cerdanya intramontane basin (Province of Lleida, eastern Pyrenees, Catalonia, Spain) are here studied from a palaeoecological perspective. Based on the palynological and macrofloristic assemblages of the Sansor and Sanavastre Mines (Puigcerdà Sub-basin), and the surface outcrops of the Bellver Sub-basin, a mixed forest of broadleaved deciduous trees (e.g., Quercus hispanica, Fagus gussonii, Tilia vidali, Carpinus spp. and Acer spp.), conifers (e.g., Pinus palaeostrobus, Cryptomeria anglica, Abies saportana, Cathaya spp. and Picea spp.), some laurophyllous plants (e.g., Daphnogene polymorpha), and a few palaeotropical elements (e.g., members of Sapotaceae and Araliaceae) made up the forested landscapes of the La Cerdanya Basin during both periods. These landscapes were floristically similar to others of the Mediterranean late Miocene (e.g., those of the Likudi-Vegora complex of Greece and Italy). The importance of the mesohygrophilous elements and conifer taxa renders the La Cerdanya Basin of special interest in the Iberian late Miocene context. The coexistence approach (CA) method provided intervals for seven palaeoclimatic parameters for the Tortonian palynological and macrofloral datasets. The palaeoclimate was warm and humid, with marked seasonality and absence of dry season during the warmest period. Precipitations were similar than today but this palaeoclimate was warmer. Comparing the palaeoclimatic data for Tortonian and early Messinian levels from La Cerdanya Basin, only slight differences, mainly for temperature values, are observed. In general, the obtained palaeoclimatic values match well with those from the late Miocene of Central Europe.

Lyell and the Spanish Geology

Lyell visited Spain in the summer of 1830, after the publication of the first volume of Principles of Geology, and in the winter of 1853 coming back from his third trip to America. In his first stay he visited, among others, the Olot region (Catalonia, NE Spain) and in the second the Canary Islands. In both cases his major aim was to study these volcanic zones since volcanism constituted for Lyell the clearest evidence of the Earth interior energy, which had led to mountain building in the past. Another of his aims during his 1830 visit was to study the Pyrenees. Lyell endeavoured to show that this orogen did not result from a violent and rapid revolution, as proposed by Elie de Beaumont, but from processes that spanned long time periods. In the Pyrenees he also made some observations on the neogene lacustrine deposits of la Cerdanya basin, while in the southern Pyrenean foreland (i.e. Ebro basin) he paid attention to facies changes and correlations in the Eocene sequences. Lyell spent some days in Barcelona during this visit but at that time the country was in political turmoil and the main scientific institutions of the city had been closed down. Once in the Olot region, Lyell paid a visit to Bolos, pharmacist and botanist who had an interest in geology and introduced him in the volcanic zone. During his second trip in 1853, Lyell visited the Canaries and limited his personal contacts to Pedro Maffiote, professor of the Nautical School of Tenerife, who had made some interesting although never published geological observations in this island. In the Canary Islands Lyell sought to demonstrate the relationship between volcanism and coastal movement, and to confirm his theory of volcanic cone growth by accretion. Lyell’s influence in Spain was not due to his personal contacts in the country but to his books and especially the translation into Spanish by Ezquerra del Bayo of the first edition of “Elements of Geology” in 1838. Lyell’s ideas and especially his geological terminology, which was one of his most important contributions, spread in Spain thanks to this translation. Both the personality and the scientific reputation of Ezquerra del Bayo helped to promote the book that became for many years the official teaching book at the Schools of Mines in Spain and Mexico. Ezquerra del Bayo carried out the first geological map of the whole of Spain (1850) adopting in this and other publications (1850-1857) Lyell’s nomenclature, although his theoretical concepts (e.g. actualism) did not exert the same influence. It should be borne in mind that Lyell regarded his Elements of Geology as a descriptive Geology, a text book for students and beginners. His more elaborated theories included in Principles of Geology resulted in little influence in Spain, since this book was not translated into Spanish.

Maximum extent of Late Pleistocene glaciers and last deglaciation of La Cerdanya mountains, Southeastern Pyrenees

This paper examines glacial evolution in the La Pera and Malniu cirques, and Arànser, La Llosa and Duran valleys, in the Cerdanya massifs on the south-facing slopes of the eastern Pyrenees. A geomorphologic analysis and dating of moraine boulders, glacially polished bedrock and rock glacier blocks were carried out by means of cosmogenic 36Cl surface exposure dating. The maximum ice advance was contemporary with the Last Glacial Maximum at 23ka ago, and it was of greater or only slightly lesser magnitude than for previous Quaternary advances. The termini of glaciers remained close to maximum positions, with minor advances and retreats until 18–17ka when the glacial tongues disappeared from the valleys. Depending on the previous topography, these glaciers left behind a single polygenic moraine, in the case of confined valleys, or multiple moraines next to each other in the case of flat, more open areas. A final glacial advance is detected during the Oldest Dryas close to the cirque headwalls, and the glaciers finally disappeared during the Bølling interstadial. The glaciers were then replaced by rock glaciers, whose front immediately became inactive, although their activity continued near their source area until the early Holocene.

Wing shape of four new bee fossils (Hymenoptera: Anthophila) provides insights to bee evolution.

Bees (Anthophila) are one of the major groups of angiosperm-pollinating insects and accordingly are widely studied in both basic and applied research, for which it is essential to have a clear understanding of their phylogeny, and evolutionary history. Direct evidence of bee evolutionary history has been hindered by a dearth of available fossils needed to determine the timing and tempo of their diversification, as well as episodes of extinction. Here we describe four new compression fossils of bees from three different deposits (Miocene of la Cerdanya, Spain; Oligocene of Céreste, France; and Eocene of the Green River Formation, U.S.A.). We assess the similarity of the forewing shape of the new fossils with extant and fossil taxa using geometric morphometrics analyses. Predictive discriminant analyses show that three fossils share similar forewing shapes with the Apidae [one of uncertain tribal placement and perhaps near Euglossini, one definitive bumble bee (Bombini), and one digger bee (Anthophorini)], while one fossil is more similar to the Andrenidae. The corbiculate fossils are described as Euglossopteryx biesmeijeri De Meulemeester, Michez, & Engel, gen. nov. sp. nov. (type species of Euglossopteryx Dehon & Engel, n. gen.) and Bombus cerdanyensis Dehon, De Meulemeester, & Engel, sp. nov. They provide new information on the distribution and timing of particular corbiculate groups, most notably the extension into North America of possible Eocene-Oligocene cooling-induced extinctions. Protohabropoda pauli De Meulemeester & Michez, gen. nov. sp. nov. (type species of Protohabropoda Dehon & Engel, n. gen.) reinforces previous hypotheses of anthophorine evolution in terms of ecological shifts by the Oligocene from tropical to mesic or xeric habitats. Lastly, a new fossil of the Andreninae, Andrena antoinei Michez & De Meulemeester, sp. nov., further documents the presence of the today widespread genus Andrena Fabricius in the Late Oligocene of France.

On the Upper Ordovician unconformity in the Pyrenees: New evidence from the La Cerdanya area

In recent years, contradictory reports about whether or not an unconformity exists at the base of the Upper Ordovician succession of the Pyrenees have been made. In the Cerdanya area (Central Pyrenees), good outcrop evidence for this unconformity is displayed at the base of the Rabassa conglomerates. In this area, the Upper Ordovician rocks overlie a tilted Cambro-Ordovician sequence, displaying an angular unconformity and indicating a break in the stratigraphic series. Moreover, the existence of such an unconformity is supported by the distribution of Variscan minor structures, suggesting that the Cambro-Ordovician and the Upper Ordovician strata initially had different orientations before the main Variscan folding.

The Messinian terrestrial record in the Pyrenees: The case of Can Vilella (Cerdanya Basin)

In this paper, a survey on the Messinian section of Can Vilella, in the intramontane basin of La Cerdanya (Pyrenees) is presented. The mammalian association, composed of insectivores, rodents and lagomorphs, is a very atypical one compared to other late Turolian (Messinian) assemblages from Spain and Western Europe, including Central European taxa such as Epimeriones aff. austriacus, which are very rare or absent in the late Miocene from Spain and, even, from Western Europe. The palynological record indicates a riparian forest with abundance of marshy herbs. A magnetostratigraphic study reveals a reverse polarity span for most of the section, whereas in the upper part normal polarities are found. According to the magnetobiostratigraphic correlation established in other basins, the normal geomagnetic episode at the top of the section should correspond either to chron C3An.2n or C3An.1n. In any case, the Can Vilella association clearly predates the onset of the Messinian Salinity Crisis (MSC) in the Mediterranean. This means that the set of climatic and palaeogeographic events associated with the MSC cannot account for the anomalous association from Can Vilella. A discussion as to whether an altitudinal component could be responsible for such an anomaly is undertaken.

Diatom Communities and Water Quality Assessment in Mountain Rivers of the Upper Segre Basin (La Cerdanya, Oriental Pyrenees)

Epilithic diatoms of mountain rivers from the upper Segre catchment (Oriental Pyrenees) were studied in 1998, during three different seasons: March, July and September. Four rivers, the river Segre and its three most important tributaries, Duran, Molina and Querol, were sampled in upstream and downstream stretches. The diatom communities were comparable in all upstream stretches of these mountain rivers draining siliceous substrates. Dominant taxa were Achnanthidium subatomus, Diatoma mesodon, Encyonema cf. minutum, E. silesiacum, Fragilaria arcus, F. capucina, Gomphonema calcifugum, G. pumilum, Meridion circulare and Nitzschia pura. Changes in water quality in the downstream stretches lead to the appearance of pollution tolerant taxa, such as Eolimna minima, Gomphoneis minuta, Navicula gregaria, and Nitzschia inconspicua. As a result, the values obtained with the diatom water quality indices (IPS Specific Polluosensitivity Index, CEE and IBD Biological Diatom Index) decreased. The diatom community composition and the derived water quality values did not change in the upstream stretches over the year. In contrast, significant changes were observed in the downstream stretches with best water␣quality in July, during high flows due to melting snow, and worst values in September, during low␣discharge. The diatom indices, especially the IPS, showed a good performance in these mountain rivers.

Palynofacies distribution in a lacustrine basin

The Miocene basin of La Cerdanya (Pyrenees, Catalonia, Spain) consist of lacustrine diatomites and fan-deltaic (palustrine) lutites with lignites. A multidisciplinary analysis of palynofacies, organic geochemistry, taphofacies of plant macroremains and sedimentology was carried out in order to characterise taphonomically this basin. Palustrine facies contain highly diverse assemblages of palynomorphs and other palynological matter. The presence of relatively high amount of planar organic remains, mostly cuticles, in this palynofacies is indicative of deposition in the proximal parts of the basin. The organic content is low (1% TOC) except in the case of lignites, where it reaches up to 50%. Generally the Hydrogen Index (HI) values of the palustrine sediments are also relatively low (HI 70–189). Diatomite samples from the lake centre are characterised by high amount of the chlorococcalean alga Botryococcus and sapropelic organic matter and a HI above 500. In contrast, samples from the lake margins comprise Botryococcus, bisaccates and other anemophilous angiosperm pollen and have HI below 410. The TOC of lacustrine samples may reach levels of up to 45.5%. Palynofacies distribution shows a positive correlation with plant taphofacies only in the palustrine sediments but not in the lacustrine facies of the basin. Taphofacies of plant macroremains in the lacustrine sediments display a downslope polarity whereas palynofacies are distributed radially. A variety of transport mechanisms and different origins of palynological matter in comparison to plant macroremains account for this difference.

Spatial Variations of Local Magnitude in Earthquakes Recorded in Northeastern Spain

Since 1984, a seismic surveillance of the Baix Ebre Region (NE of the Iberian Peninsula) and the La Cerdanya Valley (Eastern Pyrenees) has been performed by the Institut d’Estudis Catalans and the Universitat de Barcelona, by means of four digital stations. An investigation of the apparent magnitude has been carried out to explain the observed anomalous differences between the amplitude of the recorded events and their associated magnitude, as given by the different agencies. Calculating the local magnitude with independent attenuation parameters and comparing the obtained results using the different stations, we obtain differences up to 1.0. These differences are interpreted in terms of very local effects and point out the uselessness of some stations to assign magnitudes of local events. Results emphasize that the effectiveness of the trigger algorithms in digital stations rarely depends on the apparent (local) magnitude. As expected, the magnitude sensitivity is related to the values of the station correction terms, meaning that extra information is required for an optimum surveillance of a local area. A 2-D analysis of the distribution of the differences between the computed and reported magnitude shows no significant azimuthal dependence. This indicates that the obtention of a local magnitude scale with an appropriate station correction term related to epicentral distance, results in an important factor to provide magnitude to local events. The obtained results corroborate previous works done at the same area and emphasis is placed on further analysis directed to obtain a better characterization of the local site influence.

Regional-scale demography of Ramonda myconi: Remnant population dynamics in a preglacial relict species

Remnant population dynamics permit many plant species to persist timespans extending from decades up to several millenia. The regional-scalepersistence of these plant species strictly depends on the persistence of localpopulations within the region. This type of dynamics can explain the existenceof preglacial relict species in the Mediterranean today. We studied thepopulation dynamics of the long-lived iteroparous herb Ramondamyconi, a preglacial relict species with a fragmented distributioninMediterranean mountains, to evaluate the regional-scale persistence of thespecies. Demographic data were collected from 5 populations placed at LaCerdanya Pyrenean region for up to 6 years. The main life-history features ofthis species are the great longevity of adult plants and the high mortality ofseedlings. Matrix population models were used to investigate its demography.Overall, the population growth rate (λ) ranged from a low of 0.79 to ahigh of 1.06. However, λ did not differ significantly from theequilibrium point, as indicated by their confidence intervals, except for onepopulation in one year. Despite the small between-year variation in λ,variation in climatic conditions at La Cerdanya from year to year explained animportant part of such variation. Elasticity analyses were performed toevaluatethe relative importance of demographic parameters for population growth. Stasistransitions made the greatest contribution to λ. Finally, the long-termdynamics of R. myconi populations were analysed byincorporating environmental stochasticity into the models. Projectionsindicatedthat local R. myconi populations tend to decline over timebut with a long time to extinction, so the persistence ofR. myconi all over La Cerdanya is determined by thepersistence of its remnant local populations.

Chaotic behaviour of coda waves in the eastern Pyrenees

SUMMARY S-coda waves of 10 local events that occurred in the eastern Pyrenees and were recorded at La Cerdanya seismic station have been analysed to determine whether the complexity they present is chaotic deterministic or random. The data were first subjected to a qualitative analysis, the construction of a phase portrait by the delay method. This clearly displays the possibility of deterministic chaos. Under the assumption that part of the coda can be considered stationary, in the sense that transients are no longer present, we performed a non-linear analysis of coda waves. The geometry of the attractor of the motion of the system (i.e. the recorded ground velocity of the medium) was characterized by means of the correlation dimension. In all cases we obtained a fractal dimension that ranges between 3.43 and 3.94. The Kolmogorov entropy was estimated from the correlation function; in all cases it was positive and finite, and the computation of the divergence of nearby orbits revealed positive, finite maximum Lyapunov exponents for all events. Thus, all evidence is in favour of the hypothesis that the attractor is a strange attractor, and that the propagation is chaotic deterministic. Errors in the measurements are estimated at 8 per cent for the correlation dimension and 12 per cent for the Lyapunov exponent. Because of natural noise in the seismic records, the above determinations should be considered as lower bounds. The above results constitute strong evidence in favour of chaotic coda-wave propagation in the zone under study, and suggest that the chaotic behaviour is generated by multiple scattering. To account for characteristics such as those found, mathematical models should be formulated in terms of non-linear equations with a minimum of four degrees of freedom.

Plant taphonomy of La Cerdanya Basin (Vallesian, Eastern Pyrenees)

In the Vallesian fluvio-lacustrine sequences of La Cerdanya Basin (Eastern Pyrenees) eight taphofacies have been recognized based on the study of plant remains. In the deltaic swamps of the basin (as observed in the Sanavastre opencast mine) taphonomical processes were twofold. The palustrine and lacustrine muds contain an autochthonous assemblage of rooted hydrophytic plants with abundant “cyperoids”, “ceratophylloids” and Trapa, whilst lignite seams are allochthonous as they have planar bases without rootlets and show evidence of orientation of plant remains. Other less abundant taphofacies of the deltaic swamps contain parautochthonous remains of Acer, Alnus and Osmunda. In the lacustrine sector of the basin, outcrops show different taphonomic processes depending on their position in the paleolake. Outcrops located near the shallower northern margins of the lake (Coll de Saig, Camp d'En Mixela) show a dominance of highly diverse water- and wind-transported plant remains and evidence of a periodically oxygenated lake bottom. The plant remains from these outcrops contain representatives from all altitudinal vegetation zones described in the Miocene of La Cerdanya. In contrast, outcrops located near the southern margins of the paleolake (Beders, Riu de Santa Maria), which are thought to have been abrupt and deep, contain wind-transported plant assemblages of low diversity and evidence of dominant dysaerobia. The plant remains found in these beds are mainly leaves of Quercus, Alnus, Fagus and Zelkova, the most abundant taxa in the woods which surrounded the lake.

The late Miocene macroflora of the La Cerdanya Basin (Eastern Pyrenees, Spain): towards a synthesis

The late Miocene macroflora of the La Cerdanya Basin (Eastern Pyrenees, Spain): towards a synthesis