Morphotectonics of the Iberian Peninsula

A morphotectonic interpretation of the relief of the Iberian Peninsula (IP) is presented based on an analysis of its gross forms. Several geological–geophysical and geomorphological methods were used in order to build up a morphostructural sketch. Three main categories were established using the approach of Rantsman (1979): Territorial Units (1-megablock, 9-macroblocks, 34-mesoblocks, 1.374-blocks and 2.523-microblocks); Morphostructural Alignments (2-first, 8-second, 20-third and 1-fourth rank; and 43 knots between Morphostructural Alignments (second-fourth rank). The main seismic activity is concentrated on the first- and second-rank lineaments, and some important epicenters are located near the lineament intersections. The origin of the earthquakes in the vicinity of such knots can be explained by the forcing/pushing of macroblocks westwards. The existence of earthquakes along the lineaments may be explained by tension. From the present study it appears that earthquake occurrence in the IP is due principally to stress concentrations around morphotectonic zones. A seismotectonic interpretation of the IP is also presented. On this map three zones are distinguished (A, B, C), each of them with a different active level and dimensions.Received: 25 November 2000     

Holocene recurrent explosive activity at Chimborazo volcano (Ecuador)

Ice-capped Chimborazo is one of the large composite Ecuadorian volcanoes whose recent eruptive activity is poorly known. This paper presents the characteristics and the ages of a newly discovered Holocene sequence of pyroclastic deposits on the east and north sides of the cone. Lying upon a moraine of the Late-Glacial period, the most complete section of ~ 4.5 m in thickness is located 5 km from the present summit crater. It consists of seven massive or diffusely stratified ash flow layers and four fallout layers interbedded with seven paleosoils.     

Upper Neoproterozoic–Lower Cambrian sedimentary successions in the Central Iberian Zone (Spain): sequence stratigraphy, petrology and chemostratigraphy. Implications for other European zones

2 O₃, TiO₂, Zr, and Nb abundances in shales from all the units, strongly suggest a gradual compositional change within this sedimentary succession. Together with the petrological data, the chemical results do not reveal any obvious coeval volcanic contribution to the sediments. On the basis of the chemical data, a comparison is made with other European zones containing detrital sediments composed of reworked crustal components. Received: 4 January 1999 / Accepted: 1 December 1999     

Occurrence probability of moderate to large earthquakes in Italy based on new geophysical methods

We develop new approaches to calculating 30-year probabilities for occurrence of moderate-to-large earthquakes in Italy. Geodetic techniques and finite-element modelling, aimed to reproduce a large amount of neotectonic data using thin-shell finite element, are used to separately calculate the expected seismicity rates inside seismogenic areas (polygons containing mapped faults and/or suspected or modelled faults). Thirty-year earthquake probabilities obtained from the two approaches show similarities in most of Italy: the largest probabilities are found in the southern Apennines, where they reach values between 10% and 20% for earthquakes of M _W ≥ 6.0, and lower than 10% for events with an M _W ≥ 6.5.     

Hyperiid Amphipods (Crustacea: Peracarida) and Spring Mesoscale Features in the Gulf of Mexico

Abstract. The distribution and abundance of the hyperiid amphipods collected during April–May 1986 was analysed in order to study their relationship to mesoscale features in the southern Gulf of Mexico. Hyperiids were represented by 79 species, Lestrigonus bengalensis (65% of total hyperiids), Primno abyssalis (4.3%), Anchylomera blossevillei (2.3%) and Lestrigonus schizogeneios (2.3%) being the most abundant. Several mesoscale features (two cyclonic and three anticyclonic eddies, two upwelling areas) were active in the surveyed area. Cluster analysis of density and composition produced five groups of stations that were found to be related to some of these features. Overall, the mesoscale features that most influenced the local hyperiid community were the upwelling areas; they were related both with the highest and the lowest hyperiid densities and with high and low diversity figures. Overall day/night variations were normal, with highest night‐time densities; this pattern was not consistent in the different mesoscale features studied. Reverse migrations were possibly occurring, or migration patterns were lacking, at some of these systems. The hyperiid community structure related to the anticyclonic eddies differed somewhat among the eddies; however, the oceanographic exchange with the surrounding gulf waters probably obscured sharper faunistic differences between the communities.     

Changes in trace metals in Thalassia testudinum after hurricane impacts

Major hurricanes Emily and Wilma hit the Mexican Caribbean in 2005. Changes in trace metals in the seagrass Thalassiatestudinum prior to (May 2004, 2005) and following passage of these hurricanes (May, June 2006) were determined at four locations along a ∼130 km long stretch of coast. Before the hurricanes, essential metals were likely limiting and concentrations of potentially toxic Pb were high in a contaminated lagoon (27.5 μg g⁻¹) and near submarine springs (6.10 μg g⁻¹); the likely sources were inland sewage disposal or excessive boat traffic. After the hurricanes, Pb decreased to 2.0 μg g⁻¹ in the contaminated lagoon probably through flushing. At the northern sites, essential Fe increased >2-fold (from 26.8 to 68.3 μg g⁻¹ on average), possibly from remobilization of anoxic sediments or upwelling of deep seawater during Wilma. Thus, hurricanes can be beneficial to seagrass beds in flushing toxic metals and replenishing essential elements.     

Morphotectonic study of two regions in the Centre-South Segment of Spain: Córdoba and Granada

The morphotectonics of Córdoba and Granada are differentiated using the Rantsman method [53]. Over 40 quantitative geomorphologic indicators are used in the systemic classification. Both areas are included in what are known as the macroblocks no. 1 (Southern) and no. 2 (Sub-Western 2A) of the Iberian Peninsula megablock. The qua ntities of the four lowest order Territorial Units defined for Córdoba/Granada are: mesoblocks (4/4), blocks (9/9), microblocks (15/35) and nanoblocks (64/83). The main lineaments/intersections determined in Córdoba total 16/1041 and in Granada 25/633, A series of seven morphostructural scarps is found in both areas, along with important modifications (inflections) in some river beds. Some of the structures described are seismicity-related. Córdoba displays less activity than Granada. Between the towns of Loja, Beas de Granada, and Lentejí a seismoactive sector (～820 km²) with blocks B2, B3, B5, and B6 forms the area where the deep earthquakes are concentrated.     

Chemical and geological control of spring water in Eastern Guaniguanico mountain range, Pinar del Rìo, Cuba

Flows of different hierarchy, which travel through limestone, schist, sandstone and ultra-basic rocks, with ages from the Paleocene to the Jurassic, at Sierra del Rosario, Pinar del Río, Cuba, were characterized. The waters were sampled from 1984 until 2004 and the data were statistically processed by means of chemical equilibrium and physico-chemical models, under a flow system view of interpretation. Results demonstrate that the physico-chemical properties of the water are controlled by water–rock interaction resulting from residence time since rainwater infiltrate and the path it follows to the discharge zone and the type of aquifer material the different groundwater flows are in contact with. Geochemical indices allow the definition of the different types of flow (local, intermediate, regional) to be characterized, permitting a further definition of the different flow systems and rock type involved, as well as its use for water supply and medical use. The main geochemical processes which control the chemical composition acquisitions mode are: congruent dissolution of calcite, dolomite, and halite; incongruent dissolution of plagioclase and microcline minerals; pyrite oxidation, sulphate reduction, and silica dissolution at the surface or silica precipitation at deep saturation and circulation zones.     

Was FLK North levels 1–2 a classic “living floor” of Oldowan hominins or a taphonomically complex palimpsest dominated by large carnivore feeding behavior?

From excavation at FLK North levels 1–2 in 1960–1962, Mary Leakey reported approximately 1200 Oldowan artifacts and 3300 large mammal fossils as a hominin “living floor”. Preliminary taphonomic analysis by Bunn seemed supportive, based on the presence of some cut-marked bones, the concentration of several dozen bovid individuals, and the relative abundance of limbs and mandibles over other axial elements. Recent taphonomic analysis of Leakey's entire fossil assemblage by Domínguez-Rodrigo and Barba, however, documents a minor hominin role at the site, contrasted to the dominant role of carnivores. Felids brought prey animals; hyenas scavenged from abandoned felid meals. At different times, hominins butchered several bovids and discarded artifacts at this dynamic location. Since 2006, renewed excavations at FLK North and other sites by the Olduvai Paleoanthropology and Paleoecology Project (TOPPP) have expanded artifact and fossil samples and implemented new analytical approaches to clarify taphonomic histories of the Olduvai paleolandscape. At FLK North, > 1000 new large mammal fossils from levels 1 to 2 show minimal butchery evidence amid abundant evidence of carnivore gnawing/fracture, rodent gnawing, and sediment abrasion. To help guide future excavation and analyses, we have developed several alternative working hypotheses of site formation.