Central Configurations of the Planar Coorbitalsatellite Problem

We study the planar central configurations of the 1 +n body problem where one mass is large and the other n masses are infinitesimal and equal. We find analytically all these central configurations when 2≤n≤4. Numerically, first we provide evidence that when n9 the only central configuration is the regular n-gon with the large mass in its barycenter, and second we provide also evidence of the existence of an axis of symmetry for every central configuration. This revised version was published online in July 2006 with corrections to the Cover Date.     

New central configurations for the planar 5-body problem

In this paper we show the existence of three new families of planar central configurations for the 5-body problem with the following properties: three bodies are on the vertices of an equilateral triangle and the other two bodies are on a perpendicular bisector.     

Selenium and other trace elements in phosphate rock of Bayovar–Sechura (Peru)

Selenium is an essential trace element in regard to human and other animals' health, but it presents a narrow range of dietary deficiency and toxic excess. Some phosphate rocks are rich in selenium. Furthermore it is necessary to control selenium's and other trace elements’ compositions in the phosphate rocks, because phosphorite ores of different geographical sites are varied, and even ores from the same outcrop can vary substantially in trace element levels.     

Magnetic Stratigraphy from Deep Clastic Turbidites: An Example from the Eocene Hecho Group (Southern Pyrenees)

A paleomagnetic study of a 2200-meter thick section of clastic turbidites from the Eocene Hecho group (southcentral Pyrenees, Spain) allows defining its magnetostratigraphic record. Natural remanent magnetization is carried by up to three components: a viscous low-temperature component; a second component unblocked between 300°C and 345°C, likely carried by iron-sulphides; and a third component which demagnetizes at temperatures higher than 345°C and is likely carried by magnetite. The second and third components may display opposite polarities at the same site. The magnetite component delineates different polarity zones and has a more consistent behavior along section if compared with the iron-sulphide component, which displays either a normal or a reverse direction without any stratigraphic consistency along section. The bulk of iron sulphides are interpreted to be secondary in origin and to carry diagenetic overprints acquired at different times after deposition and the magnetite component is taken as the characteristic primary magnetization. As supported by biostratigraphy, the section is correlated from chrons C20r to C18n.2n (Lutetian-Bartonian transition), which indicates a mean sediment accumulation rate of about 52 cm/ky for the studied section. The new chronostratigraphy allows constraining the age of the upper Hecho Group (Banastón and Jaca allogroups) to an unprecedented level and is consistent with previous magnetostratigraphic work in younger sediments from the Jaca Basin. Deep clastic sedimentary systems should not be neglected as a target for magnetostratigraphic studies despite diagenetic growth of secondary minerals may mask the primary signal.     

Are some of the deep crustal conductive features found in SW Iberia caused by graphite?

Recent results obtained from two-dimensional inversion of magnetotelluric (MT) data acquired in SW Iberia reveal high-conductive features at the middle-lower levels of the crust. The top of these anomalous structures correlates very well with the depth (10-13 km) of an important seismic interface that has been interpreted as a regional detachment horizon. Very shallow and relatively narrow conductors in the Ossa Morena Zone appear to correspond to small-scale fluid-deposited graphite systems in the preorogenic metasedimentary sequences. Some of the midcrustal conductors can be ascribed to graphite-bearing thrust zones, the formation of graphite with variable crystallinity being a consequence of Variscan shearing processes. Deep-seated conductors are tentatively interpreted as a result of relatively continuous, highly crystalline grain-boundary graphite films presumably preserved in basement, granulite(?) rocks. Assuming that graphite occurs as interconnected films, calculations indicate that a fraction of 0.006-0.02% of this accessory mineral is enough to explain the range of the electrical resistivity estimated on the basis of MT models. The role of graphite on the thermal behaviour of the crust is also discussed. The results show that low contents of graphite do not significantly change the thermal behaviour of earth materials.     

Climate Warming, Wildfire Hazard, and Wildfire Occurrence in Coastal Eastern Spain

A climatic series (1941 to 1994) from a Mediterranean locality of NE Spain was used to calculate two wildfire hazard indices based on daily meteorological data. Both fire hazard indices increased over this period, as a consequence of increasing mean daily maximum temperature and decreasing minimum daily relative humidity. These trends were observed in both mean values of the indices and in the number of very high risk days. Annual data on the number of wildfires and burned area also show an increase from 1968 to 1994, and are significantly correlated with both fire hazard indices. Although other non-meteorological causes (e.g., human activities, fuel accumulation) have likely contributed to the observed increase of wildfires, an effect of climatic warming on wildfire occurrence is supported by this relationship.     

Untangling the Palaeocene climatic rhythm: an astronomically calibrated Early Palaeocene magnetostratigraphy and biostratigraphy at Zumaia (Basque basin, northern Spain)

The magnetostratigraphy of a 54-m-long section above the Cretaceous-Tertiary boundary at the sea-cliff section of Zumaia in the Basque basin (northern Spain) has been established. The section encompasses the entire Danian and the lower part of the Selandian stages as indicated by calcareous plankton biostratigraphy. The studied interval consists of (hemi)pelagic limestone-marl alternations in the form of couplets and bundles, which range from centimetre/decimetre to metre scale respectively and a few thin-bedded calcareous turbidites. The magnetostratigraphy, based on samples from about 200 stratigraphic levels, allows the identification of six reversal boundaries from chron C29r to C26r at a bed level. The spatial (or temporal) evolution of periodicities from a lithologically coded series is studied with the continuous wavelet transform technique. A preliminary age model based on the standard CK95 GPTS indicates that the basic lithologic carbonate-marl couplet corresponds to the 19-23-kyr precession cycle (21-31-cm cycle in the depth domain) and that a bundle cycle (usually groups of four to six basic couplets) with global periodicity centred at 1.22 m corresponds to the ∼110-kyr eccentricity cycle. We have tuned the bundle cycles to the Va03_R7 eccentricity orbital solution [Astrophys. J. 592 (2003) 620-630] following an initial match of a node of the ∼2.4-Ma eccentricity modulatory cycle in the target time series to particularly carbonate-rich bundles from the upper part of the Zumaia section that displays significant power of a 4.4-m-period cycle corresponding to the ∼404-kyr eccentricity cycle. Consistency between lithologic patterns and characteristics in the eccentricity target is reasonably met although the ∼404-kyr eccentricity cycle is not persistent throughout. The tuning, however, appears robust as it brings the age of the K/T boundary at ∼65.8 Ma. It is argued that a sea-level signal (tectonically driven?) is superimposed on the climatic forcing at the Milankovitch band masking the full expression of the low-frequency astronomical periods. We provide a cycle-tuned duration for all intervening Early Palaeocene polarity chrons and estimate relative ages for bioevents. The cycle-tuned chronology indicates that the CK95 GPTS overestimates the duration of chrons C28 and C27 by 20 and 26% respectively. Our data may prove useful to better constrain Early Palaeocene biostratigraphy of calcareous plankton and in the redefinition of the boundary between the Danian and Selandian stages.