Long-term deforestation in NW Spain: linking the Holocene fire history to vegetation change and human activities

The Holocene fire regime is thought to have had a key role in deforestation and shrubland expansion in Galicia (NW Spain) but the contribution of past societies to vegetation burning remains poorly understood. This may be, in part, due to the fact that detailed fire records from areas in close proximity to archaeological sites are scarce. To fill this gap, we performed charcoal analysis in five colluvial soils from an archaeological area (Campo Lameiro) and compared the results to earlier studies from this area and palaeo-ecological literature from NW Spain. This analysis allowed for the reconstruction of the vegetation and fire dynamics in the area during the last ca 11 000 yrs. In the Early Holocene, Fabaceae and Betula sp. were dominant in the charcoal record. Quercus sp. started to replace these species around 10 000 cal BP, forming a deciduous forest that prevailed during the Holocene Thermal Maximum until ～5500 cal BP. Following that, several cycles of potentially fire-induced forest regression with subsequent incomplete recovery eventually led to the formation of an open landscape dominated by shrubs (Erica sp. and Fabaceae). Major episodes of forest regression were (1) ～5500–5000 cal BP, which marks the mid-Holocene cooling after the Holocene Thermal Maximum, but also the period during which agropastoral activities in NW Spain became widespread, and (2) ～2000–1500 cal BP, which corresponds roughly to the end of the Roman Warm Period and the transition from the Roman to the Germanic period. The low degree of chronological precision, which is inherent in fire history reconstructions from colluvial soils, made it impossible to distinguish climatic from human-induced fires. Nonetheless, the abundance of synanthropic pollen indicators (e.g. Plantago lanceolata and Urtica dioica) since at least ～6000 cal BP strongly suggests that humans used fire to generate and maintain pasture.     

Geochemical model of a magmatic–hydrothermal system at the Lastarria volcano, northern Chile

Lastarria volcano (25°10′ S, 68°31′ W; 5,697 m above sea level), located in the Central Andes Volcanic Zone (northern Chile), is characterized by four distinct fumarolic fields with outlet temperatures ranging between 80°C and 408°C as measured between May 2006–March 2008 and April–June 2009. Fumarolic gasses contain significant concentrations of high temperature gas compounds (i.e., SO₂, HCl, HF, H₂, and CO), and isotopic ratios (³He/⁴He, δ¹³C–CO₂, δ¹⁸O–H₂O, and δD–H₂O) diagnostic of magmatic gas sources. Gas equilibria systematics, in both the H₂O-H₂-CO₂-CO-CH₄ and alkane–alkene C₃ system, suggest that Lastarria fumarolic gasses emanate from a superheated vapor that is later cooled and condensed at relatively shallow depths. This two-stage process inhibits the formation of a continuous aquifer (e.g., horizontal liquid layer) at relatively shallow depth. Recent developments in the magmatic gas system may have enhanced the transfer and release of heat causing shallow aquifer vaporization. The consequent pressure increase and aquifer vaporization likely triggered the inflation events beginning in 2003 at the Lastarria volcano.     

The Colider and Roosevelt Volcanic rocks (sw amazonian craton): geochemistry and sm-nd isotope characteristics of a silicic large igneous province

The volcanic rocks of the Colíder and Roosevelt formations are extensively exposed in the south-central portion of the Amazonian Craton where effusive and pyroclastic rocks have been mapped. Both units, topped by chemical sediments and oceanic facies as rhyolite and andesite lavas, rhyodacite, and porphyritic dacite, with frequent intercalations of pyroclastic and epiclastic deposits. Whole-rock geochemistry for 55 samples of rhyolitic to andesitic composition suggests the involvement of fertile mantle-derived components with E-MORB to OIB compositions. The analyzed rocks display calc-alkaline to shoshonitic affinity consistent with generation related to an active continental margin. The whole-rock Sm-Nd isotope data from selected felsic volcanic rocks of the Colíder and Roosevelt formations yield negative initial ε_Nd values between –3 and –9, indicating the predominantly crustal nature of the parental magmas with early Archean to late Paleoproterozoic (ca. 2.5–2.0 Ga) depleted mantle model ages.

     

Multiple Random Walk Simulation: A Fast Method to Map Grade Uncertainty with Large Datasets

Multiple Random Walk Simulation consists of a methodology adapted to run fast simulations if close-spaced data are abundant (e.g., short-term mining models). Combining kriging with the simulation of random walks attempts to approximate traditional simulation algorithm results but at a computationally faster way when there is a large amount of conditioning samples. This paper presents this new algorithm illustrating the situations where the method can be used properly. A synthetic study case is presented in order to illustrate the Multiple Random Walk Simulation and to analyze the speed and goodness of its results against the ones from using Turning Bands Simulation and Sequential Gaussian Simulation.     

Nonlinear Numerical Simulations of Magneto-Acoustic Wave Propagation in Small-Scale Flux Tubes

We present results of nonlinear, two-dimensional, numerical simulations of magneto-acoustic wave propagation in the photosphere and chromosphere of small-scale flux tubes with internal structure. Waves with realistic periods of three to five minutes are studied, after horizontal and vertical oscillatory perturbations are applied to the equilibrium model. Spurious reflections of shock waves from the upper boundary are minimized by a special boundary condition. This has allowed us to increase the duration of the simulations and to make it long enough to perform a statistical analysis of oscillations. The simulations show that deep horizontal motions of the flux tube generate a slow (magnetic) mode and a surface mode. These modes are efficiently transformed into a slow (acoustic) mode in the v _A<c _S atmosphere. The slow (acoustic) mode propagates vertically along the field lines, forms shocks, and remains always within the flux tube. It might effectively deposit the energy of the driver into the chromosphere. When the driver oscillates with a high frequency, above the cutoff, nonlinear wave propagation occurs with the same dominant driver period at all heights. At low frequencies, below the cutoff, the dominant period of oscillations changes with height from that of the driver in the photosphere to its first harmonic (half period) in the chromosphere. Depending on the period and on the type of the driver, different shock patterns are observed.     

Metals in Sediments of the Upper Laguna Madre

The Laguna Madre system is the largest hypersaline coastal basin in the United States. Surface sediments from 22 Upper Laguna Madre (ULM) sites were analyzed for grain size and metals (Cd, Cu, Ba, Cr, Mn, Ni, Pb, V, Zn, Fe, and Al) to assess the extent of contamination in the area. Sediments were found to consist mainly of sand texture. Clay and silts were minor constituents (<10%) of the sediments. Anomalies in metal concentrations were found at some sites and were related to probable sources, i.e., recreational and industrial activities. Concentrations of metals were normalized to grain size, Al, and Fe to distinguish natural and anthropogenic sources. Most metals showed positive correlations (p < 0.001) with Fe and Al, suggesting a natural variability of metal concentrations in sediments. Concentrations of metals, except Cd and Pb, at most sites were found to be below threshold concentrations thought to produce toxic effects in marine and estuarine organisms.     

A contribution to regional stratigraphic correlations of the Afro-Brazilian depression – The Dom João Stage (Brotas Group and equivalent units – Late Jurassic) in Northeastern Brazilian sedimentary basins

The Dom João Stage comprises an interval with variable thickness between 100 and 1200 m, composed of fluvial, eolian and lacustrine deposits of Late Jurassic age, based mainly on the lacustrine ostracod fauna (although the top deposits may extend into the Early Cretaceous). These deposits comprise the so-called Afro-Brazilian Depression, initially characterized as containing the Brotas Group of the Recôncavo Basin (which includes the Aliança and the Sergi Formations) and subsequently extended into the Tucano, Jatobá, Camamu, Almada, Sergipe, Alagoas and Araripe Basins in northeastern Brazil, encompassing the study area of this paper. The large occurrence area of the Dom João Stage gives rise to discussions about the depositional connectivity between the basins, and the real extension of sedimentation. In the first studies of this stratigraphic interval, the Dom João Stage was strictly associated with the rift phase, as an initial stage (decades of 1960–70), but subsequent analyses considered the Dom João as an intracratonic basin or pre-rift phase – without any relation to the active mechanics of a tectonic syn-rift phase (decades of 1980–2000). The present work developed an evolutionary stratigraphic and tectonic model, based on the characterization of depositional sequences, internal flooding surfaces, depositional systems arrangement and paleoflow directions. Several outcrops on the onshore basins were used to build composite sections of each basin, comprising facies, architectural elements, depositional systems, stratigraphic and lithostratigraphic frameworks, and paleocurrents. In addition to that, over a hundred onshore and offshore exploration wells were used (only 21 of which are showed) to map the depositional sequences and generate correlation sections. These show the characteristics and relations of the Dom João Stage in each studied basin, and they were also extended to the Gabon Basin. The results indicate that there were two main phases during the Dom João Stage, in which distinctive sedimentary environments were developed, reflecting depositional system arrangements, paleoflow directions were diverse, and continuous or compartmented basins were developed.