Study of matric potential and geotextiles applied to degraded soil recovery,Uberlândia (MG), Brazil

The aim of this paper was to analyse water dynamics in the soil from tensiometer data in two different plots, one with bare soil and another with geotextiles and grass, correlating the information generated in the study concerning biotextile efficiency in soil moisture maintenance, which is essential to vegetation development and to the recovery from and control of erosion. Tensiometers were installed on the bare soil and grass plots at different depths (15, 30, 80 and 120 cm), and the respective readings were taken with a digital tensimeter. Water dynamics inside the soil can be demonstrated by matric potential data from pressure differences. A large difference between the bare soil and grass plots was demonstrated by matric potential medium values at depths of 15, 30, 80 and 120 cm during monitoring.     

Hydrofluoric Acid‐Free Digestion of Geological Samples for the Quantification of Rare Earth Elements by Inductively Coupled Plasma‐Optical Emission Spectrometry

Rare earth elements (REEs) are very important to technological development as well as to geochemical and environmental studies. In this work, hydrofluoric acid (HF) was replaced by condensed phosphoric acid (CPA) in the digestion of geological samples, and the quantification of REEs was performed by inductively coupled plasma‐optical emission spectrometry (ICP‐OES). Six international reference materials (RMs), named DC86318, CGL 111, CGL 124, CGL 126, OKA‐2 and COQ‐1 and three Brazilian ore samples, named Araxá, Catalão and Pitinga were analysed. Only zircon and xenotime, which are potential REE‐bearing minerals, were not completely dissolved. Nevertheless, no REE associated with zircon was detected. The investigated digestion method presented many advantages: It was relatively fast (3 h), avoided fluoride precipitation, it was less hazardous because handling diluted H₃PO₄ is safer than HF, NH₄F or NH₄HF₂ aqueous solutions, it preserved the quartz fittings of the measurement equipment and the final solution contained lower levels of total dissolved solids than those produced by the fusion method.     

Liquefaction-induced structures in Quaternary alluvial gravels and gravelly sediments, NE Brazil

We have identified numerous well-preserved elutriation and fluidization structures probably induced by liquefaction in Quaternary gravels and gravelly sediments of braided fluvial channel deposits in the Rio Grande do Norte and Ceará states, northeastern Brazil. They show evidence of upward-directed water escape after sediment deposition and before sediment compaction. Among the several types of structures observed, the most frequent are pillars, pockets and dikes. These structures range in width from a few centimeters to as much as 4 m, and in height from 60 cm to 4 m. Dikes, pillars and pockets are systematically associated. Clastic dikes vented large quantities of sand to the upper layers or the surface; pebbles and cobbles from the host rock sank into the dikes and formed pillars and pockets. Pockets form the root part; pillars form the intermediate part and dike, the upper part of the composite structure. The morphology of the structures in sectional and plan views indicates a 3D geometry composed of a tabular dike and pillar that present a downward continuous transition to a bowl-shaped pocket. This “stratigraphy” of liquefaction features is different from that usually presented in the current literature.

Field data suggest that both the location and the geometry of the features were controlled by sedimentary properties rather than joints and small faults. The size and abundance of these features suggest that they were formed by great events rather than localized mechanisms. Field evidence also indicates that these features are the product of fluidization and elutriation and may have been induced by liquefaction processes associated with seismic shaking. A nonseismic origin related to elutriation processes, however, cannot be ruled out for some of the features.