The Rearticulation of Formal Sediments in Guimarães Rosas’s Literary Discourse

This article aims at analysing both the esthetical form and the rearticulation of its internal sediments as proposed by João Guimarães Rosa in his literary works. The analysis’ theoretical support is based on Theodor W. Adorno’s Teoria Estética. The broad objective of this study is to show that Rosa’s esthetical formalization is a call for changing. At the end of the article, a brief comparative study is made between Guimarães Rosa’s and Dostoievski’s calls for changing. Accordingly, some of the main issues of Bakthin’s theories about the works of the Russian writer will be reminded of and some of the main differences and similarities between Rosa’s and Dostoievski’s formal rearticulations will be pointed out.

Rapid cold water formation and recrystallization of relict bryophyte tufa at the Fall Creek cold springs, Alberta, Canada

The Fall Creek Tufa is a relict, mid- to late-Holocene freshwater carbonate spring deposit that is formed almost entirely of calcite-encased Cratoneuron commutatum gametophytes. The spring is presently active, emitting 13 °C meteorically derived waters, but it is not precipitating calcite. Wood embedded in the youngest part of the tufa yielded a radiocarbon (14C) date of 310 ± 50 years BP. The oldest parts of the deposit could not be dated by radiocarbon methods because of a lack of embedded organics. The Fall Creek Tufa, however, probably began forming ~5000 years BP in response to the same wet climatic conditions that initiated calcite precipitation at Miette Hot Springs in Jasper National Park and the Cave and Basin Hot Springs in Banff National Park. The relict deposit is composed largely of calcite cements that were precipitated around the bryophytes, with lesser amounts of internal sediments. The tufa formed through a repeated four-stage developmental process that involved (I) encrustation, (II) encapsulation, (III) cavity occlusion, and (IV) diagenetic alteration. These stages were temporally and spatially variable. Although a young deposit, much of it has undergone extensive aggrading recrystallization, whereby crystal size has increased as adjacent calcite crystals were sutured together. Epifluorescence micro s copy shows that primary depositional fabrics were masked, but not destroyed, during recrystallization. Narrow ranges of δ18O (VPDB, Vienna Pee-Dee Belemnite standard) values (–18.4‰ to –17.7‰) and δ13C (VPDB) values (–1.2‰ to 0.5‰) indicate that the calcite was in isotopic equilibrium with the water that it precipitated from, and that diagenesis did not reset the stable oxygen and carbon isotopic compositions.

Resolving the Richat enigma: Doming and hydrothermal karstification above an alkaline complex

The Richat structure (Sahara, Mauritania) appears as a large dome at least 40 km in diameter within a Late Proterozoic to Ordovician sequence. Erosion has created circular cuestas represented by three nested rings dipping outward from the structure. The center of the structure consists of a limestone-dolomite shelf that encloses a kilometer-scale siliceous breccia and is intruded by basaltic ring dikes, kimberlitic intrusions, and alkaline volcanic rocks. Several hypotheses have been presented to explain the spectacular Richat structure and breccia, but their origin remains enigmatic. The breccia body is lenticular in shape and irregularly thins at its extremities to only a few meters. The breccia was created during karst dissolution and collapse. Internal sediments fill the centimeter- to meter-scale cavities. Alkaline enrichment and the presence of Cretaceous automorphous neoformed K-feldspar demonstrate the hydrothermal origin of these internal sediments and their contemporaneity with magmatism. A model is proposed in which doming and the production of hydrothermal fluids were instrumental in creating a favorable setting for dissolution. The circular Richat structure and its breccia core thus represent the superficial expression of a Cretaceous alkaline complex with an exceptionally well preserved hydrothermal karst infilling at its summit.

Genesis of the Pb–Zn deposit at Sant’Antonio di Val D’Aspra, Southern Tuscany (Italy): disparity between geo-petrographic data and fluid inclusion microthermometry

The Pb–Zn deposit at Sant'Antonio di Val d'Aspra in the Farma Valley (Southern Tuscany) is hosted by Lower Moscovian carbonate rocks and shows many characters commonly found in Mississippi Valley type (MVT) deposits. Ore minerals (essentially sphalerite and galena) are closely confined to dolomitized portions of an only partly preserved black limestone. Mineralized carbonate rocks appear to have been eroded before the deposition of the overlying Upper Moscovian (Late Podolskian) shales. The diffuse presence of structures frequently found in internal sediments of karstic cavities indicates that supergene mechanisms have played an important role in the history of the deposit. A fluid inclusion study carried out on ore and gangue minerals revealed the presence of two different types of inclusions. The homogenization temperatures ranged from 120°C to 225°C but the most frequently found values were around 170°C. Salinity ranged from moderately low values up to 20 eq. wt. % NaCl. Lead isotopic composition rules out any relationship between the Sant'Antonio mineralization and Tertiary hydrothermal base metal occurrences in the same area. When all the data are taken together, a contrast is evident between geo-petrographic and isotopic data on the one hand, and fluid-inclusion microthermometry on the other.

The petrology of oolitic phosphorites from Esprit (Aldabra), western Indian Ocean

The island of Esprit, at the western end of Aldabra lagoon, is capped by two groups of phosphorites. Near the summit, bedded deposits rest on and in cavities within the subaerially eroded surface of the limestones forming the island. The limestones themselves have not been phosphatized. On the lower slopes, and derived from the phosphorites above, are small outcrops of coarse, phosphate-cemented, bioclastic sediments and large, irregular fans of phosphoritic conglomerates. The phosphorites can be divided into five petrographic groups. Oolitic phosphorites are the most common and are apparently primary. Associated with them are lithoclast-bearing rocks, fine-grained phosphorites, bioclastic deposits and internal sediments, all of which are also wholly phosphatic. There have been numerous reworking episodes in the history of these rocks, such that large volumes now consist only of phosphatic cement sequences (the linings of former cavities) and internal sediments. Up to fourteen changes in the depositional milieu can be seen. The distribution of both cements and internal sediments is restricted, recording the paths of particular transport streams in groundwaters. The minerals identified are carbonatian hydroxyfluorapatites. Most cements are multilayer colloform crusts with a radially fibrous structure, but, in addition, crystals show a range of morphologies, including hexagonal, monoclinic and cubic forms. Some cements are carbonate, but other minerals that may have been present have been pseudomorphed by phosphates. The primary source of the phosphate in these rocks is thought to have been avian guano, deposited on a limestone surface at a time when sealevel was 7-8 m above its present position. Phosphate-rich derivatives from this were carried downwards by surface-wash processes and precipitated in a series of caves in the limestones excavated at the water table and drained as sealevel fell. Solution pipes were formed when sealevel was at least 1-2 m below its present position, but marine coquinal sediments deposited within these suggest that it was subsequently higher. Continued erosion of the host limestones, destroying the caves, released both phosphorite detritus, redeposited as the low-level sediments and transported into beach calcarenites, and phosphatic solutions for precipitation as cements. The phosphorites are tentatively dated as deposited 170-230 ka B.P .