Showing papers in "Earth-Science Reviews in 1981"

TL;DR: Based on the nature of the crystalline basement rocks and the sedimentary cover, ten structural provinces can be distinguished: (1) Rio Branco Province, in the north of the country, occupied by the Guyana Shield and still only poorly known, with an important fold belt developed during the so-called Transamazonian Cycle (2000 ± 200m.y.) with high-grade metamorphic rocks and only slight influence of later events as mentioned in this paper.

TL;DR: In this article, a review on Brazilian alkaline rocks stresses mainly the petrographic and geologic aspects, and at least eight different rock associations are represented, and several alkaline provinces are distinguished in southern Brazil.

TL;DR: The magnitude recommendation adopted by the IASPEI Assembly at Zurich in 1967 has had both a stabilizing and a stimulating effect on magnitude determinations and related research from 1967 onwards, one magnitude research paper has appeared on the average almost every week, thus making this parameter the most studied one in seismology as mentioned in this paper.

TL;DR: In this article, four end-member sedimentation models are proposed for the interpretation of ancient deposits: (1) transgressive sheet sands associated with deltas; (2) non-deltaic transgressive sheets sands; (3) regressive sheet sands; and (4) linear sand bodies.

TL;DR: In this paper, the main evidence and conclusions regarding geological links between Brazil and Africa are summarized, with emphasis on the geochronological aspects, taking into account the geographical position, as well as the similarities in the geocronological pattern, the following main provinces of the two continents are correlated: (1) the Imataca and Falawatra complexes in the Guayana Shield and the Liberian Province of West Africa.

TL;DR: The Brazilian continental margin has become better known only during the last two decades as discussed by the authors, with its interesting morphology, structure and sediments becoming better known in the last few decades, with the exception of the Amazon cone and the marginal plateaus.

TL;DR: A comprehensive review of stable isotope geochemistry in the United States can be found in this paper, which covers papers published or presented at national meetings since the last quadrennial report.

TL;DR: The principal litho-structural units of the Brazilian Archaean terranes are characterized by mafic-ultramafic complexes, granulitic belts, greenstone belts and gneissic-granitic areas.

TL;DR: Alpine peridotites are found all over Brazil and are grouped in three main classes: the serpentinized dunites-peridotite of small and medium size; the gabbro-pyroxenite-peridea association in large complexes, the latter described only in the central part of Brazil; and the pyroxenites-gabbroic gneisses of the Goianira-Trindade type as discussed by the authors.

TL;DR: The activity of the first generation of Brazilian geologists began in the early sixties. Systematic exploration work since then has evidenced some important new mineral reserves in Brazil as discussed by the authors, including 18 × 10 9 tons of high-grade iron ore (Carajas District), formed by supergene enrichment on iron formations older than 1800 m.y.

TL;DR: The fossil record is fairly rich, including besides plants and invertebrates, also reptiles and fishes, also Reptilia and fishes in Brazil as discussed by the authors, including amphibians and fishes.

TL;DR: The Phanerozoic history of the South American Platform can be divided into three stages, called Transition, Stabilization and Reactivation, characterized by the accumulation of a number of sedimentary sequences.