A fine exposure of perennially frozen ice-rich silt and associated flora and vertebrate fauna of late-Quaternary age exists at Mamontova Gora along the Aldan River in central Yakutia, Siberia, U.S.S.R. The silt deposit caps a 50-m-high terrace and consists of three units. An upper layer 1–2 m thick overlies a 10–15-m-thick brownish to black silt layer. The lower silt layer is greenish to gray and about 15 m thick. All the silt is well sorted with 60% of the particles falling between 0.005 and 0.5 mm in diameter and is generally chemically and mineralogically homogeneous. The middle unit contains may extinct vertebrate mammal remains and ice wedges. The lower unit contains little vegetation and no ice wedges. The silt is widespread and exists as a loamy blanket on terraces at various elevations on both sides of the lower Aldan River. The origin of the silt blanket of late-Quaternary age in central Yakutia has long been controversial. Various hypotheses have been suggested, including lacustrine and alluvial, as well as frost-action origins. It is sometimes referred to as loess-like loam. Péwé believes the silt at Mamontova Gora is loess, some of which has been retransported very short distances by water. The silt probably was blown from wide, braided, unvegetated flood plains of rivers draining nearby glaciers. The silt deposits are late Quaternary in age and probably associated with the Maximum glaciation (Samarov) and Sartan and Syryan glaciations of Wisconsinan age. On the basis of biostratigraphy, 10 radiocarbon dates, and their relation to the nearby glacial record, it is felt that the upper unit at Mamontova Gora is Holocene and the middle unit is Wisconsinan. The youngest date available from the middle unit at this particular location is 26,000 years. Dates greater than 56,000 years were obtained in the lower part of the middle unit. The lower unit is definitely beyond the range of radiocarbon dating and probably is older than the last interglacial. The sediment, fauna, ice wedges, stratigraphy, and age of perennially frozen slit deposits in central Alaska are remarkably similar to those of the deposits exposed in central Yakutia. Both areas consist of unglaciated rolling lowlands and river terraces surrounded by high mountains that were extensively glaciated in Pleistocene time. The glaciers extended from the high mountains to the edges of the ranges. In both regions, extensively braided, silt-charged rivers drained the mountains and flowed through the lowlands on their way to the sea. It follows that there should be a similar late-Quaternary history.
Loesslike silt mantles upland terraces and low plateaus throughout unglaciated south-central Yakutia but is thickest along the south side of the lower Aldan River valley and the east side of the Lena River valley. The silt is probably loess deposited during glacial advances by winds blowing southward from the Verkhoyansk Range and eastward across the broad vegetation-free flood plain of the braided Lena River.The well-sorted uniform tan silt is well displayed along the Aldan and Lena Rivers; the thickest exposure measured, more than 60 m, is on the Tyungyulyu Terrace on the east side of the Lena River. On the west side of the valley, it is 10-25 m thick but thins rapidly to a featheredge west of Yakutsk. Almost all scarps along the south side of the Aldan River are capped by 10-35 m of silt.The texture and mineral composition of the loesslike silt are uniform throughout south-central Yakutia, whether it overlies limestone, poorly consolidated sandstone, alluvium, and glacial outwash. All silt samples examined contained a high percentage of quartz and feldspar. The silt stands in sheer cliffs and is massive, with little or no stratification.The origin of the loesslike silt has been ascribed to disintegration in place of country rock by a marine, estuarine, lacustrine, fluvial, residual, or eolian source, or to a combination of these processes. The marine and estuarine hypotheses have never had strong support, but the lacustrine, fluvial, and residual hypotheses have been advanced by many Soviet workers.The most widely accepted explanation of the origin of the upland silt is that it is a combination of lacustrine and alluvial deposits formed on great flood plains and marshy plains. This origin is unlikely, however, because there are no shorelines, wave-cut beaches, deltas, mudcracks, or ripple marks. Neither distinct stratification nor an appreciable amount of clay exists in the silt. Moreover, there is no definite upper boundary to the deposits, as would be expected of lacustrine deposits.The loesslike silt has also been described as a residual deposit formed by the breakdown, by freezing and thawing, of the underlying rocks. The silt bears no chemical, mineralogic, or textural relation to the underlying strata, however, and it is too thick to represent only breakdown of rocks in place.The widespread mantle of uniform loesslike silt is here considered to be windblown, derived from glacial outwash in braided streams and on broad plains, because: (1) it occurs as a surficial mantle; (2) it is lithologically independent of the underlying material; (3) it is stratified indistinctly or not at all, except in retransported material; (4) it is associated with sand dunes; (5) it contains fossils of land animals; (6) its sorting and texture are similar to that of loess and windblown dust from many places elsewhere in the world; (7) its grains are angular and relatively unweathered.
Republicação do “Mapa do Carste da Região de Pedro Leopoldo – Lagoa Santa, Minas Gerais, Brasil – 1:50.000” e comentário, originalmente publicado pelo Labora-tório de Análise e de Cartografia de Formações Superficiais da Universidade de Caen e Centro de Geomorfologia do CNRS em Caen, em junho de 1978. Pesquisa desen-volvida no âmbito do convênio entre o Laboratório de Pedologia e Sedimentologia do Instituto de Geografia / Departamento de Geografia da Faculdade de Filosofia, Letras e Ciências Humanas da Universidade de São Paulo e o Centre de Géomorphologie du CNRS - Caen, sob a coordenação de J.P. Queiroz Neto e A. Journaux. Em Minas Ge-rais, a coordenação dos trabalhos coube a H.C. Kohler, A. Prous e G. Vargas Barbosa (UFMG).
The iron mines of Schefferville, at a latitude of 55° N., are the first mines exploited in one of the best provided iron ore regions in the World ; the geosynclinal of Labrador. Their distance from the sea (360 miles to the estuary of the St. Lawrence) is compensated for by the richness of the ore deposits : abundant reserves, high percentage yield, and the quality of the mineral. The ore is mined in open pits ; the main difficulty is the harshness of the climate, which necessitates the interruption of operations from the end of November to the middle of April. The deposits are found in a subarctic taiga zone. It has been necessary to bring in all the workers ; mostly French Canadians, but also some foreigners. All tools and provisions have to be transported a great distance. The ore production is increasing rapidly : 2.25 million tons in 1954, 6 million tons in 1955, and 12 million tons in 1956. It will reach 20 million tons within the next few years. The ore is transported entirely by the railroad specially built to the port of Sept-Iles, from which it reaches, either by the sea route or by the St. Lawrence, the iron-smelting region of the north-eastern United States, where the principal outlets of the Iron Ore Co. of Canada are found. The port of Sept-Iles, which had a population of 5,573 in 1956, compared to that of 1,866 in 1951, could very possibly see its importance increase when the completion of the St. Lawrence Seaway will allow prairies grain, and possibly Pennsylvania coal, to serve as return freight for the iron ore. Close to the mines, Schefferville already has 3,500 inhabitants and has become the largest town in Labrador. Besides its purely mining junctions there are others, in particular that of a supply centre and of a transportation terminus. Its population is becoming progressively more stable and of a more balanced composition. The camp of the first prospectors is thus transformed into a permanently populated centre, of which the legal existence was recognized on the first of August, 1955.
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