Alteration,Chemical Processes,and Parent Rocks of Haléo-Danielle Plateau Bauxite,Adamawa–Cameroon     

Nyamsari  D. G.  Yalçin  M. G.  Wolfson  I. 《Lithology and Mineral Resources》2020,55(3):231-243

Lithology and Mineral Resources - The Haléo-Danielle Plateau bauxite deposit forms the largest part of the 15 km long Minim-Martap Bauxite ore district in the Adamawa Region of Cameroon. The...  相似文献   

Antarctic Bottom Water Flow through the Eastern Part of the Philip Passage in the Weddell Sea     

Morozov  E. G.  Frey  D. I.  Tarakanov  R. Yu. 《Oceanology》2020,60(5):589-592

Oceanology - Measurements of currents and Antarctic Bottom Water properties overflowing the sill from the Weddell to the Scotia Sea are described. The bottom water overflows the sill of one of the...  相似文献   

Surface melt-driven seasonal behaviour (englacial and subglacial) from a soft-bedded temperate glacier recorded by in situ wireless probes     

Jane K. Hart  Kirk Martinez  Philip J. Basford  Alexander I. Clayton  Graeme M. Bragg  Tyler Ward  David S. Young 《地球表面变化过程与地形》2019,44(9):1769-1782

We investigate the spatial and temporal englacial and subglacial processes associated with a temperate glacier resting on a deformable bed using the unique Glacsweb wireless in situ probes (embedded in the ice and the till) combined with other techniques [including ground penetrating radar (GPR) and borehole analysis]. During the melt season (spring, summer and autumn), high surface melt leads to high water pressures in the englacial and subglacial environment. Winter is characterized by no surface melting on most days (‘base’) apart from a series of positive degree days. Once winter begins, a diurnal water pressure cycle is established in the ice and at the ice/sediment interface, with direct meltwater inputs from the positive degree days and a secondary slower englacial pathway with a five day lag. This direct surface melt also drives water pressure changes in the till. Till deformation occurred throughout the year, with the winter rate approximately 60% that of the melt season. We were able to show the bed comprised patches of till with different strengths, and were able to estimate their size, relative percentage and temporal stability. We show that the melt season is characterized by a high pressure distributed system, and winter by a low pressure channelized system. We contrast this with studies from Greenland (overlying rigid bedrock), where the opposite was found. We argue our results are typical of soft bedded glaciers with low englacial water content, and suggest this type of glacier can rapidly respond to surface-driven melt. Based on theoretical and field results we suggest that the subglacial hydrology comprises a melt season distributed system dominated by wide anastomosing broad flat channels and thin water sheets, which may become more channelized in winter, and more responsive to changes in meltwater inputs. © 2019 The Authors. Earth Surface Processes and Landforms published by John Wiley & Sons Ltd.  相似文献   

Flow resistance and hydraulic geometry in bedrock rivers with multiple roughness length scales     

Robert I. Ferguson  Richard J. Hardy  Rebecca A. Hodge 《地球表面变化过程与地形》2019,44(12):2437-2449

Many models of incision by bedrock rivers predict water depth and shear stress from discharge; conversely, palaeoflood discharge is sometimes reconstructed from flow depth markers in rock gorges. In both cases, assumptions are made about flow resistance. The depth–discharge relation in a bedrock river must depend on at least two roughness length scales (exposed rock and sediment cover) and possibly a third (sidewalls). A conceptually attractive way to model the depth–discharge relation in such situations is to partition the total shear stress and friction factor, but it is not obvious how to quantify the friction factor for rough walls in a way that can be used in incision process models. We show that a single flow resistance calculation using a spatially averaged roughness length scale closely approximates the partitioning of stress between sediment and rock, and between bed and walls, in idealized scenarios. Both approaches give closer fits to the measured depth–discharge relations in two small bedrock reaches than can be achieved using a fixed value of Manning's n or the Chézy friction factor. Sidewalls that are substantially rougher or smoother than the bed have a significant effect on the partitioning of shear stress between bed and sidewalls. More research is needed on how best to estimate roughness length scales from observable or measurable channel characteristics. © 2019 John Wiley & Sons, Ltd.  相似文献   

Portlandia-dominated Communities in the Arctic: Taxonomic Composition and Structure along the Geographical Gradient     

Mokievsky  V. O.  Udalov  A. A.  Chava  A. I.  Simakova  U. V.  Kokarev  V. N.  Neretina  T. V. 《Doklady Earth Sciences》2020,493(2):645-648

Doklady Earth Sciences - The species composition and structure of bottom communities with a predominance of bivalve mollusks of the Portlandia genus, which are widespread on the shelf of the...  相似文献   

Formation Environments of Metasomatites and Ores of the Epithermal Gold–silver Deposits     

Kigai  I. N. 《Geology of Ore Deposits》2020,62(5):432-437

Geology of Ore Deposits - Preore metasomatites of epithermal gold–silver deposits are formed by various types of hydrothermal solutions—from highly acidic and oxidized (argillization,...  相似文献   

The Crust–Mantle Carbon Cycle and Origin of Abiogenic Hydrocarbons     

Sorokhtin  N. O.  Lobkovsky  L. I.  Kozlov  N. E. 《Oceanology》2020,60(2):248-258

Oceanology - Abstract—The paper studies carbon transformation and transfer processes in the crust and mantle. Sediments dragged into subduction zones are dewatered, broken down, and altered...  相似文献   

Research Results on Ecological Hazard Objects in Abrosimov Bay (Novaya Zemlya,Kara Sea)     

Rimsky-Korsakov  N. A.  Flint  M. V.  Kazennov  A. Yu.  Anisimov  I. M.  Poyarkov  S. G.  Pronin  A. A.  Tronza  S. N. 《Oceanology》2020,60(5):625-632

Oceanology - The article presents results of field research on environmental assessment in Abrosimov Bay (Yuzhny Island of Novaya Zemlya) in connection with the existing RW disposal sites in this...  相似文献   

Late Miocene evaporite geochemistry of Lorca and Fortuna basins (Eastern Betics,SE Spain): Evidence of restriction and continentalization     

Javier García-Veigas  Luis Gibert  Dioni I. Cendón  David Artiaga  Hugo Corbí  Jesús M. Soria  Tim K. Lowenstein  Enrique Sanz 《Basin Research》2020,32(5):916-948

The Lorca and Fortuna basins are two intramontane Neogene basins located in the eastern Betic Cordillera (SE Spain). During the Late Tortonian—Early Messinian, marine and continental evaporites precipitated in these basins as a consequence of increased marine restriction and isolation. Here we show a stratigraphic correlation between the evaporite records of these basins based on geochemical indicators. We use SO₄ isotope compositions and Sr isotopic ratios in gypsum, and halite Br contents to characterize these units and to identify the marine or continental source of the waters feeding the evaporite basins. In addition, we review the available chronological information used to date these evaporites in Lorca (La Serrata Fm), including a thick saline deposit, that we correlate with the First Evaporitic Group in Fortuna (Los Baños Fm). This correlation is also supported by micropalaeontological data, giving a Late Tortonian age for this sequence. The Second Evaporitic Group, (Chicamo Fm), and the Third Evaporitic Group (Rambla Salada Fm) developed only in Fortuna during the Messinian. According to the palaeogeographical scheme presented here, the evaporites of the Lorca and Fortuna basins were formed during the Late Tortonian—Early Messinian, close to the Betic Seaway closure. Sulphate isotope compositions and Sr isotopic ratios of the Ribera Gypsum Mb, at the base of the Rambla Salada Fm (Fortuna basin), match those of the Late Messinian selenite gypsum beds in San Miguel de Salinas, in the near Bajo Segura basin (40 km to the East), and other Messinian Salinity Crisis gypsum deposits in the Mediterranean. According to these geochemical indicators and the uncertainty of the chronology of this unit, the assignment of the Rambla Salada Fm to the MSC cannot be ruled out.  相似文献   

Seasonal Variations in the Grain Size Distribution and Mineral Composition of Suspended Particulate Matter of the Northern Dvina River     

Gordeev  V. V.  Dara  O. M.  Alekseeva  T. N.  Kochenkova  A. I.  Boev  A. G.  Lokhov  A. S.  Belorukov  S. K. 《Oceanology》2020,60(3):384-392

Oceanology - The paper presents the first results of a study of seasonal variations in the grain size distribution and mineral compositions of suspended particulate matter (SPM) of the Northern...  相似文献