scholarly journals The Tiskilwa Till, a Regional View of its Origin and Depositional Processes

1981 ◽  
Vol 2 ◽  
pp. 176-182 ◽  
Author(s):  
Susan Specht Wickham ◽  
W. Hilton Johnson
Keyword(s):  
Thermal Regime ◽  
Controlling Factor ◽  
Local Source ◽  
Source Areas ◽  
Depositional Processes ◽  
Red Color ◽  
Major Controlling Factor ◽  
Late Wisconsinan

The Tiskilwa Till Member of the Wedron Formation represents deposition by basal melt-outin the marginal area of the Laurentide ice sheetduring the Woodfordian (late-Wisconsinan) in Illinois. Distinctive characteristics include: a very thick, homogeneous till; relatively little ablation till; red color; sandy texture; illite content that is relatively low withrespect to other Woodfordian tills; and the presence of discontinuous basal zones of differing composition.Erosion and entrainment of debris from both distant and local source areas are evident in the Tiskilwa Jill. Basal thermal regime is suggested as a major controlling factor on the location of the zones of entrainment. The debris was homogenized en route to the margin and eventually was deposited as basal melt-out till near the margin. Deposition occurred within an interval of 6 ka or more during the first half of the Woodfordian.

scholarly journals Seasonal provenance changes in present-day Saharan dust collected in and off Mauritania

2017 ◽  
Vol 17 (16) ◽  
pp. 10163-10193 ◽  
Author(s):  
Carmen A. Friese ◽  
Johannes A. van Hateren ◽  
Christoph Vogt ◽  
Gerhard Fischer ◽  
Jan-Berend W. Stuut
Keyword(s):  
Environmental Changes ◽  
Saharan Dust ◽  
Local Source ◽  
Trade Wind ◽  
Back Trajectory ◽  
Dust Source ◽  
Western Sahara ◽  
Source Areas ◽  
Source Regions ◽  
Dust Sources

Abstract. Saharan dust has a crucial influence on the earth climate system and its emission, transport and deposition are intimately related to, e.g., wind speed, precipitation, temperature and vegetation cover. The alteration in the physical and chemical properties of Saharan dust due to environmental changes is often used to reconstruct the climate of the past. However, to better interpret possible climate changes the dust source regions need to be known. By analysing the mineralogical composition of transported or deposited dust, potential dust source areas can be inferred. Summer dust transport off northwest Africa occurs in the Saharan air layer (SAL). In continental dust source areas, dust is also transported in the SAL; however, the predominant dust input occurs from nearby dust sources with the low-level trade winds. Hence, the source regions and related mineralogical tracers differ with season and sampling location. To test this, dust collected in traps onshore and in oceanic sediment traps off Mauritania during 2013 to 2015 was analysed. Meteorological data, particle-size distributions, back-trajectory and mineralogical analyses were compared to derive the dust provenance and dispersal. For the onshore dust samples, the source regions varied according to the seasonal changes in trade-wind direction. Gibbsite and dolomite indicated a Western Saharan and local source during summer, while chlorite, serpentine and rutile indicated a source in Mauritania and Mali during winter. In contrast, for the samples that were collected offshore, dust sources varied according to the seasonal change in the dust transporting air layer. In summer, dust was transported in the SAL from Mauritania, Mali and Libya as indicated by ferroglaucophane and zeolite. In winter, dust was transported with the trades from Western Sahara as indicated by, e.g., fluellite.

scholarly journals A new approach to mapping landslide hazards: a probabilistic integration of empirical and process-based models in the North Cascades of Washington, U.S.A.

2019 ◽  
Author(s):  
Ronda Strauch ◽  
Erkan Istanbulluoglu ◽  
Jon Riedel
Keyword(s):  
Statistical Approach ◽  
Landslide Hazard ◽  
Ratio Method ◽  
North Cascades ◽  
New Approach ◽  
Source Areas ◽  
Depositional Processes ◽  
Debris Avalanches ◽  
Landslide Hazards ◽  
Infinite Slope Stability Model

Abstract. We developed a new approach for mapping landslide hazard by combining probabilities of landslide impact derived from a data-driven statistical approach and process-based model of shallow landsliding. Our statistical approach integrates the influence of seven site attributes on observed landslides using a frequency ratio method. Influential attributes and resulting susceptibility maps depend on the observations of landslides considered: all types of landslides, debris avalanches only, or source areas of debris avalanches. These observational datasets reflect the capture of different landslide processes or components, which relate to different landslide-inducing factors. Slopes greater than 35° are more frequently associated with landslide initiation, while higher landslide hazards at gentler slopes (< 30°) reflect depositional processes from observations of all landslide types or debris avalanches. Source areas are associated with mid to high elevations (1,400 to 1,800 m), where they are linked to ecosystem transition (e.g., forest to barren), while all landslides types and debris avalanches show increasing frequency in lower elevations (< 1,200 m). Slope is a key attribute in the initiation of landslides, while lithology is mainly linked to transport and depositional processes. East (west) aspect is a positive (negative) landslide-influencing factor, likely due to differences in forest cover and associated root cohesion, and evapotranspiration. The empirical model probability derived from debris avalanche source area is combined probabilistically with a previously developed processed-based probabilistic model to produce an integrated probability of landslide hazard for initiation that includes mechanisms not captured by the infinite slope stability model. We apply our approach in North Cascades National Park Complex in Washington, USA, to provide multiple landslide hazard maps that land managers can use for planning and decision making, as well as educating the public about hazards from landslides in this remote high-relief terrain.

scholarly journals Significance of Sedimentological Studies on the Wisconsinan Stratigraphy of Southern Ontario

2007 ◽  
Vol 39 (3) ◽  
pp. 255-273 ◽  
Author(s):  
David R. Sharpe ◽  
Peter J. Barnett
Keyword(s):  
Lake Basin ◽  
Glacial Ice ◽  
Southern Ontario ◽  
Depositional Processes ◽  
Stratigraphic Framework ◽  
Large Channel ◽  
Late Wisconsinan ◽  
Subglacial Meltwater ◽  
Main Effects

ABSTRACTDetailed facies mapping along Lake Erie and Lake Ontario Bluffs, plus other studies illustrate that sedimentological studies, especially those with geomorphic or landform control, have had three main effects on the Wisconsinan stratigraphy of Ontario: (1) improved understanding of depositional processes and environments of several major rock stratigraphic units, without altering the stratigraphic framework, (2) aided correlation of drift sequences, and (3) questioned previous interpretations and stratigraphic correlations of drift sequences. Thus sedimentological analysis can not be separated from stratigraphy because the interpretation of depositional environnments of many mapped strata relies on their geometry and the inclusion of regional data. The geomorphic control provided by sedimentological study of surface landforms is also important because assessment of older buried sediments such as those at the Scarborough Bluffs has been hampered by the failure to determine landform control. The Late Wisconsinan stratigraphy of Southern Ontario generally remains unchanged, except for questions on the role of climate versus ice margin dynamics. The pre-Late Wisconsinan stratigraphy is scarce and not well defined, yet sedimentary studies support the presence of glacial ice in the Ontario Lake basin for all of the Middle Wisconsinan and possibly earlier, including the formation of the Scarborough delta. Large channel cut and fill sequences in the Toronto area (Pottery Road Formation), initially interpreted as resulting from subaerial erosion, were probably formed by subaqueous or subglacial meltwater erosion. If so, the pre-Late Wisconsinan stratigraphy in southern Ontario changes because the Pottery Road Formation may not be an Early Wisconsinan correlative of the St. Pierre beds. The channel example illustrates that stratigraphie correlation without sedimentological investigations may be misleading.

scholarly journals Clay minerals as provenance indicators in continental lacustrine sequences: the Leza Formation, early Cretaceous, Cameros Basin, northern Spain

Clay Minerals ◽  
2005 ◽  
Vol 40 (1) ◽  
pp. 79-92 ◽  
Author(s):  
J. Alonso-Azcárate ◽  
M. Rodas ◽  
J. F. Barrenechea ◽  
J. R. Mas
Keyword(s):  
Clay Mineral ◽  
Source Area ◽  
Local Source ◽  
Northern Spain ◽  
Source Areas ◽  
Kübler Index ◽  
Facies Associations ◽  
Mineral Assemblages ◽  
Cameros Basin

AbstractVariations in clay mineral assemblages, changes in Kübler index (KI), and the chemical composition of chlorites are used to identify source areas in the lacustrine materials in the Lower Cretaceous Leza Limestone Formation of the Cameros Basin, northern Spain. This formation has fairly homogeneous lithological characteristics and facies associations which do not allow for identification and characterization of local source areas. The Arnedillo lithosome of the Leza Limestone Formation contains a clay mineral association (Mg-chlorite, illite and smectite) indicative of its provenance. Chlorite composition and illite KI values indicate that these minerals were formed at temperatures higher than those reached by the Leza Formation which indicates its detrital origin. The similarity in the Mg-chlorite composition between the Arnedillo lithosome and the Keuper sediments of the area indicates that these materials acted as a local source area. This implies that Triassic sediments were exposed, at least locally, at the time of deposition of the Leza Formation. The presence of smectite in the Leza Formation is related to a retrograde diagenesis event that altered the Mg-chlorites in some samples.

scholarly journals Freezing Fronts and their Possible Influence upon Processes of Subglacial Erosion and Deposition

1981 ◽  
Vol 2 ◽  
pp. 52-56 ◽  
Author(s):  
John Menzies
Keyword(s):  
Shear Strength ◽  
Pore Water ◽  
Thermal Regime ◽  
Water Movement ◽  
Water Interface ◽  
Freezing Front ◽  
Erosion And Deposition ◽  
Depositional Processes ◽  
Ice Water ◽  
Front Movement

Recent studies have shown the important influence of pore-water movement and the subglacial thermal regime on processes of erosion and deposition at the subglacial interface. the influence of migrating freezing fronts within subglacial material has been largely ignored. the phenomena of ice-water interface processes will be examined and their relevance to subglacial processes illustrated. four case studies are presented that deal with the various effects that freezing-front movement may have on pore water, consolidation, shear strength, and likely diagenetic characteristics of subglacial deposits. the influence upon erosional and depositional processes will be outlined, and a mechanism related to potential surge-like conditions within the subglacial zone postulated.

scholarly journals Aspect Ratio: A Major Controlling Factor of Radiation Characteristics of Microstrip Antenna

2011 ◽  
Vol 03 (11) ◽  
pp. 452-457 ◽  
Author(s):  
Syed Md. Danish Abbas ◽  
Sharmistha Paul ◽  
Jhelam Sen ◽  
Prity Rani Gupta ◽  
Kaushik Malakar ◽  
...  
Keyword(s):  
Aspect Ratio ◽  
Microstrip Antenna ◽  
Controlling Factor ◽  
Radiation Characteristics ◽  
Major Controlling Factor

scholarly journals OSL dating and lithological characteristics of loess deposits from Biały Kościół

2011 ◽  
Vol 38 (2) ◽  
pp. 162-171 ◽  
Author(s):  
Piotr Moska ◽  
Grzegorz Adamiec ◽  
Zdzisław Jary
Keyword(s):  
Grain Size ◽  
Size Composition ◽  
Proxy Record ◽  
Grain Size Composition ◽  
Source Areas ◽  
Depositional Processes ◽  
History Of ◽  
Absolute Dating ◽  
Loess Profile ◽  
Loess Deposits

Abstract Absolute dating using luminescence methods is widely applicable in geology, geomorphology, palaeogeography and in archaeology in establishing ages of sediments and archaeological artefacts. By creating absolute time scales for different events in the history of Earth scientists are able to reconstruct changes in climate and environment in the past, and the history of colonization and development of culture. Grain size is the most important loess lithologic property. Grain size composition depends mainly on factors connected with depositional processes (i.e. variety of source areas, distance from source areas, frequency and intensity of dust transporting winds). The influence of post depositional processes on changes in grain size composition seems to be of less importance with the exceptions for warm and long periods of intensive pedogenesis, which are favorable for formation of clay minerals. Therefore the grain size differentiation within thick loess sections may be used as a proxy record of climate changes during loess cover development. Here we present results for 12 samples dated at the profile at Biały Kościół. Obtained OSL results in some cases are quite different as compared with the OSL and TL dates obtained during last 10 years by other authors and presented in previous publications relating to this loess profile.

scholarly journals Modeling the diurnal tide with dissipation derived from UARS/HRDI measurements

1997 ◽  
Vol 15 (9) ◽  
pp. 1198-1204 ◽  
Author(s):  
M. A. Geller ◽  
V. A. Yudin ◽  
B. V. Khattatov ◽  
M. E. Hagan
Keyword(s):  
Annual Variation ◽  
Lower Thermosphere ◽  
Controlling Factor ◽  
Diurnal Tide ◽  
Tide Model ◽  
Major Controlling Factor ◽  
Model Structures

Abstract. This paper uses dissipation values derived from UARS/HRDI observations in a recently published diurnal-tide model. These model structures compare quite well with the UARS/HRDI observations with respect to the annual variation of the diurnal tidal amplitudes and the size of the amplitudes themselves. It is suggested that the annual variation of atmospheric dissipation in the mesosphere-lower thermosphere is a major controlling factor in determining the annual variation of the diurnal tide.

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