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Geologic Principles
Published in Stephen M. Testa, Geological Aspects of Hazardous Waste Management, 2020
Eolian deposits are stratigraphically complex because of (1) differing spatial relationships of large-scale forms such as dunes, interdunes, and sand-sheet deposits relative to one another and to ectradune (noneolian) sediments and (2) varying dune types, each with its own cross-bedding patterns and different degrees of mobility; thus, there are different fluid-flow properties when consolidated or lithified. Sedimentary structures within eolian deposits include ripples, contorted sand bedding, cross-bedding with great set heights, normally graded beds, inversely graded beds, evenly laminated beds, discontinuously laminated beds, nongraded beds, and lag deposits along boundary surfaces and sets. Basic eolian bed forms as related to a number of slip facies are shown in Figure 3-14.
Sedimentary Environments and Facies
Published in Supriya Sengupta, Introduction to Sedimentology, 2017
The Permian Toroweap Sandstone of Arizona, the Mesozoic Navajo Sandstone of Utah and Arizona, the Aztec Sandstone of Nevada, and the Lower Bunter Sandstone of England are some of the well-studied ancient eolian deposits. The Late Proterozoic Venkatpur Sandstone of southern India is interpreted to be of eolian origin on the basis of (i) grain-flow strata, (ii) inverse graded translatent strata, (iii) adhesion laminae and (iv) grain-fall strata. Nine facies, representing both eolian and related aqueous environments, have been recognised within what is believed to be a well-developed erg. Cosets of large-scale cross-strata are present within this sand sea which terminates at an alternate sequence of eolian and marine sediments. The horizontally stratified units within the Ventatapur sandstone have been variously interpreted to represent interdune, inland sabkha, sand sheet and coastal sand flat deposits (Chakraborty 1991).
Barrier Islands
Published in Paul D. Komar, J. Robert Moore, CRC Handbook of Coastal Processes and Erosion, 1983
The rapid widening of these back-barrier lagoons is probably due to the high rate of subsidence of the Mississippi delta lobes. Parts of the Louisiana coastal plain may have been subsiding at a rate of 1 cm/year for the last few decades. The long-term average subsidence rate is probably somewhat less. The rapid subsidence of abandoned Mississippi delta lobes has two major consequences for barrier island evolution. First, the back-barrier environment is rapidly transformed from mainland marsh to an open marine sound. The barriers in this stage evolve through a detachment process as envisioned by Hoyt45 and Swift.97 Although the barrier continuously retreats through shoreface erosion at this stage (the Gulf beach of Isle Dernieres migrated 2 km landward between 1853 and 1974, Figure 22), the islands become progressively more separated from land since the mainland shore retreats faster under continued subsidence. Secondly, the sand bodies of the deltaic source sink progressively deeper. Ultimately, they subside below the level of the retreating shoreface, at which point they cease to be active sources of barrier sand. Although stratigraphic data are limited, suggestions are that shoreface erosion no longer reaches the distributary sand bodies of the St. Bernard delta beneath the Chandeleur Islands. The islands are transgressing landward into the gradually deepening Chandeleur Sound, and they lose sand to an offshore sand sheet.90 Because there is no present sand source balancing this loss to the marine environments, the subaerial portions of the islands must be rapidly decreasing in size. Historically, this decrease in island size is quite evident.82
Late glacial and Holocene sand drift in northern Götaland and Värmland, Sweden: sediments and ages
Published in GFF, 2019
Helena Alexanderson, Martin Bernhardson
At Tidaholm (Munkaledet), three late Holocene events separated by palaeosols are dated by single samples (Figs. 11 and 14B, Table 1). The oldest of these ages, 2.36±0.17 ka (event T2), overlaps with a storminess event recognised in south-western Sweden (Fig. 13E; De Jong et al. 2006; Kylander et al. 2016), but also coincides with a significant increase in agriculture in the area (Påsse & Pile 2016a). Given the complex geomorphology and low elevation (1–2 m) of the Munkaledet dunes (Fig. 10), it is not clear if the young ages close to the surface represent dune formation, reworking of an older dune (8.7–8.2 ka; Fig. 11), or sand sheet deposition. We find it most likely that the younger ages (events T3, T4), closer to the surface, reflect local sand sheet deposition as discussed later.
Neogene Billa Kalina Basin and Stuart Creek silicified floras, northern South Australia: a reassessment of their stratigraphy, age and environments
Published in Australian Journal of Earth Sciences, 2020
The following scenario is deduced from the paleogeography, distribution and character of the sediments. Sedimentation began in the Billa Kalina Basin with distribution of a sand sheet over the eastern part of the basin area. The dominant sand supply was from the northern Gawler Ranges via the upper part of the Kingoonya Paleochannel with a lesser contribution from the Willouran Ranges. At this stage the Denison–Willouran Divide separated the region from the Lake Eyre Basin to the north. Uplift on the Stuart Range Divide on the southwest margin of the basin temporarily blocked stream flow from the paleochannel, and along with southeast tilting of the whole area, created a lake, initially in the northwestern corner of the basin. Early stage streams flowing into this lake from the north, in the vicinity of present-day Stuart Creek, accumulated plant remains and were silicified. As the lake filled, lacustrine dolomite and palygorskite clay accumulated in the west, and an extensive series of shoreline deposits formed by reworking of the existing sediment blanket to the east, assisted by southeast tilting. The channels with the plant fossils were overtopped as the lake filled, burying the fossil-bearing sands. At lake-full stage, westerly flow into the Kingoonya Paleochannel was re-established, temporarily flooding Lake Younghusband and further cutting into local basement outcrops in the vicinity. As the connection between the upper and lower sections of the Kingoonya Paleochannel reformed in the vicinity of Kingoonya township, flow was re-established to the Eucla Basin, and the lake level fell, accompanied by a change to a more arid climate.
Prediction of gully erosion susceptibility mapping using novel ensemble machine learning algorithms
Published in Geomatics, Natural Hazards and Risk, 2021
Alireza Arabameri, Subodh Chandra Pal, Romulus Costache, Asish Saha, Fatemeh Rezaie, Amir Seyed Danesh, Biswajeet Pradhan, Saro Lee, Nhat-Duc Hoang
The highest slope in the study area is 69.56° with a mean of 3.4°. The depth of soil is varied from 6.8 to 165 m. Poor rangeland and agriculture-dry farming are the major land uses practices in the study area. Pebble fan shaped debris from alluvial deposits of upper maternal materials with total slope of 3 to 8%, coarse limestone fan shaped debris along with argillaceous limestone, limestone shale, limestone marl and old alluvial deposits with slope 5% are among the most important geomorphologic units. Quaternary lithotypes including pediment fan of low level and deposition in valley terrace, salt flat, sand dunes and sand sheet and clay flat are widely observed. In addition, aridisols is the dominant soil type in the region.