The use of grain‐size distribution patterns to elucidate aeolian processes on a transverse dune of Thar Desert, India

Abstract

The grain-size distribution of aeolian dune sands in the Thar Desert, India was analyzed and compared with three model distributions -log-normal, log-hyberbolic and log-skew-Laplace -to determine the best-fi t statistical model. In total, 51 samples were collected along a single transect over a transverse dune, of which 15 were from the stoss side, 12 from the crest and 24 from the lee side. Samples were collected during a calm period in the afternoon of a winter's day. It was observed that of these 51 samples, 33 fi t best to a log-hyperbolic distribution, 14 fi t best to a normal distribution and only four fi t best to a Laplace distribution. However, it was further observed that of 24 samples from the lee side, 13 fi t best to a normal distribution, eight fi t best to a hyperbolic distribution, and three fi t best to a Laplace distribution. Of 12 samples from the crest of the dune, 11 fi t best to the log-hyperbolic distribution, only one to the Laplace distribution but none to a normal distribution. Of 15 samples from the stoss side of the dune, only one sample best-fi ts a normal distribution, 14 fi t best to a log-hyperbolic distribution, and none best fi t to a Laplace distribution.During sample collection a calm period prevailed and there was no dusty wind. It was therefore assumed that in the initial stage a mixture of coarse, medium and fi ne sands was laid down on the stoss side of the dune. As wind speeds increased and saltation started, the coarser fractions were segregated and lagged behind on the stoss slope. In the fi nal stage when the remaining intermediate and fi ner fractions reached the dune crest, the fi ner fractions were winnowed away to suspension from the crest of the dune. As a result, a narrow range of intermediate sized sediments was deposited by rolling down the lee side to explain the development of log-normality. In such a situation, both the coarser and fi ner fractions, to which the skewed distributions can be attributed, are separated from the initial mixture of coarse, intermediate and fi ne fractions. Hence the main criteria for the development of a normal distribution is the lack of skewed fractions and the concentration of the narrow, intermediate size fractions in the fi nal grain size distribution. This is also corroborated with the index of symmetry, which is a measure of the difference between the angle of two slopes of the hyperbolic distribution as represented by the coarser and fi ner fractions.

Sediment Distribution Based on Grain Size Analyses in Weda Bay, Northern Maluku

“…Beberapa peneliti terdahulu telah melakukan penelitian terkait analisis distribusi ukuran butir untuk memberikan penjelasan tentang perubahan spasial, proses pengendapan, karakteristik lingkungan sedimen, distribusi ukuran butir, proses sortasi dan mengidentifikasi sumber sedimen suspensi (Gao and Collins, 1992;Cheng et al, 2004;Folk and Ward, 1957;Passega, 1957Passega, , 1964Friedman, 1961;Glaitser and Nelson, 1974;Gao et al, 1994;Wang and Ke, 1997;Lario et al, 2002;Pascoe et al, 2002;Mc Laren et al, 2007;Poizot, 2007;Roux and Rojas, 2007;Purkait, 2010;AlHurban et al, 2008;Kurashige and Fusejima, 1997). Analisis perubahan spasial dalam parameter ukuran butir (rata-rata, sortasi dan skewness) merupakan salah satu metode yang 230 http://itk.fpik.ipb.ac.id/ej_itkt61 digunakan untuk identifikasi jalur transportasi sedimen dengan menggunakan metode analisis granulometri.…”

Response of dune mobility and pedogenesis to fluctuations in monsoon precipitation and human activity in the Hulunbuir dune field, northeastern China, since the last deglaciation

“…Thus, the mean grain size of the aeolian sand (1.88 ϕ) and sandy paleosol (2.01 ϕ) of the Hulunbuir dune field is within the range of variation of deserts elsewhere in China and worldwide (Zhu et al, 2014). Although their mean grain size is roughly comparable to that of the Mu Us dune field, the Otindag dune field and the Horqin dune field in northern China (Shen et al, 2016), it is coarser than that of the the Taklimakan Desert (Zhu et al, 2014), Badan Jaran Desert (Zhu et al, 2014), Namib Desert (Lancaster, 1981), Thar Desert (Purkait, 2010) and Simpson Desert (Folk, 1971), which are dominated by mobile dunes composed of fine sand-very fine sand (2-4 ϕ). We suggest that the coarser aeolian sand in the stabilized and semi-stabilized dunes can be attributed mainly to the relatively brief transport time and short transport distance because of the denser vegetation coverage compared to the mobile dunes.…”

“…The grain-size distribution is a fundamental physical property of clastic sediments and it is affected by sediment source, transport conditions, the sedimentary environment and post-depositional pedogenesis (Visher, 1969). Grain-size parameters and the grain-size distributions of sediments can provide insights into depositional processes and dynamics and material sources and thus they can be used to determine the type of and changes in the sedimentary environment (e.g., Folk and Ward, 1957;Visher, 1969;Folk, 1971;Lancaster, 1981;Livingstone et al, 1999;Ding et al, 2001;Purkait, 2010). The grain-size distribution data and related statistical parameters of all samples in this study are listed in Table S3.…”

The Effect of Flood to Quality Index of Soil Physical Properties at the Downstream of Kuranji River Watershed, Padang City

“…Purkait [10] also states that soil physical characteristics are often determined by soil texture, since soil texture greatly affects other physical properties, such as bulk density, groundwater movement, specific surface area and soil density.…”