GRANULOMETRY OF THE QUATERNARY SEDIMETES IN THE NASIRIYA QUADRANGLE (SHEET NH-38-03), IRAQ

Abstract

Statistical analysis is conducted for 39 sandy samples selected from 24boreholes drilled in the Mesopotamian Plain, southern Iraq. The samples are tested for grain size analysis to reveal its textural characteristics, depositional environment, transporting mechanism, and mean flow velocity during deposition. The majority of the samples are muddy sand, few are silty and clayey sand and one sample is sand. A Graphic method of frequency distribution analysis reveals that the mean size ranges from medium sand, (1.42) φ to fine silt, (6.07) φ with an average size of (4.2) φ. Skewness parameters range from (0.15) φ (fine) to 0.89 φ (very finely skewed). About 92 % of the samples lies within the very fine skewness category implying excess of fine particles (>10) %, which is a characteristic feature of old age river sediments. Sorting values range from 1.43 φ (poorly sorted) to 4.33 φ (extremely poorly sorted) with the very poorly sorted samples dominate the population. The kurtosis values range from 0.59 φ (very platykurtic) to 3.25 φ (extremely leptokurtic). About 90% of the samples are spread within the mesokurtic to very leptokurtic categories. Scatter plot diagram of graphic mean size versus graphic standard deviation indicates a river deposition environment. Probability charts of the samples point to rolling and sliding transporting mechanism for the sediments larger than 2 φ in size, as well, the saltation mechanism for the sediments in between 1.63 and 3.7 φ in size and suspension mechanism for the grains finer than 8 φ in size. The mean flow velocity during deposition ranges between 7.34 cm/s for sample with mean size of 4.9 φ and 94.77 cm/sec for sample with mean size of 1.4 φ.