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ABSTRACT
A comparison has been made of sand, silt, and clay percentage of 118 samples from the Ayeyarwady continental shelf, northern Andaman Sea, measured by the sieve-laser diffraction technique and by classical sieve-pipette methods. Clay and silt percentages determined by Malvern Mastersizer 2000 Laser Particle Size Analyzer are 37% and 157% of pipette clay and pipette silt percentages, respectively. Clay particles separated by the settling technique and having an apparent size of less than 2 µm when measured with laser diffraction show that 99% of the particles have an upper size range between 4.8 and 7.7 µm. A calibration relationship between pipette and laser diffraction techniques has been developed for the northern Andaman Sea. A clay particle size of 2 µm defined by the pipette technique corresponds best to a size of 6.2 µm defined by laser diffraction. For the laser data, when 6.2 µm is taken as the boundary between silt and clay, the results are comparable to pipette analysis. Use of the calibration relationship enables one to make use of the rapid laser diffraction size analysis technique for routine sediment texture analysis with high precision.
ADDITIONAL INDEX WORDS: Ayeyarwady continental shelf, marine sediments, size calibration relationship.
INTRODUCTION
Standard methods for grain-size analysis of coastal sediments are based on sieve analysis for the coarse fractions and on the settling technique for the fine fraction (FOLK, 1968; CARVER, 1971). The pipette methods require large amounts of material (more than 10 g), are tedious and time-consuming, and are subject to large operator error (SASTRY and MURTY, 1990; SYVITSKI, LEBLANC, and ASPREY, 1991). Classic settling techniques are therefore not suitable for rapid, accurate analysis of a large number of samples or for small sample quantities. Over the last few decades, various new methods for grain-size analyses have been developed: laser diffractometry (e.g., Malvern, Horiba, Sympatec, Coulter LS, etc. ), laser time-of-transition (e.g., Galai particle size analyzer), electroresistance particle counting (e.g., Coulter Counter), x-ray attenuation (SediGraph), etc. These new methods have several advantages. They require small amounts of sample (a few milligrams to a few hundred) and cover a wide range of grain sizes, and their measurements are very rapid (McCAVE and SYVITSKI, 1991). Some of them, like the LISST-IOO particle size analyzer, can also be...