NEARSHORE OCEANOGRAPHY

SO422, Spring 2009

 

SEDIMENT ANALYSIS LAB

 

Materials for each group of 2-3 students:

1.  Set of sieves (#5,#10,#18,#35,#60,#120,#230), pan, cover.

2.  Wire (coarse sieves) and nylon (fine sieves) brushes for cleaning sieves.

3.  Electronic balance, 0.01 g sensitivity.

4.  250 or 500 ml beaker.

5.  Sample splitter.

6.  Drying oven.

7.  Sieve shakers

7.  Log-normal graph paper.

8.  3 cycle semi-log paper.

 

Equations in SPM handout:

Mean = 0.333 * (f16+f50+f84)

Median = f50

Standard Deviation = s = 0.5 * (f84 - f16)

Skewness = a = (Mean - Median) / s  (in alphabetical order)

    (0 if mean and median are equal)

 

Conversions

Phi     =-log2(Dia mm/1mm)

logx(a) = logy(a)/ logy(x)

 

Equation not in text:

Uniformity Coefficient = U = D40(mm) / D90(mm) (These are in percent retained; alternatively the formula is often given as D60(mm) / D10(mm) which is percent passing).

 

 

Graph Paper

• Normal probability

• Semi-Log

Tools (USNA only)

• Grain shape

• Heavy mineral concentration

 

References

• Sand sizes, sieves, settling velocities  (Figure from USGS Open file Report 00-358)

• http://pubs.usgs.gov/openfile/of00-358/  USGS EAST-COAST SEDIMENT ANALYSIS: PROCEDURES, DATABASE, AND
  GEOREFERENCED DISPLAYS, U.S. GEOLOGICAL SURVEY OPEN-FILE REPORT 00-358

 

 

Procedure.

 

1.  For field samples, wash and thoroughly dry sand sample for 24 hour period in 105°C drying oven or on hot plates over low heat.  If sample contains a significant proportion of fines, it should be wet sieved (not covered in SO422).

 

2.  Insure that the sieves are clean with no sand left over from the last mids to use them.  Use the brushes to gently remove any sand: wire brush on coarse sieves, nylon brush on fine sieves. 

 

3.  Measure each sieve before the analysis, and then weigh them again after the sand has gone through the shaker.  The sand weight is the difference between the two weights.  You must use the same balance for both weighings.

 

4.  Preweigh each sieve and the pan.

 

5.  Weigh the beaker empty.

 

6.  Add about 150-300 g of sand to the beaker.  To get the sample, use the sand sample splitter to avoid bias (either subjectively selecting too many or too few of the little pebbles that may be present).  Weigh the beaker and sand, and calculate the total weight of your sand sample.  Too much sand will clog the sieves, while too little may not be representative of the overall sample.

 

7.  Sieve the sand through the nest of sieves for 5 minutes.  Insure that the sieves are in proper sequence, largest on top and smallest on the bottom.  Should the entire nest not fit, you can manually shake the top few sieves and remove them before placing on the shaker.

 

8.  Weigh each sieve and the pan, with sand.  Complete data sheet or use the computer program which will be available for Assateague samples.

 

9.  Clean up the sieves and lab.

 

Required for Lab Today:

 

For the two sand samples, perform a sieve analysis and compute appropriate graphical statistics (mean, standard deviation, and skewness).  Use both normal probability graph paper and semi-log paper.

 

For each sand, estimate the degree of rounding and the percentage of heavy (dark) minerals.

 

Insure that you can answer the following questions for the next quiz/exam; and can accurately plot data on the graphs.

a.  What is the difference between plotting diameter in phi size on an arithmetic axis and diameter in mm on a log axis? (Consider just the difference in the size axis.)

b.  What is the difference in shape of the cumulative frequency distribution on arithmetic and normal probability axes? (Consider just the difference in the percentage axis.)

c.  How does the color (mineral composition) vary from the top sieve to the bottom sieve?