Environmental Engineering Reference
In-Depth Information
Table 1.17
Classi
cation of sediments on the basis of particle size
Division
Subdivision
Diameter (mm)
Phi (
Ø
)-size
Sinking rate (cm/s)
10
6
Gravel
Boulder
>256
<
8
>4.29
×
−
2.68
×
10
5
to 4.29
×
10
6
Cobble
64
-
256
−
6to
−
8
10
3
10
5
Pebble
4
64
2to
6
1.05
×
to 2.68
×
-
−
−
2.62
×
10
2
to 1.05
×
10
3
Granule
2
-
4
−
1to
−
2
Sand
Very coarse
1
2
0 to
1
65.6
262
-
−
-
Coarse
0.5
1
+1 to 0
16.4
65.5
-
-
Medium
0.25
-
0.5
+2 to +1
4.09
-
16.4
Fine
0.125
0.25
+3 to +2
1.02
4.09
-
-
Very
ne
0.0625
-
0.125
+4 to +3
0.256
-
1.02
10
−
4
Mud
Silt
0.0039
0.0625
+8 to +4
<9.96
×
-
Clay
<0.0039
>8
Table 1.18
Types of sediment on the basis of origin
Type
Source
Favourable deposition site
Examples
Biogenous
Biota
Seabed under neritic
and oceanic zone
Coral, siliceous and calcareous oozes
Cosmogenous
Outer space
Seabed under pelagic zone
Meteorites
Hydrogenous
Chemical precipitation
from sea water
Seabed under neritic
and oceanic zone
Phosphates, manganese nodules
Lithogenous
Eroded rock, volcanoes
and airborne dust
Seabed under neritic
and oceanic zone
Boulder
-
sand, sand
-
silt, silt
-
clay
30 % of the biogenous particle, then only the
sediment may be referred to as biogenous type.
Essentially, biogenous particles may be rich in
calcium carbonate (calcareous), silicate (sili-
ceous) or phosphate (phosphatic) depending
upon whether they are derived from the shells of
foraminifers or diatoms or from the bones/scales
of marine vertebrates. The hydrogenous particles
are derived from inorganic chemical reactions in
water, which comprises the manganese nodules
of the ocean
according to the action of waves and currents.
The largest particles are deposited, whereas the
smallest grains move seaward in deep and are
eventually deposited in deep-water.
In coastal Bay of Bengal, the intertidal zone
registers a gradual change in the textural char-
acteristics from high water level to low water
level, indicating a sediment change from sandy to
silty nature. The sand
ats of the mixed and
open-sea intertidal zone consist of 90
fl
95 % of
-
c Ocean. The
lithogenous particles originate from the erosion
of rocks, the particles of which are transported in
the seas or rivers. A summary of the major types
of sediment is given in Table
1.18
. On the con-
tinental slope,
fl
oor in the Paci
ne sand. Sorting of sediments is
very systematic due to natural agents in the
present geographical locale. The surface of the
sand
ne to very
at is covered with crescentic ripples,
asymmetrical ripples, backwash ripples, ladder
back or cross ripples, swash marks, rhomboid
fl
the particles are sorted by size
