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high and IInd terrace is at the 4-11 m. height. (Fig.3) The main components of the younger alluvium is sand, silt and clay and are of different shades like yellowish brown, light yellow brown, very pale brown and reddish yellow. Sand mixed silt is commonly distributed. Fine sand in form of bands occur at Nandghat (table.1) (Plate. 1)
Table 1 S. No. Locality River Valley Colour
p.H.Value Clay Silt Grain size in mm Classification
Fine sand Coarse sand 1. Badeli
10 YR 4/4 Dark 6.8 21.250 42.000 30.150 6.600 Clay-Silty sand
yellowish brown 2. Tanhkapar Mahanadi 10 YR 714 Very 7.3 2.250 3.250 74.500 20.000 Sandy
pale brown Kasdol Mahanadi 7.5 YR 6/4 Light 7.3 25.474 4.750 66.300 5.475 Clayey sand
yellowish brown 4. Simga a Socnath river 7.5 YR 4/4 6.8 2.250 15.750 15.800 66.200 Sand
Between brown
to dark brown 5. Simga b Soenath river 10 YR 5/4 - 8.1 26.250 42.750 17.580 13.420 Clay - Silty sand
Yellowish brown 6. Sigmac Soenath river 10 YR 5/4 8.0 23.750 29.500 14.125 32.655 Silty clay sand
Yellowish brown 7. Nandghat Soenath river 7.5 YR 6/4 Light 8.3 2.000 3.250 84.5000 10.250
Sand Yellowish brown 8. Katgi Jonk river 7.5 YR 6/6 7.2 0.500 1.500 37.850 60.150 Sand
Reddish yellowish The Mahanadi and the tributaries preserve two gravels: Sandy pebbly gravel and High level gravel. The pebbles are round, semi-round and sometimes angular which are indicative of long distance travel in monsoonal floods. The torrential rain must have occurred in the valley due to which the current was so high that the river was able to cut into the Bedrock and presently flowing below 4-5 m. below the Bedrock exposed on the river bank. The younger alluvium in the valley is mostly sandy (Sandy clay, silty sand, clayey sand, silty clay sand). Sand rich sediments suggest that the alluviation in valley has taken place by short lived floods in a near channel environment. At Nandghat, these sediments occur in form of bands indicating that they were laid down in a stagnant pool environment. Laboratory studies of sediments conducted has given pH value from 6.8-8.3 with traces of carbonate and is indicative that the sediments of the valley are slightly acidic to alkaline. (Table.1) Chemical properties are also indicative of modern to strong leaching conditions in the post depositional period. The contents of organic carbon and organic matter in the Mahanadi valley is also low, suggestive of the sediments exposed to atmospheric weathering in which oxidization of sediments took place.
The alluvium laid down in the valley is by the monsoonal fed rivers and mostly are of the shades of brown. This character of sediments is again suggestive of the sediments suggestive of oxidization and formation of limonitic iron due to weathering or due to alluviation in sesquioxide horizon, may be
