Geology and Soils

Author: nick on 12-09-2013, 21:00, views: 2 853


(a) The geological formations in the area consist of the Quaternary sedimentary deposits, and the Tertiary Coastal Plain Sands, generally referred to as Calabar Formation.


The Quaternary sediments give rise to alluvial plains as well as the beach ridge sands. The alluvial plains include the mangrove mudflats, which are under the influence of tidal brackish waters along the coast and in the estuaries of rivers and creeks, and the fresh water flood plains and swamps which form the wetland environments found along the upper reaches of rivers, creeks, tributaries and meander belts. The beach ridge sands form some raised portion of land between the mangrove swamps and the shoreline. The mangrove mudflats contain strata of mixed inorganic matters and plant debris.


In the water courses of the freshwater alluvium, the sandy materials consist of yellow/milky white silt to fine-grained sand particles that are sub-angular to sub-rounded.


The flood plains and inter tributary areas have light grey to dark carbonaceous mud and clay.


The Tertiary Coastal Plain Sand, or Calabar Formation is older and consists of beds of unconsolidated coarse textured sandstones, inter-bedded with layers of fine grained massive clay.


Beach Ridge Soils The soils developed on Beach Ridge Sands are sandy and poorly drained. They are acidic, low in organic matter and clay content and, therefore, they have low capacity to adsorb and retain nutrients. They are generally poor in fertility and productivity and are, therefore, not important agriculturally. With proper management, coconut palm and cashew nut have, however, been found to thrive well in these soils.


Mangrove Soils


The mangrove soils are derived from a mixture of mineral and organic materials of marine origin. They are dark grey in colour and are periodically flooded with tidal water. They have high organic matter and are generally saline, supporting only salt-tolerant plants, such as mangrove trees and Nypa palms. When wet, they are neutral or alkaline in reaction, but when dry or drained, they become acidic. This is due to the presence of pyritic or sulphidic materials, which on aeration or oxidation, produce an appreciable amount of sulphuric acid. The soils are, in this respect, referred to as Acidic-Sulphate Soils. Being in a very difficult terrain, the soils have not been attractive for agricultural investment.


Floodplains Alluvial Soils


The soils of the floodplains, outside the influence of saline tidal waters, are non-saline, but are developed on sandy parent materials. They are low in fertility and have not been widely used for agricultural production. Because of the sandy parent materials and excessive flooding, they are also not suitable for wetland rice production. Where there is carbonaceous mud and clay, short-duration vegetable crops, like tomatoes, pepper, spinach, okra and cereals, like cowpea and maize, may be successfully and profitably raised during the short dry period of the year, when the floodplains would be dry. However, the most important economic crop in this wetland area is the raffia palm, which thrives very well in these hydromorphic soils.


Soils of the Coastal Plain Sands


The most important soils in the area are those, developed on Tertiary Coastal Plain Sands in the upland part of the local government area. Most of the farming activities are carried out in these soils. The soils cover over 60% of the total land area of the local government area.


The soils are deep, have loamy sand to sandy loam surface over clay loam to sandy clay subsoil. They have good physical attributes for seedbed preparation, but because of their sandy nature, they are fragile and highly susceptible to erosion.


The soils are acidic and are generally referred to as Acid Sands. They are well drained and strongly weathered. Generally, the soils are poor in fertility, suffering from maltinutrient deficiencies. The soils can, however, be made fertile and productive, if adequate soil management practices are adopted.

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Category: Physical Features and Natural Resources

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