IDENTIFICATION OF THE STRATA OF LATERITIC SOILS AND ALTERITES IN BENIN

Victor S. Gbaguidi 1 , Yvette Tankpinou Kiki 2 , Crépin Zevounou 1 , Nestor Vedogbeton 1 and Marcel Zankpe 1 . 1. University of Abomey-Calavi (UAC). 2. National University of Sciences, Technologies, Engineering and Mathematics (UNSTIM). ...................................................................................................................... Manuscript Info Abstract ......................... ........................................................................ Manuscript History Received: 05 July 2018 Final Accepted: 07 August 2018 Published: September 2018

The country has five main geological sites:1) the coastal sedimentary basin; 2) the Paleo-Mesozoic basin of Kandi; 3) the outer area of the Dahomeyides Pan-African chain, including the tectonic units of Atacora (quartzites, shales, prasinites, sandstones), Buem (sandstone, jasper, volcano-sediments), and their foreland, the Pendjari basin (mudstones, siltstones, clay and sandstones); 4) the internal area of the pan-African chain of Dahomeyides, including the Benin plain structural unit commonly called crystalline bedrock and pan-African syn-to-tectonic intrusions; 5) volcano-sedimentary formations consisting of rhyolites, basalts and dolerites associated with molasses' series.

Calculation of reserves
In the field, the coordinates of the summits of each site have been recorded. At the end of the works, the perimeters of the prospected sites were determined and their areas as well. Knowing the thickness of the raw material based on 284 the wells' depth, the reserves were calculated in cubic meters (m 3 ) then in tonne (t). These reserves are proven reserves, given the spatial continuity and depth of the prospected layers.

Sampling
Compared to potential sites, especially those selected for sinking wells, three (03) research wells were dug, and each of them, down to a depth of 5m for each plateau. The well has a square section, hand dug with 1m as side. Wells are sampled from 1m passes piles. The constitution of the sample, obtained representing the entire well by quartering.
285  There is a coherent appearance of the primeval lateritic soils (Fig 4). The color of these soils varies from one site to another. Nevertheless, it tends towards the brick red color. For alterites, their color is more or less hardened appearance is noted (Fig 5). The different logs and section of wells show homogeneity lateritic soils. Figure 6 shows this trend where topsoil, reddish sandy clay, and predominantly brick-red sandy clay are noted. Thus the same aspect was obtained for 13 sites out of 18: Adjarra -Allada -Ouidah -Toffo -Come -Bopa -Houeyogbe -Abomey -Lokossa -Dogbo -Aplahoue -Agbangnizoun -Zakpota.
The observation of plateaux located in the North of the Lama depression (Aplahoué, Abomey, Kétou, Zagnanado), between Lanta and Adjahonmè, along the Abomey-Azovè road showed that the brick red sand-clay formations, developed in fractured areas and on quartz sands with conglomerate levels and oblique starifications; they are alteration facies (IRB, 1985).
In Fig 11-a, the physical continuity of the gravelly horizons testifies the autochthonous character of the relics and the in-situ alteration of the clayey earth. Fig 11-b shows the clayey Earth within the sound rock in connection with particularly joint areas where fracture intensifies the pedogenetic mechanism.
Horizons A1, A2 and B are the one commonly sampled for alterite basement. Soils that are poor in clay and essentially leached (Fig 18).

Reserves evaluation
According to the departments and the geological field, table 1 and table 2 present the explored clayey soil and laterite sites, their areas, the depth of the investigated wells, the minimum volumes and the geographical coordinates of the top of each site.

Conclusion:-
This study is an exploration of sites of raw materials used in the production of soil agglomerates in Benin Republic in order to make the local building materials accessible. Lateritic soils and alterite favorable sites have been identified in many departments over the country, on the plateaux of the sedimental coastal basin (clayey soil) and the crystalline basement, Buem and the sedimental basin of Kandi.
The well sections show a homogeneity as far as clay sandy formations named 'clayed soil' are concerned, with a brick red colour prevailing; whereas the alterite sites offer a variety. Moreover, clayey soil appears as primeval coherent soils while alterites are more or less hardened. In general, the section at the basement level varies from 1.2 to 2.2m in comparison with the plateaux where the wells' depth can reach 5m. The confirmed clay reserves are evaluated at 10.410.949 m 3 and those of the laterite at 724.806 m 3 . Additional sites can also be explored. Thus, raw materials that can be used in the production of building local materials, such as agglomerate with stabilized soil exist and their exploitation should be welcome.