https://dx.doi.org/10.4314/gjgs.v17i1.4

GLOBAL JOURNAL OF GEOLOGICAL SCIENCES VOL. 17, 2019: 45-52 COPYRIGHT© BACHUDO SCIENCE CO. LTD PRINTED IN ISSN 1596-6798 45 www.globaljournalseries.com , Email: [email protected] THE BASEMENT AND TECTONISM OF THE RIVER JAMA’ARE FLOODPLAIN: DEDUCTION FROM DC RESISTIVITY DATA

M. Z. MOHAMMED (Received 25 May 2016; Revision Accepted 27 June 2016)

ABSTRACT

The analysis of DC resistivity data of part of the River Jama’are Floodplain, Northeastern Nigeria was carried out with a view to mapping the basement and the subsurface structures. One hundred and six Schlumberger Vertical Electrical Sounding (VES) stations located at the corners of a 225 x 225m square grid network were occupied. The inter- electrode spacing (AB/2) was varied from 1-225m. Results identified four subsurface geologic layers; topsoil, alluvial sand, Chad Formation/weathered column and basement bedrock as undulating and basal unit at different depths. Four major parallel basement depressions suspected to be regional faults striking approximately NW-SE were delineated. This trend correlated with the general trend of the regional structures in the Chad Basin. The isopach maps of the topsoil and alluvial sand mirrored a more recent NE-SW trend that correlated with the Tibesti-Cameroon trough. However, this recent induced tectonics was adjudged significant to hydrogeology in the area.

KEYWORDS: Resistivity, floodplain, basement, sounding, tectonics, hydrogeology

INTRODUCTION 602631.843 mE and 605356.818 mE and 1288367.009 mN and 1292062.197 mN of the Universal Traverse Geological/structural features with Mercator (UTM) coordinates of Zone 31 respectively. hydrogeological significance in semi-arid basins of the The study area covers an area extent of about 4.53 sedimentary/basement transitions include Kilometers square (Mohammed, 2007). The study area unconsolidated/consolidated deposits and narrow, is located within the southwestern edge of the Chad densely fractured zones associated with major faults or Basin of Nigeria (Hadejia-Yobe basin), and it belongs to folding axes (Medeiros and de Lima, 1989; Seaton and the sedimentary areas of the northeastern Nigeria. The Burbey, 2000). Such basins are structural depressions formations found in the study site include the that are commonly filled with Quaternary to Tertiary Cretaceous-Tertiary Chad Formation of Pleistocene age unconsolidated sediments (Mon and Vergara, 1987). In (Matheis, 1989), and alluvial deposits that overlie a typical basement terrain, troughs/depressions are directly the Chad Formation. The river alluvium deposits generally groundwater collecting centres and serve as along the major river- River Jama’are, consists of silts, aquifer units with considerably high groundwater clays, and sands while the Chad Formation constitutes potential due to their considerable thickness, high all Quaternary sediments of lacustrine origin underlying permeability and storage capacity (Olorunfemi et al, the surface deposits over a vast area in 1999). Provinces (Carter et al, 1963). Furon (1963) suggested Consequent upon this, A DC resistivity data that the Basin was a tectonic cross point between a NE- analysis was done to unravel and define the subsurface SW trending Tibesti-Cameroon trough and a NW-SE geological and tectonic settings of part of the River trending Air-Chad trough. The tectonic relief pattern of Jama’are Floodplain, Northeastern Nigeria. The study is this area may possibly consist of NW-SE trending horsts also intended to assess the influence of the subsurface and grabens with corresponding gentle undulations in geological and geologically induced tectonic settings on sedimentary cover (Schoeneich and Askira, 1990). The borehole failure or success in the area. study area is relatively flat terrain (average 370 m a.s.l.),

2. Description of the Study Area but slopes gently towards the south. A local topographic The River Jama’are floodplain is in the West Chad high is to the Northern edge of the area at Yola Basin, northern side of the – Jama’are highway, settlement. This makes the entire area vulnerable to about 30 km West of Azare town in Local periodic flooding at the peak of rainy season. Soil type is Government Area of Bauchi-State (Fig. 1 & inset), and lateritic on the topographic highs while more productive confined within longitudes 9 0 56’ 30” E and 9 0 58’ 00” E soils (sandy clay) occur along the downslope of the and latitudes 11 0 39’ 15” N and 11 0 41’ 15” N which floodplain. The drainage system is trellis type (FSN, approximate the easting and northing values of 1978).

M. Z. Mohammed , Department of Earth Sciences, Adekunle Ajasin University, Akungba-Akoko. Nigeria.

© 2019 Bachudo Science co. Ltd. This work is licensed Under Creative Commons Attribution 4.0 international license.

46 M. Z. MOHAMMED

8.00 E 10.00 E 12.00 E 14.00 E

LAKE CHAD

JIGAWA KATSINA JIGAWA YOBE

ree a r a; 'a ZAMFARA a am m Azare J a Katagum Kinsha J AZARE BIRNIN KEBBI BORNO

i Sakwa anj K L. BAUCHI KADUNA BAUCHI NIGER YOBE NIGER

FCTFCT re ABUJA a'a ABUJA 12.00 N am Sandigalou Udubo 12.00 N R. J Jama;are From Dutse Potiskum Azare To Maiduguri

Kilometre Faggo 0 100 KANO To Kano Kari

Ningi

Darazo Burra Zakara Miya

Madaki Zalanga Gubi Bure GOMBE Lame BAUCHI Bara To Gombe Alkalere KADUNA Dindima Bula Mainamaji Toro Zungun T. Wada

10.00 N 10.00 N B. Kasa Jagudi Study Area JOS Express/Major Road Tafawa Balewa Wikki Yuli State Capital Lere Boi Other Towns State Boundary

PLATEAU Kilometre

0 50 100

8.00 E 10.00 E 12.00 E 14.00 E

Fig. 1: Map of BauchiState showing the Study Area

3. METHOD OF STUDY maximum spread length of 450 m. The data were analysed and presented as depth sounding curve(s) One hundred and six (106) Schlumberger vertical /plot(s) and maps. The curves were interpreted electrical resistivity sounding data were collected with quantitatively by partial curve matching whose results PASI-E-Digit Resistivity Meter at the corners of a 225 x (geoelectric parameters i.e. layer resistivities and 225 m square grid network (Fig. 2). The inter-electrode thicknesses) were computer iterated with RESIST spacing (AB/2) was varied from 1-225 m with a software (Fig. 3) to obtain satisfactory/final results.

YOLA 53D 54 55

Disp. Schl. 52 51 50 49 48 47F G H E 1291500 R 41 43 45 1 'A A 40 42 44 46 4 M Headworks A 10 J 5 3 2 R 37 36 35 34 33 32 E 38 V I R 1291000 11 39 9 8 7 6 31 30

B21 22 23 24 25 26 27 28 29

1290500 20 19 18 17 16 15 14 13 12 I J

64 63 62 61 60 59 58 57 56

Schl. 65 66 67 68 69 70 71 72 73 1290000 Sabon Gari Fulani Hut 82 81 80 79 78 77 76 75 74 LEGEND K L Fulani Hut Preliminary Borehole 83 84 85 86 87 88 89 90 91 1289500 T Abandoned Borehole o

J a Hand Dug Well m 100 99 98 97 96 95 94 93 92 a M N ' 12 a E VES Location r A e 101 102 103 A B Geophysical Traverse 1289000 River 106 105 104 Digiza C Foot Path Minor Road 0 m 225 m 450 m From Azare Major Road 603500 604000 604500 605000

Fig. 2: Geophysical Data Acquisition Map showing VES Stations and Traverses

THE BASEMENT AND TECTONISM OF THE RIVER JAMA’ARE FLOODPLAIN 47

(KQH)

(KHKH)

Fig. 3: Computer Interpretation Result of VES Curves

4. RESULTS AND DISCUSSION The first layer constitutes the topsoil which is composecomposedd The geoelectric sections (Fig. 4) display the subsurface of dry and loose silty sand, the alluv ial sand, clay/sandy sequence and image the basement bedrock relief. The clay/Chad Formation/weathered basement column and sections show a maximum of four subsurface layers. the fresh basement bedrock.

48 M. Z. MOHAMMED

Fig. 4: Some of the Geoelectric Sections along N-S and E-W Traverses

(a) The Topsoil: It has resistivity values most northern and western edges of the site.From the topsoil occurring within 0-250 ohm–m. This indicates a wide resistivity map (Fig. 5), low and high resistivity zones textural/compositional variation in the topsoil. Typically, were delineated. More than 60% of the areal extent the resistivity of this sequence is in the lower hundreds displays low resistivity clayey horizons. The closures of ohm-m, with resistivity of <100 ohm-m typifying clay represent lateritic hardpan or sand. The thickness of the while the high resistivity (>100 ohm-m) may suggest topsoil ranges from 0.4 to 6.7 m, but is generally less sandy clay, clayey sand, sand, compact sand or lateritic than 3 m with the most frequent values occurring in the column (Ako and Olorunfemi, 1989; Olayinka and 1.0-2.0 m range. Figure 6 delineates three major parallel Olorunfemi, 1992; Olorunfemi and Okhue, 1992 and thicker portions that mirror a more recent NE-SW trend Omosuyi et al., 2003), as observed in few places, that correlated with the Tibesti-Cameroon trough. particularly in the topographical high areas in the

THE BASEMENT AND TECTONISM OF THE RIVER JAMA’ARE FLOODPLAIN 49

Fig. 5: Isopach Map of the Topsoil

YOLA 17.1 12.1

Disp. Schl. LEGEND

13.6 10.8 5.9 5.7 4.2 23.9 32 m 1.7 1291500 E 6.5 16.4 7.4 R 'A 5.3 11 11.7 4.1 A 8.3 Headworks M 28 m A 8.2 9.6 14.7 J 4.9 R 2 27.5 2.8 5.9 9.1 5.7 4 E V I 24 m R 1291000 3.5 11.3 2.1 3.9 15.1 14.2 9.3 8.7 20 m

18 14.7 9.9 7.5 4 10.1 9.9 7.8 14.9

16 m

1290500 3.6 21.2 20.5 3.9 20.1 11.7 21 26.7 13.6

12 m

10.4 7.5 8.9 5.5 5.9 8.1 32.2 13.6 10.2

Schl. 8 m

3.1 1290000 25.3 3.7 7.9 10 8 13.4 4.4 2.6 Sabon Gari Fulani Hut 4 m

5 10.5 7.3 14.1 11.9 18.3 13.9 2.5 2.3

Fulani Hut 0 m

5.8 11.5 15.5 2.1 12.6 7.3 5.4 25.9 1.7 1289500 T o Preliminary Borehole

J a m 2.6 30.8 10.8 6 21.9 16.2 5.3 10.2 1.6 a Abandoned Borehole ' a r 10 e Contour Line 2.6 9.1 14 2.1 VES Point + Thickness Value 1289000 River 17 18.4 28.8 Digiza Foot Path

Minor Road

Major Road 0 m 225 m 450 m From Azare

603500 604000 604500 605000

Fig. 6: Isopach Map of the Alluvium 50 M. Z. MOHAMMED

(b) Alluvium Layer: This layer is wet and usually layer are controlled by its degree of water saturation water saturated. It ranges in composition from silt to fine, (Zohdy, 1980; Odusanya and Amadi, 1990). Figure 7 medium and coarse sands and constitutes the second enables the spatial distribution and to a large extent, the layer with resistivity values that vary from 69 to 3079 vertical thickness of the alluvium to be evaluated. The ohm-m. The thickness of the alluvium generally varies linearly connected areas with thick alluvium may be from 1.6 to 32.2 m with the most frequently occurring indicative of network of ancient river channels within the thickness being in the 0 - 16 m range. The mean floodplain. These areas also mirror a more recent NE- thickness is 10.6 ± 7.1 m with a coefficient of variation of SW trend similar to the regional Tibesti-Cameroon 66.7%. The electrical resistivity characteristics of this trough.

YOLA 310 289.8 LEGEND

Disp. Schl.

236.9 274.8 285 314 313.9 299 350 m

F3 F4 343.4 1291500 317 319.9 337 E R 275.6 247.2 282.9 307 330 m 'A 283.6 Headworks A M 322 319 A 289.4 270.3 J R 341.1 295.9 286.6 260.3 299.8 318 328.9 E 310 m IV R 1291000 195.9 228.6 351.6 347.3 307.6 292.9 292.2 283.2 290 m

289.9 313.6 313.1 282.6 317.1 248.8 235.3 270 m F2278.6 299

1290500 329.6 233.7 261.6 329.7 290.6 274.1 194.5 276.6 217.2F4 250 m

288.3 314 325.5 330.9 308.3 318.4 232.6 322.6 236.2 230 m

Schl.

321.5 210 m 1290000 310 331.5 285.1 286.7 299.1 292.4 280.4 278.9 Sabon Gari Fulani Hut F1 190 m 268.1 297.2 276.2 213.7 322.9 323.5 325 336.5 320.3 Preliminary Borehole Fulani Hut

287.2 325.4 303 310.5 267 318 299.9 263.5 F3 196.3 Abandonned Borehole

1289500 T o Hand Dug Well

J 290 a m 293.7 304 262 306.7 311.3 215.2 325.6 273.5 274.3 Contour Line a ' a r 270.3 e VES Point + Thickness Value

283 331.2 314 1289000 Deep Faults/Fracture Zones F2 River 311.5 F1 289 284.1 Digiza Foot Path

Minor Road 0 m 225 m 450 m From Azare Major Road 603500 604000 604500 605000

Fig. 7: Basement Relief Map of the Study Area

(c) Chad Formation/weathered basement: This judging from the relatively low layer resistivity, makes it is composed of varieties of clay materials i.e. reddish, more of an aquitard. milky and pinkish clay with coarse/gravelly or oxidized quartz/dirty sands intercalations. The layer resistivity (d) Basement Bedrock: The fourth layer is the values range from 11 to 140 ohm-m, with coefficient of presumably fresh basement bedrock (see Fig. 4). The variation of 51.2 % that indicates a near homogeneous layer resistivity values are generally >1000 ohm-m and unit. The most frequent occurring resistivity value is in most cases infinite. The overburden thickness or within 20-60 ohm-m range. Resistivity values less than depth to basement bedrock varies from 18.4 to 175.5 m between 20-60 ohm-m range may suggest plastic clay with a mean value of 78.1 ± 34.5 m and a coefficient of while values greater than 100 ohm-m may be typical of variation of 44.1%. The most frequently occurring sandy clay/sand. The thickness of this layer varies from thicknesses vary from 40-100 m. 15.9-168.6 m with most frequent occurring thickness of between 20-80 m. The wide spectrum of thicknesses The bedrock elevations vary between 190 and 350 m observed is due to the uneven topography of the signifying an uneven relief of the basement bedrock. basement bedrock. Figure 7 shows several The basement depressions correlate approximately discontinuous closures of high thicknesses typifying an along four parallel regional NW-SE trends. These uneven (undulating) basement bedrock relief. These linearly correlated depressions may be indicative of closures however show three major parallel regional deep seated faults. The hydrogeological significance of NW-SE trends. Although this horizon is significantly thick the basement bedrock relief was recognized by beneath several of the VES stations, its clayey nature Olorunfemi and Okhue, 1992; Dan - Hassan and THE BASEMENT AND TECTONISM OF THE RIVER JAMA’ARE FLOODPLAIN 51 Olorunfemi, 1999; Olorunfemi et al., 1999; Bala and Ike, Bornu Provinces in North Eastern Nigeria. 2001. Basement troughs are usually identified as Explanation on 1:250,000 sheets Nos. 25, 37 groundwater collecting centres, exception to this was and 47. Geological Survey Bulletin No 30. recorded in this sedimentary/basement transition area where basement troughs are filled with a complex Dan-Hassan, M. A and Olorunfemi, M. O., 1999. variation of facies changes mainly argillaceous clayey Hydrogeological investigation of a Basement Chad Formation. The formation grades into the basal Terrain in the North-Central part of Kaduna- clayey weathered basement layer with relatively low State, Nigerian Journal of Min. and Geol., 35, resistivity values that averaged about 40 ohm-m. The (2): 189-206. layer matrix is appreciably clayey constituting an impermeable block with tendency for limited or low F. S. N., 1978. National Atlas. Federal Survey of Nigeria, groundwater yielding capacity, in spite of its significant 1st edition, Federal Surveys of Nigeria,. Pp. 5- thicknesses (up to 175 m) within axis of the deep 11, 136. basement depressions. Furon, R., 1963. The Geology of Africa. Oliver and CONCLUSION Boyd, Edinburgh and London. 377.

Four subsurface geologic layers were identified Matheis, G., 1989. Short review of the geology of the from the geoelectric sequences. These include a topsoil Chad Basin in Nigeria In Geology of Nigeria. of variable moisture, alluvial sand, Chad (Kogbe, C. A.Ed.) Rock view International, Jos. Formation/clayey weathered column and basement Nig. Pp 341-346. bedrock. The layer resistivity and thickness ranges are 5 - 5706, 69 - 3079, 11 - 140 and 994- >1000 (infinity) Medeiros, W. E and de Lima, O. A. L., 1989. A ohm-m and 0.4 - 9.3, 1.6 - 32.2, 15.9-168.6 and depth to geoelectrical investigation for groundwater in bedrock of 18.4 to 175.5 m respectively. The variation in Crystalline terrains of Central Bahia, Brazil. In the overburden thickness pattern mirrors the irregular Groundwater. Vol. 28, (4): 518-523. geometry of the basement interface in several places. The linearly connected areas with thick overburden Mon, R and Vergara, G., 1987. The geothermal area of (along axis of the basement depressions) may have the eastern border of the Andes of north imaged a network of suspected parallel approximately Argentina at Tucuma’s Province. Bull. Internat. NW-SE trending deep faults within the basement Assoc. Engr. Geologists. Vol.35: Pp. 87-92. bedrock. The bedrock elevations vary between 190 and 350 m a.s.l. signifying a thickness pattern that is Odusanya, B. O and Amadi U. M. P., 1990. An empirical generally non-uniform or an uneven relief of bedrock resistivity model for predicting shallow ridges and depressions. Both the isopach maps of the groundwater occurrence in the Basement topsoil and alluvial sand mirror a more recent NE-SW Complex. Water Resources. Journal of Nigerian trend that correlated with the Tibesti-Cameroon trough. Association of Hydrogeologist. 2, 77-87. However, the recent and shallow NE-SW structural trend and similar trend within the floodplain Olayinka. A. I and Olorunfemi, M. O., 1992. region are adjudged significant to future groundwater Determination of geoelectrical characteristics in resource development, with depthsnot greater than 35 m Okene area and implications for Borehole siting as optimum for excellent contribution to the volume of Journal of Mining and Geology. 28, (2): 403- the underground storagein the study area. 412.

ACKNOWLEDGEMENT Olorunfemi, M. O and Fasuyi, S. A., 1993. Aquifer types The management of Aim Consultants, Lagos is and the geoelectric/hydrogeologic appreciated for financing and providing logistic support characteristics of part of the central basement for the data acquisition. Also, Professor M. O. terrain of Nigeria (Niger State). Journal of Olorunfemi is acknowledged for editorial suggestions African Earth Sciences. 16, Pp. 309-317. and Late Dr. I. A. Idornegie is acknowledged for his field assistance. Olorunfemi, M. O., Ojo, J. S and Akintunde, M. O., 1999. Hydrogeophysical evaluation of the groundwater REFERENCES potentials of the Akure metropolis, Journal of Mining and Geology, 35, (2): 207-228. Ako, B. D and Olorunfemi, M. O., 1989. Geoelectric survey for groundwater inthe Newer Basalts of Olorunfemi, M. O and Okhue, E. T., 1992. Vom, Plateau State. Journal of Mining and Hydrogeologic and geologic significance of a Geology. 25, 247-250. geoelectric survey at Ile-Ife, Nigeria. Journal of Mining and Geology. 28, (2): 221-229. Bala, A. E and Ike, E. C., 2001. The aquifer of the Crystalline Basement rocks in Gusua area, Omosuyi, G. O., Ojo, J. S and Enikanselu, P. A., 2003. Northwestern Nigeria. Journal of Mining and Geophysical investigation for groundwater Geol., 37, (2): 177-184. around Obanla-Obakekere in Akure area within the Basement Complex of Southwestern Carter, J. D., Barber W., Tait, E. A and Jones, G. D., Nigerian Journal of Mining and Geology.149- 1963. The Geology of part of Adamawa, Bauchi and 151 52 M. Z. MOHAMMED Schoeneich, K and Askira, M. T., 1990. Water Zohdy, A. A. R., 1980. Electrical methods. In application resources of the Lake Chad Basin, Nigeria of surface geophysics to groundwater Journal of Nigerian Association of investigations (Techniques of water resources Hydrogeologists, Pp.56- 64. investigations of the United States Geological Survey), Bk. 2, Ch. D1, 26-27. Seaton, W. J and Burbey, T. J., 2000. Aquifer characterization in the Blue-Ridge physiographic province using resistivity profile and borehole geophysics; geologic analysis. J. Environ. Eng. Geophysics, 5, Pp. 45-58