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 NIGERIA 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 Bauchi 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 Azare – Jama’are highway, settlement. This makes the entire area vulnerable to about 30 km West of Azare town in Katagum 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 SOKOTO JIGAWA KATSINA JIGAWA YOBE ree a r a; 'a ZAMFARA a am m Azare J a Katagum Kinsha J AZARE BIRNIN KEBBI KANO BORNO i Sakwa anj K L. BAUCHI KADUNA BAUCHI NIGER Gamawa 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 Misau KANO To Kano Kari Ningi Darazo Burra Zakara Miya Madaki Zalanga BAUCHI STATE 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.