Classification of Shallow Subsurface Heterogeneity, using 2-D Wenner Array and Induced Polarization Methods, in Parts of Southern Ijaw, Bayelsa State, Nigeria

An integrated study, consisting of 2-D Wenner array and Induced Polarization (IP) measured at five profiles, were used to characterize the near surface heterogeneity in Southern Ijaw area of Bayelsa State. Using Abem Terrameter (SAS 1000) for both measurements, five 2-D resistivity profile lines with electrode spacing of 5.00m and electrode spread of 100.00m were employed. Computer software, RES2DINV was adopted for the interpretation of the data while Microsoft Excel software was used for plotting the IP chargeability anomaly against electrode distance. The results showed various resistivity distributions with the lowest value of 1.98Ωm and highest value 638Ωm indicating fine Clay and medium coarse sand respectively. The resistivity varies horizontally and vertically, and such that at the base it is higher than that of the topsoil except in profiles 3 and 5. Resistivity ranges for the profiles are profile 1 (5.96-175Ωm), profile 2 (1.98-495Ωm), profile 3 (46.5-638Ωm), profile 4 (20.3-187Ωm) and profile 5 (10.1-485Ωm). Positive and negative Induced Polarization (IP) chargeability were recorded in all the profiles. However, at Profile 1(NDU New site), negative IP effect was encountered throughout with range values between 0 and -450ms chargeability. This result is associated with the distribution of chargeable zones in the ground and also due to a thin chargeable layer at the surface. Few measurable negative values were also recorded at Profiles 2, 3, 4 and 5. Positive IP values were encountered in greater part of the profiles: profile 2 (0 – 80ms) profile 3 (0-3ms) profile 4 (0- 3ms) and profile 5(0-8ms). The signatures obtained from the IP effects are indicators of Clay sediment of various compositions which corroborate with, to a reasonable extent, the observation from the inverse 2-D resistivity section. The sediments observed in the study area can be classified into clay, clayey sand, fine clayey sand and medium...