EJERS, European Journal of Engineering Research and Science
Vol. 3, No. 12, December 2018
This study had provided information of the stratigraphic TABLE I: STRATIGRAPHIC SUCCESSION OF ROCKS IN THE STUDY AREA
properties, CBR and bearing pressure of undisturbed AGE FORMATION LITHOLOGY
Medium to coarse grained
subsurface soils in the study area through field Dynamic Miocene-Recent Benin Formation poorly consolidated with clay
Cone Penetrometer Test (DCPT). lenses and stringers.
Tertiary-
Ogwashi-Asaba Unconsolidated sand with
Oligocene-
Formation lignite at various layers.
Miocene
II. STUDY AREA DESCRIPTION Grey clayey-sand stone and
Eocene Ameki Formation
sandy clay stone.
A. Location of the study Area Paleocene Imo Shale Laminated clayey-shale.
The study area; Owerri comprises Owerri Municipal, Maastrichian- Sand stone intercalated with
Nsukka Formation
Upper Cretaceous shale and coal beds.
Owerri-west and Owerri-north Local Government Areas
with parts of Mbaitoli and Ikeduru, It lies between latitudes
5020ʹ to 5032ʹN and longitudes 6051ʹ to 7008ʹ E, covering an
area of about 740 km2 (Fig. 1). The area is predominantly
low-lying with a good road network (Fig. 1) and the terrain
is characterized by two types of land forms namely, the
undulating in the northeast and nearly flat topography in the
southwest [19]. The topographical map of the study area
shows that the highest point in the area is 121.9 meters
above mean sea level while the lowest point is 45.7 meters
above mean sea level.
Fig. 2. Geological Map of Imo State, Nigeria Showing the Study Area
a) The Nsukka Formation: This was deposited during the
Maastrichian - Upper Cretaceous age [37]. This
formation consists essentially of dark shale, sandy
shale, carbonaceous shales with thin coal seams. The
grains sizes are medium to coarse. It has some
sandstone members reported to be up to 15 meters.
Nsukka Formation is the oldest formation with the
Fig. 1. Location Map of the Study Area (Carved from NGSA [24]) thickness of more than 300 meters [26].
b) The Imo Shale: Imo Shale of Paleocene age was
B. Geology of the Study Area deposited during transgression period that followed
The study area is underlain by Benin Formation, which is the Cretaceous [37]. It developed as thick blue to
a significant geologic unit of Niger Delta Basin (Fig. 2). The greyish clay with a maximum thickness of about
Benin Formation is Oligocene in age. It is composed of 1000 meters. Uma and Egboka [37] reported Imo
continental flood plain sands and alluvial deposits. It is Shale as laminated clayey-shale which is impervious
estimated to be up to 2000 m thick [35]. The uppermost part and characterized by lateral and vertical variation in
of Benin Formation has been altered by interglacial lithology. It dips at angles 17o to 25o to the south-
transgressions during the Quaternary period [27]. The upper west and the south [36]. It includes three constituent
layers of the Late Quaternary Delta are comprised of inter- sandstones: The Igbabu, Ebenebe and Umuna
bedded layers of sand, silt and clay deposited during Sandstones outcropping at Imo River. The Umuna
changes in sea level [3]. The Benin Formation is better sandstone is composed of thick sandstone units and
minor shales and is generally less than 70 meters
known for its hydraulic properties and groundwater yielding
potential [4], [29], [25]. According to Abam et al. [1] Benin thick. The Ebenebe Sandstone occurs as a lens in the
Formation is relatively on the surface and encounters most northwestern extremity. It is similar in lithology to
physical infrastructural development that entail significant the Umuna sandstone but is relatively thicker with a
foundation engineering work, this makes the understanding maximum thickness of 130 meters [36].
of its geotechnical properties imperative. c) The Ameki Formation: Overlying the Imo Shale is the
The stratigraphy of the southeastern Nigeria (part of the Ameki Formation, which extends far south to the
study area) has been studied in detail by Uma and Egboka Okigwe area where most of it is covered by the Benin
[37]. The stratigraphic succession of rocks in the study area Formation. It was deposited during Eocene age [37]
(Table I) consists of Nsukka Formation, being the oldest and consists essentially of greenish-grey clayey
formation and followed by Imo Shale, Ameki Formation, sandstone, shale, and mudstones with interbedded
Ogwashi-Asaba Formation and Benin Formation [37]. limestone. Uma and Egboka [37] reported Ameki
Formation as grey clayey-sandstone and sandy
claystone. The lithologic units of the Ameki
Formation fall into two general groups [31], [39], [7];
an upper grey to green sandstone and sandy clay and
DOI: http://dx.doi.org/10.24018/ejers.2018.3.12.973 2
