NAPENews Magazine September 2022 Edition

Planolitesmontanus. The fossiliferrous limestone is made up essentially of mineralised bivalve shells. The abundance of trace and body
fossils suggest aerobic conditions in the water column in which organisms thrived (Ekwenye et al., 2014). This part of FA 4 is interpreted as
the foreshore (Figure 4A).
Figure 3: Fluvial and shoreface facies associations. (A) and (B) are
representative logs of the fluvial and shoreface facies
associations in the study area respectively. (C) is an
outcrop image of fluvial channel deposit at Government
Technical College, Akpoha. (D) and (E) are outcrop
images of shoreface deposits at Setraco Quarry, Amenu,
and Julius Berger Quarry, Ibi.
Figure 3: Shoreface-foreshore facies associations. (A) is a
representative log of the upper section of the shorefaceforeshore
facies associations. (C) and (D) are outcrop
images of shoreface and foreshore deposits at Ibi.
Facies Association 5 (FA 5): Tidal sand
ridges
FA 5 is dominated by planar cross-bedded
facies (Sp1 and Sp5), in addition to
h o r i z o n t a l l a m i n a t e d
s a n d s t o n e f a c i e s ( S h 1 a n d S h 3 ) ,
structureless sandstone facies (Sm1 and
Sm3), herringbone sandstone facies (Sxh),
and fine-grained bioturbated sandstone
facies (Sb1). Exposures of FA 5 are
observed at Ozara-ukwu. The sandstone
occurs as elongate ridges. Estimated
outcrop thickness is about 26m. The
outcrops are dominated by large and smallscale
cross-beds which are interpreted to
results of the migration of large- and smallscale
sand waves (Stride et al., 1982;
Bridges, 1982). The predominantly
southwest azimuths of the cross-beds
indicate unimodal paleocurrent flow
direction. However, herringbone cross-beds
as well as single sets of cross-beds in the
reverse direction are evidence of
subordinate bimodal paleocurrent flow. The
NE-SW strike/trend of the tabular beds and
ridge axes are oriented at oblique angles to
the paleo flow direction, indicating that the
sands are longitudinal bedforms which are
interpreted to be tidal sand ridges (Stride et
al., 1982; Belderson et al., 1982); otherwise
referred to as offshore or shorelineassociated
tidal sand ridges (Johnson and
Baldwin, 1996), tidal current sand ridges or
offshore sand ridges (Nichols, 2009). They
are large-scale asymmetric bedforms with
long axes oriented up to 20° to the direction
of the strongest tidal currents (Off, 1963;
Kenyon et al., 1981). Tidal sand ridges form
at near-surface mean spring tidal current
- 1
velocities of about 50 to 100cms
(Belderson et al., 1982). The sandstones
are observed to be bioturbated by
Ophiomorphaburrows.
Facies Association 6 (FA 6): Tideinfluenced
fluvial channel
FA 6 is comprised of conglomerate facies
(G3), structureless sandstone facies (Sm1
and Sm2), muddy heterolith facies (Hm),
sandy heterolith facies (Hs), horizontal
laminated sandstone facies (Sh3), the
angular-based planar crossbedded
sandstone facies with mud drapes (Sp3),
and the bioturbated sandstone facies (Sb1)
(Figure 5A). FA 6 is exposed at the road cut
section of the “Waterworks” sandstone,
located midway between the Government
College Roundabout in Afikpo and the Y-
junction (Amasiri Junction) which connects
the Afikpo-Okigwe Road and the Afikpo
Abakaliki Road. The exposure which is
about 50m thick, is made up of steeplydipping
sandstone and heterolithic facies,
which are observed to show increasingly
tidal influence with successive rock
deposition. The succession begins with
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