PALEOENVIRONMENTAL SIGNIFICANCE OF SEDIMENTARY STRUCTURES IN THE CAMPANO-MAASTRICHTIAN SUCCESSION IN THE GONGOLA BASIN NE NIGERIA

Abstract

The pre and post depositonal sedimentary structures have been examined, recorded and
interpreted from the foreshore-shoreface and alluvial facies of the Campano-Maastrichtian
succession in the Gongola Basin. Some of these structures seem to be diagnostic of the
environment, depositional processes, conditions and direction of the water current which
deposited the sediments. The upper Fika Formationis dominantly shale with bioturbatedooidal
ironstone toward the top, which indicates deposition mainly from suspension andthe
bioturbatedooidal ironstones form in agitated water as water depth decreased, increased agitation
formed clay ooids and moderate to intense bioturbation by Thalassinoides,
OphiomorphaandSkolithos.as water depths subsequently increased and finaly replacement of
kaolinitic precursors with iron oxides/hydroxides.Thetrace fossil assemblage Thalassinoides,
Ophiomorpha and Skolithosare consistent with a shallow marine setting.Their presence indicates
littoral and shallow sub-littoral environments. The Arowa Formation is made up of cycles that
are coarsening-upward and contains channel-filling sandstones in the lower part. The lower
shale-dominated part of the cycles contain interbedded sandstones and shales in which
hummocky cross stratification, ripples and trace fossils Thalassinoides, Skolithos, Ophiomorpha,
and Planolitesoccur. The sandstone-dominated portion of the Arowa Formation are mainly
parallel laminatedand dip gently (2o– 3o) seaward. The main sedimentary structure of the
DuguriFormation, is cross-bedded sandstone overlying a basal conglomerate/pebbly sandstone.
The paucity of argillaceous horizons suggests deposition in braided rivers.