FLUVIO-DELTAIC DEPOSITIONAL COMPLEX OF THE CAMPANO-MAASTRICHTIAN GOMBE FORMATION OF THE GONGOLA SUB-BASIN, NORTHERN BENUE TROUGH, N.E. NIGERIA

Evaluation of the stratigraphic architecture of the Gombe Formation of the Gongola Sub-basin in the Northern Benue Trough indicated a build-up from six facies assemblage that consist of trough crossbedded sandstone, planar crossbedded sandstone, massive bedded sandstone, ripple laminated sandstone, parallel laminated sandstone and mudstones. These units were packaged into three facies association that constitutes of bedded sandstone facies association (FAgI), interbedded sandstone and mudstone facies association (FAgII) and amalgamated trough crossbedded sandstone facies association (FAgIII). These reflects mouth-bars, pro-delta and delta slope deposits and upper delta plain respectively. This deltaic prism is characterized by unidirectional current system devoid of signatures of tide and waves hydrodynamics in the subaqueous delta regions, thus indicating that the delta system of the Gombe Formation is a fluvial dominated delta.

Morphological signature of gully development by rapid slide retrogression in a layered coarse-grained delta foreslope

Coarse-grained deltas are often characterized by steep foreslopes (often more than 10°) that are traversed by delta-front channels. The channels thus erode into relatively steeply inclined bedding. In this context, the slopes flanking the channels can be steeper than the friction angle since they include a component of dip related to the delta-front slope as well as the channel-related erosion slope. In this study, part of the Busu River delta (Papua New Guinea) was imaged using a high-resolution multibeam bathymetry survey over an area where the angle of the slopes flanking the channels locally reaches 50°. A detailed analysis of the delta slope morphology has revealed an additional source of instability due to erosion within the main channels. In some places, erosion cuts into the channel flank forming a local knickpoint inclined in a direction approaching that of the bed dip. The cut can then initiate breaching or static liquefaction failure from that point up to the crest of the interfluve resulting in a V-shaped gully.

Quantitative characterization and controlling factor analysis of the morphology of Bukuma-minor channel on southern Niger Delta slope

The target of this study is the Bukuma-minor channel that is distributed along the southern Niger Delta slope. It overlaid the eastern outer levee of the adjacent Bukuma Channel System (BCS) to the north, but it converged westward into BCS to the south. Significant morphological variations between and within these two parts (referred to here as sections A and B) as well as their controlling factors were investigated quantitatively, using high-resolution 3D seismic data: (1) Changes of palaeotopographic gradients were supposed to be the largest contributor to morphological variations in section A (consisting of sections A1 and A2). Section A1 was developed on the low-gradient sector and characterized by the wide and shallow segment, with a relatively sinuous flowpath, whereas section A2, corresponding to a steep slope, was a linearly entrenched one, characterized by the narrow and deep segment. In addition, there were some positive correlations among geometric parameters in section A1, which, however, had been undermined by the large gradient in section A2. (2) Strong confinement of BCS results in the larger width, smaller thickness, and more stable sinuosity of section B. In general, correlations among geometric parameters in this part are not significant. In light of these correlations among geometric parameters and the influence of palaeotopographic gradients, we established an evolutionary model for general submarine channels.