--> Seafloor Pockmarks and Linear Pockmark Trains Linked to Buried Turbiditic Palaeo-channel in the Niger Delta Basin, West African

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Seafloor Pockmarks and Linear Pockmark Trains Linked to Buried Turbiditic Palaeo-channel in the Niger Delta Basin, West African

Abstract

Pockmarks are normally regarded to be manifestations of fluids escape through the seabed. Using high quality 3D seismic data within the Niger Delta Basin, we have identified pockmarks and two sinuous linear pockmark trains that are aligned above the sinuous belt of a buried turbiditic palaeo-channel. Seismic profiles show that these pockmarks developed above buried channels and their underlying chimneys seem to be rooted at the channel–levee interface. Linear pockmark arrays have been observed above the length of buried channels, indicating the escape of fluid from the channel sediment, vertically upward to the seabed. The seafloor pockmarks have two characteristics 1) Within each pockmark train, the pockmarks are fairly uniform in size and spacing, 2) Non-random pockmarks show one type of organized spatial arrangement. Linear pockmark arrays have been observed above the length of buried channels, the main channel is oriented NNE to SSW, the pockmarks to be very well organized and closely follow the path of the sinuous channel. Pockmarks well develop in the northern, central-eastern and southeastern parts of the study area. They are circular, elliptical and crescentic in plan view. The cross-section of all types of pockmarks are U-shaped. Most of the single circular pockmarks are located in the northern part of the study area, pockmarks occur singly and in organized arrays or ‘pockmark trains’. Most of the elliptical pockmarks occur in the southeastern part of the study area, and the elongated orientation is to the NE and nearly parallel with the buried turbiditic channel. In the southeastern parts of the study area, pockmark trains evolve though time to form deep gullies. The immature gullies seem to be composed of several amalgamated pockmarks which are nearly all ellipse in shape and the long axis is similar with the orientation of the channel. Pockmark gullies may exceed 1 km in width and extend for 5–7 km. The distribute of pockmarks clearly indicates that fluid seeps are not randomly distributed, but their seabed organization reflects 1) the geometry and morphology of the reservoir, 2) the location of the underlying reservoir where the fluids are coming from. We hypothesize that pockmark is a pre-requisite for creation of initial channels in deep-sea environments. Linear pockmark trains and pockmark gullies may provide preferential sediment transport routes into the deep water.