Structural Growth Rate and Impact on Deepwater Depositional Systems in Deepwater Fold Belts: Gulf of Mexico, West Africa and Niger Delta

Abstract

Examples of slope channels being diverted or deflected by growth folds, salt walls or thrusts are found both at the modern seabed and in the subsurface in deep-water fold and thrust belts. Most previous descriptions of the interaction of deep-water depositional systems with growing structures have tended to be descriptive. We have quantified the shortening rate of thrust-related folds, salt-cored anticlines and faulted salt-detachment folds in each area, with the aim of investigating whether there are any predictive relationships between structural parameters such as structural relief, growth rate versus sediment accumulation rate, and depositional patterns. In each of the three study areas, we observe slope channels that modify their downstream course as they interact with growing structures. Ponded deposits, and local slumping associated with structural relief are observed in all three areas. Our work shows that the Pleistocene to Recent Niger Delta slope channel systems behave comparably to the older buried channels studied in deep-water West Africa and Gulf of Mexico. Shortening rates in the thrust-related folds of the Niger Delta and the faulted salt-detachment fold in the Gulf of Mexico are comparable, with maxima of between 100-300 m/Ma. The maxima recorded for the West African salt walls and salt-cored anticlines are lower, ranging from 30-100 m/Ma. However we note that the Pleistocene to Recent channels in the Niger Delta, and the buried Miocene channels in West Africa, are diverted and deflected by growth rates as low as 30-50 m/Ma. In general, during periods of higher growth, channels are forced to deflect or divert around growing structures. However, channels that already have established a route through a fold or salt wall (e.g. at a relay position) can continue to exploit that route down slope as long as the turbidity flows continue to have enough erosive power to keep pace with the growth of the structure. Slumping off growing structures is most prevalent immediately after times of highest structural growth when there is most structural relief. In any one area, variations in growth rate and structural relief both along the length of structures and between structures is the most important control on channel behaviour. For example channels exploit areas of low growth to get through or around structures and ponding occurs behind the parts of a structure where most growth has occurred.

AAPG Datapages/Search and Discovery Article #90259 ©2016 AAPG Annual Convention and Exhibition, Calgary, Alberta, Canada, June 19-22, 2016