THE CONTROL OF SEDIMENTARY LOADING ON ROLLOVER DEVELOPMENT AND ACCOMMODATION CREATION IN DELTAS: AN EXAMPLE FROM THE WESTERN NIGER DELTA

Three-dimensional seismic data and wireline logs from the western Niger Delta were investigated to reveal the influence of sedimentary loading on rollover development and accommodation creation in a major growth-fault depocenter comprising a kilometre-scale rollover-anticline system. The studied seismic units show a non-uniform thickness distribution with their respective maximum near the main bounding growth-fault on the landward side of the rollover. This wedge-shaped sediment-storage architecture ultimately reflects a non-uniform creation of accommodation in the study area that was controlled by 1) compaction of the hanging-wall and footwall strata, 2) hanging-wall and footwall subsidence due to sedimentary loading and local isostatic compensation, 3) fault-induced (tectonic) hanging-wall subsidence, 4) regional tectonic subsidence by e.g. thermal cooling, and 5) eustatic change through time.

Sequential decompaction and isostatic balancing of the interpreted rollover units documented that compaction and isostasy exerted the primary control for the development of accommodation on both sides of the rollover anticline, contributing in total more to the stratal bending and generation of depositional space on the rollover flanks than tectonic displacement along the main bounding fault. Stratal backstripping furthermore documented that the quantitative analysis of accommodation development in hanging-wall growth and rollover strata can be used to predict tectonic movement along synsedimentary normal faults, even if footwall data is lacking. As such, this study emphasises the strength of thorough 3D isopach and accommodation analyses in support of classic fault-kinematic analyses.