246 / 2022-03-29 08:19:38

Sedimentary-tectonic interaction on the growth sequence architecture within the intraslope basins of deepwater Niger Delta

Niger Delta; gravitational deformation; intraslope basins; growth sequence; architecture

This paper presents a 3D seismic-based case study from the deepwater Niger Delta to investigate sedimentary-tectonic interaction on growth sequence architecture within the thrust-related intraslope or piggyback basins. Gravitational contraction in the lower continental slope had yielded a series of thrust faults and associated folds in the study area, which confined several piggyback basins. These basins were filled by a suite of growth sequences with varying strata architecture. Analysis of seismic facies recognized three primary types of growth strata elements: convergent, drapping, and chaotic strata, which contain seven subtypes. These elements are combined to form different fill successions for convergent or chaotic growth sequences. The convergent growth sequences mainly occur in the deep section of basin fills during strong gravitational deformation, and always began with convergent-baselapping strata succeeded by convergent-thinning strata, representing pond-to-bypass transition in the ponded-basin accommodation space. The chaotic growth sequences mainly occur in the shallow section of basin fills in response to weak gravitational deformation, and usually began with debris-flow deposits succeeded by channel-levee complexes, reflecting dominant erosion-bypass processes in the slope accommodation space. A dynamic fill-to-spill model considering relationship between episodic sedimentation rate and structural growth rate is proposed to explain the formative mechanisms of growth strata elements and associated successions. Interaction between icehouse or greenhouse sea-level change and gravitational deformation history is suggested to have resulted in the complex stratal stacking patterns, including progradational or retrogradational stacking patterns between convergent growth sequences, and progradational stacking patterns between chaotic growth sequences.