Research On The Sequence Stratigraphy And Submarine Fan Architecture Within The Thrust-related Intraslope Minibasins Offshore West Africa

As important deposition sites for submarine fans,intraslope minibasins have huge hydrocarbon resource potential and significant research value,and thus have attracted much attension from both industry and academia.Although lots of work have been conducted on the submarine fans,understandings are still much poor in respects of sequence stratigraphy and submarine-fan architecture within the thrust-related intraslope minibasins.Taking the deep-water Niger Delta region as example,this paper integrates high-quality seismic and well data to analyse the structure styles and forming mechanisms of thrust-related minibasins,determine the sequence-stratigraphic architecture and evolution rules within thrust-related minibasins,and illustrate the submarine-fan architecture patterns and controlling factors within thrust-related minibasins.The main results and understandings achieved in this study are as follows.The thrust transitional zone of continental slope develops both strike-oriented thrust fold and dip-oriented detachment fold,which collectively confine the distribution of thrust-related minibasins.Controlled by the coupling between thrust activity and shale detachment,the dynamic evolution of thrust-related minibasins went through three stages,including the coupling of thrust activity and shale detachment,continued shale detachment,and weakened shale detachment.The development process of the dip-oriented detachment fold is crucial to the spatio-temporal evolution of thrust-related minibasins.The potential shear stress produced by differential thrust activity at the beggining may have trigged the formation of the dip-oriented detachment fold,and subsequent detachment process of shale cores that is likely to be impacted by differential loading has caused the dip-oriented detachment fold to uplift asymmetrically.The thrust-related minibasins develop varied types of strata units and assemblages,the formation and evolution of which are controlled by both thrust activity and sedimentation evolution.At times of intense thrust activity,individual 3^rd-order sequence within the minibasins was filled with dominant convergent strata assemblage,and different sequences can stack vertically producing prograding or retrograding convergent strata fill pattern as the basin A/S changes continuously.As thrust activity weakened greatly,individual 3^rd-order sequence within the minibasins was filled with dominant chaotic strata assemblage,different sequences can stack vertically producing prograding chaotic strata fill pattern as sedimentary filling process proceeded.Hierarchical architecture distribution of submarine fans within the thrust-related minibasins is controlled by the paleogeomorphology,A/S and tectonic activity.The negative landforms at early stage feature continuous lobe distribution pattern,whereas the nearly-flat landforms at late stage feature channel distribution pattern.The architectural composition within individual 3^rd-order sequence would vary from vertically stacked lobe-channel pattern to laterally stacked lobe-channel pattern and unconfined lobe pattern,in response to the decreased basin A/S.As the tectonic growth rate outpaces the sedimentation rate of deep-water channels,the channel pathways would divert off the structural highs.Otherwise,as the sedimentation rate of deep-water channels outpaces the tectonic growth rate,channels can pass over the structural highs by aggradation or incision.The aggradational channels show higher sinuosity with pronouced lateral migration process,whereas the incisional channels show lower sinuosity with pronounced downdip migration process.