Deep-water Sedimentary Characteristics Of The Miocene Strata And Salt-related Tectonic Constraints In The Sureste Basin,Gulf Of Mexico

With the diapir of the Middle Jurassic salt into the Cenozoic strata,complex and diverse salt structures were formed,which had a profound impact on the development and distribution of deep-water sedimentary systems in the Gulf of Mexico.Based on drilling wells,paleontology,cores and 3-D seismic data,the Miocene salt-related tectonic characteristics,the deep-water sedimentary distribution and evolution of the Sureste Basin in the southern Gulf of Mexico were studied.Using 3-D numerical sedimentary simulation,combined with detailed sedimentary filling analyses on typical area,the controlling effect of salt structure on the dispersion and accumulation process,and filling evolution of deep-water sediments is discussed.The study area is characterized by laterally shortened salt structures,which suggest that it is located in the contractional systems.According to the characteristics of salt-related tectonics and folds,it can be divided into 6 secondary structural units.In the southern and southeastern part of the study area(salt stock – salt canopy unit),there is a large number and high maturity of squeezed diapirs(salt stacks,salt walls and salt canopies).In the direction of west and northwest,the salt diapir quantity decreased and the continuity became worse.The salt structures transition from thrusts to low-amplitude salt anticlines or mudstone detachment folds.During Miocene period,from east to west and from south to north,the salt tectonic activity showed an overall trend of late time and decreased intensity.The deep-water depositional elements developed in Miocene include mass transport deposits,channel system,channelized-lobe complex,frontal splay and distal layered sheets.The western and northwestern part of the study area show weak tectonic activity and are represented by a simple continental slope(weakly confined systems)deposition model composed of "feeder channel-distributary channel – lobe complex".The lobe complex has the characteristic of compensational filling(or stacking)patterns.The direction and distribution of the depositional elements in the central,eastern and southern regions of the study area are controlled by the diapirs and anticlines,which show the complex continental slope(confined systems)depositional model.This model is composed of multi-steps link and combination of "lobe-turbidity channel-lobe " in three dimensions and dominated by fill and spill patterns.The relationship and interaction modes between salt structures and deep-water depositional element include seven types: blocking,confinement,diversion,migration,erosion,truncation/cutting and deformation.The distribution of different types is controlled by the development characteristics of deep-water depositional element and the salt tectonic activity.The numerical simulation shows that the filling process of static mini-basin includes four stages: ponded filling,fluid stripping,bypass and erosion/bypass.Sediment spill can cause channel incision and erosion in the area near the spill point.Geomorphologic changes and tectonic activities control the accumulation characteristics of sediments through the effects of fluid diversion,direction and blocking,and are also key factors leading to the changes of stratigraphic stacking patterns and terminational relationships.The detailed study of the key area and its analogical analysis with numerical simulation show that the change of sedimentary system is closely related to the salt tectonic activity.The equilibrium profile adjustment caused by salt tectonic activity and flow-spill process controlled the sedimentary evolution characteristics.In the process of continental slope adjustment,there are three stages: stable deposition,channel incision and filling caused by uplift of the upper slope,and lateral migration and aggradation caused by uplift and deformation of the lower slope.After the formation of the mini-basin,the filling sequence is shown as the early stage of ponding and fill of channelized-lobes or frontal splays,the middle stage of adjustment and transition(flow stripping and bypass),and late erosion/bypass.