Comparison of Salt Structure Deformation Periods of Conjugated Salt Basins in Central Segment of South Atlantic

The passive-margin salt basins in the central segment of the South Atlantic are areas with rapid growth of petroleum reserves in the world, where the distribution and structural deformation of the Aptian salt rocks have significant impacts on hydrocarbon accumulation. According to the Hotspur transform fault zone, the typical conjugated salt basins of Espirito Santo and Kwanza are selected in this study. Based on the previous seismic profiles and gravity and magnetism data, the Bouguer gravity anomaly data are superimposed on the plane in the Gplates software for reconstruction of the plates, and the Move software is used to restore balanced profile on the section. Then forward models designed according to the inversion results, and the contrast analogue experments are carried out. According to the studies, under the superposition of gravity sliding and gravity spreading, salt tectonic zones of extension-transition-contraction developed in the passive-margin basins, while factors resulted in the of salt structure deformation process among the conjugated basins, including slope angle, basement extension, the outer high barrier, salt deposition load and syn-depositional rate.(1) From Aptian to early Albian, the Espirito basin and the Kwanza basin were initially a unified salt basin. The east side of the unified basin was strongly stretched, forming faults and salt rafts in the extensional domain. At the same time, the unified basin was gradually divided, accompanied by the formation of the outer high, and the gravity deformation of salt rocks gradually slowed down. (2) From late Albian to Early Paleogene, the inherited upflit of the outer high in the Espirito Santo basin resulted in the vertical upward migrations of salt rocks; the uplift of the thick salt plateau in the Kwanza basin caused salt rocks to cross the outer high and form the thrust nappe. (3) From Late Paleogene to the present, the basement of the Espirito basin had steady thermal subsidence, and the salt structures were successively developed, then the salt rocks in the whole basin exhibit vertical migration characteristics. In the Kwanza basin, the basement was uplifted on a large scale, and the transport of salt rocks to the sea started again. Salt rafts in the extensional domain were further developed into salt rollovers; salt diapirs in the transitional zone and the contractional domain continued to rise; and the thrust nappe continued to develop, forming a large number of faults and folds in the supra salt layers. Then the salt rocks of the entire basin are continuously accumulating downslope with obvious structural zonation.