Petroleum Systems in Extensional Regimes. The formation of extensional basins may be seen as the first stage of the Wilson Cycle, which begins with thinning, stretching and rifting of the continental crust followed by continental break-up and mid-oceanic spreading. The concept of the Wilson cycle predicts that this process sometimes becomes reversed, causing closure of the ocean, collision between the adjacent continental plates, and hence the construction of a mountain chain.
