Figure 7. a. Cartoon section showing how passive margin sediments (deltas, turbidites, carbonate banks) can prograde far beyond the original position of the continental edge. 7b and 7c show a simple method of estimating and restoring crustal extension during rifting and passive margin formation. The cross-sectional area of the stretched crust (hatch-pattern) must equal that of the unstretched crust after sediment, water and mantle have been removed from the cross section.