ANALYSIS AND SEQUENTIAL RESTORATION OF ACCOMMODATION SPACES FOR GROWTH SEDIMENTS IN NATURAL DEEPWATER DETACHMENT FOLDS

Using measured excess-areas for successive layers of both growth and pre-growth sediments, the amount of growth sediment in the original accommodation space can be calculated for all measured pairs of layers. The size of the original accommodation space can be calculated if the height between the two layers, excess-areas, width of the present detachment fold and the displacement since the accommodation space was filled are known. Now, the deformed accommodation space and the excess-area added during the filling of the accommodation space can be restored to their original, undeformed shapes. First, remove the excess-area added since final filling of the accommodation space, and then remove the pure shear deformation due to detachment folding. The shape of the nonlinear excess-area curve for the growth sediments is strongly influenced by sedimentation and/or displacement rate. The reconstructed areas of the accommodation space, growth sediments and excess-area are plotted as a function of displacement. The slopes and intersections of these curves help to interpret the nature of the excess-area curve for the detachment fold. It is well understood that the accommodation space is filled both with growth sediment and by the addition of excess-area from below due to the detachment folding. Since the accommodation space shortens as it fills, its area changes by the area of a rectangle whose base is ΔH (increment of displacement) and height is ΔD (thickness of growth sediment). The rectangle is composed of two triangles. One triangle is growth sediment (base, ΔD; height, ΔH) that is added as excess-area into the growth sediments actually deposited within the accommodation space during the displacement (ΔD). The other equivalent triangle (top, ΔD; height, ΔH) represents growth sediment that is not deposited since the accommodation space is smaller due to the displacement. This sediment would be deposited elsewhere affecting calculations of sedimentation rate.