Folds overturned

Overturned fold—when the hinge surface is depressed below the horizontal (see Figure 2-42). 

We expect an efficient a — Q-dynamo to be at work in the merger remnant. The differential rotation will wind up initial poloidal into a strong toroidal field ( Q-effect ), the fluid instabilities/convection will transform toroidal fields into poloidal ones and vice versa ( a—effect ). Usually, the Rossby number, Ro = is adopted as a measure of the efficiency of dynamo action in a star. In the central object we find Rossby numbers well below unity, 0.4, and therefore expect an efficient amplification of initial seed magnetic fields. A convective dynamo amplifies initial fields exponentially with an e-folding time given approximately by the convective overturn time, rc ss 3 ms the saturation field strength is thereby independent of the initial seed field (Nordlund et al. 1992). 

Since sediments are deposited, it follows that the topmost layer in any succession of strata is the youngest. Also, any particular stratum in a sequence can be dated by its position in the sequence relative to other strata. This is the Law of Superposition. This principle applies to all sedimentary rocks except, of course, those that have been overturned by folding or where older strata have been thrust over younger rocks. Where strata are overfolded, the stratigraphical succession is inverted. When fossils are present in the beds concerned, their... 

An overthrust is a thrust fault that has a dip of 10° or less, and its net slip measures several kilometres. Overthrusts may be folded or even overturned. As a consequence, when they are subsequently eroded, remnants of the overthrust rocks may be left as outliers surrounded by rocks that lay beneath the thrust. These remnant areas are termed klippe, and the area that separates them from the parent overthrust is referred to as a fenster or a window. The area that occurs in front of the overthrust is called the foreland. 

Layered Systems with Overturned Surfaces Overturned surfaces, or folds, which cannot be represented as single valued height fields relative to any flat reference surface, may be caused by, for example, (i) compressive deformation of sufficiently plastic layers from the boundaries or (ii) deformation from below by the upward movement of subterranean salt bodies under the influence of buoyancy forces. See Figure 3. 

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