PANEL 2  Aftstøbning nr 3


                       

Slab #3 shows wave ripples that are remarkable firstly by their age.  From radiometric datings we know that the particular sandstone (Chorhat member of the Kheinjuan Formation in Central India) is 1,6 billion years old. In other words: these ripples formed three times as long ago as the Cambrian Revolution!

                      Secondly, the ripple crests in this slab are doubled. In contrast to the doubled mud cracks of Namibia (#1), this is not a result of secondary deformation, but a primary effect. As we have seen, ripple distances have a certain -- though non-linear -- relationship to the wave regime in which they formed. Consequently, they should decrease in a given place as wave energy wanes after a storm. But since they are constrained not only by the momentary regime, but also by their own history, ripple distances adjust not gradually, but by phase doubling. In most cases small secondary crests emerge in the middle of the troughs until they reach the same size as the primary ones, now with half the previous ripple distance. That in the present case period doubling initiated in the crests may have do with the slight asymmetry of these ripples. It indicates that wave action was combined with a weak current from the upper left.

                      Of course, we did not travel to India just to cast ripple marks. Rather we were lured by presumed worm traces that professor Pradip Bose had reported from these sandstones. When he and his assistant, Dr. Subir Sarkar kindly guided us to the outcrops, most of the markings turned out to be pseudofossils ("Manchuriophycus"). But others look like burrows of worm-like undermat miners. This is impossible in view of the new radiometric dates. The challenge now is to find another, non-biological explanation.

                                                                                                               
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