| Abstract: | Tectonic fold tests conducted in Namibia demonstrate that the inclination with respect to bedding of geoplumb (palaeovertical) tubular structures in the Marinoan (635 Ma) syndeglacial cap dolostone is mainly the result of tectonic strain. Therefore, tubestone inclination data cannot be used to estimate the gradient of the sea floor on the foreslope of the Otavi carbonate platform during the Marinoan glaciation. A gradient steeper than 0·1 (slope angle ca 5·7°), implying a glacial base‐level fall ≥0·5 km, is nevertheless supported by boulder‐size intraclast debrite in the falling‐stand wedge directly beneath the glacigenic sequence. Cryogenian oceans lacked skeletal carbonate production, raising the carbonate saturation state and persistent deep water anoxia excluded acid‐producing aerobic respiration, facilitating early diagenetic carbonate precipitation, lithification and steep submarine slopes. |
