Complex sentence: Above this the Nguba group until recently has been identified as starting with a diamictite layer, probably from Sturtian glacial action and is capped with another diamictite layer that may have been laid down during the Marinoan glaciation (650 to 635 Ma).
Split into simpler sentences: Above this the Nguba group until recently has been identified as starting with a diamictite layer, probably created by Sturtian glacial action. It is capped with another diamictite layer that may have been laid down during the Marinoan glaciation (650 to 635 Ma).