Carbonate oceanic red beds (ORBs) are unusual in Phanerozoic shelf settings but can be
widespread during discrete intervals. Several scenarios have been invoked to explain the
origin of these ORBs but there remains uncertainty about the process by which the red
pigmentation of ORBs forms. Here, we propose that the occurrence of ORBs at intermediate
water depths in shelf regions is controlled by fluctuations in the redox state of deeper waters.
We have examined Early Triassic Peri-Gondwana shelf sections in South Tibet which show …