The unusual sedimentary rock record of the Early Triassic: Anachronistic facies in the western United States and southern Turkey

The end-Permian mass extinction occurred ∼251 million years ago and represents the largest extinction in the history of life. Following end-Permian mass extinction, a large-scale reorganization of marine communities occurred after a delay of 4--7 million years. To better understand why this recovery was delayed, the Early Triassic has been widely studied to understand the mechanisms responsible for the suppression of metazoans during this time. The widespread occurrence of anachronistic facies has been documented globally from Lower Triassic sections. Anachronistic facies are facies that commonly formed in marine environments much earlier in time (Proterozoic-Ordovician) and thereafter became geologically rare for hundreds of millions of years. Anachronistic facies include microbial reefs, carbonate seafloor fans, flat-pebble conglomerates, and wrinkle structures. In addition to true anachronistic facies, a variety of other unusual facies are reported and described here. The unusual resurgence of anachronistic facies in the Early Triassic has been documented in this research from the Spathian Virgin Limestone of the Moenkopi Formation and Union Wash Formation, southwestern United States and the Griesbachian Katarsi, Kokarkuyu, and Sapdere Formations from southern Turkey. Anachronistic facies occur at two intervals of time that bracket the Early Triassic, and this indicates that prolonged stressful environmental conditions such as low oxygen levels and carbon dioxide poisoning persisted through much of the Early Triassic. These conditions would have suppressed the recovery of metazoans, and this suppression is reflected in the low diversity of organisms as well as low levels of bioturbation. As part of this study, trends in bioturbation were documented from Lower Triassic sections in the southwestern United States. The results of this study illustrated that equatorial regions likely recovered more slowly from the end-Permian mass extinction than mid-high latitudes. Through study of anachronistic facies and the unique bioturbation record of the latest Early Triassic, it can be concluded that deleterious environmental conditions played a role both in the formation of the anachronistic facies and the suppression of marine organisms. This suppression likely delayed the biotic recovery from the end-Permian mass extinction.