Article

A highly diverse ichnofauna in Late Triassic deep-sea fan deposits of Oman

01/2007; DOI: 10.2110/palo.2006.p06-098r
Source: OAI

ABSTRACT We encountered a highly diverse ichnofauna within the deep-sea fan deposits of the Upper Triassic Al Ayn Formation in Oman. It com- prises 32 ichnogenera: 18 ichnogenera represent predepositional gra- phoglyptids and other trace fossils that are preserved as casts on turbidite soles, and 14 ichnogenera represent postdepositional trace fossils that penetrate turbidite beds. The relatively large size of the area studied certainly favors encountering a high number of ichno- genera. The diversity we found approximately doubles the value that has often been stated in the literature and contradicts the paradigm that the Triassic represents a time of low ichnodiversity in the deep sea. Although the data are limited, in general the recovery of deep- sea tracemakers has been very slow owing to environmental distur- bances that resulted from cold-bottom-water circulation after the Carboniferous-Permian glaciation. The high ichnodiversity in the Al Ayn Formation is explained by its paleogeographic position and lo- cally formed warm bottom waters. The Al Ayn deposits accumulated adjacent to wide evaporitic and carbonate shelves, indicating contin- uous warm conditions. The Al Ayn clastic system was likely influ- enced by dense, salt-rich, warm water flowing back to the ocean from the carbonate and evaporitic shelf area. The downwelling water may have reduced the effects of cold water that formed during the Late Paleozoic glaciation and the Permian-Triassic anoxia, and, thus, it may have provided a refuge habitat. Despite the global trend of low- diversity deep-sea ichnocoenoses, refuge habitats may have been es- tablished in areas less affected by the otherwise harsh conditions.

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