A Highly Diverse Ichnofauna in Late Triassic Deep-Sea Fan Deposits of Oman

Abstract

We encountered a highly diverse ichnofauna within the deep-sea fan deposits of the Upper Triassic Al Ayn Formation in Oman. It comprises 32 ichnogenera: 18 ichnogenera represent predepositional graphoglyptids 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 ichnogenera. 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 deepsea tracemakers has been very slow owing to environmental disturbances 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 locally formed warm bottom waters. The Al Ayn deposits accumulated adjacent to wide evaporitic and carbonate shelves, indicating continuous warm conditions. The Al Ayn clastic system was likely influenced 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 lowdiversity deep-sea ichnocoenoses, refuge habitats may have been established in areas less affected by the otherwise harsh conditions.

Sedimentology of early Pliocene sandstones in the south-western Taiwan foreland: Implications for basin physiography in the early stages of collision

“…the locomotion traces of small bivalves, and their rarity suggests possible import from the shallow marine environments (Ekdale and Bromley, 2001;Wetzel et al, 2007) Typical are sand beds normally with erosive bases marked by flute casts (Fig. 14 C).…”

Trace fossils from the Lower Muschelkalk of Raciborowice Górne (North Sudetic Synclinorium, SW Poland) and their palaeoenvironmental interpretation

“…Sedimentary environment: Archaeonassa, Lockeia, Skolithos and Protovirgularia are usually interpreted as characteristic of shallow environments, from nearshore to lower offshore (Uchman et al 2004a;Bradshaw 2010;Cabrera and Olivero 2011;Nagel et al 2013;Olivero and Cabrera 2013) but they also appear in deep-sea settings (Uchman 2004;Poursoltani et al 2007;Wetzel et al 2007;Zhang et al 2008;Nara and Ikari 2011;Uchman and Rattazzi 2011;Greene et al 2012). They are also known from marginal-marine and freshwater settings (McIlroy 2004b;Carmona et al 2009;Buatois and Mángano 2011;Gingras et al 2011;Melchor et al 2012b;Scott et al 2012).…”

Reply on ‘Sequence stratigraphy of an argillaceous, deepwater basin plain succession: Vischkuil Formation (Permian), Karoo Basin, South Africa’ from van der Merwe, Flint and Hodgson (Marine and Petroleum Geology, 2010, 27, 321–333)

“…Higgs would prefer it had we accepted his (Higgs, 2010) lacustrine interpretation for the Ecca Group Formations, which is bewildering since he admits that the ichnofauna Chondrites, Lophoctenium and Lorenzinia are "invariably marine". He emphasizes the two ichnogenera Gordia and Helminthopsis which apparently support his non-marine interpretation, except that they are also common to marine deposits, including those of the deep sea (e.g., Wetzel et al, 2007;Gingras et al, 2008;Heard and Pickering, 2008). In fact, Helminthopsis is commonly recognized in association with the Cruziana, Zoophycos, and Nereites ichnofacies (Pemberton et al, 2001;MacEachern et al, 2007).…”