The first report of the Eocene annelid worms (Polychaeta) of Sarakeh syncline (Soh area - northwest of Isfahan - Central Iran)

Generally, the rotularians have high frequency in bioturbated environment in moderate to high water energy. Rotularians were also cemented to the substrate during their earliest growth stage, but they became detached shortly after the formation of first whorls. Tube records of rotularia are known from Mesozoic (Late Jurassic) to Early Tertiary sediments, becoming very common during the Cretaceous and Eocene and also has a global distribution. The fossil species Rotularia spirulaea has become extinct close to the end of Eocene - Oligocene time (Howell, 1962; Fauchald & Jumars, 1979; Macellari, 1984; Ruppert et al., 2004; Hove & Kupriyanova, 2009; Sørensen & Surlyk, 2010). 

Outcrops in the Soh area include the widely distributed Paleozoic (Zahedi, 1973; Adhamian, 2003; Wendt et al., 2005; Ghobadipour et al., 2013; Bahrami et al., 2015) and Mesozoic deposits (Mannani & Yazdi, 2009; Yazdi et al., 2010), as well as the Paleocene to Oligo-Miocene deposits, the youngest marine sequences, which start with terrigenous red to white sequence of Paleocene conglomerate and sandstone, continued by Eocene fossiliferous carbonates and marls. The Sabkha deposits at the top of the Oligo-Miocene Qom Formation terminates the depositional cycle of the marine sequence. A thick Eocene succession is widely exposed in the studied region (Sadri, 2011; Janssen et al., 2013). The studied section is located near the village of Soh-in Sarakeh Syncline (90 km Northwest of Isfahan)  and  is accessible by a 35 km unpaved road off the Isfahan - Tehran highway. The section is situated on the right side of a seasonal river valley that is observable from a distance in the plain. Coordinates for the fossil locality are: N 33º28´36˝, E 51º27´6˝. Structurally, the locality belongs to the Central Iran microplate, which is restricted by the NW-SE Sanandaj- Sirjan metamorphic belt to the West, and by the Great Kavir fault to the East.

The studied section is about 354 meters thick. Based on field observation, sedimentological features and fossil contents, 11 lithological packages are discriminated. 18 meters of Marl at the base of the Eocene (Package 1) contains rich with high diversity of marine faunas e.g. : Benthic foraminifers, Crustacean remains, bivalves, Gastropods and Polychaet tube worms (Rotularia spirulaea). Fossil rotularia with accompanying fauna: crab remains, gastropods, bivalves and benthic foraminifers are indicatives of warm shallow marine paleoenvironments during the deposition of the studied interval. Specimens are deposited in the Department of Geology, Faculty of Science, University of Isfahan, 81746, Iran, under acronym EUIC.

This study undertaken at the Department of Geology, Faculty of Science, University of Isfahan. The financial supports by the Vice Chancellor for Research and Technology, University of Isfahan highly appreciated.