Benthic and Planktonic Gastropods from Eocene deposits in the Soh and Zefreh areas, north of Isfahan, central Iran

In the Paleocene-Eocene boundary, major climate and geological events have occurred throughout the world (PETM), which has led to an increase in deep water temperatures and has caused significant changes in the marine Organisms environment (Bown & Kochpl, 2004). The Eocene deposits in the central Iran extends very wide from the western border of the Zagros Mountains, in to the the northern border of the Alborz Mountains and its southern border extends to the Sirjan and southern Kerman areas (Hajiian, 1996). In Isfahan basin, the age of Eocene deposits are predominantly lutetian, the sedimentary unit including periodic conglomerate, marl and limestone (Zahedi, 1991). Eocene deposits at the Soh and Zefreh areas consist of the macrofossils such as bivalves, gastropods, crab, and microfossils such as foraminifera, charophyte and ostracod (Zahedi, 1991; Sadri, 2011; Khodaverdi Hassan-vand et al., 2016, 2018). This research is focused on the systematic paleontology and paleoecology of the gastropods.

In order to study of the gastropods from the Soh and Zefreh areas (central Iran), 300 fossils samples were collected and classified based on the shape of shells and their external and internal structural characteristics, e.g.: ratio of length to width, apertural shape and existence or absence of siphonale canal. In addition, to study the paleoecology and palaeoenvironment of these areas, 200 thin sections and also 50 marl samples were prepared and processed.

Gastropods are one of the most abundant macrofossils found in the Eocene deposits in the Soh and Zefreh areas. In this research, 15 families from gastropods, consisting of 14 families (Aprrhaidae, Campanilidae,  Cancellaridae, Cerithiidae, Columbellidae, Cymatidae, Naticidae, Neritidae, Rissoida, Seraphsidae, Turritellidae, Volutomitridae and Xenophoridae), including 14 genera (Aporrhais, Bonellitia, Campanile,  Cerithium, Cymatium, Lutetiella, Mesalia, Microvoluta, Mitrella, Natica, Pseudotaphrus, Seraphs, Velates and Xenophora) and 3 species (Seraphs Sopitus, Seraphs volutatus and Velates perversus) from Benthic gastropods, also, 1 family (Limacinidae), from pelagic gastropods (pteropoda)  including 3 genera (Altaspiratella, Heliconoides and Limacina) and 4 species (Altaspiratella gracilens, Altaspiratella tavianii, Heliconoid mercinensis and Limacina aryanaensis) were identified. In addition to the gastropods, large benthic foraminifers are one of the most important microfossils that can be found in the Soh and Zefreh areas. The presence of large benthic foraminifers such as, Alveolina, Discocyclina, Nummulites and Miliolida can help to determine the palaeoenvironmental analysis of the deposits (Reiss & Hottinger, 1984; Racey, 1994; Loucks et al., 1998; Geel, 2000; Beavington-Penney & Racey, 2004; Beavington-Penney et al., 2006; Papazzoni et al., 2006).

Many of the identified gastropods have been reported from the Eocene deposits of other Eocene outcrops in the world, e.g.; Eastern and Western Europe, Africa and parts of Asia that shows these areas were part of the Tethys (Indopacific-Atlantic). According to, the distribution of gastropods the paleo environments is been controlled by trophic habitats that directly depend on the environmental changes such as water turbulence, sedimentation and suspension rates and water energy and also the presences of large benthic foraminifers (Alveolina, Discocyclina, Nummulites and Miliolida) interpret a shallow marine with  a higher energy.