Review of the Ordovician stratigraphy and fauna of the Anarak Region in Central Iran

Abstract

ABSTRACT:Popov, L.E., Hairapetian, V., Evans, D.H., Ghobadi Pour, M., Holmer, L.E. and Baars, C. 2015. Review of the Ordovician stratigraphy and fauna of the Anarak Region in Central Iran. Acta Geologica Polonica, 65 (4), 403-435. Warszawa.The Ordovician sedimentary succession of the Pol-e Khavand area, situated on the northern margin of the Yazd block, has important differences from those in other parts of Central Iran. It has been established that the presumably terminal Cambrian to Lower Ordovician volcano-sedimentary Polekhavand Formation, exposed in the Pol-e Khavand area, has non-conformable contact with greenschists of the Doshakh Metamorphic Complex. The succeeding, mainly siliciclastic Chahgonbad Formation contains low to moderately diverse faunal assemblages, including brachiopods, cephalopods, trilobites and tentaculitids. The Darriwilian age of the lower part of the formation is well established by the co-occurrence of brachiopod genera Camerella, Phragmorthis, Tritoechia and Yangtzeella. The associated rich cephalopod fauna is different from the Darriwilian cephalopod associations of the Alborz terrane and may show some affinity with warm water faunas of North China and South Korea. It is likely that the Mid Ordovician fauna recovered from the lower part of the Chahgonbad Formation settled in the area sometime during a warming episode in the late Darriwilian. By contrast the low diversity mid Katian brachiopod association includes only three taxa, which occur together with the trilobite Vietnamia cf. teichmulleri and abundant, but poorly preserved tentaculitids questionably assigned to the genus Costatulites. This faunal association bears clear signatures linking it to the contemporaneous cold water faunas of the Arabian, Mediterranean and North African segments of Gondwana. Four brachiopod species recovered from the Chahgonbad Formation, including Hibernodonta lakhensis, Hindella prima, Lomatorthis? multilamellosa and Yangtzeella chupananica are new to science.

The Bohemo‐Iberian regional chronostratigraphical scale for the Ordovician System and palaeontological correlations within South Gondwana

“….32), Popov et al . () and Hairapetian et al . () mentioned, within the Chahgonbad Formation, a lower assemblage with brachiopods, cephalopods and ostracods (Schallreuter et al .…”

“…In a different region of central Iran (Anarak; Fig. 6.32), Popov et al (2015) and Hairapetian et al (2015) mentioned, within the Chahgonbad Formation, a lower assemblage with brachiopods, cephalopods and ostracods (Schallreuter et al 2006) of Middle Ordovician age. In the upper third of the same formation, trilobites (Vietnamia cf.…”

“…The formation ranges from lowermost Tremadocian to upper Darriwilian and still has not been subdivided in formal members, although the Simeh-Kuh and Gerd-Kuh sections (eastern Alborz) comprises numerous fossiliferous beds, many of them reasonably well studied. Tremadocian strata yielded diverse assemblages of trilobites, brachiopods, conodonts and rare graptolites, described in the papers of Bruton et al (2004), Ghobadi Pour (2006), Ghobadi Pour et al (2007a,b, 2015a, Popov et al (2008Popov et al ( , 2009Popov et al ( , 2015, Evans et al (2013), Kebria-ee Zadeh et al (2015) and Jahangir et al (2016), among others. Of special interest is the early record of the orthoidean brachiopods Paralenorthis, Ranorthis, Gondwanorthis and Tarfaya (a 'Moroccan-Argentinian' genus; see Benedetto & Muñoz 2016), which were widespread during the Arenigian in South Gondwana.…”

Silurian stratigraphy of Central Iran – an update

“…Recent studies by Hairapetian et al (2015) and Popov et al (2015b) revealed that the lower Palaeozoic succession of the Anarak Region differs significantly from those in the other parts of Iran. In particular, it was confirmed that the presumably Furongian to Lower Ordovician Polekhavand Formation introduced in these papers has a sharp unconformable boundary with the underlying Doshakh metamorphic complex presumably of Cambrian age.…”

“…The Middle to Upper Ordovician part of the succession has been assigned to the Chahgonbad Formation, which rests unconformably on the Polekhavand Formation and contains a bed of oolitic ironstones in its basal part. The Darriwilian to Katian age of the unit is based on brachiopod and trilobite faunas (Popov et al 2015b). Text- fig.…”