Microstratigraphy of the Late Ediacaran to the Ordovician in NW Iran (Takab area)

Abstract

Platform sediments of Iran span the Late Ediacaran and extend into the Palaeozoic. They are primarily clastic and carbonaceous in nature, deposited in coastal and lagoonal settings. They crop out in the Takab area, as the Soltanieh Formation (Late Proterozoic to Atdabanian), the Barut Formation (Early Bottomian), the Zaigun Formation (Middle Bottomian), the Lalun Formation (Late Bottomian) and the Mila Formation (Middle Cambrian to Early Ordovician). A Precambrian–Cambrian assemblage has been identified at the base of Member 3 and the top of Member 2 in the Soltanieh Formation. The Soltanieh Formation consists of shallow marine sediments. Vertical microfacies variation reflects two regressive sequences, the earliest Cambrian System being a regressive cycle. The presence of Chuaria and Vendotaenia in the Soltanieh Formation allows correlation of Iranian sequences to those elsewhere in the world, indicating a late Neoproterozoic age. Detailed facies analyses of the Soltanieh, Barut, Zaigun, Lalun, and Mila formations allow refined palaeoenvironmental reconstructions to be made for the Ediacaran–Cambrian/Ordovician in Iran.

Provenance and geochemical variations across the Ediacaran–Cambrian transition in the Soltanieh Formation, Alborz Mountains, Iran

“…The Soltanieh Formation is composed of five members; from base to top these are (Hamdi, Brasier & Zhiwen, 1989) the Lower Dolomite Member (LDM), the Lower Shale Member (LSM; Chopoghlu Shale), the Middle Dolomite Member (MDM), the Upper Shale Member (USM) and the Upper Dolomite Member (UDM). The PC-C boundary in the Soltanieh Formation is identified based on biostratigraphy; the majority of previous studies have established that this boundary is located near the top of the LSM, where early skeletal fossils such as Protohertzina anabarica and index trace fossils such as Treptichnus pedum appear in the succession (Hamdi, Brasier & Zhiwen, 1989;Ciabeghodsi et al 2005Ciabeghodsi et al , 2006Ciabeghodsi, 2007;Jafari, Shemirani & Hamdi, 2007). The MDM, USM and UDM contain a rich assemblage of small shelly fauna, which are similar to the well-documented lower Cambrian strata of the Nemakit-Daldyn Formation in Siberia and southern and central Asia (Hamdi, Brasier & Zhiwen, 1989;Kimura et al 1997;Kimura & Watanabe, 2001;Ciabeghodsi et al 2005Ciabeghodsi et al , 2006Ciabeghodsi, 2007;Jafari, Shemirani & Hamdi, 2007).…”

“…These two shale members are separated by a dolomite member. The PC-C boundary is located almost at the top of the Lower Shale Member of the Soltanieh Formation, 200-300 m above its basal contact with the Kahar Formation as documented by biostratigraphic data (Hamdi, Brasier & Zhiwen, 1989;Ciabeghodsi et al 2005Ciabeghodsi et al , 2006Ciabeghodsi, 2007;Jafari, Shemirani & Hamdi, 2007;Ghorbani, 2013). However, Shahkarami, Mángano & Buatois (2017) have recently suggested that the Ediacaran-Cambrian boundary is located at the base of the Soltanieh Formation.…”

“…Despite the significance of the Soltanieh Formation for reconstructing the tectonic history of Iran and finding possible geochemical changes during the Ediacaran-Cambrian transition, previous studies on this formation are dominantly focused on its palaeontology (Hamdi, Brasier & Zhiwen, 1989;Ciabeghodsi et al 2005Ciabeghodsi et al , 2006Ciabeghodsi, 2007;Jafari, Shemirani & Hamdi, 2007;Shahkarami, Mángano & Buatois, 2017) and, to some limited extent, on the geochemistry of mudrocks (Brasier et al 1990;Kimura et al 1997;Kimura & Watanabe, 2001).…”

Diverse Assemblage of Ediacaran fossils from Central Iran

“…Late Ediacaran fossils from the Lower Shale Member (Chopoqlu Shale) of the Soltanieh Formation of northern Iran 18 and shale deposits of the Kushk Series in central Iran 19 – 21 include the type material of Permedusites changazensis Hahn and Pflug 1980, however previous reports of Dickinsonia? , Palaeoplatoda?…”

“…, and Kushkia? require further investigation in light of recent taxonomic and taphonomic studies 18 – 21 . Here we report the discovery of several new field sites from central Iran (Fig.…”