Ichnostratigraphy of the Ediacaran-Cambrian boundary: new insights on lower Cambrian biozonations from the Soltanieh Formation of northern Iran

Abstract

Abstract.-Strata in the Central Alborz Mountains, northern Iran, are interpreted to show continuous sedimentation from Ediacaran through Cambrian times. The Soltanieh Formation consists of five members: Lower Dolomite, Lower Shale, Middle Dolomite, Upper Shale and Upper Dolomite members. The clastic units (Lower and Upper Shale members) represent sedimentation in distal marine settings, ranging from the shelf to offshore, and contain abundant trace fossils of biostratigraphic utility. Four ichnozones have been recognized. Ichnozone 1, containing Helminthoidichnites tenuis, Helminthopsis tenuis, and Cochlichnus anguineus, is early Fortunian based on small shelly fossils, and is interpreted as a distal expression of the Treptichnus pedum zone. Ichnozone 2, comprising the first occurrence of T. pedum, is middle Fortunian, and is best regarded as the upper half of the Treptichnus pedum Zone. Ichnozone 3 is late Fortunian-Cambrian Age 2, characterized by a sudden change in abundance and complexity of trace fossils. Main elements in this ichnozone include Cruziana problematica, Curvolithus isp., Phycodes isp., Treptichnus pedum, Treptichnus pollardi, and Treptichnus isp. Ichnozone 4 is of Cambrian Age 2-Age 3 and marked by the first appearances of Psammichnites gigas, Rusophycus avalonensis, and Didymaulichnus miettensis. Integration of trace fossils with small shelly fossils suggests that the Ediacaran-Cambrian boundary should be placed at the base of the Soltanieh Formation or within the Lower Dolomite Member. The delayed appearance of T. pedum and the low ichnodiversity in the Lower Shale and lower interval of the Upper Shale reflect limited colonization of settings below storm wave base during the early Fortunian.

Updated stratigraphic framework and biota of the Ediacaran and Terreneuvian in the Alcudia-Toledo Mountains of the Central Iberian Zone, Spain

“…Stöcklin et al, 1964) and occur in the underlying Cíjara Formation. Shahkarami et al (2017) discussed the stratigraphic implications of the Iranian material and comparable material from South China, and concluded that they are not reliable indicators of pre-Cambrian age.…”

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

“…Moreover, a remarkable negative δ 13 C excursion (-7 to -9 ‰) has been identified at the middle of the LSM, and was globally linked to an isotopic anomaly due to oceanic environmental change just before the PC-C boundary (Kimura et al 1997). Shahkarami, Mángano & Buatois (2017) proposed the new position for the PC-C boundary based on the report of Hyolithellus sp. from the LDM in the Vali-Abad section by Hamdi, Brasier & Zhiwen (1989), and new sedimentological data from the Garmab and the Type section in Zanjan (Fig.…”

“…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).…”

Lithostratigraphy and sedimentary environment of the Precambrian Kushk Series of central Iran

“…The Kushk Series is extensive and well exposed in the region, with a measured thickness of more than 500 m in some areas, and is known for its black shales that host economically viable lead-zinc deposits (Yaghubpur and Mehrabi 1997;Rajabi et al 2014;Rajabi et al 2012a). The Kushk Series represents a relatively deep-water paleo-environment when compared to the northern fossiliferous Soltanieh Formation (Stöcklin et al 1964;Shahkarami et al 2017a;Shahkarami et al 2017b), allowing for comparisons of fossil diversity and community ecology across a major bathymetric divide across the Ediacaran-Cambrian boundary.…”