New and revised small shelly fossil record from the lower Cambrian of northern Iran

Abstract

Small shelly fossils (SSFs) are highly informative of the ‘Cambrian explosion’. Their palaeobiodiversity has been documented from lower Cambrian deposits worldwide but it remains elusive in areas such as Iran, despite this region occupying a critical position on the north‐western Gondwana margin during the early Cambrian. This new study of the SSFs of the lower Cambrian of northern Iran provides a large new dataset from this understudied area. We revise the micropalaeontological signal of the Soltanieh Formation of the Alborz Mountains and introduce novel data from the Soltanieh and overlying Barut Formations of the Soltanieh Mountains. The new, solid taxonomic and stratigraphic SSF data enable us to distinguish two successive microfaunal assemblages. The first occurs in the Soltanieh Formation of the Soltanieh and Alborz Mountains and is dominated by anabaritids (Anabarites trisulcatus, A. ex gr. trisulcatus, A. tristichus, A. dalirense sp. nov., Cambrotubulus decurvatus) along with protoconodonts (Protohertzina anabarica and P. unguliformis), maikhanellids (Maikhanella multa, Purella squamulosa and Purella sp.), Aetholicopalla adnata, indeterminate cones and irregular tubes. The second assemblage, from the Barut Formation, is dominated by a diverse assemblage of molluscs (Oelandiella korobkovi and cap‐shaped morphotypes). Siphogonuchitid sclerites also occur in both assemblages. The two SSF assemblages are characteristic of the Terreneuvian. Our dataset enables us to assess the sequence of faunal change of the Ediacaran–Cambrian transition; in contrast to the tube–sclerite–brachiopod succession presented in the literature, the Iranian fauna changes from one dominated by tubes and sclerites, to one dominated by molluscs and sclerites.

Cryogenian and Ediacaran integrative stratigraphy, biotas, and paleogeographical evolution of the Qinghai-Tibetan Plateau and its surrounding areas

“…Overlying the Kahar Formation, the Bayandor Formation is dominated by dolostone and minor mudstone, and is conformably overlain by the Soltanieh Formation. The Soltanieh Formation is assigned to the early Cambrian age based on the occurrence of trace fossils, especially Treptichnus pedum, and small shelly fossils (Shahkarami et al, 2017;Devaere et al, 2021).…”

Paleobotany to understand evolution and biodiversity in Mexico

“…This requires a better understanding of the lithologies and their fossil content, and comparative studies with coeval biotas from other regions of the world. With such studies, Mexican fossils could provide exciting and complementary information on the Ediacaran faunas and the Cambrian explosion, which generated the major animal phyla recognized today (Budd 2013), as well as others that became extinct, and even species that could have been endemic to the Mexican territory (e.g., Rajonia ornata, Devaere et al 2021). Rocks of this age in Mexico have not been explored thoroughly and existing studies have addressed mostly the invertebrate faunas, but this rock record could contain traces of the first disarticulated vascular plants of the Lower Paleozoic, which would be crucial for discussions on their meaning and evolutionary history, given the geographic location that they would have had in the past.…”