Late Ordovician–Early Silurian facies development and environmental changes in the Subpolar Urals

Abstract

The continuous Upper Ashgill–Sheinwoodian carbonate succession in the most eastern Kozhym River area in the Subpolar Urals comprises the Yaptikshor (Rawtheyan), Kamennaya baba (Hirnantian), Ruchej and Manyuku (Llandovery–?Sheinwoodian) formations. The facies of the deep subtidal Yaptikshor Fm. mark an abrupt sea‐level rise following emergence of the Bad’ya reef (Rawtheyan). Carbonate breccias at the base of the Kamennaya baba Fm. correlate with the beginning of the Hirnantian glaciation and change upwards towards the Ordovician–Silurian boundary with the development of light‐grey massive boundstone/packstone shoal deposits. An abrupt change in facies to the Rhuddanian–Aeronian Ruchej Fm. continental slope environment marked the start of a long‐term sea‐level rise. The uppermost Aeronian–?Sheinwoodian is represented by submarine canyon carbonate conglobreccias of the Manyuku Fm. unconformably underlying the Balban’yu reef. The rapid facies changes at the base of the Hirnantian and at the Ordovician–Silurian boundary were of global eustatic origin. In contrast, the abrupt changes in the Rawtheyan and the formation of the Manyuku Fm. conglobreccias were of local or regional origin associated with tectonics. They were followed by the start of a regional transgression (Yaptikshor Fm.) and a global transgression marked by the initiation of the Balban’yu Reef in the Sheinwoodian.

Ooid-stromatolite association as a precursor of bioevents (Silurian, Timan–northern Ural Region)

“…1c). Sea level falls and rises are well observed during the Silurian period in the lithology, facies movements, breaks in sedimentation, and changes in faunal communities in the Timan-northern Ural region sedimentary basin (Männik and Martma, 2000;Antoshkina, 2008). A summary of major events known from Silurian times in the region has been presented (Antoshkina, 2007;Shebolkin and Männik, 2014).…”

Lithogenetic systematization and formation conditions of the Wenlockian sequences belonging to the Subpolar Urals and the Chernyshev Ridge

“…Кроме того, в верхней части толщи конглобрекчий на правом берегу р. Кожым, в районе порога Манюку, отмечены крупные обломки светлых рифогенных доломитов, из которых, как и из цемента конглобрекчий, П. Мянником определены конодонты позднего теличия-раннего шенвудия? [Antoshkina, 2008]. Возможно, с этого времени (устьдурнаюское) на окраине шельфа, на фундаменте из обломочного потока возобновилось рифообразование (риф Балбанью).…”

Chapter 13 The Timan–Pechora sedimentary basin: Palaeozoic reef formations and petroleum systems

“…After the global sea-level rise, there was a sharp fall linked with the final phase of the Late Ordovician glaciation during the Early Hirnantian, which was reflected in the formation of exogenous breccias (Antoshkina 2008). In Late Hirnantian time unclearly bedded ('reef-like') boundstones (up to 60 m in thickness) formed in shoal conditions.…”

“…In Late Hirnantian time unclearly bedded ('reef-like') boundstones (up to 60 m in thickness) formed in shoal conditions. They were interrupted by the eustatic sea-level rise at the Ordovician -Silurian boundary, accompanied by the global biotic extinction event, the Hirnant Event (Sepkovski 1995;Kaljo et al 2003;Antoshkina 2008;Fig. 13.3(1)).…”