Middle Ordovician carbonate facies development, conodont biostratigraphy and faunal diversity patterns at the Lynna River, northwestern Russia

A Dronov,A Lindskog,C M Rasmussen,J A Rasmussen,M E Eriksson

doi:10.3176/earth.2020.03

A Dronov, A Lindskog + Show 3 more

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https://doi.org/10.3176/earth.2020.03

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Abstract

The Ordovician Period has emerged as a highly dynamic time in Earth history. Comprehensive work on chrono, chemo-and biostratigraphy has resulted in an overall wellconstrained systemic framework, but several local successions around the globe still await detailed analysis in many respects. Herein we perform a highresolution analysis of abiotic and biotic signals in the Lynna River section, a key locality in northwestern Russia. As this section has been pivotal in documenting the temporal evolution of the Great Ordovician Biodiversification Event on Baltica, the macroscopic and microscopic characteristics of the local succession reveal important paleoenvironmental information that ties into the global development during the Middle Ordovician. The results add particularly to the understanding of the characteristics and largescale sedimentary ‘behavior’ of the Baltoscandian paleobasin. Microfacies vary consistently with the macroscopic appearance of the rocks, with intervals characterized by competent limestone being associated with coarser carbonate textures and intervals dominated by marly beds associated with finer textures. Along with carbonate textures, fossil grain assemblages vary in a rhythmic (~cyclic) manner. The local rocks are commonly partly dolomitized, with the proportion of dolomitization increasing upsection. Regional comparisons suggest that the changes in overall macro and microfacies were strongly related to variations in sea level. New highresolution conodont biostratigraphic data largely confirm previous regional correlations based on lithostratigraphy and trilobite faunas, and enable more robust correlations worldwide. (Less)

Highlights

Ordovician sedimentary rocks record profound changes in the global abiotic and biotic realms
As this section has been pivotal in documenting the temporal evolution of the Great Ordovician Biodiversification Event on Baltica, the macroscopic and microscopic characteristics of the local succession reveal important paleoenvironmental information that ties into the global development during the Middle Ordovician
Micro facies vary consistently with the macroscopic appearance of the rocks, with intervals characterized by competent limestone being associated with coarser carbonate textures and intervals dominated by marly beds associated with finer textures

Summary

Introduction

Ordovician sedimentary rocks record profound changes in the global abiotic and biotic realms. The East Baltic area hosts numerous excellent outcrops of lower Paleozoic strata and the St Petersburg (temporarily Petrograd, Leningrad) region in Russia has long held a prominent role in the scientific work concerning the Ordovician System (e.g., Pander 1830; Schmidt 1858, 1881, 1882; Lamansky 1905; Alikhova 1960; Sergeyeva 1962). The regional sedimentary succession has become an important archive for the understanding of the paleontologic and paleoenviron mental development during the Great Ordovician Biodiversification Event (GOBE; e.g., Tolmacheva et al 1999; Hansen & Harper 2003; Rasmussen et al 2007, 2009, 2016; Koromyslova 2011; and references therein) and the strata even hold possible clues to events in our solar system (Korochantsev et al 2009; Lindskog et al 2012; Heck et al 2016, 2017). Recent global biodiversity data highlight the lowermost Darriwilian – the very interval covered by the succession at the Lynna River – as pivotal for the biotic development during the GOBE (Rasmussen et al 2019)

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