Microfossils from the lower Mesoproterozoic Kaltasy Formation, East European Platform

Abstract

Basinal shales of the lower Mesoproterozoic Kaltasy Formation, sampled from three boreholes drilled into the southeastern East European Platform, Russia, contain abundant and moderately well preserved microfossils. 34 distinct entities have been identified, most assigned to simple sphaeromorphic or small filamentous taxa found widely and characterized by long stratigraphic ranges. Ornamented microfossils found in coastal successions of other lower Mesoproterozoic basins are absent, but large filamentous microfossils interpreted as possible benthic photosynthetic eukaryotes are recorded, drawing comparisons to relatively deep water shales in Siberia. In overall aspect, the Kaltasy microfossils are consistent with other broadly coeval assemblages, but they highlight the importance of environment, as well as age, in determining the distributions of remains that record the early diversification of marine eukaryotes. Rectia magna is described as a new species.

The Boring Billion, a slingshot for Complex Life on Earth

“…Complex cellular morphological capacities (cytoskeletal architecture) were observed and eukaryote habitation spread to a wider range of environments 20 , 21 . Diversification of eukaryotes is also noted in the Kamo Gp (1.3 Ga) 53 ; Kaltasy Fm (1.4–1.45 Ga) 54 ; Sarda Fm (~1.3 Ga), India 55 ; Arctic Canada (~1.3 Ga) 56 , 57 ; in the 1.1–0.9 Ga Mbuyi-Mayi Supergroup, DR Congo 58 ; in the 1.1 Ga Atar/El Mreiti Gp, Mauritania 59 . This was followed by the diversification of crown group eukaryotes between 1200–1100 Ma 15 and the emergence of a gene (1000–800 Ma), recently identified, that is linked with protein and choline kinases responsible for cell adhesion and transfer of signals within cells efficiently 60 , 61 .…”

Absence of biomarker evidence for early eukaryotic life from the Mesoproterozoic Roper Group: Searching across a marine redox gradient in mid‐Proterozoic habitability

“…Mesoproterozoic eukaryote diversity as gauged from acritarchs (Beghin et al, 2017;Javaux et al, 2004), even from settings interpreted as oxic in the Mesoproterozoic ocean (Sergeev, Knoll, Vorob'eva, & Sergeeva, 2016;Sperling et al, 2014). Furthermore, the apparent disparity between some occurrences of Mesoproterozoic eukaryotic acritarchs yet no detectable record of regular steranes appears to continue till 1.0 Ga in the Malgin Formation of the Siberian Platform (Suslova, Parfenova, Saraev, & Nagovitsyn, 2017), while thermally immature rocks from the 1.1 Ga Atar Group were also shown to be devoid of steroid biomarkers (Blumenberg et al, 2012).…”

Microbial assemblage and palaeoenvironmental reconstruction of the 1.38 Ga Velkerri Formation, McArthur Basin, northern Australia

“…However, in spite of apparent homogeneous and widespread anoxia in deep-water Mesoproterozoic oceans, redox heterogeneities and fluctuations have been identified from the ca. 1.4 Ga Kaltasy Formation, Southern Ural Mountains, Russia, a carbonaceous shale deposited in a basinal, oxic environment (Sperling et al, 2014;Sergeev, Knoll, Vorob'eva, & Sergeeva, 2016); the ca. 1.4 Ga Xiamaling Formation of the North China craton, a siliciclastic shale deposited in a low-energy deep, sub-tidal environment (Canfield, 2014;Diamond, Planavsky, Wang, & Lyons, 2018), and the age equivalent Velkerri Formation (Cox et al, 2016), Roper Group, northern Australia (Figure 1) suggesting that Mesoproterozoic sequences previously studied may have reflected geochemistry of restrictedbasin settings and contained a taphonomic bias that a larger sample set of biomarker, fossil and geochemistry of different depositional environments including nearshore and oxygenated sedimentary basins may rectify.…”