Late Ediacaran redox stability and metazoan evolution

Abstract

Abstract:The Neoproterozoic arrival of animals fundamentally changed Earth's biological and geochemical trajectory. Since the early description of Ediacaran and Cambrian animal fossils, a vigorous debate has emerged about the drivers underpinning their seemingly rapid radiation.Some argue for predation and ecology as central to diversification, whereas others point to a changing chemical environment as the trigger. In both cases, questions of timing and feedbacks remain unresolved. Through these debates, the last fifty years of work has largely converged on the concept that a change in atmospheric oxygen levels, perhaps manifested indirectly as an oxygenation of the deep ocean, was causally linked to the initial diversification of large animals.What has largely been absent, but is provided in this study, is a multi-proxy stratigraphic test of this hypothesis. Here, we describe a coupled geochemical and paleontological investigation of Neoproterozoic sedimentary rocks from northern Russia. In detail, we provide iron speciation data, carbon and sulfur isotope compositions, and major element abundances from a predominantly siliciclastic succession (spanning > 1,000 meters) sampled by the Kel'tminskaya-1 drillcore. Our interpretation of these data is consistent with the hypothesis that the pO 2 threshold required for diversification of animals with high metabolic oxygen demands was crossed prior to or during the Ediacaran Period.Redox stabilization of shallow marine environments was, however, also critical and only occurred about 560 million years ago (Ma), when large motile bilaterians first enter the regional stratigraphic record. In contrast, neither fossils nor geochemistry lend support to the hypothesis that ecological interactions altered the course of evolution in the absence of environmental change. Together, the geochemical and paleontological records suggest a coordinated transition from low oxygen oceans sometime before the Marinoan (~635 Ma) ice age, through better oxygenated but still redox-unstable shelves of the early Ediacaran Period, to the fully and persistently oxygenated marine Johnston et al., Ediacaran Redox Stability 3 environments characteristic of later Ediacaran successions that preserve the first bilaterian macrofossils and trace fossils. INTRODUCTIONThe hypothesis that increased oxygen availability facilitated Ediacaran (635-542 Ma) metazoan evolution dates back more than half a century (Cloud and Drake, 1968; Nursall, 1959).This hypothesis posits that an increase in the oxygen content of shallow-marine environments was physiologically necessary for the emergence of large, highly energetic animals (Raff and Raff, 1970; Rhoads and Morse, 1971). Ecological and physiological observations place lower dissolved oxygen (DO) limits for ocean waters in which different types of animals can live (e.g., (Diaz and Rosenberg, 1995; Levin, 2003)). They further make predictions about body shape in early animals, based on diffusion length-scales for organisms that lack a circulatory system for bulk oxy...

The evolution of Earth's biogeochemical nitrogen cycle

“…This interpretation implies expansion of oxygenated water masses in the Neoproterozoic. Although various paleoredox proxies indeed point to an increase in atmospheric and oceanic oxygen between ~800 and ~550 Ma (Canfield et al, 2007;Fike et al, 2006;Johnston et al, 2012;Kendall et al, 2015b;Planavsky et al, 2014b;Sahoo et al, 2012), others suggest anoxic conditions in roughly coeval strata Johnston et al, 2013;Schröder and Grotzinger, 2007;Sperling et al, 2015). Hence like the Neoarchean and Mesoproterozoic, the Neoproterozoic may have been a time of dynamic spatial and temporal redox fluctuations where NO 3 -was not abundant globally at all times.…”

Dynamic redox conditions control late Ediacaran metazoan ecosystems in the Nama Group, Namibia

“…Indeed, the global response of ocean redox chemistry to rising oxygen levels through this period has been shown to be complex (Fike et al, 2006;Canfield et al, 2008;Johnston et al, 2010Johnston et al, , 2012bSperling et al, 2013a) A c c e p t e d M a n u s c r i p t 6 state existed until at least ~580 Ma, and beyond in certain areas (Canfield et al, 2008;Planavsky et al, 2011;Poulton and Canfield, 2011), whereas surface-water oxygenation is thought to be a near-continuous feature throughout the latter half of the Ediacaran (Canfield et al, 2008). Indeed some have argued that pervasive and persistent oxygenation of the deep ocean did not occur until the later Palaeozoic (e.g.…”

“…Indeed, the global response of ocean redox chemistry to rising oxygen levels through this period has been shown to be complex (Fike et al, 2006;Canfield et al, 2008;Johnston et al, 2010Johnston et al, , 2012bSperling et al, 2013a), including in South China the presence of metastable zones of euxinic (anoxic and sulfidic) waters impinging on the continental shelf and sandwiched within ferruginous [Fe(II)-enriched] deep waters (Li et al, 2010). Detailed reconstructions of ocean chemistry suggest that a globally anoxic and ferruginous deep ocean M a n u s c r i p t 6 state existed until at least ~580 Ma, and beyond in certain areas (Canfield et al, 2008;Planavsky et al, 2011;Poulton and Canfield, 2011), whereas surface-water oxygenation is thought to be a near-continuous feature throughout the latter half of the Ediacaran (Canfield et al, 2008).…”

“…This has variously been interpreted as being due to oxidation of a substantial reservoir of organic carbon dissolved in the deep ocean (Rothman et al, 2003;Fike et al, 2006), to a large flux of methane released from clathrates (Bjerrum and Canfield, 2011), or to diagenetic phenomena (Derry, 2010). The models of Bristow and Kennedy (2008), however, suggest that there were not enough oxidants available for the model proposed by Fike et al (2006), and thus that the Shuram could not have represented a large scale oxidation event.Indeed, the global response of ocean redox chemistry to rising oxygen levels through this period has been shown to be complex (Fike et al, 2006;Canfield et al, 2008;Johnston et al, 2010Johnston et al, , 2012bSperling et al, 2013a) A c c e p t e d M a n u s c r i p t 6 state existed until at least ~580 Ma, and beyond in certain areas (Canfield et al, 2008;Planavsky et al, 2011;Poulton and Canfield, 2011), whereas surface-water oxygenation is thought to be a near-continuous feature throughout the latter half of the Ediacaran (Canfield et al, 2008). Indeed some have argued that pervasive and persistent oxygenation of the deep ocean did not occur until the later Palaeozoic (e.g.…”

Geological characteristics and age of the Dahongliutan Fe-ore deposit in the Western Kunlun orogenic belt, Xinjiang, northwestern China

“…In comparison with Superior-type BIF, the Dahongliutan BIF exhibits similarity in host rocks, mineral assemblages, and banded compositions and structures. The Dahongliutan BIF may represent a case for the reappearance of iron formation during the Neoproterozoic, which reflecting the recurrence of anoxic ferruginous conditions in the Neoproterozoic-Early Cambrian deep sea (Isley and Abbott, 1999; Kump and Seyfried, 2005;Canfield et al, 2007Canfield et al, , 2008Johnston et al, 2010Johnston et al, , 2012Basta et al, 2011;Shields and Och, 2011;Cox et al, 2013 …”