Sulfur isotopes of hydrothermal vent fossils and insights into microbial sulfur cycling within a lower Paleozoic (Ordovician‐early Silurian) vent community

Abstract

Symbioses between metazoans and microbes involved in sulfur cycling are integral to the ability of animals to thrive within deep-sea hydrothermal vent environments; the development of such interactions is regarded as a key adaptation in enabling animals to successfully colonize vents. Microbes often colonize the surfaces of vent animals and, remarkably, these associations can also be observed intricately preserved by pyrite in the fossil record of vent environments, stretching back to the lower Paleozoic (Ordovician-early Silurian). In non-vent environments, sulfur isotopes are often employed to investigate the metabolic strategies of both modern and fossil organisms, as certain metabolic pathways of microbes, notably sulfate reduction, can produce large sulfur isotope fractionations. However, the sulfur isotopes of vent fossils, both ancient and recently mineralized, have seldom been explored, and it is not known if

Fossilized giant sulfide‐oxidizing bacteria from the Devonian Hollard Mound seep deposit, Morocco

“…Similar conclusions have been drawn from fossilized microbial assemblages in anoxic subseafloor environments from the 1.8 Ga Duck Creek and the 2.3 Ga Turee Creek formations (Schopf et al., 2015). These Proterozoic ecosystems harbored non‐phototrophic sulfide‐oxidizing bacteria, reflecting little to no ecological or morphological change over a period of more than one billion years, demonstrating that chemosynthesis‐based ecosystems may enter phases of long‐lasting evolutionary stasis (Georgieva et al., 2022; Schopf et al., 2015). Although this notion does not hold true for most of the seep‐endemic megafaunal invertebrate communities (Kiel & Peckmann, 2019), the Hollard Mound deposit provides evidence that chemosynthesis‐based ecosystems have the potential to cope with macrofaunal evolutionary change and still function in a similar fashion despite changes in the phylogenetic affiliation of most of its metazoan members.…”

“…It seems that the large sulfide-oxidizing bacteria are particularly prone to preservation in the rock record including Neoarchean and Proterozoic sedimentary rocks (e.g., Bailey et al, 2007Bailey et al, , 2013Czaja et al, 2016;Georgieva et al, 2022) simply due to their large cell size and the amount and composition of mucilaginous sheath and cell wall material capable of withstanding decay (cf. Cunningham et al, 2012).…”