256-12 Ocean Stratification and Anoxic and Dysoxic Proteobacteria as Potential Keystones in Heterotrophic Reef System Nutrient Pathways

Session: Life and Environments Through Time and Space: Multi-Record Approaches to Stratigraphic Paleobiology, Part I

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Fossils of anoxic and dysoxic microbes coincident with evidence for ocean stratification shed light on nutrient pathways for ancient reefs. Mississippian mounds in New Mexico and the Permian Reef in west Texas provide sedimentological and mineralogical evidence of interaction with a pycnocline and oxygen minima coincident with basal reef growth. Basal Mississippian mound facies contain glaucony and hematite rich redbed layers with traces and mineralized sheathes and filaments similar to the modern anoxic sulfur oxidizing gammaproteobacteria Thioploca. Redbeds are composed of red, twisted stalks tangled into layers of mats similar to iron rich biofilms made by dysoxic iron oxidizing zetaproteobacteria Mariprofundus. Basal Permian Reef facies contain shrubby growths that are cored by tubular sheathes that contain red, hematite coated sausage-linked cells similar to zetaproteobacteria.

These anoxic and dysoxic microbial communities occur at the interface where it is proposed that the pycnocline and OMZ impinge upon the sea floor. Metabolic byproducts of microbial carbon fixation and nitrate production welled upwards through interaction of the substrate with internal waves. This mixed nutrient rich, anoxic water below with nutrient poor, oxygenated water above, providing sustenance for plankton and thus prolific growth of reef and mound filter feeders. Fluctuation of the pycnocline likely resulted in periodic kill-offs of invertebrate communities. Attrition likely resulted in communities dominated by stemmed or vertical growing organisms and colonies, such as crinoids and fenestellid bryozoans, which could stand above small rises of the OMZ, or organisms that could tolerate periodic low oxygen levels such as sponges.

Geological Society of America Abstracts with Program. Vol. 57, No. 6, 2025

doi: 10.1130/abs/2025AM-9108

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