Microbioirrigation of marine sediments in dysoxic environments: Implications for early sediment fabric formation and diagenetic processes

It is manifest in the study of dysoxic sediments from the geological record that infaunal burrowing is considered so severely limited by the lack of d issolved oxygen as to be nonexistent. Although the effects of megafauna and macrofauna on sedimentary and geochemical processes are well known, the ef fects of meiofauna are largely ignored. Here we document abundant meiofauna in the recent severely dysoxic, laminated sediments from the Santa Barbara basin, California margin, and also microcavities and microtunnels in lamin ated deglacial sediments from Palmer Deep, west Antarctic Peninsula, that w e interpret to be open, relict nematode burrows. Santa Barbara basin box-co re subcores were sieved to quantify metazoan abundance, and others were emb edded with resin for examination of meiofaunal life positions using confoca l microscopy. Metazoan densities in the surface centimeters of sediment ran ge from 80.7 to 117.9 cm(-3), and nematode populations, together with their abundant burrows, remain quite high to at least 3 cm. Scanning electron mi croscope analysis of fractured surfaces in Palmer Deep sediments revealed t hat the rigid diatom ooze framework aids the preservation of similar to 50 mum diameter open nematode burrows. These structures were observed to at le ast 40 m below the seafloor surface. This is the first description of a nem atode-produced open burrow network preserved in the geological record. Opti cal microscopy of resin-embedded thin sections revealed widespread sediment redistribution without significant lamina disruption. The implications of abundant nematode burrows in surface sediments, and their preservation in t he geological record, are wide ranging for both modern and ancient dysoxic marine environments, including for determining early sediment fabric produc tion, geochemical processes, and diagenetic reactions in the oxic and subox ic zones.