Impact of sedimentation, climate and sea level on marine sedimentary pyrite sulfur isotopes: Insights from the Valle di Manche section (Lower-Middle Pleistocene, southern Italy)

WashU affiliated authors: J. Houghton, D.A. Fike (Dept. of Earth and Planetary Sciences)

Abstract: Variations in the isotopic composition of sulfur in sedimentary pyrite (δ34Spyr) are often used to reconstruct global sulfur biogeochemical cycling and Earth’s surface oxidation state over Earth history. Recent work, however, has shown that δ34Spyr is strongly impacted by local depositional conditions, which both confounds attempts to reconstruct global sulfur cycling and provides a new proxy for investigating local paleoenvironmental conditions. We present a chemostratigraphic record of δ34Spyr in a detailed paleoenvironmental and sequence stratigraphic framework spanning the Early-Mid Pleistocene transition from the Crotone Basin (Calabria, Southern Italy). Bulk δ34Spyr data parallel transgressive-regressive cycles and enable the differentiation of progradational and retrogradational stacking patterns, where δ34Spyr values decrease toward −50‰ in outer shelf deposits during late transgression and become more positive and variable in prograding sedimentary units accumulated in shallower environments. In parallel with the observed variations in δ34Spyr, complementary data on organic carbon abundance and isotopic composition and total nitrogen abundance document changes in terrestrial delivery of sediment to the basin, as a consequence of glacial-interglacial eustatic sea-level changes, regional climate and local tectonics. The chemostratigraphic record of δ34Spyr appears sensitive to variations in sedimentation rates and local erosional surfaces and therefore may represent a powerful tool to assess stratal stacking patterns for sequence stratigraphic interpretations of siliciclastic successions. These results highlight the role of local conditions in controlling sedimentary δ34Spyr records and illustrate how isotopic data can be used to reconstruct key parameters of the sedimentary environment that might not otherwise be accessible, especially in deep-time strata.

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