Stratigraphic and micropetrographic occurrences of pyrite in sediments at the confluence of carbonate and peat-forming depositional systems, southern Florida, U.S.A.

This study was undertaken to investigate peat/carbonate relationships in a modern coal-forming setting, with initial research on pyrite and sulfur contents relative to stratigraphic and petrographic conditions. Over 40 closely spaced cores were taken from transects from Florida Bay inland through mangrove swamps and freshwater Everglades. Core stratigraphy confirms on overall transgressive sequence, but new evidence supports a small regression within the overall transgression. On average, both total S and pyrite are lowest at inland sites, highest near the coastline, and intermediate in Florida Bay sediments. Total S is higher in marine than freshwater peats, but freshwater peats overlain by marine peats are enriched in S. In cores that start with peat at the top, pyrite is generally absent or very low in the top 20 cm. Higher percentages of pyrite occur in carbonate rather than peat facies. Pyrite exists in three forms, framboidal aggregates, minute crystals, and large solitary crystals. Most of the pyrite occurs as minute crystals (< 2 μm) and framboidal aggregates. The occurrence of large crystals (> 2 μm) is less common and generally restricted to the cavities of larger cells or cavities within other organics (e.g. formminifera, pollen grains, fungal sclerotia). A general relationship seem to exist in certain cases between the occurrence of spherical organic cell fillings and the occurrence of the framboidal form of pyrite.