Algal borings and framboidal pyrite in Upper Ordovician brachiopods

Algal borings in the shells of the articulate brachiopods Plaesiomys subquadrata (Hall) and Hebertella sinuata (Hall) from the Richmond Formation of Ohio are empty, or partially to entirely filled with pyrite. The pyrite occurs as single framboids and other crystal forms, or in chains filling the bores. The borings provide some insight into the early diagenetic history of the Richmond sediments near Cincinnati. Pyritization probably occurred within a few years, only a short distance (a few centimeters) below the sediment surface through the activities of sulfur-reducing bacteria. Pyrite precipitated around a nucleus such as a bacterium or algal cell, or developed within an organic structure such as an algal cell or organic membrane.