In sedimentary rocks, pyrite framboids are subspherical aggregates of microcrystals that form during decay of organic matter by sulfate reducing organisms (SRO). We report on pyrite found on a Permian silicified articulate brachiopod shell and address the implications for the pyritization and silicification processes. Four pyrite forms occur, in order of abundance: spherical to subspherical aggregates of microcrystals (framboids), rod-shaped aggregates of microcrystals (pyrite rods), euhedral crystals, and loose microcrystals. It is the pyrite rods that are of most interest here. Pyrite framboids and rods are found scattered in the silica that replaces the shell and in large groups in the surrounding silicified matrix. The microcrystals in pyrite rods have the same morphology and size distribution as those in framboids. The diameter of pyrite rods is slightly less than framboids, but the length is significantly greater. We interpret the pyrite rods as forming just like framboids by burst nucleation of pyrite microcrystals, but within a rod-shaped microbial cell, thus permineralizing that cell. Interestingly, the volume of rods and framboids are similar, suggesting that only cells of the right size and shape were recognizably permineralized. This is the first example of framboid-like pyrite permineralizing isolated microbial cells rather than multicellular microbial filaments. The abundance of pyrite framboids and rods embedded in silica strongly confirms the connection between microbial decay, here specifically including SRO, in a microbial ecosystem, and the silicification process.

An important scientific contribution of ichnological research is to expand knowledge of animal behavior through the study of trace fossils. Ophiomorpha isp. is the dominant trace fossil preserved in Late Pleistocene shallow-marine grainstones throughout the Bahama Archipelago. These large, distinctive, and complex burrows commonly display elements reflecting specialized activities. Pouchlike structures of Ophiomorpha from two Exuma sites are interpreted as sequestrichnia—in this case, chambers constructed by callichirid shrimp specifically for storage of seagrasses and algae as food resources. Two morphologies are recognized: structures with radiating arms and blunt endings, and rectangular forms with pairs of arms separated by a short tunnel. These morphologies compare closely with structures present in modern burrow casts of Neocallichirus maryae from shallow-marine sands in Graham's Harbour, San Salvador Island. Additional structures, termed loops and nodes, were recognized in both modern casts and as trace fossils from the Harry Cay study site on Little Exuma. Previously reported carbon and nitrogen stable isotope analyses of callichirid soft tissues from San Salvador indicated that seagrass is a major food source for Bahamian callichirids, providing strong evidence for interpretation of the pouchlike Ophiomorpha structures as sequestrichnia. Establishing the presence of seagrass beds in Late Pleistocene shallow-marine grainstones from the Exumas provides useful supplemental information for more detailed paleoenvironmental interpretations. Finally, the literature on modern callichirids and other shallow-marine decapod crustaceans includes numerous burrow diagrams illustrating structures that presumably were constructed for food storage. Additional sequestrichnia and other structures reflecting specialized activities within fossilized callichirid burrow systems likely will be discovered in the future.