Knowledge Bank

SEM and EDX technology has been used to analyze pyrite concretions from black shale layers of the Dunkirk Shale Member of the Canadaway Formation (Upper Devonian) at Point Gratiot, Dunkirk, New York. Point Gratiot is the type locality of the Dunkirk Shale Member. Black-colored spores observed in studied samples are identified as Protosalvinia. Two sizes ranges of spores are present. Smaller spores range in size from 0.5 to1 mm in diameter. Larger spore capsules are 4 to 6 mm in diameter. Small spores tend to be dispersed across bedding planes. Pyrite framboids were observed on the surface of larger spores. These larger spores may in fact be spore capsules. Framboidal pyrite, presumed to have developed around bacteria, are associated with the larger spores. Most pyrite concretions in the studied samples are surrounded by halos of limonite and anhydrous iron sulfide, presumably the result of of weathering.