Fossil charcoal in sandstone from the Pennsylvanian of Ohio, USA. (~3.8 cm across at its widest)

This fossiliferous rock sample is from the Pottsville Group of eastern Ohio. The Pottsville Group is a Pennsylvanian-aged cyclothemic succession containing nonmarine shales, marine shales, siltstones, sandstones, coals, marine limestones, and chert ("flint"). The lower Pottsville dates to the late Early Pennsylvanian. The upper part dates to the early Middle Pennsylvanian. The Lower-Middle Pennsylvanian boundary is apparently somewhere near the Boggs Limestone horizon (?).

This is a small sample of muscovitic quartz sandstone with a piece of fossil charcoal (= black-colored chunk at upper right). The Pennsylvanian was a time of relatively high atmospheric oxygen (O2) levels, and forest fires were relatively common events. Charcoalized fossil wood can be found in some abundance in Pennsylvanian sedimentary successions. The original wood microstructure is usually well preserved, but the charcoal fragments themselves are quite delicate. A gentle rub with a finger turns these fragments into black powder.

Stratigraphy: float from Pottsville Group, Middle Pennsylvanian (loose piece was found below the Lower Mercer Limestone & above the Boggs Limestone)