PORT KENNEDY BONE CAVE - REDISCOVERED WITH GEOPHYSICS

A recent geophysical survey whose purpose was to locate a filled solution cavity known as the “Port Kennedy Bone Cave” was conducted at the Valley Forge National Historical Park, located in Southeastern Pennsylvania. The “Bone Cave” was an excavation into and through unconsolidated fill within a solution cavity, a sinkhole. This filled sinkhole is located in a dolomite quarry near Port Kennedy. The Bone Cave contained one of the most important middle Pleistocene (Irvingtonian, approximately 750,000 years ago) fossil deposits in North America. These fossils included plants, insects, turtles, snakes, birds, and mammals that included giant tapirs, ground sloths, sabre-tooth cats, bears, and mammoths. This filled sinkhole was discovered in 1871 and lost by flooding in 1896. In the early 1900s, the flooded quarry was filled in with slurry waste from a nearby boiler and insulating company near Valley Forge. The lack of adequate mapping during the investigations of the 1800s allowed the Bone Cave to be lost from history. With the passage of time, the quarry become overgrown and the Bone Cave once again became lost not only in location but also in memory. Daeschler et al. (2003) conducted an extensive literature search to determine the location of the Bone Cave within the filled and abandoned quarry. To confirm this location, a geophysical survey was proposed and completed. This survey included microgravity to identify the filled sinkhole; electrical imaging to contrast the electrical properties of the quarry walls and the quarry filling; and a magnetometer to identify a long rumored wreck of a train locomotive used in a movie. Analysis of the geophysical data concludes that a distinct low gravity anomaly with a coincident resistivity anomaly. These two anomalies indicate that a less dense material fills a cavity within the dolomite bedrock. Analysis also indicates no locomotive within the abandoned quarry. The Port Kennedy Bone Cave has once again been found, with the aid of geophysics.