EFFECTS OF FLUVIAL SYSTEMS ON ARTIFACTS: TRANSPORT DISTANCE AND WEATHERING DISTORTION

Pre-historic cultures tended to establish settlements within close proximity to streams for a variety of reasons. As a consequence artifacts left behind by indigenous peoples can be subjected to fluvial transport for an unknown length of transport. We sought a means of determining likely distance artifacts could be transported by streams of various sizes as well as if fluvial transport distorted artifacts beyond recognition. We attempted to ascertain the strength of artifacts of different material make up and the distance these artifacts could be transported in fluvial systems of various sizes. First, we subjected three common artifact materials, consisting of bronze, chert, and clay pottery, to a rotating rock tumbler for specified periods of time to simulate fluvial abrasion during transport. The materials were then observed, and any obvious abrasion and distortion was recorded. Each artifact’s size, shape, and weight were compared to their pre-tumbler conditions to determine how much change had occurred. The artifacts were scanned using a 3-D scanner before and after being tumbled in a rock tumbler as well as weighed to quantify how the shape of the artifacts was changing and how much mass was lost. This data provides us with a way to quantify when an artifact is no longer recognizable. After each tumbler run the artifacts were also converted to a particle grain size to compute transport rate using sediment transport equations. Transport rates were calculated based on the geometry of local streams. Preliminary results suggest that the bronze artifacts are distorted by fluvial transport but are still recognizable, and are only transportable by larger streams. Chert artifacts are recognizable after low amounts of abrasion but become unrecognizable after long term abrasion, and are able to be transported by most local streams. Lastly, clay pottery artifacts break down the fastest due to abrasion and become unrecognizable. They can be transported by any of the local streams based on what size pieces the artifacts have broken into. Our results suggest that artifacts can be transported by fluvial networks and can potentially be deposited some distance from their place of origin. In addition, prolonged transport in fluvial systems can render some artifacts unrecognizable.