Evidence for a rapid anthropoclastic rock cycle

Abstract

Humans generate, transport, and subsequently deposit vast quantities of natural and anthropogenic waste material across the globe. However, the subsequent redistribution and lithification of this material is yet to be understood. Here, we document a rapid “anthropoclastic rock cycle” in a coastal setting, with the formation of an anthropogenic rock through the erosion, transportation, deposition, and lithification of legacy waste material that has occurred over <150 years. Field observations from West Cumbria, UK (a major iron and steel making area in the nineteenth and twentieth centuries), have identified a cemented conglomerate-like rocky foreshore platform that is dominantly composed of slag clasts (byproduct from iron and steel making). Clast shape and sedimentary structure analysis demonstrates that the material has eroded from an adjacent slag heap and has been transported and deposited by natural coastal processes. Microstructural and geochemical analyses have identified calcite, goethite, and brucite cements, with anthropogenic material (e.g., aluminum can tab) indicating cementation has occurred within the past 35 years. These results indicate that lithification is unprecedently fast for a clastic rock, and this process is driven by the chemistry of the waste material. The recognition of a rapid anthropoclastic rock cycle challenges conventional understanding of the natural clastic sedimentary rock cycle, with anthropoclastic rocks forming over decadal time scales rather than thousands to millions of years. Our findings highlight the need for updates to rock coastal models as new anthropogenic landforms and materials are forming, with important implications for changing coastal dynamics and the management of anthropogenic landscapes.