Subaerial exposure surfaces in carbonate successions throughout the geologic record include blackened clasts, but the origin of these clasts has remained the subject of debate. In this contribution, Miller et al. describe the distribution, microstructure, and diagenesis of blackened clasts in the Neogene succession of Australia. The results illustrate that the clasts are colored by organic carbon, interpreted to be formed in shallow the subsoil (B-C soil horizon) by a complex mix of dissolution and trapping of soil-derived organic matter by rhizogenic calcification. The results illustrate the complex genesis of these features and the climatic conditions under which they form.
Genesis of Blackened Limestone Clasts At Late Cenozoic Subaerial Exposure Surfaces, Southern Australia by Cody R. Miller, Noel P. James, and T. Kurtis Kyser