The base sand layers of the aeolian Great Dune of Pilat, which stretches along the coast of Arcachon Bay, have been locally impregnated with a dark brown to black amorphous organic substance of humate composition. The humate-cemented sand forms a well-indurated horizon 40-50 cm in thickness that developed immediately beneath the Holocene peaty layer (P1 "paleosoil"). The humate, identified by means of FT-IR and Raman micro-spectroscopy, acted both as a cementing agent and as a coloring agent; it formed thin coats and meniscus cements between individual sandstone grains which, in turn, caused the dark, asphaltic-like appearance of the sandstone. Field observations, combined with geochemical analyses, and the presence of identical geochemical compounds recognized in the peat and sandstone humate cement, suggest that the peat-containing low-coalified (R-r = 0.2%) fragments of higher, submerged and floating plants and marine algae deposited in a saline and reducing environment served as an obvious source rock for the humate. The humate derived from decaying organic remains that descended from the peat into the permeable sand, where it indurated irreversibly over a period shorter than 3500 years. The present-day actions of waves and tides contribute to the erosion of the frontal parts of the humate-impregnated sandstone horizon, resulting in the formation of the dark rounded sandstone slabs and pebbles that are deposited on nearby beaches. This process provides a fine example of recent black pebble formation that derived from pre-existing organic matter-impregnated source rocks. In contrast to their tropical carbonate counterparts, however, the humate-induced blackening of the sandstone pebbles appears to be relatively unstable, as the impregnated fragments bleach when exposed to air and seawater for a few seasons. (C) 2013 Elsevier B.V. All rights reserved.