Rock art taphonomy in Lesser Antilles: study of wall weathering and engravings preservation in two preColumbian caves on Marie-Galante Island.

International audienceThe islands of Guadeloupe deliver some caves and rock shelters occupied in precolumbian times, including rare engraved caves whose age of occupation remains unclear and some burial caves used in the Late Ceramic Age. Question arises whether the absence of engravings in these latter sites reflects an archaeological reality or, in contrast, is linked to poor conditions for the preservation of cave art. Here we present a study carried out to determine the conditions of conservation of precolumbian rock art. This study was conducted in two sites of Marie-Galante, the cave Blanchard, without obvious engravings but with a funeral dimension, and the Morne Rita cave, rich in engravings. This work includes a series of hygrothermal measurements, the determination of authigenic minerals, and the study of both cave sediments.Two types of cavities can be opposed in terms of micro-climate pattern and transformation of the walls. Caves acting as trap cold air, like Morne Rita cave, have a high humidity which causes a light corrosion of the rock and mineral crust formation. Engravings modification proceeds mainly by their recovery by mineralization and the petroglyphs are relatively well preserved. In contrast, sites acting as warm air traps, like Blanchard cave, are characterized by an unstable air mass that promotes the entrance of drying air rich in salt-sprays, especially when sites are not far from the coast, which is the most frequent case in the Lesser Antilles. As a result, rock is exposed to salt weathering, and walls retreat caused by this phenomenon has been estimated in the order of a millimeter per century. This rate is sufficient to result in the disappearance of engravings that could exist in such sites. The walls of the Blanchard cave were examined in detail to find any traces of weathered petroglyphs, and we present here a wall morphology that could be explained by this hypothesis.This study highlights the control of site microclimatic pattern on the preservation of petroglyphs and concludes, therefore, on the existence of a bias in the distribution of rock caves in the Lesser Antilles where decorated caves were probably many more that which is currently found. The implications of this result on precolumbian cave occupation models are finally discussed