The unsuitability of calcite spherulites as indicators of subaerial exposure

Thin layers with calcite spherulites are demonstrated to have formed along the base of subhorizontal cracks within Quaternary palustrine deposits from eastern central Namibia. The development of the spherulites was probably conditioned by light that penetrated the cracks from the vertical face of the exposure. Development within subhorizontal cracks implies that their presence cannot be used as a criterion for the recognition of surfaces that were once subaerially exposed, irrespective of whether either bacterial or cyanobacterial activity is involved.