Issues

COVER EXPLANATION.—Cluster of decimeter-size, partially exposed carbonate stromatolitic oncoids (upper half and lower left and right corners). In the center, note the smaller size, subaqueous oncoid covered by a thin, pink to orange colored biofilm where abundant carbonate precipitation takes place. These are associated with well-stratified pink to orange microbial mats typically seen in the Laguna Negra hypersaline lake, a high-altitude Andean lake in Catamarca Province, Argentina. See Gomez et al., this issue.