Patterns of limestone and dolomite weathering by lichens and blue-green algae and their palaeoclimatic significance

Danin, A., Gerson, R., Marton, K. and Garry, J., 1982. Patterns of limestone and dolomite weathering by lichens and blue-green algae and their palaeoclimatic significance. Palaeogeogr., Palaeoclimatol., Palaeoecol., 37 : 221--233. Surface weathering of massive Turonian limestones was studied along a transect from the Judean Mountains to the Dead Sea with mean annual rainfall ranging from 550 mm (Mediterranean zone)to 100 mm (desert). In the Mediterranean zone micro-grooves 0.1 mm deep occur between colonies of endolithic lichens producing a pattern which looks like a jigsaw puzzle. In the vicinity of the 300 mm isohyet there are no endolithic lichens, instead the rock faces are entirely covered with blue-green algae living in 0.1 to 0.3 mm deep pits. Similar algae carve pits and channels 10 to 30 mm deep in the area with 100 mm of rainfall. emnants of the jigsaw puzzle-like weathering characteristic for Mediterranean conditions have repeatedly been observed on hard limestone in semi-arid and arid zones. These are interpreted as indicating more humid climatic conditions prevailing there in the past. Similarly, fossil deep pitting and channelling observed in the mediterranean zone on rock surfaces protected from weathering are evidence of a former arid climate.