Lichenometric dating (lichenometry) and the biology of the lichen genus rhizocarpon:challenges and future directions

Lichenometric dating (lichenometry) involves the use of lichen measurements to estimate the age of exposure of various substrata. Because of low radial growth rates and considerable longevity, species of the crustose lichen genus Rhizocarpon have been the most useful in lichenometry. The primary assumption of lichenometry is that colonization, growth and mortality of Rhizocarpon are similar on surfaces of known and unknown age so that the largest thalli present on the respective faces are of comparable age. This review describes the current state of knowledge regarding the biology of Rhizocarpon and considers two main questions: (1) to what extent does existing knowledge support this assumption; and (2) what further biological observations would be useful both to test its validity and to improve the accuracy of lichenometric dates? A review of the Rhizocarpon literature identified gaps in knowledge regarding early development, the growth rate/size curve, mortality, regeneration, competitive effects, colonization, and succession on rock surfaces. The data suggest that these processes may not be comparable on different rock surfaces, especially in regions where growth rates and thallus turnover are high. In addition, several variables could differ between rock surfaces and influence maximum thallus size, including rate and timing of colonization, radial growth rates, environmental differences, thallus fusion, allelopathy, thallus mortality, colonization and competition. Comparative measurements of these variables on surfaces of known and unknown age may help to determine whether the basic assumptions of lichenometry are valid. Ultimately, it may be possible to take these differences into account when interpreting estimated dates

Mineralogy and chemistry of Late Pliocene-Early Pleistocene paleosols on Mount Kenya:Weathering indices of relative age and paleoenvironmental reconstruction

Sherpa Romeo green journal. Permission to archive accepted author manuscript.Iron and Al extracts as weathering indices in paleosols have been used in many localities to determine relative age, transformation of total chemical element concentrations to secondary forms, translocation of organicallycomplexed Al and long-standing inundation of soils with groundwater. On Mt. Kenya, a succession of paleosols straddling the Olduvai subchron are here analyzed to determine the degree to which Fe/Al extracts assist paleoenvironmental reconstruction, especially relative age determination, genesis and translocation of alteration products and the effect of paleoclimatic deterioration with the advent of glaciation ca. 2.0 Ma, and possibly before. Warmer/humid climate from the onset of the Plio-Pleistocene to the Olduvai subchron, thereafter reverting to a long episode of oscillating drier/wetter ice age perturbations is written into the profile morphologies, mineralogies and chemistries supporting earlier stratigraphic interpretationsYe