Bed thicknesses in terrigenous clastics have long been observed to follow a lognormal distribution but data on carbonate rocks are rare. Studies of facies intervals, determined by detailed thin-section analysis, and bed thicknesses, described in field notes, for the Bird Spring Group and Callville Formation (Pennsylvanian and Permian) of southern Nevada have revealed that limestones also follow a lognormal trend. This is true for the separately investigated limestone facies (F 1 : micrite; F 2 : sparsely fossiliferous micrite; F 3 : packed biomicrite or pelmicrite; F 4 : biopelsparite) and for the data resulting when all these facies are combined. The universality of a lognormal distribution for populations of facies and bed thicknesses in limestones precludes the use of Markov chain analysis in which lithologic identifications are made at equal intervals along a vertical section.

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