Petrology of the Pliocene Pisolitic Limestone of the Great Plains
Abstract
Petrographic study of 34 oriented samples of pisolitic ("algal") limestone from the upper part of the late Tertiary Ogallala Formation in Kansas, Oklahoma, and west Texas indicates that the rock sampled was developed by predominantly soil-forming processes acting upon sands and silts of the uppermost Ogallala. The absence of fossils, replacement of sand grains by calcite, anomalous distribution of detrital grains with respect to oölites and bulbous structures, and the inverted orientation of the bulbous structures themselves, all argue against algal origin of the rock.
The origin of the limestone is similar to that of the well-developed caliche in southeastern New Mexico described by Bretz and Horberg, except that limestone gravels were not required for formation of the Kansas rock. The concretionary structures are analogous to those formed in bauxites. Conditions favoring development of pisolitic limestone were (1) presence of rocks containing easily soluble minerals yielding residues rich in Ca2+ ion; (2) effective rock permeability; (3) deficient rainfall and long dry periods; (4) low topographic relief; and (5) time.
