The Lipalian Interval: A Forgotten, Novel Concept in the Geologic Column
Fieldwork of C. D. Walcott during his U.S. Geological Survey career may be artificially divided into two, intertwined segments, an earlier one concerned mainly with Paleozoic beds, but especially the Cambrian, and a later one involved mainly with strata below undoubted Cambrian rocks. Despite Walcott's diligent search, hardly any fossils were found in these older strata, and those discovered did not assist in biostratigraphy. Years later, when attempting to explain the issue of a diverse Cambrian fauna seemingly without any antecedents, Walcott developed a hypothesis to explain the absence of earlier fossils based on geological, rather than biological, features. He suggested that a widespread unconformity at the top of the Proterozoic represented an interval of time, the Lipalian, in which such an earlier fauna developed elsewhere, but was not recorded in any outcrop. The concept of naming a gap, to represent a major missing segment of geologic time, did not result in any comment from the geologic community and the Lipalian Interval vanished. The recently accepted Ediacaran Period, at the end of the Proterozoic, in a sense validates Walcott's concept of the Lipalian.