Walcott’s Insights on Lower Cambrian Biostratigraphy: Stratigraphy and Palaeontology of the Esmeralda Basin, Nevada and California  

Charles Doolittle Walcott was certainly the premier Cambrian stratigrapher and paleontologist in North America during his 50-year career, which ended in 1927.  One notable and oft-neglected accomplishment was his recognition of early lower Cambrian faunas in thick sequences of lower Cambrian rocks in the White-Inyo Mountains of eastern California and the adjacent areas of Esmeralda County in western Nevada.  Walcott’s field investigations in this area were limited to brief periods in 1894, 1896 and 1897.  He collected fossils and measured a nearly complete Lower Cambrian section at Waucoba Springs.  In 1899 he sent an assistant to the area to measure the Barrel Springs section and to collect more fossils.  Unfortunately, Walcott never returned to this area.  In 1910 he published descriptions of the trilobites and suggested a zonation beginning with Nevadia, Elliptocephala, and Callavia Zones and ending with the Olenellus Zone at the top of the Lower Cambrian.  The recognition that Nevadia was the oldest was significant, but these observations were completely neglected by B. F. Howell and the Cambrian subcommittee in their correlation chart published in 1944.

Mapping in the region by C. A. Nelson began around 1960.  He recognized the Fallotaspis assemblage as even older than the Nevadia fauna.  In 1972, W. H. Fritz proposed a lower Cambrian trilobite zonation consisting of Fallotaspis, Nevadella and Bonnia-Olenellus zones based largely on his work in northwestern Canada.  This zonal scheme has been widely accepted for North America.  Recent work in the Esmeralda Basin has led to the designation of an even older trilobite interval, the Fritzaspis Zone, beginning with the oldest trilobites in Laurentia; and to a possible five-zone breakdown of the Nevadella Zone.  Meanwhile the internationally accepted base of the Cambrian was moved downward to include the small shelly faunas and placed at the first appearance of the trace fossil Treptichnus pedum in Newfoundland.

Walcott had an amazing ability to find trilobites and it is surprising that he travelled within a hundred yards of Fallotaspis-bearing rocks on Westgard Pass, California, and that his assistant collected an abundant fauna of younger trilobites within yards of a second Fallotaspis occurrence, without ever finding this important fauna.  The Barrel Springs section measured by Weeks, rather than by Walcott, was confused by faulting and intrusive rocks – so much so that the collections were out of sequence and this section has not yet been convincingly relocated.  Perhaps another field session by Walcott would have solved these problems, but even with limited data, he reached the important conclusion that this area had the oldest Laurentian trilobites in thick, complete lower Cambrian sections.