A survey of lower Cambrian faunas in the southern Great Basin, California and Nevada Robert G. Eby 3619 Underwood Street, Houston, TX 77025 [email protected]

abstract—Fossiliferous lower Cambrian sedimentary rocks are exposed in many mountain ranges of the southern Great Basin from central Nevada southward to the central Mojave Desert and from California’s White and Inyo Mountains eastward into western Utah. The fossil faunas in these rocks include, in addition to the relatively common olenelline trilobites, two other orders of trilobites, articulate and inarticulate brachiopods, hyolithids, archaeocyathids, echinoderms, small conical fossils of uncertain affinities, and remains of soft-bodied panarthropods. These fossils are in an easterly thinning wedge of sedimentary rocks formed as the Late Proterozoic to Cambrian seas prograded eastward from the continental margin onto the craton. The thickest sections, in the White and Inyo Mountains, continue upward from Proterozoic through Cambrian and higher sedimentary rocks while the thinnest sections, in the eastern areas, contain only uppermost lower Cambrian and higher sedimentary rocks.

Introduction below the oldest olenellines. These older fossil types were Charles Doolittle Walcott (1891) first suggested not seen to range through the Precambrian, rather their subdividing the Cambrian System into Lower, Middle lowest occurrences were often not far below the lowest and Upper Series. Walcott (1912) further suggested trilobites. The progression of the recognition of the lower the name Waucoban be used for the lower Cambrian boundary of the Cambrian has been described with after fossiliferous sections near Waucoba Springs in the references by Palmer (1998). Presently, the International northern Inyo Mountains of California. Historically, the Union of Geological Sciences, through its Subcommission Cambrian has been subdivided on the basis of its trilobite on Cambrian Stratigraphy, has refined and renamed the faunas, with the lower Cambrian of most of North subunits of the Cambrian so that they may be recognized America defined by the range of trilobites of the suborder internationally (Gradstein, et al., 2012). This subdivision Olenellina. While the lower-middle Cambrian boundary is shown in figure 1 where some of the series and stages was rather well defined at the extinction level of the have been given provisional numerical names until formal olenellines, the base of the lower Cambrian has long been names are adopted. poorly defined. This is because no trilobites and few other Whereas the Cambrian had previously been subdivided fossils had been found below the lowest occurrence of the into the three Lower, Middle and Upper Series, it is now olenellines. subdivided into four series. Furthermore, another entire The arrangement of the continents today is very system, the Ediacaran, has been identified below the different than during the Cambrian because of the Cambrian. The Ediacaran is based on a fossil fauna of rare continual rearrangement of the earth’s surface by plate small shelly fossils of unknown affinities and enigmatic tectonics. While most of North America, including Greenland, belonged to a single paleo-continent referred to as Laurentia, pieces of other continents have since been added and parts have been taken away. Northern Scotland was part of Laurentia that was lost when the Atlantic Ocean opened and coastal New England, the Canadian maritime provinces and eastern Newfoundland belonged to the paleo-continent Avalonia. The fossil faunas of these paleo continents seem to have been very different from one another, usually not even sharing the same families. Because of these differences, precise correlations between the continents can be quite difficult. While the lower Cambrian had been defined by the range of the Olenellina, the sedimentary rocks below the Cambrian, the Precambrian, had historically been seen to Figure 1. International Cambrian zonation showing currently largely lack fossils. However, with time and more study, recognized ages of boundaries and approximate correlations to various fossil types were recognized to consistently occur Laurentian zonation.

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Stratigraphy The Lower Cambrian rocks in the region discussed here are exposed over an area of roughly 15,000 square miles. Stratigraphically, they range in thickness from no more than 250 meters in the southeast to well over 1,500 meters to the northwest representing an onshore to offshore distance of more than 250 miles (Stewart, 1970). Because of these great ranges, it is not surprising that coeval stratigraphic sections have greatly differing lithologies, both in detail and through the entire section. Therefore, rock units in nearby areas have been given differing formational names that have successfully Figure 2. Correlations of the various stratigraphic units in the four areas of the Southern Great Basin been applied over many areas with lower Cambrian exposures. The Laurentian lower Cambrian stages are also shown. Note that the columns here are not to scale as the upper units are somewhat thinner than the lower ones and the decades of research. stratigraphic columns represented on the left are much thicker than those on the right. The greatest differences in contemporaneous impressions of soft-bodied animals in sedimentary stratigraphic sections are rocks. The lowest Cambrian stage, the Fortunian of the seen to represent differences across depositional dip, Terreneuvian Series, is based on the earliest occurrences from onshore to offshore. At the same time, stratigraphic of trace fossils left by animals that burrowed into the differences along depositional strike, that is parallel to sediments, the earliest being Treptichnus pedum. Older shore, are seen to be much less. In general, four areas have animals are thought to have lived on or slightly above the been taken as representing these varying distances along seafloor and did not burrow into it. The next Cambrian depositional dip and the formation names from these stage, Stage 2 of the Terreneuvian, is defined by the first areas have been successfully applied along depositional occurrence of small shelly fossils, many attributable to strike. These four areas are: 1) the White and Inyo primitive mollusks, and the heavily calcified sponge group Mountains of California and the neighboring Esmeralda Archaeocyatha. The Terreneuvian Series in Laurentia County, Nevada; 2) the area around Death Valley National has been named the Begadean (Palmer, 1998) to simplify Park and the Spring Mountains of Nevada; 3) the central intra-continental correlation. The oldest trilobites, of Mojave Desert area of California and 4) the area farther the Olenellina, first appear in the following Cambrian north in eastern Nevada. Diagrammatic lower Cambrian Stage, Stage 3 of Series 2. This corresponds to the lower stratigraphic columns for these four areas and their half of Walcott’s Waucoban and has been named the correlations are shown in figure 2. Montezuman (Palmer, 1998) within Laurentia. Within Paleontology Laurentia, this stage includes the range of the Olenellina but is below the range of the family Olenellidae and its The principal information here is shown in figures 3A genus Olenellus. The next higher stage, Stage 4 of Series and 3B. There, 12 localities in the southern Great Basin 2, corresponds to the upper half of Walcott’s Waucoban with relatively well-described lower Cambrian faunas are and has been named the Dyeran (Palmer, 1998, Webster, listed. These localities are indicated on figure 4. In figure 2011a) in Laurentia. Within Laurentia, this stage is defined 3A the olenelline trilobites found in these areas are listed by the range of the Olenellida family and its Olenellus with Xs indicating occurrences described in the available genus. It is overlain by the Middle Cambrian Stage 5 of literature. Likewise, figure 3B lists the non- olenelline Series 3, named the Delmaran in Laurentia. trilobites and the other invertebrate taxa described in the literature. Over the last few decades, the systematic relationships of the Olenellinae has been significantly

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Figures 3A and 3B. Tables of the occurrences of species of lower Cambrian faunas in 12 areas of the Southern Great basin. Figure 3A lists only the olenellin Trilobites and Figure 3B lists the non-olenellin trilobites and other invertebrate fossils from available literature. For each location, all lower Cambrian taxa described in the literature from there are listed regardless of their stratigraphic occurrences. revised, with many species formerly assigned to Olenellus by cyanobacteria, such as Girvanella. They seem to form reassigned to several new genera, such as Bolbolenellus by overgrowths on core particles and are rolled around by and Nephrolenellus (Palmer and Repina, 1993, Palmer, water currents to become rounded. During the Cambrian, 1998 and Lieberman, 1998, 1999). The fossils listed for they appear to have been formed under intertidal or very each location represent all the lower Cambrian species shallow subtidal conditions and are rather common in and genera described from that location, grouping shallow water limestones. together taxa from differing stratigraphic horizons. While there are more than 40 mountain ranges and Two of the specimens listed, at the bottom of figure other areas of significant lower Cambrian outcrops in 3B, are shown with asterisks for most localities. That the southern Great Basin, most have not had detailed is because hyolith fossils are somewhat common in paleontological sampling. Many of these areas have had most fossiliferous sections but are not commented on preliminary sampling by field geologists to identify rock because they seem to not be stratigraphically significant. ages but not many more than the 12 listed here have The other group, girvanellid oncolites, are actually been seriously studied paleontologically. Three of these ellipsoidal to sub-spherical sedimentary features formed areas have been very well studied and therefore have

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from Webster (2011b). Palmer and Halley (1979) provide data for the Last Chance Range, California, Grapevine Mountains, California, Funeral Mountains, California, Groom Range, Nevada, Eagle Mountain, California, Resting Springs Range, California, Nopah Range, California, and the Desert Range, Nevada. Hunt and Maybe (1966) also provided some data for the Last Chance Range, Grapevine Mountains and the Funeral Mountains, all of California. Webster et al. (2011) also provided data for the Groom Range, Nevada. Data for the Pioche District, Nevada come from Webster (2011c) and Palmer in Merriam (1964). Mount (1980) provided the data for the Marble Mountains, California. References Gradstein, F. M., Ogg, J. G., Schmitz, M. D. and Ogg, G. M., eds., 2012, The Geologic Time Scale 2012, Volume 1, Elsevier, Oxford, 1176 pp. Hunt, C. B. and D. R. Mabey, 1966, Stratigraphy and Structure, Death Valley, California, U. S. Geol. Surv. Profess. Paper 494-A, Washington, D. C., 168 pp. Lieberman, B. S., 1998, Cladistic analysis of the Early Cambrian olenelloid trilobites, Journal of Paleontology, 72, p. 59-78. Lieberman, B. S., 1999, Systematic Revision of the Olenelloidea (Trilobita, Cambrian), Peabody Museum of Natural History, Yale University, Bulletin 45, 160 pp. Merriam, C. W., 1964, Cambrian Rocks of the Pioche Mining Figure 4. Map of the southern Great Basin of California and Nevada District, Nevada, U. S. Geol. Surv. Profess. Paper 469, showing the general locations of the fossil localities discussed here. Washington, D. C., 63 pp. WI: White and Inyo Mountains; SM: Split Mountain; LC: Last Chance Range; GV: Grapevine Mountains; FM: Funeral Mountains; GR: Groom Mount, J. D., 1980, Characteristics of Early Cambrian faunas Range; EM: Eagle Mountain; RS: Resting Springs Range; NR: Nopah from eastern San Bernardino County, California, So. Calif. Range; DR: Desert range; PD: Pioche District; MM: Marble Mountains. Paleo. Soc. Spec. pub. no. 2, p. 19-23. Palmer, A. R., 1998, Terminal Early Cambrian extinction of longer lists of described fossils. The area of the White and the Olenellina: Documentation from the Pioche Formation, Inyo Mountains of California and the adjacent area in Nevada: Journal of Paleontology, v. 72, p. 59-78. western Esmeralda County, Nevada, have been known Palmer, A. R. and R. B. Halley, 1979, Physical Stratigraphy and for their Cambrian rocks since the mid 19th century. Trilobite Biostratigraphy of the Carrara Formation (Lower It was here that Walcott established his type section and Middle Cambrian) in the Southern Great Basin, U. S. for the Waucoban stage. In addition, the University of Geol. Surv. Profess. Paper 1047, Washington, D. C., 171 pp. California has long had its summer geology field camp Palmer, A. R. and L. N. Repina, 1993, Through a Glass Darkly: here and generations of students have mapped the area. taxonomy, phylogeny and biostratigraphy of the Olenellina, The district around the old mining town of Pioche, Lawrence KS: Univ. Kans. Paleontol. Contrib., New Series 3, Nevada also has excellent lower Cambrian exposures that 35 pp. became well known because some of the uppermost lower Signor, P. W. and J. F. Mount, 1985, Lower Cambrian Cambrian rocks were frequently mineralized with silver stratigraphic paleontology of the White–Inyo Mountains of ore. Later study also found that some horizons contained eastern California and Esmeralda County, Nevada, p. 6-15, silicified fossils that could be extracted by dissolving the in Hall, C. A. and D. M. Young, eds. Natural History of the limestone in weak acid. The third area is in the Marble White-Inyo Range, Eastern California and Western Nevada Mountains of the central Mojave Desert. Although the and High Altitude Physiology, White Mtn. Res. Sta. Symp. fossiliferous interval there is relatively thin and represents Vol.1, 241 pp. only the uppermost lower Cambrian, this area seems to Stewart, J. H., 1970, Upper Precambrian and Lower Cambrian be so well studied because of its easy access by amateur Strata in the Southern Great Basin, California and Nevada, paleontologists. U. S. Geol. Profess. Paper 620, Washington D. C., 212 pp. White and Inyo Mountains, California (also Walcott, C. D., 1891, Correlation Papers – Cambrian, Bull. U. S. neighboring western Esmeralda County, Nevada) data Geol. Surv. 81. comes from many sources, all summarized in Signor and Mount (1985). Split Mountain, Nevada data comes

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Walcott, C. D., 1912, Group terms for the Lower and Upper Cambrian series of formations, Cambrian geology and Paleontology, Smiths.Misc. Colln. 57, no. 10, p. 305-307. Webster, M., 2011a, Trilobite biostratigraphy and sequence stratigraphy of the upper Dyeran (traditional Laurentian “Lower Cambrian”) in the southern Great Basin, U. S. A., p. 121-154, in Hollingsworth, J. S., F. A. Sundberg and J. R. Foster, eds., Cambrian Stratigraphy and Paleontology of Northern Arizona and Southern Nevada: Museum of Northern Arizona Bulletin 67, Flagstaff, Arizona. Webster, M. 2011b. Upper Dyeran litho- and biostratigraphy of the Split Mountain area, Nevada. p. 236-246, in Hollingsworth, J. S., F. A. Sundberg and J. R. Foster, eds., Cambrian Stratigraphy and Paleontology of Northern Arizona and Southern Nevada: Museum of Northern Arizona Bulletin 67, Flagstaff, Arizona. Webster, M. 2011c. Litho- and biostratigraphy of the Dyeran- Delamaran boundary interval in the Pioche-Caliente region, Nevada. p. 203-215 in J. S. Hollingsworth, J. S., F. A. Sundberg, and J. R. Foster, eds., Cambrian Stratigraphy and Paleontology of Northern Arizona and Southern Nevada. Museum of Northern Arizona Bulletin 67, Flagstaff, Arizona. Webster, M., L. B. McCollum, and F. A. Sundberg. 2011. Upper Dyeran and Lower Delamaran litho- and biostratigraphy of the northern Groom Range, Nevada. p. 226-236, in J. S. Hollingsworth, J. S., F. A. Sundberg, and J. R. Foster, eds., Cambrian Stratigraphy and Paleontology of Northern Arizona and Southern Nevada. Museum of Northern Arizona Bulletin 67, Flagstaff, Arizona.

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