Latham Shale trilobites, California

Trilobites of the Latham Shale, California
last revised 13 September 2011 by S.M. Gon III

Locality: Marble & Providence Mountains, San Bernadino County, California, USA
Stratigraphy: Latham Shale Formation
Age: Early Cambrian - ca 515 mya

The Latham Shale, Marble Mountains, San Bernadino County, California.
©2003 Stephen M. Damiani All Rights Reserved

In the Cambrian, the continent of Laurentia (now the majority of North America), was near equatorial, and oriented about ninety degrees from its current position. Close to the shorelines of Laurentia, limestone was deposited as shallow-water reefs. Beyond the limestone belt, fine sediments built in deeper offshore contours, sometimes rapidly via undersea landslides off the reef platform. These offshore deposits along the paleoequator include much of the Wheeler Shale, the Burgess Shale of western Canada, and other sites from California through Utah to the Northwest territories of Canada. All of these sites yield remarkably preserved Cambrian fossils.


Location of California today	Locality of California during the Early Cambrian

The Marble Mountains is one of the best-known and most productive Cambrian trilobite localities in the state of California. This is a rather small mountain range in one of the harshest, driest parts of the Mojave Desert, in southeastern California near the towns of Chambless and Cadiz. Its trilobite-bearing rocks include exposures of the Latham Shale, but there are several related formations represented in San Bernadino, including (from oldest to youngest): the Wood Canyon Fm., Zabriskie Quartzite, Latham Shale, Chambless Fm., and the Cadiz Fm. These are all of Early Cambrian age, in the Waucoban Stage, upper Bonnia-Olenellus Zone. Outcrops occur throughout the Mojave desert in the Marble Mts., Providence Mts., Kelso Mts., New York Mts., Mesquite Mts., and the Silurian and Salt Spring Hills.

The Latham Shale is of late Early Cambrian age and occurs in outcrops scattered widely throughout San Bernardino and Inyo Counties, California. At least 12 trilobite species (mostly olenellids) have been documented there. The lower parts of the Bright Angel Shale, Arizona; the Pioche Shale, Nevada; and the Carrara and Saline Valley Fms., California are considered of equivalent age. The Latham Shale occupies the Bristolia subzone, oldest of the three subzones of the Bonnia-Olenellus Zone. Specimens below are from the Latham Shale and equivalent-aged formations.

Peachella iddingsi REDLICHIIDA Family Olenellidae	Bristolia insolens REDLICHIIDA Family Olenellidae		Bristolia bristolensis REDLICHIIDA Family Olenellidae
Olenellus gilberti REDLICHIIDA Family Olenellidae	Olenellus clarki REDLICHIIDA Family Olenellidae	Mesonacis fremonti REDLICHIIDA Family Olenellidae	Bristolia mohavensis REDLICHIIDA Family Olenellidae

The trilobites of the Latham Shale includes one species that shows a remarkably long persistence in the fossil record. Mesonacis fremonti appears in the same lower layers of the Latham Shale as Olenellus clarki and Bristolia mohavensis, but it persists through the end of the Latham Shale and occurs in the Cadiz Formation. It has a stratigraphic range that encompasses all of the other known trilobites of the Latham, Chambless Limestone, and Cadiz Formations! The details of this remarkable stratigraphic range may be found in the paper by Webster et al (2003), available in pdf here.

It is notable that the trilobite fauna of the Latham Shale, being a Early Cambrian locality, is dominated by Redlichiida, Suborder Olenellina. The Latham Shale has also yielded other fossils, including some of the earliest articulate brachiopods (brachiopods with hinge teeth) known. Hyoliths, (Mount 1974, 1980) and trace fossils left by worms, trilobites, and other invertebrates are also fairly common. Eocrinoid echinoderms, segmented worms, algae, and the appendages of Anomalocaris have been found (Durham 1978; Mount 1980; Briggs and Mount 1982; Waggoner and Hagadorn 1999).

TRILOBITA OF THE LATHAM SHALE FORMATION, CALIFORNIA
courtesy of the Western Trilobites Association

Order Redlichiida Richter, 1932
Suborder Olenellina Walcott, 1890
Family Olenelllidae Walcott, 1890

Bristolia anteros Palmer, 1979

Bristolia bristolensis (Resser, 1928)

Bristolia aff. fragilis A

Bristolia aff. fragilis B

Bristolia harringtoni*

Bristolia insolens (Resser, 1928)

Bristolia new species (see Mount, 1980)

Mesonacis sp. A

Olenellus clarki (Resser, 1928)

Olenellus fremonti Walcott, 1910 ?= Mesonacis fremonti

Olenellus gilberti Meek in White, 1874

Olenellus aff. gilberti A

Olenellus aff. gilberti B

Olenellus mohavensis (Crickway, 1933)? = Bristolia mohavensis*

Olenellus nevadensis (Walcott, 1910)

Olenellus aff. terminatus

Olenellus new species A (see Mount, 1980)
Peachella iddingsi (Walcott, 1884)

Order Ptychopariida Swinnerton 1915
Suborder Ptychopariina
Family Antagmidae Hupé, 1953
Onchocephalus new species (see Mount, 1980)

*Bruce Lieberman (1999) described a form of Latham Shale Bristolia bristolensis as Bristolia harringtoni.
In the same paper he reassigned Olenellus mohavensis to Bristolia.

Some Latham Shale literature:

Briggs, D. E. G., and J. D. Mount. 1982. The occurrence of the giant arthropod Anomalocaris in the Lower Cambrian of Southern California and the overall distribution of the genus. Journal of Paleontology 56:1112-1118.

Durham, J. W. 1978. A Lower Cambrian eocrinoid. Journal of Paleontology 52:195-199.

Lieberman, Bruce S. (1999) Systematic Revision of the Olenelloidea (Trilobita, Cambrian). Bulletin 45, Peabody Museum of Natural History, Yale University

Mount, J. D. 1974. Early Cambrian faunas from the Marble and Providence Mountains, San Bernardino County, California. Bulletin of the Southern California Paleontological Society 6:1-5.

Mount, J. D. 1980. Characteristics of Early Cambrian faunas from eastern San Bernardino County, California. Southern California Paleontological Society, Special Publication 2:19-29, 33 figs.

Palmer, A. R., and R. B. Halley. 1979. Physical stratigraphy and trilobite biostratigraphy of the Carrara Formation (Lower and Middle Cambrian) in the southern Great Basin. U. S. Geological Survey Professional Paper 1047:1-139 p.

Waggoner, B. M. and J. W. Hagadorn. 1999. Unusual Lower Cambrian fossils from the Latham Shale: What, if anything, is a Lagerstatten? Geological Society of America Abstracts with Programs 31(6):A105.

Webster, M, Sadler, P. M., Kooser, M. A., & Fowler, E. (2003) Combining stratigraphic sections and museum collections to increase biostratigraphic resolution. Application to Lower Cambrian trilobites from southern California. in: Approaches in High-Resolution Stratographic Paleontology, Chapter 3, ed. P. J. Harries, Kluwer Academic Publishers, The Netherlands.

Localities of the Cambrian: The Marble Mountains. by the University of California, Berkeley Museum of Paleontology

Latham Shale Trilobites by the Western Trilobites Association.

Collecting Trilobites in California. by the California Fossil Forum

Paleontological Tour of the Mohave Desert by J.D. Mount.

ACKNOWLEDGEMENTS: Thanks to encouragement, comments, images, source references, and suggested revisions by George Ast, James Cook, Perry Damiani, Chris Gass, Rik Hill, Carl Locker, John Spina, Steve Hess (image Bristolia mohavensis) and others.

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