TRILOBITES OF THE LOWER CAMBRIAN OF SAN BERNARDINO COUNTY, CALIFORNIA

 

includes: LATHAM SHALE, WOOD CANYON FM., ZABRISKIE QUARTZITE, CHAMBLESS LIMESTONE, and CADIZ FM.

 

    Five Lower Cambrian formations occur in eastern San Bernardino County, California. From oldest to youngest, they are: the Wood Canyon Fm., Zabriskie Quartzite, Latham Shale, Chambless Fm., and the Cadiz Fm. A total of 18 species of trilobites have been identified (so far). The most productive unit for trilobites is the Latham Shale, where 12 species (mostly olenellids) occur. See below (Comments) for more information on the formations and the biozones and subzones.

 

Trilobites (of all 5 formations):

 

Bolbolenellus brevispinus

Bolbolenellus euryparia

Bristolia anteros Palmer, 1979

Bristolia bristolensis (Resser, 1928)

Bristolia aff. fragilis A

Bristolia aff. fragilis B

Bristolia aff. fragilis C

Bristolia harringtoni

Bristolia insolens (Resser, 1928)

Bristolia mohavensis  (old name Olenellus mojavensis)

Bristolia new species (see Mount, 1980)

Mesonacis sp. A

Mexicella robusta

Nephrolenellus geniculatus

Nephrolenellus multinodus

"Olenellus" brachyomma

Olenellus clarki (Resser, 1928)

Olenellus fowleri

Olenellus fremonti Walcott, 1910 ?= Mesonacis fremonti

Olenellus gilberti Meek in White, 1874

Olenellus aff. gilberti A

Olenellus mohavensis (Crickway, 1933)? = Bristolia mohavensis

Olenellus nevadensis (Walcott, 1910)

Olenellus puertoblancoensis (Lochman, 1952)

Olenellus terminatus

Olenellus aff. terminatus

Olenellus new species A (see Mount, 1980)

Olenellus new species B (see Mount, 1980)

Olenellus new species C (see Mount, 1980)

Olenellus species indeterminate (see Mount, 1980)

Onchocephalus new species (see Mount, 1980)

Peachella iddingsi (Walcott, 1884)

Zacanthopsis sp.

olenellid - new genus and species (see Mount, 1980)

ptychopariid new genus and species (see Mount, 1980)

ptychopariid sp.

 

Latham Shale trilobites:

(Marble and Providence Mts.)

 

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)

Onchocephalus new species (see Mount, 1980)

Peachella iddingsi (Walcott, 1884)

 

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

 

Chambless Limestone trilobites:

(Marble and Providence Mts.)

 

Bolbolenellus euryparia

Bristolia bristolensis (Resser, 1928)

Bristolia aff. fragilis C

Olenellus clarki (Resser, 1928)

Olenellus fremonti Walcott, 1910 ?= Mesonacis fremonti

Olenellus gilberti Meek in White, 1874

Olenellus puertoblancoensis (Lochman, 1952)

Olenellus terminatus

Olenellus new species B (see Mount, 1980)

ptychopariid new genus and species (see Mount, 1980)

 

Cadiz Formation trilobites:

 

Bolbolenellus brevispinus

Mexicella robusta

Nephrolenellus geniculatus

Nephrolenellus multinodus

"Olenellus" brachyomma

Olenellus clarki (Resser, 1928)

Olenellus fowleri

Olenellus fremonti Walcott, 1910 ?= Mesonacis fremonti

Olenellus gilberti Meek in White, 1874

Olenellus aff. gilberti B

Olenellus puertoblancoensis (Lochman, 1952)

Olenellus terminatus

Olenellus new species C (see Mount, 1980)

olenellid - new genus and species (see Mount, 1980)

Zacanthopsis sp.

ptychopariid sp.

 

Zabriskie Quartzite trilobites:

 

Olenellus species indeterminate (see Mount, 1980)

 

Wood Canyon Formation trilobites:

 

-no trilobites reported in the Mojave sections

 

 

Comments:

 

    The Lower Cambrian of eastern San Bernardino County, California is divided into 5 formations consisting of (in ascending order): the Wood Canyon Fm., Zabriskie Quartzite Fm., Latham Shale Fm., Chambless Fm., and the Cadiz Formation. All 5 formations are within the Early Cambrian, Waucoban Stage, upper Bonnia-Olenellus Zone. These formations outcrop 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 of the Marble Mountains is the most famous of these localities for trilobites. The Latham Shale is a 50- to 100-foot thick formation of late Early Cambrian age exposed in outcrops scattered widely throughout San Bernardino and Inyo Counties, California.

    The Wood Canyon Formation has no reported trilobites in the Mojave sections, although some trilobites occur in the Nopah Range. The Zabriskie Quartzite is also basically unproductive with only 1 poorly preserved specimen found. The Latham Shale is by far the most productive unit for trilobites with at least 12 species reported. Laterally equivalent strata are the lower parts of the Bright Angel Shale of Arizona, the Pioche Shale of Nevada, and the Carrara and Saline Valley Formations of California. In the Chambless limestone, trilobites are rare and poorly preserved. Trilobites are moderately abundant in 2 shale layers near the base of the Cadiz Formation. The boundary with the Middle Cambrian occurs within the Cadiz Formation. This unit is overlain by the Middle Cambrian Bonanza King Formation.

    The Latham Shale, Chambless, Limestone, and part of the Cadiz Fm. are subdivided into 3 Subzones (see Mount, 1980) which do not all coincide with the formational boundaries. The oldest is the Bristolia Subzone, which ranges from the base of the Latham Shale to about 15-30 meters above the base of the Chambless Formation. From here begins the Olenellus puertoblancoensis subzone, which ranges upward to the Chambless-Cadiz Fm. contact. The Olenellus multinodus Subzone comprises the lower part of the Cadiz Formation. All 3 Subzones occur in the upper part of the Bonnia-Olenellus Zone. The upper 139-191 m. of the Cadiz Formation has faunas from the Middle Cambrian Plagiura-Poliella, Albertella and Glossopleura Zones.

 

 

References:

 

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

 

Mount, Jack D. (1980)  Characteristics of Early Cambrian Faunas from Eastern San Bernardino County, California. Southern California Paleontological Society Special Publications, no. 2, p. 19-29, 33 figs.

 

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.

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