Trilobites of the Twin Knobs Formation, Naomi Peal Limestone, and Brigham Quartzite


Twin Knobs Formation, Malad Range, Idaho

Two Mile Canyon Section (from Fritz, in Oriel & Armstrong, 1971, USGS Prof. Paper 394)

-compiled by Dr. L. McCollum (site currently under investigation)



1.  Albertella cf. A. proveedora Lochman 1952
2.  Albertelloides sp.
3.  Amecephalus? sp.
4.  Chancia venusta (Resser 1939b)
5.  Kootenia brevispina Resser 1939b
6.  Kootenia convoluta Resser 1939b
7.  Nyella granosa (Resser 1939b)  (=Caborcella)
8.  Onchocephalus sp.
9.  Oryctocephalus? maladensis Resser 1939b
10. Pagetia resseri Kobayashi 1943
11. Poliella germana (Resser 1939b)
12. Ptarmigania exigua Resser 1939b
13. Ptarmiganoides propinqua (Resser 1939b)  (=P. communis)
14.  Zacanthoides alatus (Resser 1939b)



Naomi Peak Limestone (8m thick)

Antimony Canyon section, Wellsville Mountains, Utah
Ptarmiganoides propinqua Assemblage:



1.  Albertelloides dispar (Resser 1939b)
2.  Albertelloides mischi (Fritz 1968) (= A. "fritzi" in Campbell 1974)
3.  Chancia venusta (Resser 1939b)
4.  Kootenia n. sp. 
5.  Nyella n. sp. 1
6.  Nyella n. sp. 2
7.  Olenoides maladensis Resser 1939b
8.  Oryctocephalites typicalis Resser 1939b
9.  Oryctocephalus? maladensis Resser 1939b
10. Pagetia resseri Kobayashi 1943
11. Paralbertella judithi (Fritz 1968)
12. Poliella germana (Resser 1939b)
13. Poliella n. sp.  
14. Ptarmigania exigua Resser 1939b
15. Ptarmiganoides propinqua (Resser 1939b)
16. Ptarmiganoides n. sp. 


Brigham Quartzite (upper meter only) (underlies the Naomi Peak Limestone)

Albertella Biozone: Albertellina aspinosa Subbiozone:




1. Albertella fritzi Eddy and McCollum 1998 ( = A. "gynthos" in Campbell 1974)
2. Albertellina aspinosa Palmer 1979
3. Mexicella? sp.




The Naomi Peak Limestone Member is the basal member of the Langston Formation and was named by George B. Maxey {p.671} in a 1958 GSA Bull [v.69, p. 647-688] "Lower and Middle Cambrian Stratigraphy in northern Utah and southeastern Idaho". Since the overlying Spence Shale Member was raised to formational status, so should the Naomi Peak Limestone. The Twin Knobs Fm. [SE Idaho] is the stratigraphic equivalent to the Naomi Peak Limestone [Utah usage]. The overlying units are the Spence Shale in Utah and adjacent Idaho {and is the stratigraphic equivalent to the Lead Bell Shale in the rest of SE Idaho}. The reason Steven Oriel and Frank Armstrong did not want to use the long established geologic formation names from northern Utah can be found in the 1971 USGS Professional Paper 394 "Uppermost Precambrian and Lowest Cambrian Rocks in Southeastern Idaho. The Naomi Peak Limestone and Twin Knobs Formation contain an Albertella biozone fauna and the Spence Shale and Lead Bell Shale have a Glossopleura Biozone fauna.





Gunther, L.F., and Gunther, V.G. 1981. Some Middle Cambrian fossils of Utah. Brigham Young University Geology Studies 28, 1-81. Very good identification source to many of the Marjum Fm., Wheeler Fm., and Spence Shale fauna, still in print and available for about $10.00 from BYU.


Fritz, in Oriel & Armstrong, 1971. USGS Prof. Paper 394


Hintze, Lehi F. (1973) Geologic History of Utah. Brigham Young University, Geology Studies 20(3):15-164


Liddell, W David; Wright, Scott H.; Brett, Carlton E.; 1997. Sequence stratigraphy and paleoecology of the Middle Cambrian Spence Shale in northern Utah and southern Idaho. Brigham Young University, Geology Studies 42(1):59-78


Maxey, G. B. (1958) Lower and Middle Cambrian Stratigraphy in northern Utah and southeastern Idaho. GSA Bull., v.69, p. 647-688


McCollum, L. (research in progress)


Oriel, S. and Armstrong, F. (1971) Uppermost Precambrian and Lowest Cambrian Rocks in Southeastern Idaho. USGS Professional Paper 394.


    If you know of any other species from this formation, or have additional specimens or information, please contact Dr. Linda McCollum at: Eastern Washington University 130 Science Building Cheney, WA99004-2439 USA,


*researched and compiled by Linda McCollum, Kevin D. Brett


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