Harkless Formation

Harkless Formation
Stratigraphic range: Lower Cambrian PreꞒ Ꞓ O S D C P T J K Pg N [1]
Type	Formation
Sub-units	See: Members
Underlies	Saline Valley Formation Mule Spring Limestone (Split Mountain)
Overlies	Poleta Formation
Thickness	0–3,600 ft (0–1,097 m) [1]
Lithology
Primary	Siltstone
Other	Quartzite, Limestone
Location
Region	Nevada and California
Country	United States
Type section
Named for	Harkless Flat

The Harkless Formation is a geologic formation in Nevada and California. It preserves fossils dating back to the Cambrian period. ^{[1] [2]}

It is named from exposures on a divide south of Harkless Flat in the southern half of the Waucoba Mountain 15-min quadrangle in the Inyo Mountains of central eastern California. ^[3]

Geology

The Harkless Formation is mainly composed of siltstones, with many layers of fine to medium-grained quartzites, with limestone within the lower parts of the formation, although differs in various parts of the formation. ^[1] In the Split Mountain area, the formation underlies the Mule Spring Limestone, ^{[1] [4]} whilst in other areas it underlies the Saline Valley Formation. ^[1]

Members

The formation contains two members, ^[4] which are as follows, in ascending age:

• Weepah Member: Near the Andrews Mountain, at the type area of the formation, the member is dominated by greenish-gray and light-olive-gray siltstone, alongside a few layers of yellowish-gray fine to medium grained quartzite. The quartzite layers are identical to the layers found in the Zabriskie Quartzite. The siltstone ranges from grayish-olive, pale-olive, and dark-greenish-gray, and is composed of silt-size grains within a matrix of muscovite and chlorite, and is thinly laminated. They have also slightly metamorphosed, resulting in phyllite or hornfels. The hornfels are primarily composed of muscovite, chlorite, biotite, and quartz. Trace fossils are relatively common within the type area. ^[1] Within the Esmeralda County, Nevada, the lower sections of the member is still dominated by siltstone, although this differs greatly from the siltstones higher up in the formation. This is due to the layers being quartzitic, coarser and more resistant to natural erosion. The sizes of the grains within these layers hovers around the boundary between coarse silt and very fine sand. ^[1]

• Alkali Member: The upper Alkali member is composed of limestone layers, up to 100 ft (30 m) thick, inter-stratified with siltstone, and contain an abundance of archeocyathid sponges. Further still there are light-brown limestone layers, only up to 1 ft (0.30 m) thick, that contain Salterella , and are also inter-stratified with the siltstone layers in the middle of the formation. More limestone can be found at the top of the member, being gray or locally yellowish-brown, and up to 40 ft (12 m) thick. ^[1] In some areas of the member, there are also tongues from the Zabriskie Quartzite, composed primarily of medium-grained quartzite, and can get up to 300 ft (91 m) thick in some places, and inter-stratify with the siltstones. The colour of the quartzite is commonly yellowish-gray or greenish-gray. It is also laminated to thin-bedded. Trace fossils are also common within these quartzite tongues, also appearing on the underlying siltstone layers. ^[1]

Paleobiota

The Harkless Formation contains a number of sponge spicules, hyoliths, brachiopods, and other small shelly fauna. ^{[5] [2]} Alongside this, there are a myriad of arthropods, namely trilobites, ^[6] including a single bradoriid, Mongolitubulus . ^[7]

Color key Taxon Reclassified taxon Taxon falsely reported as present Dubious taxon or junior synonym Ichnotaxon Ootaxon Morphotaxon		Notes Uncertain or tentative taxa are in small text; crossed out taxa are discredited.

Arthropoda

Genus	Species	Notes	Images
Mesonacis [6]	M. fremonti	Olenellid trilobite, originally described as Fremonita. [8]
Olenellus [1] [6] [4]	Olenellus sp. O. clarki O. glabrum	Olenellid trilobite.
Wanneria [9]	Wanneria sp.	Olenellid trilobite.
Ogygopsis [6] [4]	Ogygopsis sp.	Dorypygid trilobite.
Bonnia [6] [4]	Bonnia sp. B. brennus B. columbensis	Dorypygid trilobite.
Ovatoryctocara [4]	O. yaxiensis	Corynexochid trilobite.
Oryctocephalops [4]	O. frischenfeldi	Corynexochid trilobite.
Zacanthopsis [4]	Zacanthopsisi sp. Z. levis	Corynexochid trilobite.
Protoryctocephalus (?) [4]	P. articus (?)	Corynexochid trilobite.
Bristolia [6] [4]	B. bristolensis B. mohavensis	Biceratopsid trilobite, previously reported as Olenellus gilberti. [1]
Anebocephalus [4]	A. silverpeakensis	Trilobite, family unknown.
Coenoides [4]	C. scholteni	Trilobite, family unknown.
Harklessaspis [4]	H. rasettii H. parvigranulosus	Trilobite, family unknown.
Arcuolenellus [4]	A. megafrontalis	Trilobite, family unknown.
Crassifimbra [4]	Crassifimbra sp. C. walcotti	Trilobite, family unknown.
Mongolitubulus [7]	M. squamifer	Bradoriid arthropod.

Lophotrochozoa

Genus	Species	Notes	Images
Hyolithellus [5] [2]	H. insolitus	Lophotrochozoan hyolith. May possibly be an annelid. [10]
Kyrshabaktella [5] [7]	K. hicksi	Linguliform brachiopod.
Eothele (?) [5]	E. spurri (?)	Acrotheloid brachiopod.
Hadrotreta [5] [7]	H. primaea	Acrotheloid brachiopod.
Obolella [11]	Obolella sp.	Obelellid brachiopod.
Mickwitzia [11]	M. occidens	Mickwitziid brachiopod.
Micromitra [7]	Micromitra sp.	Paterinid brachiopod.
Anuliconus [7]	Anuliconus sp.	Helcionellid mollusc.
Davidonia (?) [7]	D. rostrata (?)	Helcionellid mollusc.
Pelagiella [9] [7]	P. subangulata	Pelagiellid mollusc.
Harkless bryomorph [12]	???	Probable bryozoan, though this has been contested. [13]

Chancelloriidae

Genus	Species	Notes	Images
Allonia [7]	Allonia sp.	Chancelloriid.
Chancelloria [7]	Chancelloria sp.	Chancelloriid.

Cnidaria

Genus	Species	Notes	Images
Sphenothallus [5] [2]	Sphenothallus sp.	Cnidarian conulariid.

Echinodermata

Genus	Species	Notes	Images
Echinoderm Ossicles [5] [2] [7]	???	Calcareous element that makes up the endoskeleton of echinoderms.

Porifera (Sponges)

Genus	Species	Notes	Images
Retilamina [9]	R. debrenneae	Archeocyathid sponge.
Robertiolynthus [9]	R. handfieldi	Archeocyathid sponge.
Cjulanciella (?) [7]	C. asimmetrica (?)	Hexactinellid sponges.
Archeocyathids [1] [7]	???	Archeocyathid sponge fragments, found in the lower layers of the formation.
Hexactinellid spicules [5] [9]	???	Sponge skeleton, with four rays.
Heteractinida spicules [5] [9] [7]	???	Sponge skeleton, composed of four rays radiating outwards, and two rays rising up from the plane.

incertae sedis

Genus	Species	Notes	Images
Volborthella [6]	Volborthella sp.	Tubular salterellid fossil.
Salterella [1] [6] [7]	S. conulata	Tubular salterellid fossil.
Lidaconus [14]	L. palmettoensis	Tubular fossil.

Flora

Genus	Species	Notes	Images
Renalcid-like [9]	???	Cyanophyte cyanobacteria.

Ichnogenera

Genus	Species	Notes	Images
Cruziana [6]	Cruziana sp.	Trails.
Planolites [6]	Planolites sp.	Trails.
Scolicia [6]	Scolicia sp.	Burrows.
Monocraterion [6]	Monocraterion sp.	Burrows.
Rusophycus [6]	Rusophycus sp. R. didymus	Resting trace of trilobites.
Skolithos [6]	Skolithos sp.	Burrows.
Bergaueria [6]	Bergaueria sp.	Resting trace of cnidarians.
Diplichnites [6]	Diplichnites sp.	Arthropod trackways.
Archaeonassa [6]	Archaeonassa sp.	Burrows.
Monomorphichnus [6]	M. multilineatus	Trilobite feeding traces.
Asteriacites (?) [6]	Asteriacites (?) sp.	Sea star burrows.

See also

• Earth sciences portal
• United States portal
• Paleontology portal

• List of fossiliferous stratigraphic units in Nevada
• Paleontology in Nevada

References

1. Stewart, J. H. "Upper Precambrian and Lower Cambrian Strata, in the Southern Great Basin California and Nevada" (PDF). U.S. Geological Survery. Geological Survey Professional.
2. Wotte, Thomas; Sundberg, Frederick A. (September 2017). "Small shelly fossils from the Montezuman–Delamaran of the Great Basin in Nevada and California". Journal of Paleontology. 91 (5): 883–901. doi:10.1017/jpa.2017.8.
3. "Geologic Unit: Harkless". National Geologic Map Database. U.S. Geological Survey. Retrieved 23 April 2022.
4. Sundberg, Frederick A.; Webster, Mark (July 2022). ""Ptychoparioid" trilobites of the Harkless Formation and Mule Spring Limestone (Cambrian Series 2, Stage 4), Clayton Ridge, Nevada". Journal of Paleontology. 96 (4): 886–920. doi:10.1017/jpa.2021.124.
5. Skovsted, Christian B.; Holmer, Lars E. (December 2006). "The Lower Cambrian brachiopod Kyrshabaktella and associated shelly fossils from the Harkless Formation, southern Nevada". GFF. 128 (4): 327–337. doi:10.1080/11035890601284327.
6. Alpert, Stephen P. (1976). "Trilobite and Star-like Trace Fossils from the White-Inyo Mountains, California". Journal of Paleontology. 50 (2): 226–239. ISSN   0022-3360.
7. Bennett, Casey C.; Mate, Clare; Jacquet, Sarah M. (July 2025). "Small shelly fauna biodiversity from reef-adjacent facies of the lower Cambrian Harkless Formation, Nevada". Palaeogeography, Palaeoclimatology, Palaeoecology. 669 112922. doi:10.1016/j.palaeo.2025.112922.
8. Firby, Jean B.; Durham, J. Wyatt (1974). "Molluscan Radula from Earliest Cambrian". Journal of Paleontology. 48 (6): 1109–1119. ISSN   0022-3360.
9. Pruss, Sara B.; Smith, Emily F.; Leadbetter, Olivia; Nolan, Rhiannon Z.; Hicks, Melissa; Fike, David A. (December 2019). "Palaeoecology of the archaeocyathan reefs from the lower Cambrian Harkless Formation, southern Nevada, western United States and carbon isotopic evidence for their demise". Palaeogeography, Palaeoclimatology, Palaeoecology. 536 109389. doi:10.1016/j.palaeo.2019.109389.
10. Skovsted, Christian B.; Peel, John S. (January 2011). "Hyolithellus in life position from the Lower Cambrian of North Greenland". Journal of Paleontology. 85 (1): 37–47. doi:10.1666/10-065.1.
11. Rowell, A. J. (1977). "Early Cambrian Brachiopods from the Southwestern Great Basin of California and Nevada". Journal of Paleontology. 51 (1): 68–85. ISSN   0022-3360.
12. Pruss, Sara B.; Leeser, Lexie; Smith, Emily F.; Zhuravlev, Andrey Yu.; Taylor, Paul D. (22 April 2022). "The oldest mineralized bryozoan? A possible palaeostomate in the lower Cambrian of Nevada, USA". Science Advances. 8 (16). doi:10.1126/sciadv.abm8465. PMC   9020656 .
13. Yang, Jie; Lan, Tian; Zhang, Xi-guang; Smith, Martin R. (16 March 2023). "Protomelission is an early dasyclad alga and not a Cambrian bryozoan". Nature. 615 (7952): 468–471. doi:10.1038/s41586-023-05775-5.
14. Onken, Beth R.; Signor, Philip W. (1988). "Lidaconus palmettoensis n. gen. and sp.: An Enigmatic Early Cambrian Fossil from Western Nevada". Journal of Paleontology. 62 (2): 172–180. ISSN   0022-3360.

• Various Contributors to the Paleobiology Database. "Fossilworks: Gateway to the Paleobiology Database". Archived from the original on 25 March 2022. Retrieved 17 December 2021.