Harkless Formation

The Harkless Formation is a geologic formation in Nevada and California. It preserves fossils dating back to the Cambrian period.

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.

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. In the Split Mountain area, the formation underlies the Mule Spring Limestone, whilst in other areas it underlies the Saline Valley Formation.

Members The formation contains two members, which are as follows, in ascending stratigraphic order (lowest to highest):

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. 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.

Alkali Member: The upper Alkali member is composed of limestone layers, up to thick, inter-stratified with siltstone, and contain an abundance of archeocyathid sponges. Further still there are light-brown limestone layers, only up to 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 thick. 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 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.

Paleobiota The Harkless Formation contains a number of sponge spicules, hyoliths, brachiopods, and other small shelly fauna. Alongside this, there are a myriad of arthropods, namely trilobites, including a single bradoriid, Mongolitubulus.

Arthropoda

GenusSpeciesNotesImagesMesonacis M. fremontiOlenellid trilobite, originally described as Fremonita.Olenellus Olenellus sp. O. clarki O. glabrumOlenellid trilobite.Wanneria Wanneria sp.Olenellid trilobite.Ogygopsis Ogygopsis sp.Dorypygid trilobite.Bonnia Bonnia sp. B. brennus B. columbensisDorypygid trilobite.Ovatoryctocara O. yaxiensisCorynexochid trilobite.Oryctocephalops O. frischenfeldiCorynexochid trilobite.Zacanthopsis Zacanthopsisi sp. Z. levisCorynexochid trilobite.Protoryctocephalus (?) P. articus (?)Corynexochid trilobite.Bristolia B. bristolensis B. mohavensisBiceratopsid trilobite, previously reported as Olenellus gilberti.Anebocephalus A. silverpeakensisTrilobite, family unknown.Coenoides C. scholteniTrilobite, family unknown.Harklessaspis H. rasettii H. parvigranulosusTrilobite, family unknown.Arcuolenellus A. megafrontalisTrilobite, family unknown.Crassifimbra Crassifimbra sp. C. walcottiTrilobite, family unknown.Mongolitubulus M. squamifer Bradoriid arthropod.

Lophotrochozoa

GenusSpeciesNotesImagesHyolithellus H. insolitusLophotrochozoan hyolith. May possibly be an annelid.Kyrshabaktella K. hicksiLinguliform brachiopod.Eothele (?) E. spurri (?)Acrotheloid brachiopod.Hadrotreta H. primaeaAcrotheloid brachiopod.Obolella Obolella sp.Obelellid brachiopod.Mickwitzia M. occidensMickwitziid brachiopod.Micromitra Micromitra sp.Paterinid brachiopod.Anuliconus Anuliconus sp.Helcionellid mollusc.Davidonia (?) D. rostrata (?)Helcionellid mollusc.Pelagiella P. subangulataPelagiellid mollusc.Harkless bryomorph ???Probable bryozoan, though this has been contested.

Chancelloriidae

GenusSpeciesNotesImagesAllonia Allonia sp.Chancelloriid.Chancelloria Chancelloria sp.Chancelloriid.

Cnidaria

GenusSpeciesNotesImagesSphenothallus Sphenothallus sp.Cnidarian conulariid.

Echinodermata

GenusSpeciesNotesImagesEchinoderm Ossicles ???Calcareous element that makes up the endoskeleton of echinoderms.

Porifera (Sponges)

GenusSpeciesNotesImagesRetilamina R. debrenneaeArcheocyathid sponge.Robertiolynthus R. handfieldiArcheocyathid sponge.Cjulanciella (?) C. asimmetrica (?)Hexactinellid sponges.Archeocyathids ???Archeocyathid sponge fragments, found in the lower layers of the formation.Hexactinellid spicules ???Sponge skeleton, with four rays.Heteractinida spicules ???Sponge skeleton, composed of four rays radiating outwards, and two rays rising up from the plane.

incertae sedis

GenusSpeciesNotesImagesVolborthella Volborthella sp.Tubular salterellid fossil.Salterella S. conulataTubular salterellid fossil.Lidaconus L. palmettoensisTubular fossil.

Flora

GenusSpeciesNotesImagesRenalcid-like ???Cyanophyte cyanobacteria.

Ichnogenera

GenusSpeciesNotesImagesCruzianaCruziana sp.Trails.PlanolitesPlanolites sp.Trails.ScoliciaScolicia sp.Burrows.MonocraterionMonocraterion sp.Burrows.RusophycusRusophycus sp. R. didymusResting trace of trilobites.SkolithosSkolithos sp.Burrows.BergaueriaBergaueria sp.Resting trace of cnidarians.DiplichnitesDiplichnites sp.Arthropod trackways.ArchaeonassaArchaeonassa sp.Burrows.MonomorphichnusM. multilineatusTrilobite feeding traces.Asteriacites (?)Asteriacites (?) sp.Sea star burrows.

Harkless Formation

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