Depositional Environments of Lower Paleozoic Rocks in the White-Inyo Mountains, Inyo County, California

PACIFIC COAST PALEOGEOGRAPHY FIELD GUIDE

Ed i tors

Johnnie N. M o o r e A.Eugene Fritsche

October 16, 1976

Published by

The Pacific Section Society of Economic Paleontologists and Mineralogists Los Angeles, California U.S.A. _ r, n , TRACE FOSSILS OF THE WHITE-INYO MOUNTAINS faeftc Coos*

f)Oth>'je«f/~t>ft y Stephen P. Aipert r-,c a-,Jit 1 Department of Geology r'eUniversity of California Los Angeles, Calif. 9002b

INTRODUCTION tive gastropod-like molluscs, possibly shell-less, that crawled or grazed horizontally on or within the Trace fossils (or ichnofossils) are biosedimen- substrate. tary structures formed by the activity of living Typical molluscan trails consist of horizontal organisms on or in the substrate. The most common longitudinal grooves and ridges in varied arrange- types of trace fossils are burrows, tracks, trails, ment (Fig. 1H-M), formed as the animal plowed and borings. In the Precambrian-Cambrian section of through or crawled over the substrate. Some fossil the White-Inyo Mountains, trace fossils are abundant forms are similar to modern mollusc trails. and diverse and are evidence of the presence of many If the animal burrowed horizontally within the classes or phyla of organisms not represented by the sediment, a similar three-dimensional ribbon-like also abundant and diverse skeletal fauna in the burrow may be produced. Transverse markings may be section. Most of the trace fossils present sire suf- present, representing peristaltic movement or a ficently distinctive to indicate the type of organism backfilling of the burrow. that made the structure. Trilobites made distinctive Various molluscan trails and burrows have been structures, as did molluscs and coelenterates (sea assigned many ichnogeneric names (such as Aulichni- anemones). Cylindrical burrows probably were made by tes, Bolonia, Archaeonassa, Psammichnites, Subphyl- worms or worm-like organisms. lochorda, Paleobullia, Didymauli chnus, Olivellites, In the White-Inyo Mountains, trace fossils occur and Curvolithus) but~possibly they all could be put primarily in shale, siltstone and quartzite; very few into synonymy with the oldest genus, Scolicia. are found in limestone. The great majority of trace Scolicia sp., consisting of a groove bordered fossils indicate intertidal to shallow water areas of by two lateral ridges, up to 50 mm in diameter (Fig. deposition. 1L), is common in the upper Poleta and basal. Hark- In sections such as this one, spanning the Pre- less Formations. The trails cover large bedding cambrian- Cambrian boundary, trace fossils are impor- surfaces, commonly cross themselves, and may form tant for the information they provide about early distinctive loops. Transverse markings are not metazoans, and for their possible use in delineating present. This ridge-groove-ridge formula also oc- or defining the basal Cambrian boundary. curs at a much smaller scale in the trail Archaeo- nassa fossulata (Fig. 1H). TRACE FOSSILS AND THE ORGANISMS THAT MADE THEM Less commonly, in the Campito and Harkless For- mations, molluscan trails occur with groove-ridge- TRILOBITES groove (Fig. IK), and ridge-groove-ridge-groove- ridge (Fig. 1M) formulas. The trilobite trace fossils in the White-Inyo A new genus of molluscan trail occurs in the Mountains (Aipert, 1976) consist of four ichnogen- Campito and Poleta Formations. These trails are era: flat, smooth, and ribbon-like, and b to ^0 mm wide. Rusophycus - bilobed resting burrows (Fig. 1A). The surface of the trail is smoother than the sur- Cruziana - elongate bilobed furrows (Fig. 13). rounding rock and commonly a different color. These Diplichnites - walking trackways (two separated rows are probably mucus trails of molluscs. Three spe- of individual inprints) (Fig. 1C). cies of these "smooth trails" are present (Figs. 1E- Monomorphichnus - parallel scratchmarks made by G): no longitudinal ridges or grooves; lateral lateral movement (Fig. ID). ridges or grooves; median ridge or groove. In addition, individual claw scratchmarks are pres- Also present are assorted wide trails, 3 to 9 ent. cm wide, in the Campito and Harkless Formations, and Rusophycus is the most common trilobite trace annulated trails in the middle member of the Deep fossil, and is locally abundant in the Deep Spring, Spring Formation (Cloud & Nelson, 1966; Durham, Campito, and Harkless Formations. Several species 197*0, which may be molluscan in origin. or forms each of Rusophycus, Cruziana, and Diplich- nites are present (Aipert, 1976). WORMS The trilobite trace fossils may be used to delineate the basal Cambrian boundary (see last sec- The following trace fossils were made by un- tion of paper). known organisms, most probably worms or worm-like animals. MOLLUSCS Vertical uribranched burrows: Skolithos - vertical, cylindrical burrows, about 5 The only molluscan body fossils present in the to 15 mm wide (Aipert, 1975), (Figs. 2A, llE). Cambrian of the White-Inyo Mountains are small coni- Monocraterion - similar to Skolithos, but with a cal shells of probable molluscan affinities, but funnel-like expansion at the top of the burrow these are far too small to have produced the mollus- (Fig. 2B). can trace fossils that occur in this section. The Laevicyclus - similar to Skolithos, but with circu- molluscan trace fossils probably were made by primi- lar markings on the bedding surface around the

43 44 STEPHEN P. ALPERT

Figure 1. Lower Cambrian trace fossils. A-D. Trilobite trace fossils, bedding plane views. A. Rusophycus, x 1. B. Cruziana, x 1. C. Diplichnites, x 1. D. Monomorphichnus, x 2. E-M. Molluscan trails, oblique views. E. smooth ribbon trail, x 1.5. F. smooth ribbon trail with lateral ridges, x 1.5. G. smooth ribbon trail with median groove, x 1. H. Archaeonassa fossulata, x 2.5. I. Archaeonassa, x 5. J. Scolicia x 1. K. Scolicia, x 1.5. L. Scolicia, x 1. M. Scolicia, x 1. TRACE FOSSILS 45 top of the burrow (Fig. 2C). 800 ft, 21+0 m thick). The quartzite and sandstone Simple horizontal feeding burrows: beds of the Hines Tongue contain questionable speci- Planolites - unbranched cylindrical burrows, primar- mens of Planolites. Wyattia, the oldest shelled ily horizontal, from 1 to 20 mm wide (Figs. 2F- fossil in the section, occurs in the top of the Reed I). Generally nondescript with an irregular Dolomite and base of the overlying Deep Spring For- course. This is the most abundant and wide- mation. spread trace fossil in the White-Inyo Mountains (Aipert, 1975). DEEP SPRING FORMATION Cochlichnus - similar to Planolites, but burrow has The Deep Spring Formation (1,500 ft, U60 m) a sinusoidal course (Fig. 2J). consists of three members. The lower member con- Belorhaphe - similar to Planolites, but burrow has a tains rare Planolites. The middle member contains zig-zag course (Fig. 2K). Planolites and annulated trails and burrows which Helminthopsis - similar to Planolites, but burrow are uncommon in the quartzite beds. Shrinkage has a loose meandering course (Fig. 2M). cracks that resemble trace fossils are abundant. More complex horizontal feeding burrows: The first abundant trace fossils occur in the Palaeophycus - similar to Planolites, but with bran- quartzitic sandstone of the upper member. The first ching of burrows (Fig. 2L). trilobite or arthropod traces appear here. Ruso- Phycodes - bundled, branching burrows (Fig. 20). phycus is the most common trilobite trace; Diplich- Arthrophycus - similar to Phycodes, but with trans- nites and Monomorphichnus are also present. Plano- verse constrictions (resembles branching cri- lites is common, Skolithos and Monocraterion are noid stems), (Fig. 3A). present but rare. Zoophycos - circular feeding structure with spiral markings (Fig. 3B) CAMPITO FORMATION Star-like traces (Aipert, 1976) were possibly also The Campito Formation (3,500 ft, 1070 m) con- made by worms (Figs. 2N,P). sists of two members: the Andrews Mountain Member Vertical feeding burrows: (about 2,500 ft, 760 m thick) and the Montenegro Teichichnus - horizontal, cylindrical burrow that Member (about 1,000 ft, 310 m thick). was systematically displaced upward or downward, The Andrews Mountain Member comprises the lower forming a wall-like structure (Fig. 2E). two-thirds to three-fourths of the formation, and consists of interbedded dark-gray quartzitic sand- SEA ANEMONES stone, siltstone, and shale beds. The lowest trilobite in the section, Fallotaspis, occurs in the mid- Sea anemones form trace fossils by burrowing dle and upper part of the member, and is rare. vertically into the substrate until their oral end Trace fossils in this member occur mainly on bedding is more or less flush with the sediment surface. planes and shaly partings between sandstone and After the animal dies, the burrow is filled with siltstone beds; they rarely penetrate the beds more sediment from above, and a cast of the burrow is than a few millimeters. In the lower half of the formed, which closely reflects the aboral end of the member, below the trilobites, the following trace anemone. Sea anemone burrows (or casts) have radial fossils have been found: Planolites, Scolicia, symmetry, are shallow to deep, and in general are Archaeonassa, Rusophycus, Bergaueria?, Belorhaphe, larger in diameter than vertical burrows made by Cochlichnus, and Helminthopsis. Also present are worms. Some burrows are hemispherical, others are agglutinated worm tubes composed of imbricated mica cylindrical to conical with a rounded lower end. flakes (Wiggett, 1973). The casts commonly weather out of the rock (Figs. Above the lowest Fallotaspis, the trace fossils are more diverse and abundant, and include Rusophy- The sea anemone ichnogenus Bergaueria (Figs. cus, Cruziana, Diplichnites, Planolites, Bergaueria, UA-D) is common in siltstone and quartzite in the Arthrophycus, Riycodes, Teichichnus, Zoophycos, and White-Inyo Mountains (Aipert, 1973). Specimens smooth ribbon trails. commonly occur in pairs (Figs. 4A,B). Bergaueria The contact between the Andrews Mountain Member occurs in the Campito, Poleta, and Harkless Forma- and the Montenegro Member is gradational. In the tions . Montenegro Member, shale predominates over siltstone The ichnogenus Dolopichnus Aipert & Moore and sandstone, and limestone occurs near the top. (1975) is also present (Fig. 2D"). These anemone The first abundant trilobites occur in this member. burrows are larger and deeper than Bergaueria and The trace fossils present include Planolites, smooth apparently contain a cast of the coelenteron or ribbon trails, Archaeonassa, Skolithos, Monocrater- stomach, discernible as a cylindrical column in the ion, Teichichnus, Cruziana, Astropolithon?, and center of the burrow. The coelenteron cast may con- Dactyloidites. tain stomach contents of the anemone, primarily trilobite hash. Dolopichnus occurs in the Poleta For- POLETA FORMATION mation. The Poleta Formation (1,200 ft, 370 m) consists of two members. The lower member, limestone with a STRATIGRAPHIC DISTRIBUTION OF thin shale unit, contains rare Planolites in the TRACE FOSSILS BY FORMATION shale and limestone. Pellet-lined burrows are reported in the limestone by Nations and Beus (197*0. WYMAN FORMATION The upper member consists of shale, limestone, The Wyman Formation (9,000 ft, 2800 m) is the and quartzite units. Trace fossils below the quart- oldest formation exposed in the White-Inyo Mountains. zite unit include Planolites, Archaeonassa, smooth Rare horizontal burrows (Planolites?) a. few millime- ribbon trails, Teichichnus, and trilobite claw ters wide (Langille, 1973), from near the top of the scratchmarks. The quartzite unit near the top of formation, are the only trace fossils known. the member contains abundant trace fossils. Skolith- os is most abundant and forms a distinct marker bed. REED DOLOMITE Also present are Planolites, Laevicyclus, Monocra- The Reed Dolomite (2,000 ft, 610 m) consists of terion, Scolicia, Bergaueria, Dolopichnus, Arthro- upper and lower members of dolomite (without trace phycus ?, Rusophycus, and Psammichnites?. fossils) and the middle Hines Tongue Member (up to 5 STEPHEN P. ALPERT

C-Z

' J.

Figure 2 TRACE FOSSILS 47

Figure 2. Lower Cambrian trace fossils. A-E. Vertical trace fossils, x 0.7. A. Skolithos B. Monocraterion C. Laevicyclus D. Dolopichnus E. Teichichnus F-P. Horizontal trace fossils. F. Planolites montanus, x 1 Pisolites beverleyensis, x 0.7 H. Planolites striatus, x 0.7 I. Planolites virgatus, x 0.5 J. Cochlichnus, x 1 K. Belorhaphe, x 1 L. Palaeophycus?, x 1 M. Helminthopsis, x 0.3 N. Asteriacites?, x 1 0. Phycodes, x 0.5 P. Dactyloidites, x 1

Harkless (A-D) Formations. A-D. Bergaueria. A. basal view of two specimens. x0.6 B. vertical section through two specimens. x 0.6 C.D. weathered out specimen, basal and top views. x o. 8 E. Skolithos, side view, xo.9

Mountain) contain Skolithos, Planolites, Bergaueria, Rusophycus, Monomorphichnus, Archaeonassa, and Teichichnus. No trace fossils were found in the upper half of the Harkless Formation.

SALINE VALLEY FORMATION This formation (850 ft, 260 m thick) was not examined extensively for trace fossils, but Teich- Figure 3. Trace fossils from the Andrews Mountain ichnus , Planolites, and Cruziana were found in silt- Member, Campito Formation. A, Arthrophycus. stone of the upper member of the formation. B, Zoophycos, x 0.6. TRACE FOSSILS AND THE BASE OF THE CAMBRIAN

HARKLESS FORMATION The Precambrian-Lower Cambrian section in the The Harkless Formation (2,000 ft, 6l0 m) con- White-Inyo Mountains displays the difficulties asso- sists of shale, quartzitic siltstone and sandstone, ciated with the placement of the basal Cambrian and quartzite. Trace fossils sire abundant in the boundary. The section lends itself to the study of basal shale and siltstone beds, and include Plano- the base of the Cambrian because it apparently spans lites, Bergaueria, Rusophycus, Cruziana, Diplichni- the boundary and contains an abundant and diverse tes, Skolithos, Monocraterion, Scolicia, Archaeo- fauna of both body and trace fossils. nassa, and Asteriacites?. The quartzite units of the The Lower Cambrian extends downward at least to lower middle part of the formation (near Andrews the presently known base of the Fallotaspis Zone, '48 STEPHEN P. ALPERT

where the lowest trilobite body fossils occur, in the used as indices of the Early Cambrian include the middle of the Andrews Mountain Member of the Campito following ichnogenera: Diplocraterion, Monocraterion, Formation. However, if one includes all shelled Laevicyclus, Bergaueria, Phycodes, Arthrophycus, Zoo- metazoans in the Lower Cambrian, the base of the Cam- phycos, Teichichnus, Rhizocorallium, Chondrites, Sy- brian would here be lowered to within the uppermost ringomorpha, Cochlichnus, Belorhaphe, Plagiogmus, and part of the Reed Dolomite, where the small, conical, Psammichnites. shelled Wyattia occurs. Another possibility is Ichnogenera which cannot be used in this manner, placing the basal Cambrian boundary at the first un- because they are known or reported to occur in rocks conformity below the lowest trilobite (here the base below the lowest trilobite trace fossils, include of the Reed Dolomite; the underlying Wyman Formation Skolithos, Planolites, Scolicia, Curvolithus, and is considered Precambrian). simple, unbranched, horizontal trails or burrows. The interval between the lowest trilobite and In summary, the use of trilobite trace fossils the unconformity separating the Wyman Formation and as indices of Cambrian age and as an aid in deline- Reed Dolomite has been referred to as "Cambrian or ating the base of the Cambrian is advisable for the Precambrian?." Similarly labelled intervals occur following reasons. in other Precambrian-Cambrian transitional sections 1. The base of the Cambrian is still founded on the around the world, where small shelled fossils, abun- presence (though indirect) of trilobites. dant trace fossils, or soft-bodied metazoans occur 2. The first appearance of trilobite trace fossils below the lowest trilobite, brachiopod, or archaeocy- roughly coincides with the first appearance of other athid body fossils. trace fossils (U-shaped burrows, anemone burrows, With the use of trace fossils to delineate or branched burrows, various feeding burrows). This define the base of the Cambrian, the troublesome relatively sudden appearance and abundance of trace "Cambrian or Precambrian?" interval can be eliminated fossils (made by arthropods, worms, coelenterates) in most sections. probably represents the first explosive radiation and Stratigraphic sections that span the Precambrian evolution among the metazoans, and thus affords a -Cambrian boundary have been described, with emphasis convenient and meaningful position for the base of on the contained trace fossils, from the following the Cambrian. areas: southern Cordillera of Canada, east Greenland, 3. Trace fossils are abundant and widespread in rocks Finnmark, southern Sweden, South West Africa, and of earliest Cambrian age. southern and central Australia. Almost all bear sim- The contents of this section are more fully ilarities to the White-Inyo Mountains section in the discussed in Alpert (in press). relationship of the trace fossils to the body fossils. The general pattern that emerges is that in rocks of REFERENCES definite Early Cambrian age (above the lowest trilobite body fossils), trace fossils are abundant, di- Alpert, S. P.. 1973, Bergaueria Prantl (Cambrian and verse, and structurally complex. Below the lowest Ordovician), a probable actinian trace fossil: trilobites, in the "Cambrian or Precambrian?" inter- Jour. Paleontology, v. 1+7, p. 919-92*+. vals, trilobite trace fossils such as Rusophycus and , 1975, Planolites and Skolithos from the Upper Cruz1ana occur, along with other trace fossils. Be- Erecambrian-Lower Cambrian, White-Inyo Mountains, low the lowest trilobite trace fossils, trace fossils California: Jour. Paleontology, v. 1+9, p. 508-521. are rarer and structurally simpler, primarily hori- , 1976, Trilobite and star-like trace fossils zontal unbranched trails and burrows, or simple ver- from the White-Inyo Mountains, California: Jour. tical burrows. The soft-bodied metazoans (Ediacara Paleontology, v. 50, p. 226-239. and similar faunas), where present, occur below the , (in press), Trace fossils and the basal Cam- lowest trilobite trace fossils. Finally, in rocks of brian boundary, in Crimes, T. P., ed., Trace definite Precambrian age, trace fossils are very rare Fossils, v. 2, Geological Jour., special issue. or questionable. , and Moore, J. N., 1975, Lower Cambrian trace If the beginning of the Cambrian is to be based fossil evidence for predation on trilobites: on the first appearance of trilobites, then the base Lethaia, v. 8, p. 223-230. of the Cambrian could be lowered to the lowest trilo- Cloud, P. E., and Nelson, C. A., 1966, Rianerozoic- bite trace fossils, because trilobite trace fossils Cryptozoic and related transitions: new evidence: axe an indication of the existence of trilobites or Science, v. 15U, p. 766-770. the trilobite grade of organization. The fact that Durham, J. W., 197^-, On the Precambrian-Early Cambri- trilobite body fossils are not found in the units an trace fossil Plagiogmus: Geol. Soc. America containing the lowest trilobite trace fossils prob- Abstr. with Programs, v. 6, no. 3, p. 170. ably indicates that the earliest trilobites had ion- Langille, G. B., 1973, "Uppermost Precambrian-Lower- mineralized exoskeletons unsuitable for preservation. most Cambrian" ichnocoenoses, Inyo County, Calif- I favor placing the base of the Cambrian just ornia: Geol. Soc. America Abstr. with Programs, below the lowest trilobite trace fossils. In the v. 5, no. 2, p. 186. White-Inyo Mountains section, this is at the base of Nations, Dale, and Beus, Stanley, 197*+, Pellet-lined the upper member of the Deep Spring Formation. burrows in Poleta Formation (Lower Cambrian) of The use of trilobite trace fossils to delineate White-Inyo Mountains, California: Geol. Soc. the base of the Cambrian enables the use of other America Abstr. with Programs, v. 6, no. 3, p. 225. trace fossils to be used as indices of the Lower Cam- Wiggett, G. J., 1973, Occurrence and implications of brian. Many trace fossils occur in the Lower Cambri- trace fossils in the Lower Cambrian of the White- an and below the lowest trilobite body fossils, but Inyo Mountains, California: Geol. Soc. America do not occur below the lowest trilobite trace fossils. Abstr. with Programs, v. 5, no. 1, p. 122. Thus the presence of one or more of these trace fossils in rocks of Precambrian-Cambrian transitional sequences or in rocks of doubtful Lower Paleozoic or Precambrian age, would indicate a Cambrian age. These trace fossils can be used where trilobite traces are absent, or as a check on the use of trilobite traces to delineate the base of the Cambrian. The non-trilobite trace fossils which can be