13-Lucas and Orchard (Currie).p65

Lucas, S.G. and Spielmann, J.A., eds. 2007, Triassic of the American West. New Mexico Museum of Natural History and Science Bulletin 40.
119
TRIASSIC LITHOSTRATIGRAPHY AND BIOSTRATIGRAPHY
NORTH OF CURRIE, ELKO COUNTY, NEVADA
SPENCER G. LUCAS1 AND MICHAEL J. ORCHARD2
2
1
New Mexico Museum of Natural History, 1801 Mountain Road NW, Albuquerque, NM 87104;
Geological Survey of Canada, 101-605 Robson Street, Vancouver, British Columbia V6B 5J3, Canada
Abstract—The Triassic section north of Currie in southern Elko County, Nevada, is almost 500 m thick and is
assigned to the Thaynes Group and overlying Shinarump Formation of the Chinle Group. The Thaynes Group
disconformably overlies the Permian Gerster Formation and is mostly calcareous shale with interbedded wackestones
that yield marine invertebrate fossils, especially ammonoids. The Shinarump Formation disconformably overlies
the Thaynes Group and is up to 5 m of silica-pebble conglomerate, conglomeratic sandstone and quartzose
sandstone containing abundant silicified wood. Overlying siltstone-dominated strata long assigned to the Chinle
Group are here considered to more likely be outcrops of the Lower Jurassic Kayenta Formation of the Glen
Canyon Group. North of Currie, the Thaynes Group yields ammonoids from three stratigraphic intervals: (1)
“Meekoceras assemblage”, upper Smithian Anasibirites kingianus zone; (2) tirolitid assemblage, lower Spathian;
and (3) “Keyserlingites” assemblage, middle Spathian. Conodonts from just below the tirolitid assemblage are:
Platyvillosus asperatus, Icriospathodus collinsoni, and Novispathodus abruptus, and Columbitella elongate;
Triassospathodus ex gr. homeri is associated with the ammonoids, and “Neospathodus” hungaricus occurs above.
The conodont succession is correlated with the Columbites beds of early Spathian age.
INTRODUCTION
Triassic strata exposed north of Currie and in the southern Pequop
Mountains of Elko County, Nevada (Fig. 1) encompass a section almost
500 m thick that includes strata of Early and Late Triassic age. Although
there have been various studies that review all or parts of this section,
most lack detail (Clark, 1957), and the most complete study (Nelson,
1956) was never published. Here, we present a lithostratigraphy and
biostratigraphy of the Triassic section north of Currie.
PREVIOUS STUDIES
Wheeler et al. (1949) briefly described the section north of Currie,
noting the presence of “Chinle-like beds.” Unpublished theses by Scott
(1954), Snelson (1956) and Nelson (1956) provided detailed data on the
Triassic rocks north of Currie, and assigned them to the Dinwoody,
Thaynes, Timothy, Shinarump and Chinle formations (Fig. 2).
Clark (1957, 1960) reviewed the Triassic section north of Currie
(his localities J, K, O) and in the Southern Pequop Mountains at Spruce
Mountain (his locality P). He disagreed with Scott’s (1954) and Nelson’s
(1956) use of the term Dinwoody Formation in this area, pointing out
that the base of the Thaynes section includes Meekoceras, so it is younger
than the Dinwoody Formation. Clark (1957) also did not accept application of the terms Shinarump or Chinle to the nonmarine strata above the
Thaynes.
Sirkin (1970) focused on the Aztec (= Nugget) Sandstone outcrops north of Currie, and accepted previous workers assignment of
underlying strata to the Chinle Formation. Collinson et al. (1976) described the unconformity between the Permian Gerster Formation and
the Triassic Thaynes Formation, marked by a silica-pebble conglomerate, north of Currie. Fraser et al. (1986) published a geologic map of part
of the Southern Pequop Mountains that encompasses the Lower Boone
Spring outcrops discussed here.
Coates (1987), in a report and geologic map of Elko County at
1:250,000 scale, assigned the Permian strata immediately under the Triassic Thaynes Formation to the Park City Group (Gerster Formation).
Coates (1987) questioned identification of the Timothy, Chinle and Nugget formations north of Currie, and merely referred to these rocks as
nonmarine rocks of Triassic-Jurassic age.
Lucas and Marzolf (1993) described the Chinle section north of
FIGURE 1. Map of the area north of Currie, Elko County, Nevada, showing
distribution of Triassic outcrops and measured sections (A-Fig. 3, B-Fig.4,
C-Fig.5) (geology after Coats, 1987).
120
FIGURE 2. Comparison of stratigraphic nomenclature of Triassic strata
north of Currie used by some earlier workers (well summarized by Nelson,
1956) and that advocated here.
Currie (as identified by Nelson [1956] and others) and assigned it to the
Shinarump and Rock Point formations. Zamudio and Atkinson (1995)
briefly summarized the Triassic section north of Currie, assigning it to
the Thaynes (above Gerster) and Chinle (below Aztec) formations.
LITHOSTRATIGRAPHY
FIGURE 3. Measured stratigraphic section of the Thaynes Group in secs. 79, T29N, R64E, Elko County, Nevada.
Outcrops
Permian Gerster Formation
Triassic strata crop out north of Currie in two areas: (1) in the low
topography of cuestas, strike valleys and hills about 10 km north of
Currie in T29N, R64E; and (2) in a faulted, SW-NE trending syncline on
the eastern flank of the Southern Pequop Mountains (Fig. 1). In the low
topography in T29N, R64E, we measured the Triassic section approximately west to east across parts of sections 7, 8 and 9 (Fig. 3). In the
Southern Pequop Mountains, we measured a small portion of the Triassic section near Lower Boone Spring in sec. 20, T31N, R65E (Fig. 4).
In the hills north of Currie, the base of the Triassic section crops
out near the boundary of sections 7 and 8, where limestones of the
underlying Permian Gerster Formation form a cuesta that strikes nearly
north-south. These Gerster limestones are light gray to medium gray and
are full of dark yellowish orange, silicified brachiopod shells, as well as
crinoids and bryozoans. They correspond well to the description of the
Gerster Formation by Wardlaw et al. (1979, p. 11) as “cherty bioclastic
limestone containing minor beds of chert, dolomite, and siltstone. Crinoid
121
FIGURE 5. Measured stratigraphic section of Shinarump and Kayenta?
strata in sec. 9, T29N, R64E and photographs of a Shinarump outcrop.
and bryozoan fragments and, commonly, silicified whole brachiopods
make up much of the rock.” Clark (1957, p. 2206) referred to the brachiopod assemblage present in the uppermost Gerster in eastern Nevada as
the “Punctospirifer pulcher fauna.”
Lower Triassic Thaynes Group
FIGURE 4. Measured stratigraphic section of part of Thaynes Group at
Lower Boone Spring.
North of Currie, the Thaynes Group crops out as an ~ 470 m
thick, essentially homoclinal, east-dipping (dips are 16-20o to ~ S70oE)
section (Fig. 3). Most of the Thaynes Group section is shale with a few
thin beds and nodules of limestone (~ 84% of the section), and a minority
of the section (16%) is cuesta-forming limestone, most of which is
wackestone.
As Clark (1957) well observed, the base of the Thaynes Group
north of Currie is Smithian, so it is younger than the Dinwoody Formation. Indeed, the Griesbachian Dinwoody Formation is mostly olive gray
and greenish gray siltstone and shale up to 745 m thick, and very different lithologically from the strata north of Currie that have been assigned
to the Dinwoody (Paull and Paull, 1983). Therefore, we reject assignment of the lowermost Triassic strata north of Currie to the Dinwoody
122
FIGURE 6. Selected ammonoids from the Thaynes Group north of Currie, Elko County, Nevada. A, Anasaibirites kingianus (Waagen), NMMNH (New
Mexico Museum of Natural History) P-45327, from NMMNH locality 5704. B-C, Tirolites sp., NMMNH P-45218 from NMMNH locality 3625. D-E,
Stacheites sp., NMMNH P-45307 from locality 5711. F-G, Silberlingeria bearlakensis (Kummel), NMMNH P-42498 from NMMNH locality 3623. All
scale bars = 1 cm.
Formation (Fig. 2). Also, the term Timothy Sandstone refers to a sandstone unit in the uppermost Thaynes Group of eastern Idaho-western
Wyoming (Kummel, 1954), and we see no lithostratigraphic basis for
applying this term to any interval of the Currie section. Therefore, we
assign all strata between the Gerster and Shinarump north of Currie to
the Thaynes Group (Figs. 2-3).
At our measured section north of Currie (Fig. 3), the base of the
Triassic section is a thin (up to 0.3-m-thick) chert-pebble conglomerate
that has a sharp basal contact on Gerster Formation limestone. An ~ 4 m
thick interval of shale (mostly covered) follows, and it is overlain by ~ 5
m of interbedded shale and thin-bedded, grayish orange and pink limestones with a few, very poorly-preserved ammonoids. This is the lowest
occurrence of Triassic ammonoids in the section and the base of the
“Meekoceras beds” of previous authors. A prominent, dark brown limestone cuesta ~ 10 m thick (beds 14-18) full of ammonoids overlies these
basal beds and constitutes the bulk of the “Meekoceras beds.”
The overlying strike valley is underlain by ~ 40 m of poorlyexposed, grayish orange calcareous shale. Overlying lenticular limestone
beds in shale yield numerous brachiopods and a few bivalves. The next
cuesta is beds 23-27; bed 23 is a medium gray wackestone ledge overlain
by shale with brachiopod packstones in its lower part. Bed 29 is a
medium gray, cherty algal wackestone.
The next strike valley begins with a bed of thin-bedded, dark
yellowish orange and moderate brown calcarenite (bed 30A). The over-
123
FIGURE 7. Conodonts from the Lower Spathian interval of the Thaynes Group near Lower Boone Spring (Fig. 4). Scale bar is 200 microns for all figures
(x 80) except 19, 20.1-3, Platvillosus asperatus Clark, Sincavage & Stone, lateral, lower and upper view, GSC 120365, from sample SL1/ GSC loc. C306987. 4-7, 13-15, Icriospathodus collinsoni (Solien). 4-5, lateral and upper views, GSC 120366, 13-15, lateral, upper and detail, GSC 120367, both from
sample SL6/ GSC loc. 306992; detail shows initial splitting of carinal nodes in form close to I? crassatus. 6, 7, lower and upper views, GSC 120368, from
sample SL4/ GSC loc. C-306990. 8, 9, Triassospathodus ex gr. homeri (Bender), lower and lateral views, GSC 120369, from sample SL8/ GSC loc. C306994. 10-12, Novispathodus abruptus Orchard, lower, upper, and lateral views, GSC 120370, from sample SL4/ GSC loc. C-306990. 16-18, “Neospathodus“
cf. hungaricus (Kozur & Mostler), lower, lateral, and upper views, GSC 120371, from sample SL10/ GSC loc. 306996. 19-22, Columbitella elongata
(Sweet), 19, 20, upper and lateral views, GSC 120372, x160, from sample SL10/ GSC loc. 306996, 21, 22, lateral and upper views, GSC 120373, from
sample SL6/ GSC loc. 306992.
lying shale is poorly exposed and very thick (~ 130 m). Bed 31 is a
medium gray wackestone that forms a thin but prominent cuesta. More
shale (~ 95 m) follows until the next prominent cuesta (beds 35-40),
which overlies a slope that begins with light brown, ledgy wackestones
containing abundant Lingula. The limestones of this cuesta are medium
gray to dark gray wackestones with numerous ammonoids
(“Keyserlingites” assemblage). They are overlain by a prominent bed of
calcarenite (bed 40) having abundant Lingula and marine reptile bones
(ichthyosaurs and thalattosaurs?).
Bed 42 is a light brown wackestone with bivalves (Aviculopecten).
Overlying limestones (beds 44-55) are mostly medium gray to yellowish
gray lime mudstones with ripple laminations or algal laminae. The top
bed of the Thaynes (bed 56) is a red sandy siltstone that is about 4-5 m
thick.
In the Southern Pequop Mountains, George Fraser of the U. S.
Geological Survey discovered an ash bed near Lower Boone Spring. The
ash bed crops out on both flanks of a syncline developed in the Thaynes
Group. On the east flank of the syncline, we measured a section through
this ash bed (Fig. 4). The lower 10 m of this section are thin-bedded and
nodular wackestones that yield bivalves and conodonts, and the overlying strata are mostly black and olive gray shale that includes the ash bed,
which is a few m above shale beds with tirolitid ammonoids. The ash bed
is a tuff about 70 cm thick that consists of a lower unit ~ 18 cm thick,
overlain by ~ 18 cm of shale in turn overlain by ~ 34 cm of tuff. Fraser et
al. (1986) reported a K/Ar age of ~ 248 Ma for this ash bed, and we are
attempting more precise radioisotopic dating.
We measured approximately 200 m of stratigraphic separation
between the Meekoceras beds and the tirolitid beds on the east flank of
124
the syncline near Lower Boone Spring. This suggests that the tirolitid
beds should be in the strike valley below unit 31 in our measured section
north of Currie (Fig. 3). However, lack of outcrop in this strike valley has
prevented locating the tirolitid beds more precisely.
Upper Triassic Chinle Group and
Lower Jurassic Glen Canyon Group
In sec. 9, T29N, R64E, the Thaynes Group is overlain by a 3-5 m
thick, crossbedded unit of quartzose sandstone and siliceous conglomerate containing abundant petrified wood (Fig. 5). We agree with most
previous workers and assign this unit to the Shinarump Formation of the
Chinle Group (Lucas and Marzolf, 1993). The best Shinarump outcrop
(see Fig. 5) is at UTM zone 11, 689487E, 4474343N (NAD 27).
Overlying strata are at least 170 m of siltstones associated with a
few beds of sandstone and sandy limestone that have been assigned to
the Chinle Group by various workers (see review by Lucas and Marzolf,
1993). However, these strata are lithologically very similar to Kayenta
Formation strata in southern Nevada (Wilson and Stewart, 1967), and
not as similar to Chinle strata. Therefore, we tentatively assign them to
the Lower Jurassic Kayenta Formation. We follow Sirkin (1970) in assigning overlying sandstones to the Lower Jurassic Aztec (= Nugget)
Sandstone of the Glen Canyon Group.
BIOSTRATIGRAPHY
Invertebrate fossils are found at various stratigraphic levels in the
Thaynes Group section north of Currie and include bivalves, gastropods, ammonoids and brachiopods (Fig. 3). Here, we briefly discuss the
ammonoid assemblages and document conodonts recovered from the
lower Spathian portion of the Thaynes section.
termed Keyserlingites. It is evolute with a broadly rounded umbilicus and
a thick shell (whorls are wider than high) with rounded (convex) flanks
and a broadly arched venter. The ornamentation consists of spines on the
whorl flanks and faint ribs that cross the venter. It closely resembles
specimens assigned to Keyserlingites bearlakensis by Kummel (1969),
to which it is assigned. This species is reassigned to Silberlingeria in a
manuscript in press (J. Jenks, written commun., 2007).
Conodonts
Eleven conodont samples were collected from the Spathian portion of the Thaynes section near Lower Boone Spring north of Currie
(Fig. 4). All of these produced conodonts (Fig. 7), most coming from the
lowest 12 m of section, below the occurrence of tirolitid ammonoids.
One further collection was recovered from within the ammonoid-bearing
strata, and another from about 28 m above.
Bed 2 (Fig. 4) contains Platyvillosus asperatus Clark, Sincavage
and Stone, Icriospathodus collinsoni (Solien) and Novispathodus abruptus
Orchard. The latter two species range through beds 10 and 8 respectively, and in those two beds are joined by Columbitella elongata (Sweet).
Platyvillosus asperatus was originally described from the Butte
Mountains in eastern Nevada (Clark et al., 1964) from strata erroneously
regarded as Smithian in age. Later, the species was recognized as an early
Spathian form and chosen as the index for the basal Spathian, which is
Zone 10 of Sweet et al. (1971). The taxon is apparently restricted to the
western USA. Icriospathodus collinsoni is the index fossil of Zone 11 of
Sweet et al. (1971). Originally described from the Salt Lake City section
of the Thaynes Group (Solien, 1979), it has subsequently been reported
from throughout Eurasia (see Orchard, 1995). In the western USA, it is
most commonly found in association with ammonoids of the Columbites
zone, alongside Columbitella elongata. The latter species was originally
Ammonoids
Three stratigraphic intervals yield ammonoids of Smithian and
Spathian age north of Currie (Lucas, 2004). Previous workers have discussed the stratigraphically-lowest ammonoid assemblage north of Currie
as the Meekoceras beds (e.g., Nelson, 1956; Clark, 1957; Collinson et al.,
1976; Coates, 1987). Most of the ammonoid fossils are casts and
steinkerns that may be Meekoceras but are too poorly preserved for
identification. However, some of the better preserved specimens (Fig.
6A) can be identified as Anasibirites kingianus (Waagen). They are moderately involute, somewhat compressed laterally, have a rounded venter
except for larger (outer) whorls where the venter is flattened with distinct shoulder angles, and are ornamented with numerous ribs that run
nearly straight up the flanks and cross the venter. Thus, they thus show
characters diagnostic of Anasibirites (see especially Mathews, 1929;
Smith, 1932; Kummel and Erben, 1968), and, pending a revision of the
genus, we assign the specimens to A. kingianus as used by Kummel and
Erben (1968).
The middle assemblage comes from an ~ 6 m thick interval of black
shale interval near Lower Boone Spring (Fig. 4). Here, numerous compressions of ammonoids are assigned to Tirolites sp (Fig. 6B-C). These
are evolute with a wide and shallow umbilicus, lack ornamentation on the
innermost whorls (the “seminudi form” of earlier teminology: Kummel,
1969) and have ornamentation of radial ribs that extend across the flanks
and end at ventro-lateral tubercles. They well match published descriptions of some Tirolites (e.g., Smith, 1932; Kummel, 1969) but are not
well enough preserved (no venters can be examined) to assign to a species. Based primarily on the conodont data (see below), they are assigned
an early Spathian age equivalent to the classic Columbites beds.
The upper assemblage is the “Keyserlingites” assemblage. Two
taxa are common. One is assigned to Stacheites (Fig. 6D-E). It is a laterally compressed form that is involute and has a tabulate venter. The
preservation of the specimens, though, is otherwise poor, though the
resemblance to Stacheites (e.g., Kummel, 1969) is striking.
The other ammonoid (Fig. 6F-G) is what would classically be
FIGURE 8. Summary of Triassic lithostratigraphy and age assignments
north of Currie, Elko County, Nevada.
125
described from Pakistan, as Neogondolella, but has been commonly confused with “Neogondolella” jubata, an index of Spathian Zone 12 of
Sweet et al. (1971). Neospathodus abruptus, introduced by Orchard
(1995) based on material from Oman and North America, also has a wide
distribution and is typically found in association with the ammonoids
Columbites and Procolumbites. This species was recently assigned to
Novispathodus Orchard based on its distinctive multielement apparatus
(Orchard, 2005).
The conodont fauna of beds 2-10 (Fig. 4) is assigned to the range
zone of Icriospathodus collinsoni, which suggests a correlation with the
Columbites beds. Its lower and upper parts contain, respectively,
Platvillosus and Columbitella, whose mutual exclusion may have value in
subdividing the interval, but discrete zonal intervals 10 and 12 of Sweet
et al. (1971) are not differentiated. Solien (1979, fig. 4) recorded a similar
situation in his Utah section where P. asperatus and (probably) C.
elongata co-occurred with I. collinsoni in the lower and upper parts of
the latter species range through some 78 m of section.
Within the 6 m of ammonoid-bearing beds at Lower Boone Spring
(Fig. 4), a single conodont collection from Bed 14 contains
Triassospathodus ex gr. homeri (Bender). This species and allied forms
occur worldwide and are dominant in late Spathian faunas of the Haugi
Zone. However, allied forms were recorded as low as in beds with
Icriospathodus collinsoni by Solien (1979) and more recently by Zhao et
al. (in press) in China. This group needs some taxonomic work.
Well above the ammonoid-bearing strata, bed 23 (Fig. 4) produced
a small conodont fauna that contains indeterminate Neogondolella sp.
and, notably, elements close to, if not identical with “Neospathodus“
hungaricus, a species described by Kozur and Mostler (1970) from the
Tirolites beds at Felsörs, Hungary. This species has recently been reported from Spathian strata in the Idrija-Ziri area of Slovenia by KolarJurkovšek (pers. comm., 2007), but otherwise has not been reported
elsewhere. Nevertheless, Kozur (e.g. 2003, fig. 1) has regarded the species as the nominal index for the basal Spathian. In Nevada, this record
clearly postdates the Columbites beds equivalent, but its occurrence
nevertheless argues for a relatively low position in the Spathian for the
entire portion of the section depicted in Figure 4.
SUMMARY
The Triassic section north of Currie in southern Elko County,
Nevada, is assigned to the Thaynes Group and overlying Shinarump
Formation of the Chinle Group (Fig. 8). The Thaynes Group disconformably overlies the Permian Gerster Formation, and the Shinarump
Formation disconformably overlies the Thaynes Group. Overlying siltstone-dominated strata long assigned to the Chinle Group are more likely
outcrops of the Lower Jurassic Kayenta Formation of the Glen Canyon
Group. The Thaynes Group yields ammonoids from three stratigraphic
intervals—upper Smithian, lower Spathian and middle Spathian— as
well as early Spathian conodonts.
ACKNOWLEDGMENTS
The field assistance of Viorel Atudorei, Tom Goodspeed, Jim
Jenks, Vincent Morgan and Larry Tanner is acknowledged. Jim Jenks and
Norman Silberling provided helpful reviews of the manuscript.
REFERENCES
Clark, D.L., 1957, Marine Triassic stratigraphy in eastern Great Basin:
American Association of Petroleum Geologists, Bulletin 41, p. 21922222.
Clark, D.L., 1960, Triassic biostratigraphy of eastern Nevada; in Boettcher,
J.W. and Sloan, W.W., Jr., eds., Geology of east-central Nevada: Intermountain Association of Petroleum Geologists, Guidebook 11, p. 122125.
Clark, D.L., Sincavage, J.P. and Stone, D.D., 1964, New conodont from the
Lower Triassic of Nevada: Journal of Paleontology, v. 38, p. 375-377.
Coats, R.R., 1987, Geology of Elko County, Nevada: Nevada Bureau of
Mines and Geology, Bulletin 101, 112 p.
Collinson, J.W., Kendall, C.G. St.C. and Marcantel, J.B., 1976, PermianTriassic boundary in eastern Nevada and west-central Utah: Geological
Society of America, Bulletin 87, p. 821-824.
Fraser, G.D., Ketner, K.D. and Smith, M.J., 1986, Geologic map of the
Spruce Mountain 4 quadrangle, Elko County, Nevada: U. S. Geological
Survey, Miscellaneous Field Studies Map MF-1846.
Kozur, H., 2003, Integrated ammonoid, conodont and radiolarian zonation
of the Triassic and some remarks to Stage/Substage sub-division and the
numeric age of the Triassic stages: Hallesches Jahrbuch Geowissenschaft,
v. 25, p. 49-79
Kozur, H. and Mostler, H., 1970, Neue conodonten aus der Trias: Berichte
Natur-Medizin Vereins Innsbruck, v. 58, p. 429-464.
Kummel, B., 1954, Triassic stratigraphy of southeastern Idaho and adjacent
areas: U. S. Geological Survey, Professional Paper 254-H, p. 165-194.
Kummel, B., 1969, Ammonoids of the late Scythian (Lower Triassic):
Bulletin of the Museum of Comparative Zoology, v. 137, p. 311-702.
Kummel B. and Erben, H.K., 1968, Lower and Middle Triassic cephalopods
from Afghanistan: Palaeontographica A, v. 129, p. 95–148.
Lucas, S.G., 2004, Stratigraphy and ammonite zones of the Lower Triassic
Thaynes Group, southern Elko County, Nevada: Geological Society of
America, Abstracts with Programs, v. 36, p. 6.
Lucas, S.G. and Marzolf, J.E., 1993, Stratigraphy and sequence stratigraphic
interpretation of Upper Triassic strata in Nevada; in Dunne, G.C. and
McDougall, K.A., eds., Mesozoic paleogeography of the western United
States-II: Los Angeles, Pacific Section SEPM, p. 375-388.
Mathews, A.A.L., 1929, The Lower Triassic cephalopod fauna of the Fort
Douglas area, Utah: Walker Museum, Memoir 1, 46 p.
Nelson, R.B, 1956, The stratigraphy and structure of the region surrounding
Currie, Elko County, Nevada [M. S. thesis]: Seattle, University of Washington, 66 p.
Orchard, M.J., 1995, Taxonomy and correlation of Lower Triassic (Spathian)
segminate conodonts from Oman and revision of some species of
Neospathodus: Journal of Paleontology, v. 69, p. 110-122.
Orchard, M.J., 2005, Multielement conodont apparatuses of Triassic
Gondolelloidea: Special Papers in Palaeontology, v. 73, p. 73-101.
Paull, R.K. and Paull, R.A., 1983, Revision of type Lower Triassic Dinwoody
Formation, Wyoming, and designation of principal reference section:
Contributions to Geology, University of Wyoming, v. 22, p. 83-90.
Scott, W.F., 1954, Regional physical stratigraphy of the Triassic in a part of
the eastern Cordillera [Ph. D. thesis]: Seattle, University of Washington, 152 p.
Sirkin, G.L., 1970, The petrology and petrography of the Triassic-Jurassic
sandstone, Currie, Nevada [M. S. thesis]: Lincoln, University of Nebraska, 60 p.
Smith J.P., 1932, Lower Triassic ammonoids of North America: U. S. Geological Survey, Professional Paper 167, 199 p.
Snelson, S., 1956, The geology of the southern Pequop Mountains, Elko
County, Nevada [M.S. thesis]: University of Washington.
Solien, M.A., 1979, Conodont biostratigraphy of the Lower Triassic Thaynes
Formation, Utah: Journal of Paleontology, v. 53, p. 276-306.
Sweet, W.C., Mosher, L.C., Clark, D.L., Collinson, J.W. and Hasenmueller,
W.A., 1971, Conodont biostratigraphy of the Triassic: Geological Society of America, Memoir 127, p. 441-465.
Wardlaw, B.R., Collinson, J.W. and Maughan, E.K., 1979, Stratigraphy of
Park City Group equivalents (Permian) in southern Idaho, northeastern
Nevada, and northwestern Utah: U. S. Geological Survey, Professional
Paper 1163-C, p. 9-16.
Wheeler, H.E., Scott, W.F. and Thompson, T.L., 1949, Permian-Mesozoic
stratigraphy in northeastern Nevada: Geological Society of America,
126
Bulletin 60, p. 1928.
Wilson, R.F. and Stewart, J.H., 1967, Correlation of Upper Triassic and
Triassic(?) formations between southwestern Utah and southern Nevada: U. S. Geological Survey, Bulletin 1244D, p. 1-20.
Zamudio, J.A. and Atkinson, W.W., Jr., 1995, Mesozoic structures of the
Dolly Varden Mountains and Currie Hills, Elko County, Nevada: Geological Society of America, Special Paper 299, p. 295-311.
Zhao Laishi, Orchard, M.J., Tong J., Sun Z., Zuo J., Zhang S. and Yun, A., in
press, Lower Triassic conodont sequence in Chaohu, Anhui Province,
China and its global correlation: Palaeogeography, Palaeoclimatology,
Palaeoecology.