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40Ar/39Ar age of the Kaiparowits Formation, southern Utah, and correlation of contemporaneous Campanian strata and vertebrate faunas along the margin of the Western Interior Basin

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Laser-fusion 40Ar/39Ar analysis of four bentonite horizons produces the first absolute ages for the 860-m-thick Kaiparowits Formation and resolves previous age uncertainty caused by ambiguous biostratigraphy. A late Campanian (Judithian) age of ca. 76.1–74.0Ma is determined, resulting in a high-resolution temporal framework for the richly fossiliferous formation. Detailed stratigraphic correlation reveals that the Kaiparowits Formation is contemporaneous with many of the most important vertebrate fossil-bearing formations in the Western Interior Basin, and with other well-studied strata across Utah and southeastern Wyoming, including portions of the Book Cliffs sequence. The Judithian age determination and correlations for the Kaiparowits Formation presented here provide a new chronological basis for addressing questions relating to mammal biostratigraphy, vertebrate evolution, biodiversity and paleobiogeography (e.g., dinosaur provincialism) in the Cretaceous Western Interior Basin.
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40
Ar/
39
Ar age of the Kaiparowits Formation, southern Utah, and
correlation of contemporaneous Campanian strata and vertebrate
faunas along the margin of the Western Interior Basin
Eric M. Roberts
a,
*, Alan L. Deino
b
, Marjorie A. Chan
a
a
Department of Geology and Geophysics, University of Utah, Salt Lake City, UT 84112, USA
b
Berkeley Geochronology Center, Berkeley, CA 94709, USA
Received 10 June 2004; accepted in revised form 11 January 2005
Available online 16 March 2005
Abstract
Laser-fusion
40
Ar/
39
Ar analysis of four bentonite horizons produces the first absolute ages for the 860-m-thick Kaiparowits
Formation and resolves previous age uncertainty caused by ambiguous biostratigraphy. A late Campanian (Judithian) age of ca.
76.1e74.0 Ma is determined, resulting in a high-resolution temporal framework for the richly fossiliferous formation. Detailed
stratigraphic correlation reveals that the Kaiparowits Formation is contemporaneous with many of the most important vertebrate
fossil-bearing formations in the Western Interior Basin, and with other well-studied strata across Utah and southeastern Wyoming,
including portions of the Book Cliffs sequence. The Judithian age determination and correlations for the Kaiparowits Formation
presented here provide a new chronological basis for addressing questions relating to mammal biostratigraphy, vertebrate evolution,
biodiversity and paleobiogeography (e.g., dinosaur provincialism) in the Cretaceous Western Interior Basin.
Ó2005 Elsevier Ltd. All rights reserved.
Keywords: Cretaceous; Geochronology; Stratigraphy; North America; Vertebrata
1. Introduction
Foreland basins commonly preserve thick, richly
fossiliferous, nonmarine sedimentary sequences that are
important for reconstructing the tectonic and evolution-
ary histories of ancient terrestrial ecosystems (Hunt, 1991;
Rogers, 1993; Badgley and Behrensmeyer, 1995). The
Western Interior Basin (WIB), extending from Alberta to
Mexico, is among the most well-studied foreland basins in
the world, particularly with regard to vertebrate evolu-
tion. However, temporal correlation of strata and faunas
in the WIB remains problematic. A paucity of fossil
vertebrates and limited radiometric age control of non-
marine strata in the central WIB in Utah (e.g., Kaiparowits
Basin, Book Cliffs) has, until now, hampered stratigraphic
and faunal correlation with more well-studied northern
and southern regions (Sampson et al., 2002).
Recent fossil discoveries in the Kaiparowits Formation
are beginning to improve our understanding of Late
Cretaceous vertebrate faunas from Utah (Weishampel
and Jensen, 1979; DeCourten and Russell, 1985; Eaton
and Cifelli, 1988; Cifelli, 1990a,b; Hutchison et al., 1997;
Eaton, 2002). The Kaiparowits Formation is particularly
important because it is one of the few richly fossiliferous
Late Cretaceous formations in the central WIB, and is
thus crucial for linking fossil-rich northern and southern
strata, and for testing paleogeographic hypotheses on
evolution and provinciality among terrestrial vertebrate
* Corresponding author. Department of Geosciences, Idaho State
University, Pocatello, ID 83209, USA.
E-mail address: robeeric@isu.edu (E.M. Roberts).
0195-6671/$ - see front matter Ó2005 Elsevier Ltd. All rights reserved.
doi:10.1016/j.cretres.2005.01.002
www.elsevier.com/locate/CretRes
Cretaceous Research 26 (2005) 307e318
faunas (e.g., Horner et al., 1992; Lehman, 1997; Weil,
1999). Here we report the first radioisotopic ages for the
Kaiparowits Formation. Detailed
40
Ar/
39
Ar analysis of
four altered ash beds (bentonites) results in a high-
resolution chronostratigraphy and permits detailed cor-
relation between other strata and vertebrate faunas.
2. Geologic setting
The Kaiparowits Formation is exposed in the
Kaiparowits Basin of southern Utah, primarily within
the boundaries of the Grand Staircase-Escalante Na-
tional Monument (Fig. 1). Because of its rich and
relatively unexplored fossil resources (e.g., dinosaurs),
the Kaiparowits Formation represents an important
area in the United States for new fossil discoveries. The
formation is easily recognized by its distinctive, bad-
land-forming blue-gray sandstones and mudstones,
which are in stark contrast to the typical tan sandstones
of the underlying Wahweap and Straight Cliffs for-
mations and the overlying, maroon conglomerates of
the Canaan Peak Formation. At ca. 860 m thick, the
Kaiparowits Formation comprises nearly half of the 2-
km-thick Upper Cretaceous sequence in the Kaipar-
owits Basin. The section is informally subdivided into
three units (lower, middle, upper), based on distinct
changes in alluvial architecture (Fig. 2).
Kaiparowits strata were deposited as part of a single
prograding clastic wedge, derived from a source area
located ca. 300e650 km to the southwest in the Sevier
fold and thrust belt in southeastern Nevada and eastern
California (Eaton, 1991; Goldstrand, 1992). The fine-
grained nature of the sediment and nonmarine fauna
suggest deposition upon a low-relief, inland alluvial
plain setting. Sedimentological analysis suggests a rela-
tively warm, humid paleoclimate dominated by fluvial
and paludal environments (Eaton, 1991; Little, 1995;
Roberts et al., 2003). The relative isolation of the
formation and the lack of correlative or bounding
marine units with reliable index fossils have hampered
previous age assessments. Preliminary investigation of
the palynology and vertebrate paleontology of the
formation suggested a Maastrichtian age for these strata
(e.g., Lohrengel, 1969; DeCourten and Russell, 1985).
However, more recent work on mammals in the
formation (e.g., Eaton and Cifelli, 1988; Cifelli,
1990a,b; Eaton, 2002) and re-examination of palyno-
morph data (Eaton, 1991) suggest a Campanian age.
3. Bentonites
Eight discrete bentonites were identified within the
composite 860-m-thick succession (Fig. 2). The benton-
ites are primarily composed of smectitic clay, which
produces a distinctive, easily recognizable popcorn-style
weathering. Individual phenocrysts of euhedral biotite,
plagioclase, and sanidine are localized along basal
contacts, and they are typically between 200e700 mm.
Bentonite beds range in thickness from 10 to 50 cm, are
commonly pale olive (10Y 6/2) to yellowish gray (5Y 7/2)
in color and have sharp to wavy basal contacts. Upper
contacts are commonly gradational. The abundance of
Fig. 1. General locality map for the Kaiparowits Formation and primary study locations.
308 E.M. Roberts et al. / Cretaceous Research 26 (2005) 307e318
paludal environments in the formation likely resulted in
enhanced preservation of these ashes.
The relative thinness of individual beds and the
smallemedium size of most phenocrysts recovered from
the bentonites suggest that ashes were derived from
a fairly distant source area, likely within or to the west
of the Sevier thrust belt. The source area is difficult to
determine due to post-depositional erosion; however
several late Campanian volcanic centers have been
identified. The most well known of these volcanic
centers is the Elkhorn Mountain Volcanics in central
Montana, considered to have produced one of the
largest ash flow tuff fields in the world (Smith, 1960;
Smedes, 1966). Campanian bentonites across the WIB,
from Alberta, Montana, Wyoming, Nebraska, and the
Dakotas have been linked to the Elkhorn Mountain
Volcanics (Spivey, 1940; Gill and Cobban, 1973;
Thomas et al., 1990; Rogers et al., 1993; Roberts and
Hendrix, 2000). The numerous interpretations for an
eastern source area in the Elkhorn Mountain Volcanics
suggest a dominantly eastward wind-transport direction
in the WIB during the Late Cretaceous. Other possible
contemporaneous sources have been identified to the
south in Arizona, eastern California, and northern
Mexico (Hayes, 1970; Drewes, 1978; Dickinson et al.,
1989).
4.
40
Ar/
39
Ar dating
We applied the
40
Ar/
39
Ar laser-fusion dating tech-
nique to four of the most phenocryst-rich bentonites
from the formation (KDR-5; KBC-109; KBC-144;
Fig. 2. Composite measured section of the Kaiparowits Formation in the Grand Staircase-Escalante National Monument. Location and
40
Ar/
39
Ar
ages of the four bentonites dated in this study are shown to the right.
309E.M. Roberts et al. / Cretaceous Research 26 (2005) 307e318
KBO-37), employing a tightly focused, continuous laser
beam to fuse individual sanidine phenocrysts for
isotopic age analysis. The lowest bentonite, KDR-5,
was collected from ca. 80 m above the base of the section
in the Death Ridge area, ca. 20 km south of Utah
Highway 12 (Figs. 1, 2;Table 1). The other three
bentonites were collected in the Blues area, along Utah
Highway 12 (Fig. 1), at ca. 420 m (KBC-109), ca. 490 m
(KBC-144), and ca. 790 m (KBO-37) above the base of
the formation (Figs. 1, 2;Table 1).
4.1. Methods
Approximately 20 kg of each bentonite were disag-
gregated using warm tap water and repeated agitation,
and then sieved through 20, 40, 60 and 100 mesh screens.
Feldspars were separated from the coarse fractions with
a Franz isodynamic separator, and sanidine was isolated
from plagioclase by density separations using heavy
liquids.
Sanidine crystal concentrates were loaded into wells
in an aluminum disk in preparation for irradiation. The
arrangement consisted of 12 wells (0.80$deep !0.130$
diameter) in a 0.260$diameter circle, with four stand-
ards at the cardinal points and unknowns in the
remaining positions. After additional protective pack-
aging, the samples were irradiated for 200 h in the Cd-
lined, in-core CLICIT facility of the Oregon State
University TRIGA reactor. Sanidine from the Fish
Canyon Tuff of Colorado was used as a mineral
standard, with a reference age of 28.02 Ma (Renne et al.,
1998).
40
Ar/
39
Ar extractions were performed at the Berkeley
Geochronology Center, using a focused CO
2
laser to
fuse and rapidly liberate trapped argon from individual
sanidine crystals. Gasses were scrubbed with SAES
getters for several minutes to remove impurities (CO,
CO
2
,N
2
,O
2
, and H
2
), followed immediately by
measurement of the purified Noble gasses for five argon
isotopes on a MAP 215-50 mass spectrometer for
approximately 30 min. From 10 to 40 grains were
analyzed per sample, the greatest number of analyses
being necessary where contamination with older feld-
spars was heaviest.
The neutron fluence parameter, J, appropriate to
each unknown was predicted from a planar, multiple-
regression model of standard Js against known disk
positions. A conservative, arbitrary uncertainty of 0.2%
is assigned to J, though residuals of the fit would suggest
0.1% or better. Weighted-mean ages of the Kaiparowits
sanidine populations were calculated after elimination
of analyses that failed one of multiple criteria: (1)
radiogenic
40
Ar content less than 96% of total
40
Ar; (2)
Ca/K ratio greater than one (indicating plagioclase); (3)
very low
39
Ar yield indicating incomplete fusion or non-
feldspar composition (i.e., quartz); (4) obviously too-old
age (O78 Ma); and (5) a final outlier detection scheme
based on deviation from the median age (1.4 normalized
median absolute deviations from the median). Weight-
ed-mean ages were calculated from the remaining 15e27
analyses per sample.
4.2. Results
Summary
40
Ar/
39
Ar analytical data for the four
bentonite samples are presented in Table 2 (full
analytical data to be made available in Roberts’ PhD
dissertation). Age-probability spectra are shown in
Fig. 3. All samples yield gaussian-like unimodal age
distributions. The most significant variable controlling
Table 1
Location and characteristics of dated bentonite horizons within the Kaiparowits Formation
Sample Location Stratigraphy Sedimentology
KDR-5 Death Ridge area; UTM 0434999/4156941
Death Ridge Quadrangle
w80 m above base of Kaiparowits
Formation
w50 cm thick; pale yellow-green; sharp
basal contact
KBC-109 Blues area; UTM 0424535/4165074 Upper
Valley Quadrangle
w420 m above base of Kaiparowits
Formation
w10 cm thick; olive green; wavy basal
contact
KBC-144 Blues area; UTM 0425382/4165351 Upper
Valley Quadrangle
w490 m above base of Kaiparowits
Formation
w30 cm thick; dark green; sharp basal
contact
KBO-33 Blues area; UTM 0424773/4167799 Upper
Valley Quadrangle
w790 m above base (w70 m below
top) of Kaiparowits Formation
w50 cm thick; pale yellow-green wavy
basal contact
Table 2
Summary of the analytical data for
40
Ar/
39
Ar analysis of four bentonites from the Kaiparowits Formation
Sample Lab
ID#
J
(!10
ÿ3
)1s
Ca/K
1s
39
Ar Mol
!10
ÿ14
40
Ar*/
39
Ar
1s
Age (Ma)
1s
(with GJ)
1s
MSWD Prob. n/n
total
KBC-109 22644 52.60 0.10 0.0124 0.0002 5.1 0.8072 0.0005 75.02 0.05 0.15 1.02 0.43 23/30
KBC-144 22647 52.81 0.10 0.01183 0.00016 6.1 0.8040 0.0004 75.02 0.04 0.15 0.94 0.55 27/34
KBO-37 22625 52.85 0.10 0.0050 0.0006 2.4 0.7946 0.0012 74.21 0.11 0.18 1.66 0.06 15/40
KDR-5 22646 52.74 0.10 0.01068 0.00004 38.3 0.8154 0.0003 75.96 0.02 0.14 0.36 1.00 21/23
310 E.M. Roberts et al. / Cretaceous Research 26 (2005) 307e318
the spread of the age population is predominately grain
size; improvement in analytical precision tracks the
increase in grain size from KBO-37 with the smallest
sanidine (!0.180 mm) to KDR-5 with the largest (0.55e
0.71 mm). Relative grain size is approximated by the
39
Ar abundance released during total fusion (Fig. 3;
Table 2) if potassium contents of these sanidines are
approximately equal (an assumption supported by the
narrow range of Ca/K ratios observed).
The stratigraphically lowest bentonite (KDR-5)
dated in this study yielded an age of 75.96 G0.14 Ma
(Fig. 3;Table 2). Within the middle unit, two bentonites
within 70 m of each other (KBC-109, KBC-144) gave
identical ages of 75.02 G0.15 Ma (Fig. 3;Table 2). The
highest bentonite (KBO-37), in the upper unit, yielded
an age of 74.21 G0.18 Ma (Fig. 2;Table 2).
5. Campanian/Maastrichtian boundary
Correlations of the middle Campanianeearly Maas-
trichtian in the WIB are presented based on a synthesis
of ammonite zones with radiometric determinations,
magnetostratigraphy, and North American land mam-
mal ‘‘ages’’ (Lillegraven and McKenna, 1986; Kennedy
et al., 1992; Obradovich, 1993; Gradstein et al., 1994).
The placement of the Campanian/Maastrichtian bound-
ary in the WIB of North America is subject to
considerable debate (e.g., Obradovich and Cobban,
1975; Bergstresser and Frerichs, 1982; Berggren et al.,
1985; Lillegraven and McKenna, 1986; Eaton, 1987;
Lillegraven, 1991; Kennedy et al., 1992; Obradovich,
1993; Gradstein et al., 1994). The magnetobiochrono-
logic Campanian/Maastrichtian boundary of ca.
71.3 Ma, accepted by Kennedy et al. (1992), Obradovich
(1993), Gradstein et al. (1994), and others is followed in
this study.
6. Age of Kaiparowits Formation
Calculation of the average rock accumulation rate for
strata bracketed between the basal sample, KDR-5, and
the highest sample, KBO-37, permits an estimate of the
total duration of the Kaiparowits Formation. These
samples bracket ca. 710 m of strata. By dividing this
Fig. 3. Age-probability spectra of single-crystal, total-fusion
40
Ar/
39
Ar analyses of sanidine from four Kaiparowits bentonites. The relative
probabilities displayed in the lower panel are generated by summing the assumed gaussian errors of the individual analyses for a given sample.
Dashed curves incorporate all analyses; solid curve represents age-probability distributions generated after trimming outliers from the data set.
Weighted-mean ages and 1sstandard error of the mean are displayed by the diamond and error bars associated with each distribution. The inner tics
on the error bar represent the uncertainty excluding the error in the neutron fluence parameter, J, while the outer tics incorporate a 0.2% error in J.
The middle panel displays ordered individual ages and 1serrors, while the upper panel shows a rough proxy for grain size, the total moles of
39
Ar
released upon fusion of a grain.
311E.M. Roberts et al. / Cretaceous Research 26 (2005) 307e318
thickness by the time duration (1.75 Ma) calculated
between samples KDR-5 and KBO-37, an average rock
accumulation rate of ca. 41 cm/ka is obtained. Rock
accumulation rates of 39 cm/ka and 42 cm/ka were
calculated, respectively, for the lower part of the
formation between KDR-5 and KBC-109/KBC-144,
and for the upper part of the formation, between KBC-
109/KBC-144 and KBO-37. The similarity between each
of these calculated rates demonstrates that sedimenta-
tion rates remained relatively constant throughout the
formation (Fig. 4).
Utilizing an average rock accumulation rate of
41 cm/ka, the ca. 860-m-thick Kaiparowits Formation
accumulated for ca. 2.1 Ma, from ca. 76.1e74.0 Ma. This
estimate demonstrates that the formation is late Campa-
nian in age, spanning the upper part of the Judithian
land mammal ‘‘age’’ (Lillegraven and McKenna, 1986).
7. Stratigraphic correlations
The
40
Ar/
39
Ar ages reported here are the first
radiometric dates for the Kaiparowits Formation. This
study permits high-resolution temporal correlation of
coeval strata and contemporaneous terrestrial vertebrate
faunas across the WIB. Chronstratigraphic, magneto-
stratigraphic, biostratigraphic and lithostratigraphic
data were utilized to construct the detailed correlations
presented here (Lillegraven and McKenna, 1986;
Obradovich, 1993; Gradstein et al., 1994). Radiometric
ages provide the most accurate framework for large-
scale regional correlations in terrestrial settings and
have been utilized in correlations wherever possible
(Goodwin and Deino, 1989; Eberth and Hamblin, 1993;
Rogers et al., 1993; Rogers, 1994; Fassett and Steiner,
1997; McDowell et al., 2004).
7.1. Regional correlations
The Kaiparowits Formation correlates with portions
of the well-studied Book Cliffs in central Utah.
Correlative strata (in the Book Cliffs) west of Green
River include the Upper Castlegate Sandstone, the
Bluecastle Tongue of the Castlegate Sandstone, and
the basal Price River Formation (Fouch et al., 1983;
Lawton, 1986; Willis, 2000)(Figs. 5, 6). To the east of
Green River, the Neslen Formation, the Bluecastle
Tongue of the Castlegate Sandstone, and the basal
Farrer Formation are correlative with the Kaiparowits
Formation (Fouch et al., 1983; Lawton, 1986; Willis,
2000)(Figs. 5, 6). Both the ‘‘beds on Tarantula Mesa’’,
in the Henry Basin of central Utah, and the upper
Ericson Sandstone in the Rock Springs Uplift of
southwestern Wyoming are also contemporaneous
(Peterson and Ryder, 1975; Eaton, 1990; Martinsen
et al., 1999)(Figs. 5, 6).
7.2. Faunal correlations
The Kaiparowits Formation was deposited during an
important period of Late Cretaceous dinosaur evolution,
during the zenith of dinosaur diversity (Sloan, 1976;
Dodson, 1983; Clemens, 1986; Dodson and Tatarinov,
1990). Many of the most fossiliferous, vertebrate-bearing
formations in the WIB are closely contemporaneous with
Fig. 4. Stratigraphic height above the base of formation vs. age of the
Kaiparowits Formation. A strong linear correlation (R
2
Z0.98)
suggests a roughly constant rock accumulation rate (ca. 41 cm/ka).
Fig. 5. Map of Utah showing location of major Late Cretaceous age
exposures in Utah and NW Wyoming. Symbols: A, Markagunt and
Paunsaugunt plateaus; B, Kaiparowits Plateau; C, Henry Mountains;
D, Book Cliffs, west of Green River; E, Book Cliffs, east of Green
River; F, Rock Springs Uplift. Black line through localities represents
the stratigraphic transect (AeF) presented in Fig. 6.
312 E.M. Roberts et al. / Cretaceous Research 26 (2005) 307e318
the Kaiparowits Formation. Principally, to the north, the
fossil-rich Dinosaur Park Formation and the most
fossiliferous, upper portions of the Judith River and
Two Medicine formations are coeval (Figs. 7, 8);
temporally constrained by multiple
40
Ar/
39
Ar ages
(Goodwin and Deino, 1989; Eberth and Hamblin, 1993;
Rogers et al., 1993; Rogers, 1994). To the southeast, the
Fruitland and lower Kirtland formations (Fassett and
Steiner, 1997) in New Mexico are partially correlative
with the Kaiparowits Formation (Figs. 7, 8). However,
the primary fossil bearing units of the Fruitland and
Kirtland formations are mostly younger and do not
correlate as well with fossil-bearing portions of the
Kaiparowits Formation, which are concentrated in the
middle and lower units (Hunt and Lucas, 1992; Roberts,
unpublished data) (Fig. 8). Further south, the upper shale
member of the Aguja Formation (Texas) is considered to
be partially correlative with the Kaiparowits Formation
based on biostratigraphic and chronostratigraphic data
from bounding units and correlative marine strata (Rowe
et al., 1992; Cifelli, 1994; Lehman, 1997; Sankey, 2001;
McDowell et al., 2004)(Figs. 7, 8). Dating of the Aguja
Formation is currently too poor to reveal the precise
temporal relationships of the Aguja and Kaiparowits
faunas.
8. Discussion
The Kaiparowits Formation contains one of the
richest and most diverse vertebrate faunas for all Late
Cretaceous terrestrial sequences in the WIB. The
formation occupies a relatively central position in the
basin, and thus provides a crucial faunal data set for
addressing recent hypotheses relating to Mesozoic
mammal biostratigraphy, and vertebrate evolution,
biodiversity, and provinciality (Lillegraven and McKen-
na, 1986; Horner et al., 1992; Lehman, 1997; Weil,
1999).
8.1. Mammal biostratigraphy
Dated bentonite horizons provide temporal con-
straints for this important fauna, and bracket mammal
localities in the Kaiparowits Formation, corroborating
the Judithian land mammal ‘‘age’’ reported by Eaton
Fig. 6. Correlation chart showing age relations of late Campanian strata in Utah and SW Wyoming (see transect line in Fig. 5). Time scale from
Gradstein et al. (1994). Western Interior ammonite zones from Obradovich (1993). The following sources of data are denoted by the numbers at the
top of the columns: 1, Lawton et al. (2003);2,Eaton (1991); 3, Roberts et al. (this study); 4, Eaton (1990);5,Fouch et al. (1983);6,Lawton (1986);7,
Willis (2000);8,Martinsen et al. (1999).
313E.M. Roberts et al. / Cretaceous Research 26 (2005) 307e318
and Ciffeli (1988), Cifelli (1990a,c) and Eaton (2002).
Eaton (2002) suggested that the Kaiparowits mammal
fauna may be slightly older than the type Judith River
Formation because of several taxa found in the
Kaiparowits Formation that are more closely related
to Aquilan than Judithian faunas. However, based on
the ages reported in this study, the Kaiparowits
Formation is shown to be entirely contemporaneous
with the upper portion of the Judith River Formation
(Fig. 8).
The ages reported here also have bearing on the
recently constructed Kirtlandian land vertebrate ‘‘age’’
of Sullivan and Lucas (2003). The Kirtlandian was
created in order to fill a reported ‘‘biochronologic gap’’
between the Judithian and ‘‘Edmontonian’’ land mam-
mal ‘‘ages’’ (74.9e72.0 Ma). It is characterized by the
vertebrate fossil assemblages of the Fruitland and
Kirtland formations, and is reported to correlate to
the lower part of the Bearpaw Formation in Montana
and Alberta and the Kaiparowits Formation (Sullivan
and Lucas, 2003). Based on the
40
Ar/
39
Ar ages reported
herein for the Kaiparowits Formation, and an evalua-
tion of the Kaiparowits fauna, a Judithian age
assignment is considered to be more parsimonious than
a Kirtlandian assignment.
Evidence in support of this includes the distribution
of diagnostic mammal taxa throughout the formation,
including the presence of Dakotamys magnus and
Gypsonictops lewisi, taxa considered to be unique to
the Judithian (Lillegraven and McKenna, 1986), from
high in the section (Fig. 2, ca. 640-m level; Eaton, 2002).
Additionally, the principle index fossil for the Kirtlan-
dian, Pentaceratops sternbergii, has not yet been
identified from the Kaiparowits Formation, while
multiple specimens of a new, undescribed ceratopsian
dinosaur occur within it (Getty et al., 2003; Smith et al.,
2004). Given the paleoenvironmental similarities and
close spatial relationships (!300 km apart) between the
two formations, some overlap in the distribution of
these two taxa is expected. The lack of apparent overlap
suggests that the Kirtland-Fruitland and Kaiparowits
faunas were probably not entirely contemporaneous.
Although less likely, the absence of both taxa from the
two formations could also be due to sampling bias or
paleoenvironmental differences. Several other taxa
considered as potential index fossils for the Kirtlandian
land vertebrate ‘‘age’’ have been identified in the
Kaiparowits Formation (e.g., Parasaurolophus,Krito-
saurus;Sullivan and Lucas, 2003); however, they were
recovered from low in the section (200e350 m level) and
Fig. 7. Map showing the paleogeographic relationships of Campanian strata (in black) in the Western Interior Basin. Symbols: A, Dinosaur
Provincial Park; B, Judith River Type Area; C, Two Medicine River; D, Kaiparowits Basin; E, San Juan Basin; F, Big Bend N.P. Modified from
Lehman (1997).
314 E.M. Roberts et al. / Cretaceous Research 26 (2005) 307e318
are bracketed by mammals and ash beds indicating
a Judithian age, no younger than 75 Ma.
A review of the distribution of major fossil localities
in the Kirtland-Fruitland and Kaiparowits formations
also reveals little temporal overlap between formations
(Fig. 8). Principle vertebrate localities of the Kirtland-
Fruitland formations (Hunter Wash and Willow Wash
local faunas) are located in the Fossil Forest, Hunter
Wash, and De-na-zin members (Hunt and Lucas, 1992),
dated between 74.5 and 73.0 Ma (Fassett and Steiner,
1997; Sullivan and Lucas, 2003). The majority of fossil
localities documented in the Kaiparowits Formation are
from the upper part of the lower unit and the middle
unit (Eaton and Cifelli, 1987; Eaton, 1991; Hutchison
et al., 1997; Roberts et al., 2003), ranging from ca. 75.9
to 74.8 Ma (see Fig. 4). The few fossil localities in the
upper unit of the Kaiparowits Formation contain
Dakotamys magnus and Gypsonictops lewisi (Cifelli,
1990c; Eaton, 2002), bracketing them as Judithian.
Thus, there appears to be limited evidence supporting
a Kirtlandian age assignment for the Kaiparowits
Formation. Additionally, the presence of well-docu-
mented Judithian mammals as high as 640 m in the
Kaiparowits Formation suggests that the upper bound-
ary of the Judithian land mammal ‘‘age’’ is no older
than ca. 74.6 Ma (Fig. 4).
9. Conclusions
This study was aimed at resolving the disputed age of
the Kaiparowits Formation (see Eaton, 1991).
40
Ar/
39
Ar
dating of four bentonite horizons distributed through-
out the 860-m-thick section produces the first absolute
ages for the formation. New data indicate a late
Campanian (Judithian) age, between ca. 76.1 and
74.0 Ma. These findings are consistent with the mammal
biostratigraphy of Eaton (2002), and provide geochro-
nologic evidence supporting an upper bracket, no older
than ca. 74.6 Ma, for the Judithian land mammal ‘‘age’’.
Fig. 8. Correlation chart showing the age relations of important late Campanian (Judithian) dinosaur-bearing formations in the Western Interior
Basin. Time scale from Gradstein et al. (1994); Western Interior ammonite zones from Obradovich (1993). The following sources of data are denoted
by the numbers at the top of the columns: 1, Eberth and Hamblin (1993); 2, D. Eberth (pers. comm. 2004); 3, Goodwin and Deino (1989);4,Rogers
et al. (1993);5,Rogers (1994);6,Rogers (1998);7,Rogers and Kidwell (2000);8,Eaton (1991); 9, Roberts et al. (this study); 10, Hunt and Lucas
(1992); 11, Fassett and Steiner (1997); 12, Sullivan and Lucas (2003); 13, Lehman (1997); 14, Rowe et al. (1992); 15, Sankey (2001); 16, McDowell
et al. (2004).
315E.M. Roberts et al. / Cretaceous Research 26 (2005) 307e318
The results of this study allow for improved
correlation of contemporaneous strata and vertebrate
faunas in Utah and the WIB, and lay the groundwork
for future geochronologic refinement of strata in the
Kaiparowits Basin. Rapid deposition (ca. 41 cm/ka) and
distribution of dated ash beds throughout the richly
fossiliferous Kaiparowits Formation permits the evalu-
ation of recent hypotheses relating to the diversity,
latitudinal distribution, and evolution of Late Creta-
ceous vertebrate faunas in the WIB (e.g., Horner et al.,
1992; Lehman, 1997; Weil, 1999).
Bentonites documented in this study are also
recognized as laterally extensive marker beds, providing
a means of correlating stratigraphic sections and fossil
localities throughout this important and otherwise
monotonous nonmarine record. This permits correla-
tion of sections and fossil localities across the O800 km
2
of outcrop area. In addition, the rapid accumulation of
strata, coupled with preliminary magnetostratigraphic
investigations by Imhof and Albright (2003), highlight
the potential for high-resolution magnetostratigraphy in
the formation, particularly within the upper unit.
Acknowledgements
Fieldwork and funding for this project were support-
ed by the BLM-Grand Staircase Escalante National
Monument and a grant from the Monument to EMR
and MAC. We thank Doug Powell for facilitating this
research and for his help in obtaining collection and
research permits. Additional funding awarded to EMR
by the AAPG, the Rocky Mountain Section of the
SEPM, and RMAG also supported this research. We
thank Leif Tapanila and Ray Rogers for constructive
discussions that contributed to the development of this
paper. This manuscript was also improved by the
comments provided by two anonymous reviewers.
References
Badgley, C., Behrensmeyer, A.K., 1995. Two long geological records
of continental ecosystems. Palaeogeography, Palaeoclimatology,
Palaeoecology 115, 1e11.
Berggren, W.A., Kent, D.V., Flynn, J.J., 1985. Jurassic to Paleogene:
Part 2. Paleogene geochronology and chronostratigraphy. In:
Snelling, N.J. (Ed.), The Chronology of the Geological Record.
Blackwell Scientific Publications, Oxford, pp. 141e195.
Bergstresser, T.J., Frerichs, W.E., 1982. Planktonic foraminifera from
the Upper Cretaceous Pierre Shale at Red Bird, Wyoming. Journal
of Foraminiferal Research 12, 353e361.
Cifelli, R.L., 1990a. Cretaceous mammals of southern Utah, I.
Marsupials from the Kaiparowits Formation (Judithian). Journal
of Vertebrate Paleontology 10, 295e319.
Cifelli, R.L., 1990b. Cretaceous mammals of southern Utah, II.
Marsupials and marsupial-like mammals from the Wahweap
Formation (early Campanian). Journal of Vertebrate Paleontology
10, 320e345.
Cifelli, R.L., 1990c. Cretaceous mammals of southern Utah, IV.
Eutherian mammals from the Wahweap (Aquilan) and Kaipar-
owits (Judithian) formations. Journal of Vertebrate Paleontology
10, 346e360.
Cifelli, R.L., 1994. Therian mammals of the Terlingua local fauna
(Judithian), Aguja Formation, Big Bend of the Rio Grande.
Contributions to Geology, University of Wyoming 30, 117e136.
Clemens, W.A., 1986. Evolution of the terrestrial vertebrate fauna
during the Cretaceous-Tertiary transition. In: Elliott, D.K. (Ed.),
Dynamics of Extinction. John Wiley and Sons, New York,
pp. 63e85.
DeCourten, F.L., Russell, D.A., 1985. A specimen of Ornithomimus
velox (Theropoda, Ornithomimidae) from the terminal Cretaceous
Kaiparowits Formation of southern Utah. Journal of Vertebrate
Paleontology 59, 1091e1099.
Dickinson, W.R., Fiorillo, A.R., Hall, D.L., Monreal, R.,
Potochnik, A.R., Swift, P.N., 1989. Cretaceous strata of southern
Arizona. In: Jenney, J.P., Reynolds, S.J. (Eds.), Geologic evolution
of Arizona. Geological society digest 17, 447e461.
Dodson, P.J., 1983. A faunal review of the Judith River (Oldman)
Formation, Dinosaur Provincial Park, Alberta. Mosasaur 1, 89e
118.
Dodson, P.J., Tatarinov, L.P., 1990. Dinosaur extinction. In:
Weishampel, D.B., Dodson, P.J., Osmolska, H. (Eds.), The
Dinosauria. University of California Press, Berkeley, pp. 55e62.
Drewes, H., 1978. The Cordilleran orogenic belt between Nevada and
Chihuahua. Geological Society of America, Bulletin 89, 641e647.
Eaton, J.G., 1987. The Campanian-Maastrichtian boundary in the
Western Interior of North America. Newsletters on Stratigraphy
18, 31e39.
Eaton, J.G., 1990. Stratigraphic revision of Campanian (Upper
Cretaceous) rocks in the Henry Basin, Utah. The Mountain
Geologist 27, 27e38.
Eaton, J.G., 1991. Biostratigraphic framework for the Upper
Cretaceous rocks of the Kaiparowits Plateau, southern Utah. In:
Nations, J.D., Eaton, J.G. (Eds.), Stratigraphy, depositional
environments, and sedimentary Tectonics of the Western Margin,
Cretaceous Western Interior Seaway. Geological Society of
America, Special Paper 260, 47e61.
Eaton, J.G., 2002. Multituberculate mammals from the Wahweap
(Campanian, Aquilan) and Kaiparowits (Campanian, Judithian)
formations, within and near Grand Staircase-Escalante National
Monument, southern Utah. Miscellaneous Publication 02-4, Utah
Geological Survey, 66 pp.
Eaton, J.G., Cifelli, 1988. Preliminary report on Late Cretaceous
mammals of the Kaiparowits Plateau, southern Utah. University of
Wyoming, Contributions to Geology 26, 45e55.
Eberth, D.A., Hamblin, A.P., 1993. Tectonic, stratigraphic and
sedimentologic significance of a regional discontinuity in the upper
Judith River Group (Belly River wedge) of southern Alberta,
Saskatchewan, and northern Montana. Canadian Journal of Earth
Sciences 30, 174e200.
Fassett, J.E., Steiner, M.B., 1997. Precise age of C33N-C32R magnetic-
polarity reversal, San Juan Basin, New Mexico and Colorado.
New Mexico Geological Society Guidebook 48, 239e247.
Fouch, T.D., Lawton, T.F., Nichols, D.J., Cashion, W.B.,
Cobban, W.A., 1983. Patterns and timing of synorogenic
sedimentation in Upper Cretaceous rocks of central and northeast
Utah. In: Reynolds, M.W., Dolley, E.D. (Eds.), Mesozoic
paleogeography of the West-Central United States. Society of
economic paleontologists and mineralogists, Rocky Mountain
Section, Rocky Mountain paleogeography symposium 2, 305e312.
Getty, M., Roberts, E.M., Loewen, M., Smith, J., Gates, T.A.,
Sampson, S., 2003. Taphonomy of a chasmosaurine ceratopsian
skeleton from the Campanian Kaiparowits Formation, Grand
316 E.M. Roberts et al. / Cretaceous Research 26 (2005) 307e318
Staircase-Escalante National Monument, Utah. Journal of Verte-
brate Paleontology 23, 54.
Gill, J.R., Cobban, W.A., 1973. Stratigraphy and geologic history of
the Montana Group and equivalent rocks, Montana, Wyoming,
and North and South Dakota. US Geological Survey, Professional
Paper 776, 37 pp.
Goldstrand, P.M., 1992. Evolution of the Late Cretaceous and early
Tertiary basins of southwest Utah based on clastic petrology.
Journal of Sedimentary Petrology 62, 495e507.
Goodwin, M.B., Deino, A.L., 1989. The first radiometric ages from
the Judith River Formation (Upper Cretaceous), Hill County,
Montana. Canadian Journal of Earth Sciences 26, 1384e1391.
Gradstein, F.M., Agterberg, F.P., Ogg, J.G., Hardenbol, J., van
Veen, P., Thierry, J., Huang, Z., 1994. A Mesozoic time scale.
Journal of Geophysical Research 99 (B12), 24051e24074.
Hayes, P.T., 1970. Cretaceous paleogeography of southeastern
Arizona and adjacent area. US Geological Survey, Professional
Paper 658-B, 1e42.
Horner, J.R., Varricchio, D.J., Goodwin, M.B., 1992. Marine trans-
gressions and the evolution of Cretaceous dinosaurs. Nature 358,
59e61.
Hunt, A.P., 1991. Integrated vertebrate, invertebrate and plant
taphonomy of the Fossil Forest area (Fruitland and Kirtland
formations: Late Cretaceous), San Juan County, New Mexico,
USA. Palaeogeography, Palaeoclimatology, Palaeoecology 88,
85e107.
Hunt, A.P., Lucas, S.G., 1992. Stratigraphy, paleontology and age
of the Fruitland and Kirtland Formations (Upper Cretaceous),
San Juan Basin, New Mexico. In: New Mexico Geological
Society Guidebook, 43rd Field Conference, San Juan Basin IV,
pp. 218e239.
Hutchison, J.H., Eaton, J.G., Holroyd, P.A., Goodwin, M.B., 1997.
Larger vertebrates of the Kaiparowits Formation (Campanian) in
the Grand Staircase-Escalante National Monument and adjacent
areas. In: Hill, L.M. (Ed.), Learning from the Land, Grand
Staircase Escalante National Monument Science Symposium
Proceedings. US Department of the Interior, Bureau of Land
Management, pp. 391e398.
Imhof, M., Albright, L.B., 2003. Preliminary magnetostratigraphic
analysis of the Upper Cretaceous Kaiparowits Formation,
southern Utah. Journal of Vertebrate Paleontology 23 (Supplement
to No. 3), 65A.
Kennedy, W.J., Cobban, W.A., Scott, G.R., 1992. Ammonite
correlation of the uppermost Campanian of Western Europe, the
U.S. Gulf Coast, Atlantic Seaboard and Western Interior, and
the numerical age of the base of the Maastrichtian. Geological
Magazine 129, 497e500.
Lawton, T.F., 1986. Fluvial systems of the Upper Cretaceous
Mesaverde Formation, Central Utah: a record of transition from
thin-skinned to thick-skinned deformation in the foreland region.
In: Peterson, J.A. (Ed.), Paleotectonics and sedimentation in the
Rocky Mountain Region. American association of petroleum
geologists, memoir 41, 423e442.
Lawton, T.F., Pollock, S.L., Robinson, R.A.J., 2003. Integrating
sandstone petrology and nonmarine sequence stratigraphy:
application to the Late Cretaceous fluvial systems of
southwestern Utah, U.S.A. Journal of Sedimentary Research 73,
389e406.
Lehman, T.M., 1997. Late Campanian dinosaur biogeography in
the western interior of North America. In: Wolberg, D.L.,
Stump, E., Rosenberg, G.D. (Eds.), Dinofest International.
Philadelphia Academy of Natural Sciences, Philadelphia,
pp. 223e240.
Lillegraven, J.A., 1991. Stratigraphic placement of the Santonian-
Campanian boundary (Upper Cretaceous) in the North American
Gulf Coastal Plain and Western Interior, with implications to
global geochronology. Cretaceous Research 12, 115e136.
Lillegraven, J.A., McKenna, M.C., 1986. Fossil mammals from
the ‘‘Mesaverde’’ Formation (Late Cretaceous, Judithian) of the
Bighorn and Wind River basins, Wyoming, with definitions of Late
Cretaceous North American land-mammal ‘‘ages’’. American
Museum Novitates 2840, 1e68.
Little, W.W., 1995. The influence of tectonics and eustacy on alluvial
architecture, middle Coniacian through Campanian strata of the
Kaiparowits Basin, Utah. Unpublished PhD thesis, University of
Colorado, Boulder, 328 pp.
Lohrengel, C.F., 1969. Palynology of the Kaiparowits Formation,
Garfield County, Utah. Brigham Young University Geology
Studies 6, 61e180.
Martinsen, O.J., Ryseth, A., Helland-Hansen, W., Flesche, H.,
Torkildsen, G., Idil, S., 1999. Stratigraphic base level and fluvial
architecture: Ericson Sandstone (Campanian), Rock Springs
Uplift, SW Wyoming, USA. Sedimentology 46, 235e259.
McDowell, F.W., Lehman, T.M., Connelly, J.N., 2004. A U-Pb age
for the Late Cretaceous Alamosaurus vertebrate fauna of west
Texas. Geological Society of America, Abstracts with Programs 36
(4), 6.
Obradovich, J.D., 1993. A Cretaceous time scale. In:
Caldwell, W.G.E., Kauffman, E.G. (Eds.), Evolution of the
Western Interior Basin. Geological Association of Canada, Special
Paper 39, 379e396.
Obradovich, J.D., Cobban, W.A., 1975. A time scale for the Late
Cretaceous of the Western Interior of North America. In:
Caldwell, W.G. (Ed.), The Cretaceous System in the Western
Interior of North America. Geological Society of Canada, Special
Paper 13, 31e54.
Peterson, F., Ryder, R.T., 1975. Cretaceous rocks in the Henry
Mountains region, Utah, and their stratigraphic relation to
neighboring regions. In: Fassett, J.E. (Ed.), Canyonlands Country.
Four Corners Geological Society Guidebook, 8th Field Confer-
ence, pp. 167e189.
Renne, R.R., Swisher, C.C., Deino, A.L., Kaarner, D.B., Owens, T.L.,
DePaolo, D.J., 1998. Intercalibration of standards, absolute ages
and uncertainties in
40
Ar/
39
Ar dating. Chemical Geology 145, 117e
152.
Roberts, E.M., Chan, M.A., Sampson, S.D., 2003. Taphonomic
analysis of the Late Cretaceous Kaiparowits Formation in the
Grand Staircase-Escalante National Monument, southern Utah.
Geological Society of America, Abstracts with Programs 35, 591.
Roberts, E.M., Hendrix, M.S., 2000. Taphonomy of a petrified forest
in the Two Medicine Formation (Campanian) northwest Montana:
implications for palinspastic restoration of the Boulder batholith
and Elkhorn Mountains Volcanics. Palaios 15, 476e482.
Rogers, R.R., 1993. Systematic patterns of time-averaging in the
terrestrial vertebrate record: a Cretaceous case study. In:
Kidwell, S.M., Behrensmeyer, A.K. (Eds.), Taphonomic ap-
proaches to time resolution in fossil assemblages. Paleontological
society, short courses I-paleontology 6, 228e249.
Rogers, R.R., Swisher III, C.C., Horner, J.R., 1993.
40
Ar/
39
Ar age
correlation of the nonmarine Two Medicine Formation (Upper
Cretaceous), northwestern Montana, U.S.A. Canadian Journal of
Earth Sciences 30, 1066e1075.
Rogers, R.R., 1994. Nature and origin of through-going discontinu-
ities in nonmarine foreland basin strata, Upper Cretaceous,
Montana: implications for sequence analysis. Geology 22, 1119e
1122.
Rogers, R.R., 1998. Sequence analysis of the Upper Cretaceous Two
Medicine and Judith River formations, Montana: nonmarine
response to the Claggett and Bearpaw marine cycles. Journal of
Sedimentary Research 68, 615e631.
Rogers, R.R., Kidwell, S.M., 2000. Associations of vertebrate skeletal
concentrations and discontinuity surfaces in terrestrial and shallow
marine records: a test in the Cretaceous of Montana. Journal of
Geology 108, 131e154.
317E.M. Roberts et al. / Cretaceous Research 26 (2005) 307e318
Rowe, T., Cifelli, R.L., Lehman, T.M., Weil, A., 1992. The
Campanian Terlingua local fauna, with a summary of other
vertebrates from the Aguja Formation, Trans-Pecos, Texas.
Journal of Vertebrate Paleontology 12, 472e493.
Sampson, S.D., Loewen, M.A., Gates, T.A., Zanno, L.E.,
Kirkland, J.I., 2002. New evidence of dinosaurs and other
vertebrates from the Upper Cretaceous Wahweap and Kaiparowits
formations, Grand Staircase-Escalante National Monument,
southern Utah. Geological Society of America, Rocky Mountain
Section, 54th Annual Meeting, Abstracts with Programs, 34, 5.
Sankey, J.T., 2001. Late Campanian Southern Dinosaurs, Aguja
Formation, Big Bend, Texas. Journal of Paleontology 75, 208e215.
Sloan, R.E., 1976. The ecology of dinosaur extinction. In:
Churcher, C.S. (Ed.), Essays on Palaeontology in Honour of Loris
Shano Russell. University of Toronto Press, Toronto, pp. 134e155.
Smedes, H.W., 1966. Geology and igneous petrology of the northern
Elkhorn Mountains, Jefferson and Broadwater Counties, Mon-
tana. US Geological Survey, Professional Paper 510, 116 pp.
Smith, R.L., 1960. Ash flows. Geological Society of America, Bulletin
71, 795e841.
Smith, J., Sampson, S., Roberts, E., Getty, M., Loewen, M., 2004. A
new chasmosaurine ceratopsian from the Upper Cretaceous
Kaiparowits Formation, Grand Staircase-Escalante National
Monument, Utah. Journal of Vertebrate Paleontology 24, 114.
Spivey, R.C., 1940. Bentonite in southwestern South Dakota.
South Dakota Geological Survey, Report of Investigations 36,
56 pp.
Sullivan, R.M., Lucas, S.G., 2003. The Kirtlandian, a new land-
vertebrate ‘‘age’’ for the Late Cretaceous of western North
America. In: Lucas, S.G., Semken, S.C., Berglof, W.R., Ulmer-
Scholle, D.S. (Eds.), Geology of the Zuni Plateau. New Mexico
Geological Society, Guidebook 54, 369e377.
Thomas, R.G., Eberth, D.A., Deino, A.L., Robinson, D., 1990.
Composition, radioisotopic ages, and potential significance of an
altered volcanic ash (bentonite) from the Upper Cretaceous Judith
River Formation, Dinosaur Provincial Park, southern Alberta.
Cretaceous Research 11, 125e162.
Weil, A., 1999. Multituberculate phylogeny and mammalian bio-
geography in the Late Cretaceous and earliest Paleocene Western
Interior of North America. Unpublished PhD thesis, University of
California, Berkeley, 243 pp.
Weishampel, D.B., Jensen, J.A., 1979. Parasaurolophus (Reptilia:
Hadrosauridae) from Utah. Journal of Paleontology 53, 1422e
1427.
Willis, A., 2000. Tectonic control of nested sequence architecture in the
Sego Sandstone, Neslen Formation and Upper Castlegate Sand-
stone (Upper Cretaceous), Sevier Foreland Basin, Utah, USA.
Sedimentary Geology 136, 277e317.
318 E.M. Roberts et al. / Cretaceous Research 26 (2005) 307e318
... Dinosaur Provincial Park (DPP; the Park), a small geographic area (80 km 2 ) in southern Alberta, Canada (Fig. 1), yields a rich and uniquely diverse assemblage of Late Campanian vertebrates, including non-avian dinosaurs. The Park is famous for abundant articulated and associated fossil skeletons and bonebeds that contribute to our understanding of peak dinosaur diversity during the Late Campanian and patterns of latitudinal variation in dinosaurian megaherbivore taxa across the Western Interior Basin (WIB) of North America (Lehman 1997(Lehman , 2001Currie and Koppelhus 2005, and papers therein; Barrett et al. 2009;Sampson et al. 2010;Gates et al. 2012;Eberth 2015;Ramezani et al. 2022;Roberts et al. 2005Roberts et al. , 2013. ...
... Discrete beds of bentonite claystone are common in Upper Cretaceous strata of the WIB and throughout the stratigraphic section at DPP. Thomas et al. (1990) and documented 15 discrete bentonite beds in the Oldman, Dinosaur Park, and Bearpaw formations at DPP, and since then a few additional bentonites have been noted. WIB bentonites represent diagenetically altered air-fall deposits of pyroclastic ash and tephra and have been commonly sampled for radioisotopic dating of their magmatic minerals (e.g., Goodwin and Deino 1989;Thomas et al. 1990;Obradovich 1993;Rogers et al. 1993;Lerbekmo 2002;Roberts et al. 2005;Foreman et al. 2008;Jinnah et al. 2009;Ramezani et al. 2022). ...
... high-resolution, reproducible geochronology for the Park and the BRG, as well as correlation to other Campanianage dinosaur sites with 40 Ar/ 39 Ar ages in the WIB (e.g., Goodwin and Deino 1989;Rogers et al. 1993;Ogg et al. 2004;Roberts et al. 2005Roberts et al. , 2013Foreman et al. 2008;Jinnah et al. 2009). ...
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... The overlying 1005-m-thick Kaiparowits Fm. 88,89 represents extensive flood basin pond, lake, and river deposition on a low-relief alluvial plain characterized by a warm, subhumid paleoenvironment 90 . High volcanic input and rapid rock accumulation rates due to active tectonic subsidence characterizes this unit 28,91,92 . The Kaiparowits Fm. preserves an abundant and remarkably diverse flora and fauna ranging from invertebrates to large vertebrates 7,93,94 . ...
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... Following deposition of the Tropic Shale, the shallow sea regressed, and marine shales were replaced in GLCA by beach and coastal plain deposits of the Straight Cliffs Formation (Peterson, 1969;Anderson et al., 2010). The Seaway fully retreated from the GLCA area during the last phases of the Sevier Orogeny about 71 Ma, prior to the regional unconformity that developed between the Sevier and Laramide orogenies (Cather, 2003;Roberts, 2005;Roberts et al., 2005). The Upper Cretaceous Straight Cliffs Formation marks the end of the Mesozoic at GLCA. ...
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... In addition, the presence of several bentonites throughout the formation, dating it to~76.6e72.8 Ma, using maximum depositional age from detrital zircons and 40 Ar/ 39 Ar on sanidine, suggests that the Kaiparowits Formation is coeval to other important fossiliferous Campanian formations throughout the WIB, such as the Dinosaur Park Formation, and sections of the Judith River, Two Medicine, Fruitland, and Aguja formations (Titus et al., 2005;Roberts et al., 2005Roberts et al., , 2013Beveridge et al., 2020). ...
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Although turtles are common Mesozoic fossils, their eggs and nests are rare. Here, we describe an in-situ clutch of turtle eggs from the Upper Cretaceous Kaiparowits Formation of southern Utah. The clutch is preserved in a green mudstone associated with aquatic terrestrial gastropods. Eggshell is broadly distributed across an area of 3.75 m² with three nearly complete, spherical eggs ∼2.9 cm in diameter, and another three partial eggs identified. The aragonitic eggshell is 0.7-1.2 mm thick and consists of closely packed, slightly domed shell units with a height to width ratio of 3.7:1 and nodular ornamentation 53-71 μm in diameter. Eggshell orientation (concave up/concave down) of 54:46 is consistent with in-situ preservation. An eggshell porosity of 42.5 mm correlates to a humid nesting environment. Extrapolating from egg size, the producing adult carapace length is estimated at 24.45 cm with an average clutch size of 9.91 eggs. The unique attributes of the eggshell warrant naming of a new oospecies, Testudoolithus tuberi. This fossil occurrence is another example of exceptional preservation in the Western Interior Basin associated with the Campanian “taphozone.”
... Many similar stratigraphic intervals elsewhere in the Western Interior preserve multiple, biostratigraphically-defined local faunas, including the Fruitland and Kirtland formations of northwestern New Mexico (e.g., Fig. 9. Generalised temporal correlation of lower to middle Campanian strata across the Western Interior (~north to south, left to right). Geochronologic framework was adapted from Payenberg et al. (2002), Cather (2004), Cifelli et al. (2004), Roberts et al. (2005), Foreman et al. (2008), Jinnah et al. (2009), Corbett et al. (2011), Seymour and Fielding (2013, Albright and Titus (2016), Eberth (2015), Rogers et al. (2016), Fassett and Heizler (2017). Sullivan and Lucas, 2003;Lucas et al., 2006), the Two Medicine and Judith River formations of Montana (e.g., Horner et al., 2001;Trexler, 2001;Mallon et al., 2016), and the Aguja Formation of West Texas (e.g., Lehman et al., 2017Lehman et al., , 2019. ...
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The Western Interior of North America preserves one of the most complete successions of Upper Cretaceous marine and non-marine strata in the world; among these, the Cenomanian-Campanian units of the Kaiparowits Plateau in southern Utah are a critical archive of terrestrial environments and biotas. Here we present new radioisotopic ages for the Campanian Wahweap Formation, along with lithostratigraphic revision, to improve the geological context of its fossil biota. The widely accepted informal stratigraphic subdivisions of the Wahweap Formation on the Kaiparowits Plateau are herein formalized and named the Last Chance Creek Member, Reynolds Point Member, Coyote Point Member, and Pardner Canyon Member (formerly the lower, middle, upper, and capping sandstone members respectively). Two high-precision U-Pb zircon ages were obtained from bentonites using CA-ID-TIMS, supported by five additional bentonite and detrital zircon LA-ICP-MS ages. Improved geochronology of the Star Seep bentonite from the base of the Reynolds Point Member via CA-ID-TIMS demonstrates that this important marker horizon is over a million years older than previously thought. A Bayesian age-stratigraphic model was constructed for the Wahweap Formation using the new geochronologic data, yielding statistically robust ages and associated uncertainties that quantifiably account for potential variations in sediment accumulation rate. The new chronostratigraphic framework places the lower and upper formation boundaries at 82.17 + 1.47/−0.63 Ma and 77.29 + 0.72/−0.62 Ma, respectively, thus constraining its age to the first half of the Campanian. Additionally, a holistic review of known vertebrate fossil localities from the Wahweap Formation was conducted to better understand their spatio-temporal distribution including revised ages for early members of iconic dinosaur lineages such as Tyrannosauridae, Hadrosauridae, and Centrosaurinae. Chrono- and lithostratigraphic refinement of the Wahweap Formation and its constituent biotic assemblages establishes an important reference for addressing questions of Campanian terrestrial paleoecology and macroevolution, including dinosaur endemism and diversification throughout western North America.
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Over the past thirty years, exploration of the terrestrial Mesozoic section in Utah has resulted in a more than fivefold increase in the known species of dinosaurs. A highly resolved temporal and sequence stratigraphic framework for these strata is facilitating the utility of these newly discovered dinosaur assemblages in geologic, evolutionary, paleoecologic, and paleogeographic research. Local subsidence due to salt tectonics in the northern Paradox Basin is responsible for this region of eastern Utah preserving basal Cretaceous dinosaur faunas, known nowhere else in North America, that document paleobiogeographic connections across the proto-North Atlantic with Europe. The more medial Cretaceous strata west of the San Rafael Swell, in central Utah, preserve a unique dinosaur assemblage on an isolated North America. These strata also record the first immigration of Asian dinosaurs into North America and the last occurrences of a number of endemic North American dinosaur lineages. Through the Late Cretaceous, extensive, fossiliferous floodplain deposits are exposed in the high plateaus of southern Utah within the Grand Canyon Bight on the western side of the Late Cretaceous Western Interior Seaway. Research on microvertebrate sites has resulted in a diverse record of vertebrate life substage by substage through most of the Upper Cretaceous sequence. Particularly, rich dinosaur-bearing beds through the Campanian have resulted in the discovery of many new dinosaur species distinct from the coeval dinosaur-bearing beds farther north along the western coast of the Western Interior Seaway in Montana and Alberta. The further development of these numerous rich dinosaur assemblages will provide the basis for considerable research in the future.
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An unabated surge of new and important discoveries continues to transform knowledge of pen-naraptoran biology and evolution amassed over the last 150+ years. This chapter summarizes progress made thus far in sampling the pennaraptoran fossil record of the Mesozoic and Paleocene and proposes priority areas of attention moving forward. Oviraptorosaurians are bizarre, nonparavian pennaraptorans first discovered in North America and Mongolia within Late Cretaceous rocks in the early 20th century. We now know that oviraptorosaurians also occupied the Early Cretaceous and their unquestionable fossil record is currently limited to Laurasia. Early Cretaceous material from China preserves feathers and other soft tissues and ingested remains including gastroliths and other stomach contents, while brooding specimens and age-structured, single-species accumulations from China and Mongolia provide spectacular behavioral insights. Less specialized early oviraptorosaurians like Incisivosaurus and Microvenator remain rare, and ancestral forms expected in the Late Jurassic are yet to be discovered, although some authors have suggested Epidexipteryx and possibly other scansoriopterygids may represent early-diverging oviraptorosaurians. Long-armed scansoriopterygids from the Middle-Late Jurassic of Laurasia are either early-diverging oviraptorosaurians or paravians, and some have considered them to be early-diverging avialans. Known from five (or possibly six) feathered specimens from China, only two mature individuals exist, representing these taxa. These taxa, Yi and Ambopteryx, preserve stylopod-supported wing membranes that are the only known alternative to the feathered, muscular wings that had been exclusively associated with dinosaurian flight. Thus, scansoriopterygid specimens-particularly those preserving soft tissue-remain a key priority for future specimen collection. Dromaeosaurids and troodontids were first discovered in North America and Mongolia in Late Cretaceous rocks. More recent discoveries show that these animals originated in the Late Jurassic, were strikingly feathered, lived across diverse climes and environments, and at least in the case of dromaeosaurids, attained a global distribution and the potential for aerial locomotion at small size.
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Snakes comprise nearly 4,000 extant species found on all major continents except Antarctica. Morphologically and ecologically diverse, they include burrowing, arboreal, and marine forms, feeding on prey ranging from insects to large mammals. Snakes are strikingly different from their closest lizard relatives, and their origins and early diversification have long challenged and enthused evolutionary biologists. The origin and early evolution of snakes is a broad, interdisciplinary topic for which experts in palaeontology, ecology, physiology, embryology, phylogenetics, and molecular biology have made important contributions. The last 25 years has seen a surge of interest, resulting partly from new fossil material, but also from new techniques in molecular and systematic biology. This volume summarises and discusses the state of our knowledge, approaches, data, and ongoing debates. It provides reviews, syntheses, new data and perspectives on a wide range of topics relevant to students and researchers in evolutionary biology, neontology, and palaeontology.
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Snakes comprise nearly 4,000 extant species found on all major continents except Antarctica. Morphologically and ecologically diverse, they include burrowing, arboreal, and marine forms, feeding on prey ranging from insects to large mammals. Snakes are strikingly different from their closest lizard relatives, and their origins and early diversification have long challenged and enthused evolutionary biologists. The origin and early evolution of snakes is a broad, interdisciplinary topic for which experts in palaeontology, ecology, physiology, embryology, phylogenetics, and molecular biology have made important contributions. The last 25 years has seen a surge of interest, resulting partly from new fossil material, but also from new techniques in molecular and systematic biology. This volume summarises and discusses the state of our knowledge, approaches, data, and ongoing debates. It provides reviews, syntheses, new data and perspectives on a wide range of topics relevant to students and researchers in evolutionary biology, neontology, and palaeontology.
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Superb outcrop exposures and abundant subcrop data allow the accurate tracing of two stratigraphie discontinuities updip into fully nonmarine strata of the Campanian Two Medicine and Judith River formations (Western Interior foreland basin, Montana). These throughgoing discontinuities delimit "regressive" and "transgressive" alluvial equivalents of two third-order sea-level cycles, and provide ground truth for recent conceptual models of alluvial sequence stratigraphy. An erosional disconformity interpreted to mark the boundary between regressive and transgressive alluvial deposits crops out in nonmarine strata of the Two Medicine Formation in northwestern Montana. It is embedded in relatively flat-based fluvial sandstone sheets dominated by downstream accretion elements, and is marked by several meters of internal erosional scour, a thick and laterally persistent intraclast lag faciès, pervasive oxidation, and a shift from fine- to medium/coarse-grained sandstone. Physical stratigraphie and geochronometric evidence indicate that this fluvial disconformity, which can be traced throughout the outcrop belt, correlates with the widespread 80 Ma sequence boundary developed in distal parts of the Western Interior Basin. The erosional disconformity in the Two Medicine Formation reflects a negative base-level adjustment that occurred during the Telegraph Creek-Eagle regression (R7), and conforms to the standard definition of a sequence boundary. Identification of the 80 Ma sequence boundary in alluvial faciès of the Two Medicine Formation is significant in that it is one of very few well-documented examples of a nonmarine sequence boundary, but unlike most others, it is not characterized by a readily apparent faciès tract dislocation reflecting a basinward shift in facies (e.g., braided-stream deposits sharply juxtaposed over coastal coal-bearing facies). A second throughgoing discontinuity embedded within fully nonmarine deposits of the Judith River Formation in central Montana is interpreted to separate regressive and transgressive alluvial deposits that accumulated during the Claggett regression (R8) and subsequent Bearpaw transgression (T9). This discontinuity correlates with the erosional base of a backstepping composite sequence set of shoreface strata, and can be traced inland to the western limit of Judith River strata preserved in central Montana (~ 50 km). The Judith River discontinuity is not erosional, but rather reflects a very abrupt change in alluvial architecture, most notably an abrupt shift from a sand- to a mud-dominated section that can be traced in outcrop and subcrop throughout north-central Montana and into southern Alberta. The throughgoing discontinuity in the Judith River record does not conform to conventional definitions of a sequence boundary, and it apparently did not form in response to a fall in relative sea level. This discontinuity instead appears to record an abrupt increase in the rate of generation of accommodation in the Montana portion of the foreland basin (presumably related to flexural subsidence), and it is provisionally interpreted as the nonmarine equivalent of a third-order transgressive surface coincident with the updip correlative conformity.
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One of the southernmost North American late Campanian microvertebrate assemblages was collected from the upper Aguja Formation, Big Bend National Park, Texas. The dinosaurs provide additional evidence that distinct southern and northern terrestrial vertebrate provinces occurred contemporaneously during this time due to latitudinal differences in temperature and rainfall. Southern areas, such as west Texas, were warm dry, with non-seasonal climates, and with open-canopy woodlands; they appear to be less fossil-rich and less diverse than northern areas. Nine dinosaurs are present, based on isolated teeth: pachycephalosaurid; hadrosaurid; ceratopsian; tyrannosaurid; Saurornitholestes cf. langstoni (Sues, 1978); Richardoestesia cf. gilmorei (Currie et al., 1990); a new species of Richardoestesia , which is named here; and a undetermined theropod unlike any previously described. Previous reports of Troodon sp. from the Talley Mt. and Terlingua microsites are mistaken; they are a pachycephalosaurid. Many of the dinosaur teeth are small, and are probably from juveniles or younger individuals, evidence that dinosaurs nested in the area. Paleoecologically, the upper Aguja was probably more similar to the lower and more inland faunas of the Scollard Formation (~66 Ma) of Alberta than to contemporaneous northern faunas: both had drier, open environments and lower dinosaur abundance. This connection between climate and dinosaur abundance suggests that climatic factors were important in the Late Cretaceous dinosaur extinctions.