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RRH: DEPOSITIONAL CONSTRAINTS STIKES QUARRY
LRH: J.I. KIRKLAND ET AL.
Research Article
DOI: http://dx.doi.org/10.2110/palo.2016.041
DEPOSITIONAL CONSTRAINTS ON THE LOWER CRETACEOUS STIKES QUARRY
DINOSAUR SITE: UPPER YELLOW CAT MEMBER, CEDAR MOUNTAIN FORMATION,
UTAH
JAMES I. KIRKLAND,1 EDWARD L. SIMPSON,2 DONALD D. DeBLIEUX,1 SCOTT K.
MADSEN,1 EMILY BOGNER,2 AND NEIL E. TIBERT3
1Utah Geological Survey, PO Box 146100, Salt Lake City, Utah, 84114-6100 USA
2Deparment of Physical Sciences, Kutztown University, Kutztown, Pennsylvania 19530 USA
3Department of Earth and Environmental Sciences, University of Mary Washington,
Fredericksburg, Virginia 22401 (deceased)
Abstract: A new mass death assemblage in Lower Cretaceous strata of east-central Utah contains
well-preserved skeletons representing an ontogenetic series of individuals of Utahraptor, and at
minimum two iguanodont grade ornithischian skeletons. The dinosaurs were entombed in ovoid-
lensoidal, fine-grained sandstone sills linked by sandstone pipes and/or dikes and another basal
lensoidal mass with scattered and broken iguanodont and sauropod bones and to an underlying
gravelly sandstone bed. Exposed in the excavation high-walls are syndepositional normal-faults
bounding graded ripple strata. Multiphased fluid over-pressurization in an artesian setting
creating the structures. Trapping, killing, and subsequent burial mechanism was generated by
variations of pressure in a localized artesian spring system that breached the surface and is the
first such mechanism documented with numerous dinosaur victims.
INTRODUCTION
Taphonomic processes affecting modern vertebrate carcasses have been documented in a
variety of continental settings (Weigelt 1989; Behrensmeyer 1991; Rogers et al. 2007). For
example, the recognition of the taphonomic biases introduced by a mud miring mechanism has
permitted unraveling the population structure in a mass-accumulation of small herbivorous,
theropod dinosaurs (Varricchio et al. 2008).
The Stikes Quarry is a recently discovered concentration of a tightly packed Utahraptor
and iguanodontid skeletons in 125 million year old Lower Cretaceous strata (north of Arches
National Park) in east-central Utah. The quarry is within the upper Yellow Cat Member of the
Cedar Mountain Formation (Fig. 1). This study examines the soft-sediment deformation
structures and strata entombing the Utahraptors and iguanodont grade ornithischians (hereafter
referred to as iguanodonts) proposing the hypothesis that a localized artesian system with a
hydrologic head powerful enough to cause quicksand development, trapping, and the unique
burial of at least eight Utahraptor dromaeosaurids (Fig. 1). This proposed hypothesis will be
tested during the preparation of the large Utahraptor block through more detailed analysis of the
spatial arrangement of the bones and taphonomic data.
GEOLOGICAL SETTING
The Early Cretaceous Cedar Mountain Formation with discrete terrestrial faunas is one of
the most important sources of Lower Cretaceous dinosaurs (Kirkland et al. 1997, 1999, 2015;
Cifelli et al. 1999; Kirkland and Madsen 2007, Kirkland and Farlow 2012). In the stratigraphic
section that includes the Stikes Quarry, the Cedar Mountain Formation unconformably overlies
the Morrison Formation with a hiatus of approximately 20 Ma (Kirkland and Madsen 2007;
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Hendrix et al. 2015) and in turn is overlain by the Naturita Formation (Young 1960, 1965;
Carpenter 2014).
In the northern Paradox Basin of east-central Utah, the Cedar Mountain Formation is
subdivided into members, from oldest to youngest, Yellow Cat, Poison Strip, and Ruby Ranch
(Kirkland et al. 1997, 1999; Sprinkle et al. 2012; Doelling and Kuehne 2013; Fig. 1). Well-
developed paleosols, spring deposits, lacustrine limestones, mudstones, siltstones, and
sandstones linked to northeast-directed fluvial systems characterize the Yellow Cat Member
(Kirkland et al. 1997; DiCroce and Carpenter 2001; Greenhalgh and Britt 2007; Kirkland and
Madsen 2007; Suarez et al. 2007a, 2007b). The Yellow Cat Member is subdivided into two
informal units. At the Stikes Quarry section the lowest unit is ~ 29 m thick and consists of
mainly stacked paleosols. The upper unit is ~ 14 m thick and dominantly a lacustrine system.
The basal boundary of the upper Yellow Cat Member is placed at the top of a regional bench-
forming calcrete paleosol (Figs. 1, 2; Kirkland and Madsen 2007; McDonald et al. 2010;
Kirkland et al. 2012) that once defined the base of the Cedar Mountain Formation (Aubrey
1998). U-Pb single crystal detrital zircon analysis of the upper Yellow Cat Member yields a
maximum age of approximately latest Barremian to basal Aptian age, 124±2.5 Ma (Greenhalgh
et al. 2006; Britt et al. 2009; Ludvigson et al. 2010), whereas other studies based on detrital
zircons and microfossils suggest considerably older Early Cretaceous dates (Sames et al. 2010;
Sames 2011a, 2011b; Martin-Closas et al. 2013; Hendrix et al. 2015).
Yellow Cat strata were deposited under arid to semi-arid conditions with monsoonal
overprinting (Kirkland et al. 1999; Kirkland and Madsen 2007; Suarez et al. 2014). At the Stikes
locality, the overlying 15 m thick Poison Strip Sandstone preserves northeast-directed, low- to
moderate-sinuosity channels with lateral bars characteristic of distal braided stream systems that
overstepped the lacustrine shoreline sandstones of the upper Yellow Cat Member (Stikes 2007;
Lockley et al. 2015). The Ruby Ranch Member consists of northeast-directed, fluvial “ribbon”
sandstones with overbank deposits containing abundant carbonate nodules and is ~ 30 m thick
across the northern Paradox Basin. Along the west side of Arches National Park, the thickness
more than doubles with a well-developed lacustrine system forming the upper half of the
member (Harris 1980; Kirkland et al. 1997; Kirkland and Madsen 2007; Williams et al. 2009;
Ludvigson et al. 2010; Montgomery 2014).
PALEONTOLOGICAL SETTING
The upper Yellow Cat Member preserves a distinctive fauna dominated by the
polacanthid ankylosaur Gastonia, diverse iguanodontid including Hippodraco, and several
sauropod species including the brachiosaurid Cedarosaurus and a basal macronaran (Tidwell et
al. 1999; Kirkland and Madsen 2007; Britt et al. 2009; McDonald et al. 2010). Utahraptor
ostrommaysorum is the most common theropod (Kirkland et al. 1993; Britt et al. 2009) along
with other small theropods. Additional faunal elements include diverse bony fish, hybodont
sharks, lungfish, turtles, a choristothere, sphenodontids, crocodilians, and a mammal (Kirkland
and Madsen 2007; Britt et al. 2009). Vertebrate trace fossils from the upper Yellow Cat include
the oldest bird tracks in North America (Lockley et al. 2015).
FACIES
The Stikes Quarry is in the upper Yellow Cat Member. Six facies are exposed in the
quarry highwall and laterally along the newly constructed haul road (Fig. 1D, 2): (1) dark gray
shale; (2) lower rippled sandstone; (3) heterolithic red mudstone; (4) bone-bearing lensoidal-
ovoid-shaped sandstone masses; (5) rippled sandstone and mudstone; and (6) upper rippled
sandstone.
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Dark Gray Shale
Description.—Thin laminations of siltstone are interbedded with the predominant dark
gray shale (N2 to N3). Fish scales and poorly preserved gastropods are present (Fig. 1D). In
addition, microfossils include an assemblage of four nonmarine ostracode species (Fig. 3). The
most common taxon from the Stikes Quarry is Cypridea Bosquet (Sames 2011a, 2011b). In
lesser abundance are well-preserved, small and more ornate specimens of C. (Longispinella)
longispina, and Mongolianella stirlingensis (Loranger 1951).
Interpretation.—This facies developed from tractional deposition followed by suspension
settling in an offshore lacustrine setting (Smoot 1991; Smoot and Olsen 1994; Arenas and Pardo
1999). The ostracode Cypridea confirms this interpretation as a lacustrine setting because this
taxon is regarded as tolerant of drought prone conditions (Horne 2002). Therefore, the
predominance of Cypridea is a strong indication of ephemeral ponding in a lacustrine system
during times of increased aridity in the Stikes Quarry strata (Carbonel et al. 1988; Horne 2002;
Horne and Colin 2005; Trabelsi et al. 2011).
Lower Rippled Sandstone
Description.—The lower rippled sandstone forms the floor of the Stikes Quarry (Figs.
1D, 4, 5). Medium- to fine-grained sandstone is yellowish gray in color (5Y 8/1), ~ 2 m thick,
and laterally continuous for over 200 m. Chert granules are present on horizontal partings and
form laminations throughout this facies. Low-angle, cross beds are present. Rare, green-gray
siltstone and mudstone interlaminations separate beds.
Soft-sediment deformation structures are present throughout the quarry and the haul road.
A broad dome-like structure is centered in the quarry and preserved on the upper bedding plane
of the lower sandstone (Fig. 5A). Internally, the dome has upward arching laminations that are
near parallel to the upper bedding surface (Fig. 5A). Exposed along the haul road, 30 m to the
east of the Stikes Quarry are thin (< 10 cm wide) flame structures within the facies (Fig. 5B),
fluidization, and load features (sensu Lowe, 1975). Connected to the lower rippled sandstone and
crosscutting the overlying heterolithic mudstone facies is a small, 40 cm tall vertical pipe
composed of fine-grained sandstone (Fig. 6).
Interpretation.—The lower rippled sandstone facies in conjunction with the underlying
dark gray shale facies is best interpreted as a prograding clastic lacustrine shoreline deposit
(Fraser and Hester 1977; Bracken 1994; Ilgar and Nemec 2005). Fraser and Hester (1977) report
similar type of sandstone with coarse-grained laminations and wavy horizontal laminations in the
shoreface settings in modern Lake Erie.
The soft-sediment deformation features in this facies are consistent with overpressuring
and fluidized deformation that generate convoluted bedding and cause vertical migration of over-
pressured fluids (Lowe 1975; Allen 1982, 1986; Mills 1983; Maltman 1984; Owen 1987, 1996;
Nichols et al. 1994; Frey et al. 2009). Not all primary structures in the lower sandstone were
obliterated by the loss of internal shear strength and mobilization (Surlyk et al. 2007).
Heterolithic Red Mudstone
Description.—The heterolithic red mudstone facies groups together red sandy mudstones,
red siltstones, red fine-grained sandstones, gray mudstones and gray carbonate nodules. Color
varies from dark gray (N2) to dusky red (5R 3/4). This facies grades from siltstone rich beds at
the base to mudstone dominated at the top (Fig. 7). Gray mudstone is more prevalent on the west
quarry wall and adjacent to the sandstone lenses elsewhere in the facies is dusky red. Carbonate
nodules varying from 10–20 cm and are concentrated in the lower portion of the facies, near the
level of the Utahraptor block.
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The lens-shaped sandstones preserving the Utahraptor and iguanodont fossils are
encapsulated by this facies (Fig. 4). The heterolithic mudstone and sandy red and gray mudstone
facies together with the underlying and upper rippled sandstone facies extend laterally for more
than 500 m (Fig. 4C). Along the haul road the thickness of the heterolithic mudstone facies
varies from 3.6 to 2.9 m, an approximate 20% reduction in thickness at the center of the quarry
(Fig. 1D). At the eastward termination of the haul road a pebbly mudstone dike cross cuts the
lower siltstones and originates in this facies (Fig. 7).
Interpretation.—This facies is best interpreted as a flood plain deposit (Stear 1978; Miall
1996; Bridge 2003; Ghosh et al. 2006) with possible pedogenic carbonates (Suarez et al. 2014).
Paleosol features appear absent from the quarry area although slickensides are reported by Poole
(2008).
Within a few meters of the surface the permeability of the lower rippled sandstone and
the lower strata of this facies mainly siltstones, are close to equal. These specific conditions
induced fluidization of the lower rippled sandstone and the overlying host sediment together as
recorded in the pebbly mudstone dikes in this facies (see Jonk (2010) for a parallel interpretation
for a similar setting)
Bone-Bearing Lensoidal-Shaped Sandstone
Description.—In the field, four ovoid lens-shaped sandstone masses with bone were
discovered and given identifiers: Poole, iguanodont, Utahraptor, and iguanodont-sauropod (Fig.
8). Sandstones and siltstones are very light gray (N8) to light greenish gray (5GY 8/1).
Mudstones clasts are dusky green (10GY 3/2) to yellowish gray (5Y 8/1) and up to 4 cm.
Granules and pebbles are present. These sandstones are in sharp contact with the surrounding
heterolithic mudstone facies.
The Poole block was the first encountered during east-side excavation of the upper strata
of the site and was removed in 2005 (Figs. 2, 8). Little was recorded concerning the margins of
this block (Poole 2008). Grain-size difference caused separation at its base from the underlying
Utahraptor block. When prepared, the Poole block yielded a partial juvenile iguanodont skeleton
with some articulated elements and diagnostic elements of an adult Utahraptor (Fig. 9; Poole
2008). Small-scale inclined sandstones were observed in the Poole block.
The ~ 500 kg iguanodont block on the west side contains parts of a large iguanodont and
at least one baby and one juvenile Utahraptor. A thin clastic dike connects this block to the
underlying main Utahraptor block (Fig. 8). The underside of the iguanodont block has a sharp,
irregular vertical contact between sandstone and gray shale of the heterolithic mudstone facies
(Fig. 10A, 10D). Slickenlines are apparent on this vertical contact. Exposed in the block is a
large iguanodont limb bone that extends through the connecting dike into the Utahraptor block
(Fig. 10B).
The plaster field jacket dimensions of the Utahraptor block are 3.2 m by 2.5 m with a
thickness of 0.50 to 0.85 m (Fig. 4). During the excavation of this lensoidal block, the
surrounding unfossiliferous heterolithic mudstone and sandy red and gray mudstone facies was
excavated and its limited extent documented. The absence of the fossiliferous lens from the
excavation walls indicates that the block was not a sheet-form or channel-form geometry but
lensoidal (Figs. 2, 4, 8). The southern limit of the Utahraptor-bearing sandstone mass is the
modern erosion surface.
The Utahraptor lens contains a spectrum of different sized Utahraptor skeletons, a
minimum of two babies (skull length ~ 10 cm), four juveniles, and one adult based on material
exposed at the mass margins and at the top of the block during excavation while reducing block
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dimensions and placing of the plaster jackets (Fig. 9; Kirkland et al. 2011). Teeth have not
shifted in the aveoli of the 10 currently known jaws from the site (Fig. 9). Several articulated
skeletons have been identified on the exposed portions of the block.
A near-vertical pipe composed of fine-grained sandstone connects the large Utahraptor
block to the iguanodont-sauropod block approximately 75 cm below and to the west that
preserves disarticulated and broken iguanodont and sauropod bones along with an isolated
maxilla of a juvenile Utahraptor (Figs. 2, 4, 8, 11A). The iguanodont-sauropod block was only
partially excavated, covered, placed in a plaster jacket, and was reburied in the quarry for future
research.
The pipe is approximately 0.5 m in diameter and connects to the underside of main
Utahraptor block at its northwestern margin (Fig. 11A). The pipe margins are sharp with
elongate green to light tan mudstone clasts aligned parallel to the long axis and margins of the
pipe (Fig. 11B). The longest clast axis is ~ 4 cm. Small gray and green mudstone clasts are
elongate to rounded and present throughout the interior of the pipe and in the blocks, along with
scattered 3–5 mm isolated chert granules (Fig. 11B, 11C). Chert granules in the pipe are similar
in composition and grain size to those constructing the horizontal partings in the lower rippled-
sandstone facies. The pipe and blocks contain angular fragments of bone (Fig. 11B). Within the
pipe, there are at least two generations of clasts, the more common gray green mudstone rip up
clasts, and medium gray clasts that host gray green rip up clasts (Fig. 11C). The internal clasts in
the gray rip-up clasts have different orientations than the surrounding clasts (Fig. 11B, 11C).
Interpretation.—The geometry of the pipe and dike connecting sill-like structures is
consistent with over pressuring and vertical mobilization of sediment. The relative structureless
nature and grain size of the dike and pipe fill indicates over-pressuring resulting in fluidization of
the underlying lower rippled sandstone and forceful injection of sediment-fluid mixture via a
conduit into the overlying strata (Daley 1971; Owen 1987; Cosgrove 2001; Draganits et al.
2003). The sand-fluid moved vertically following the dropping lithostatic pressure and when
reaching the surface produced sand volcanoes (see Obermeier 1996, 1998). Cylindrical
fluidization pipes are emplaced in shallow depths from 0.5 to 20 m and have diameters
commonly less than 0.5 m, but may be up to 1.5 m (see Gill and Kuenen 1957; Seed 1979;
Walsh et al. 1995; Obermeier 1996; Gallo and Woods 2004). Emplacement processes
incorporated mudstones from the lower rippled sandstone and the heterolithic red mudstones.
Dikes and pipes were the locus of multiple generations of flow as evidenced by the internal
rotated clasts.
Jolly and Lonergan (2002) demonstrated that the more irregular-shaped the sandstone
body, dikes, and sills are the shallower the emplacement. This is exemplified by the irregular
nature of the fossiliferous sills. The intrusions were exposed to surface processes incorporating
vertebrate fossils and producing the inclined tractional structures present in the Poole block.
Bone fragments attest to the turbulent and abrasive nature of fluid flow that generated the
sandstone bodies.
Rippled Sandstone and Mudstone
Description.—The rippled sandstone and mudstone facies is bound by normal faults and
is preserved only in the associated grabens or footwalls. Fine- to very fine-grained sandstones
and siltstones are very light gray (N8) to light greenish gray (5GY 8/1). Mudstones are dusky
green (10GY 3/2). Graded beds range from 2–3 mm to 2–3 cm in thickness. Sandstones have
loaded to irregular bases overlain by graded beds. Dusky green mudstone rip up chips from 1–2
mm to 3 cm occur at the bases.
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In all the grabens, this facies is deformed into larger-scale synclinal folds that increase in
dip towards the syndepositional fault plane (Fig. 12B). An additional graben filled rippled
sandstone and mudstone facies occurs 15 m from the center of the quarry (Fig. 6). Soft-sediment
fault structures extend to the base of the overlying rippled-sandstone. Normal and reverse slip
faults form graben-like structures (Figs. 2, 4B, 12). The fault planes strike approximately NE-
SW and have steep dips that flatten with depth near the stratigraphic level of the Utahraptor
mass. On the northern and southern ends of the walls are normal faults that have slickensides
indicating near-vertical down-dip movement (Fig. 12). Displacement on the faults is
approximately 1.0 m or less.
Sediment deformation in this facies increases towards the syndepositional faults,
changing from near pristine preservation of the graded beds to complexly folded to homogenized
strata directly adjacent to the faults (Fig. 13). Because fluidization overprinted the ripple and
mudstone facies, no vertical or horizontal trend in thickness is apparent (Fig. 13).
Interpretation.—The syndepositional faults are the result of brittle behavior of the red
mudstone facies. Variation in fault dip is related to the change in rheological properties with
depth (see Price 1966; Davison 1987; Ferrill and Morris 2003). Brittle behavior of sediment is
initiated by a variety of mechanisms including sediment loading, slope failure and seismic
activity (Seilacher 1969; Rider 1978; Field et al. 1982; Grimm and Orange 1997; Strachan 2002).
Emplacement of clastic intrusions have been linked to both polygonal and ring faulting
(Cartwright et al. 2007; Shoulders et al. 2007; Cartwright 2010; Ross et al. 2014).
The restricted nature of the rippled sandstone and mudstone facies to the footwall of the
faults indicates an original position stratigraphically higher. The down-dip movement preserved
this facies while stratigraphically higher remnants were eroded because of the absence in the
hanging wall. Fault slip initiated by sediment fluidization in the hanging wall is evidenced by
increasing soft sediment deformation intensity towards the fault. No apparent growth strata are
developed in the hanging wall sediment.
Graded beds and associated sedimentary structures represent multiple episodes of
decreasing current velocity (Harms et al. 1982; Boguchwal and Southard 1990; Southard and
Boguchwal 1990). Variation in fluid expulsion rates produce graded beds separated by fine-
grained sediment in sand volcanoes (Quigley et al., 2013; Rodríguez-Pascua et al. 2015). In
addition, multiple reactivation of small-scale sand blows occurs in areas experiencing successive
earthquakes (Quigley et al. 2013) or may be related to local unstable topography related to
seismic disturbance (Rodríguez-Pascua et al. 2015). Reactivation or the longer-term exploitation
of soft-sediment deformation conduits by a later event or continuous gas generation and fluid
migration is common (Hurst et al. 2003; Perez-Garcia et al. 2009; Quigley et al. 2013; Bastin et
al. 2015). Quigley et al. (2013) recognized significant subaerial erosion of the features including
vent degradation, rill development, erosion of fine-grained layers, and development of ripples
and microdunes.
Upper Rippled Sandstone
Description.—The upper rippled sandstone is laterally continuous and was traced across
the outcrop for about a kilometer (Figs. 1D, 4D, 15). The medium-grained sandstone has floating
granules and is light gray (N8). Dusky green mudstone (10GY 3/2) ripped chips are present.
Thickness ranges from 0.5 to 1.2 m. Climbing ripple cross laminations, small-scale, trough cross
bedding and parallel laminations are present. This facies exhibits better sorting than all the
others. Petrographically, the lower sandstone and lensoidal bodies are similar to this facies (Fig.
14). The lower sandstone is less sorted than the lensiodal bodies with the upper sandstone having
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coarse to very fine sands (Fig. 15) and laminae of 2–5 mm angular chert granules that form
horizontal partings.
Interpretation.—The overall fining and thinning upward of the deposit coupled with the
suite of sedimentary structures indicates this bed is the product of waning flows either in a
crevasse splay (see Bristow et al. 1999), sheet-flood (Tooth 1999; Blair 2000; Fisher et al. 2007)
or in the context of the overlying lacustrine beds, a transgressive lacustrine unit (Fraser and
Hester 1977; Bracken 1994; Ilgar and Nemec 2005). This facies was not disturbed by the older
fluidization events.
DISCUSSION—THE STRATIGRAPHIC AND SEDIMENTOLOGIC MODEL
The associated sedimentary facies, synsedimentary faults, suite of soft-sediment
deformation structures, lensiodal bone-bearing blocks, connected by a pipe and dike, coupled
with the near pristine fossil preservation (i.e., preservation of delicate elements and partial
articulation) in the Stikes Quarry eliminates most commonly documented taphonomic
mechanisms for forming bone beds. Facies, facies relationships, and soft-sediment deformation
structures exposed in the Stikes Quarry point to a localized artesian spring system source capable
of generating quicksand in the crater (Fig. 16). This hypothesis will be further constrained and
tested during the preparation of the large Utahraptor block. No matter what the additional data
collection yields, any new hypothesis must incorporate the association of soft-sediment
deformation structures and stratigraphic relationships outlined here.
The generation of soft-sediment deformation structures is often attributed to seismic
activity (Sims 1973, 1975; Allen 1982, 1986; Owen 1987; Pratt 1994; Obermeier 1996; Jones
and Omoto 2000; Moretti 2000; Moretti and Sabato 2007; Montenat et al., 2007; Spalluto et al.
2007; Reicherter et al. 2009; El Taki and Pratt 2012; Loope et al. 2013; Törő and Pratt 2015;
Wizevich et al. 2016). Consensus has centered on a number of criteria that, when recognized in
strata, indicates a high probability that the soft-sediment deformation structures are seismogenic
in origin (seismites sensu Seilacher 1969; Wheeler 2002). These key criteria include: (1)
association of soft-sediment deformed structures with a potential consanguineous fault; (2)
deformation consistent with seismicity supported by presence of field and experimental analogs;
(3) widespread synchronous soft-sediment deformed structures in a bed or layer; (4) spatial
variation in intensity towards the consanguineous fault; (5) elimination of other possible causal
mechanisms; (6) recurrence over time, in the same facies; (7) bracketed by undisturbed
sediments; (8) associated colluvial breccias, conglomerates and massive sandstones; and (9) soft-
sediment deformed structures that cross cut regional and facies boundaries (Sims 1973, 1975;
Obermeier 1996; Rossetti 1999; Jones and Omoto 2000; Ettensohn et al. 2002; Montenat et al.
2007; Moretti and Sabato 2007; Moretti and Sabato 2007; Reichter et al. 2009; Van Loon 2009;
Audemard and Michetti 2011; Hilbert-Wolf and Roberts 2015).
Movement on salt structures in the Arches National Monument during the development
of the Cedar Mountain Formation influenced its overall geometry (Kirkland and Madsen 2007;
Doelling 2010). The Stikes Quarry soft-sediment deformation however is limited to the
immediate vicinity of the bone bed and is not linked with a specific fault and therefore, does not
satisfy enough of the criteria outlined above, making a seismic origin extremely unlikely. In the
absence of these key seismic criteria an alternate mechanism to cause over pressuring, associated
soft-sediment deformation structures and the vertical migration of sand-size material is required.
Localized artesian systems have been documented to breech surficial deposits in fluvial,
delta, and shoreline systems and produce sedimentary features similar to those recorded in the
Stikes Quarry (Guhman and Pederson 1992; Younger and McHugh 1995; Massari et al. 2001;
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Heubeck 2009; Fig. 16A). In addition to water, crater-like structures on subaerial sediment
surfaces can develop from a combination of gas, water and sediment expulsion (Fig. 16B;
Maxson 1940; Jianhua et al. 2004; Netoff et al. 2010; Livingston et al. 2014; Miller et al. 2015;
Sherrod et al. 2016).
We propose the following sequence of events for the Stikes Quarry sedimentologic and
stratigraphic setting (Fig. 17): (1) Development of an artesian setting: the lower sandstone (the
aquifer), sealed by the underlying dark gray shale and overlying heterolithic mudstone,
(aquitards), and elevation generated either by local elevation variation, halokinesis, lowering of
base level linked surrounding lake levels, or a combination (Fig. 1E); (2) Up-arching of the
heterolithic mudstone as pressure built initiating mobilization and fluidization of sediment, the
lower rippled sandstone; (3) Intrusion sediment-rich fluid from the lower rippled sandstone into
the overlying heterolithic mudstone and breaching; (4) Elutriation of fines from the slurry to
form mud-sand volcanoes at the surface breech; (5) Construction of a mud-sand volcano with
unsteady flow creating the vertically stacked waning flow deposits; (6) Formation of over-
pressured water-filled crater with sand left by elutriation of fines recorded in the iguanodont-
sauropod block/sill that is an attritional bone accumulation similar to the Cleveland-Lloyd
Quarry (Gates 2005) and the Mygatt-Moore Quarry (Kirkland and Armstrong 1992; Kirkland et
al. 2005); (7) Multiple generations of horizontal sands at the base of the crater separated by
partial crater infill, Utahraptor block followed by either the iguanodont or the Poole blocks; tops
of sand intrusions are exposed subaqueously or subaerially for an extended period of time; (8)
Deformation of crater walls by normal faulting preserved the rippled sandstone and mudstone
facies on the footwall block—the relative timing of the deformation is linked the formation of
crater sands so which phase is uncertain; and (9) Destruction of elevated portion of the crater by
erosion, sediment infilling the crater and subsequent burial by the upper rippled sandstone.
Documented examples of artesian systems producing soft-sediment deformation
structures similar to the Stikes Quarry include: (1) the modern Dismal River in Nebraska (Fig.
16A); (2) Holocene mire in England; and (3) modern crater features on the Lake Powell delta
(Fig. 16B).
Guhman and Pederson (1992) recognized near vertical, large conduits that parallel the
Dismal River in the Sand Hills of Nebraska (Fig. 16A). A drop in base level caused rapid
incision of the Dismal River into the underlying confined aquifer releasing pressure by
producing the large diameter pipes. The conduit craters contain roiling water with suspended fine
sands creating spatially variable quicksand conditions. A significant pressure gradient caused the
robust vertical flow in the artesian spring system even though the surrounding area’s elevation is
very limited. These spring-generated craters are up to 10 m in diameter with estimated depths of
~ 44 m with a water level up to 3 m below the rim level. Over time, the flow rate and surface
area of vertical flow diminished (Fig. 16A). Flow rates in the Dismal River craters are non-
steady and subject to variations in air pressure and water recharge. During low-flow rates the
sands on the periphery of the pipe reestablish grain-to-grain contact and are capable of
supporting weight; variations in flow rate changes the width of this marginal firm sand band, but
quicksand conditions were still present away from the margins (D.T. Pederson personal
communication 2015). In the Stikes Quarry the Utahraptor block is the largest and therefore
reflects the greatest magnitude and probable longest pressure release event. The iguanodont and
Poole sills record resurgent events.
On a smaller scale, Younger and McHugh (1995) illustrate both conical and cylindrical
sand bodies preserved in a Holocene mire in East Yorkshire, UK. They attribute the injected
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sand bodies to the establishment of vigorous artesian springs. Structureless sands and preserved
trees record the development and onset of quicksand conditions caused by the over pressuring of
the artesian system. These Holocene sand bodies have similar geometry to pipes and sandstone
lensoidal sills present in the Stikes Quarry. The lateral extent of the known soft-sediment vertical
disruption in the Stikes Quarry is less than 50 m and therefore is comparable to both the boiling
springs and this mire size. The 3-m depth from the youngest disrupted surface to the Utahraptor
lensoidal bone bed comparable to the Holocene mire dimensions but not to the Dismal River
boiling sand pipe depth of 44 m.
At the modern Hite delta formed by the Colorado River entering Lake Powell, Netoff et
al. (2010) recognized a localized artesian system charged additionally with locally generated
methane that deformed the confining muddy delta top sediments into dome-like features that
initially developed subaqueously (Fig. 16B). As water levels in Lake Powell rapidly diminished,
the domes were breeched followed by the development of craters and mud volcanoes. These
fluid expulsion features continued to discharge fluid and methane for more than seven months
(Netoff et al. 2010). After a period of time the associated sediment surface collapsed creating a
crater that had a central vent (Fig.16; Livingston et al. 2014, 2015; Sherrod et al. 2016). These
craters develop ponds with rising lake levels that are exploited by flora and fauna (Miller et al.
2015; Sherrod et al. 2016). Sherrod et al. (2016) used geophysical techniques to demonstrate the
change in thickness in the overlying confining sediment and the presence of pipe-like features.
Some breeched the overlying sediments whereas others did not. These soft-sediment deformation
structures are akin to those observed in the Stikes Quarry.
Additional insights into the trapping mechanism of the Stikes Quarry may be gleaned
from the Pleistocene Rancho La Brea tar deposits (Woodard and Marcus 1973). The Ranch La
Brea deposit was thought to trap animals in erupting viscous hydrocarbons followed by the
luring of predators to the site, thereby producing a predator trap (Merriam 1911; Stock 1965).
The predator trap was then subjected to convective overturn by rising hydrocarbons that created
“pit wear” on bone. Woodard and Marcus (1973) examined the historical records of excavation,
internal stratigraphy, and drill hole data proposing that the fill formed by fluvial incursion into
pits or craters delivering a diverse suite of transported, single vertebrate elements to the pit. This
infilling model has crude vertical stratigraphy. More recent taphonomic examination has
reinvigorated the tar-based predator trap model based on the absence of a good definable internal
stratigraphy and mixed ages of the isolated single element bones (Akersten el al. 1983; Spencer
et al. 2003; Friscia et al. 2008). The disarticulated nature and pit wear on the bones requires that
the tar pit taphonomy be unique, and may be the result of increased bone compaction through
time (Friscia et al. 2008). The Stikes Quarry trapping mechanism must be different because of
articulated remains.
Miring in mud is a well-recognized mechanism for killing dinosaurs (Hungerbühler 1998;
Varricchio et al. 2008). In the upper Yellow Cat Member, the miring of Nedcolbertia is inferred
because of the bias of preserving only lower limbs and tails (Kirkland et al. 1998). Why were the
dinosaurs at the Stikes locality trapped in the sands and not in the adjoining muds? Bryant and
Miall (2010) report two articulated vertebrates (protosuchid crocodylomorphs; Lucas et al. 2005)
they inferred to be killed and buried in a liquefaction event. Khaldoun et al. (2005) conducted a
series of controlled experiments involving a mixture of fine sand, clays, and salt water to create a
natural colloidal gel that resists flowage equivalent to quicksand. A colloidal gel differs from
typical quicksand in that the absence grain-to-grain contact is minimized by surface chemistry. If
a colloidal gel developed, then the movement by a body, such as a struggling dinosaur, alters the
10
colloidal gel to a two-phase liquid and solid sand that induces sinking and trapping. The wet sand
phase has a high enough viscosity to trap the animals. Natural upwelling may not be of sufficient
flow rate to convert the wet sand back into a colloidal gel. These potential conditions coupled
with vigorous vertical flow would preferentially trap smaller, weaker dinosaurs over larger,
healthy animals. Clays are present in the sandstone masses containing the Utahraptor skeletons
but are not required to enhance trapping ability. Saline groundwater at least periodically
increases the probability of generating quicksand gel, based upon the Khaldoun et al. (2005)
experiments. Periodic variations in salinity may have been present from four lines of evidence:
(1) movement on the salt structures during Cedar Mountain Formation time (Kirkland and
Madsen 2007); (2) semi-arid to arid setting with monsoons (Kirkland et al. 1999; Suarez et al.
2007a, 2007b, 2014; Arens and Harris 2015); (3) barite crystals in the upper Yellow Cat
lacustrine sediments (Kirkland and Madsen 2007); and (4) sandstone masses being hosted in a
red mudstone with carbonate nodules, as documented in the Ruby Ranch Member (Ludvigson et
al. 2010).
Articulated theropods trapped in saturated, trampled sediments have been reported from
the Jurassic of China (Eberth et al. 2010). The Shisugou Formation deposits are associated with
extensive soft-sediment deformation attributed to vertical loading. The Stikes Quarry exhibits no
evidence of vertical loading but extensive mobilization and injection from underlying
stratigraphic levels.
SUMMARY
Previously reported mechanisms that generate bone beds are not sufficient to explain the
linkage by dikes and pipes of sill-like clustered bone beds and other related soft-sediment
deformation features discovered in the Lower Cretaceous, upper Yellow Cat Member of the
Cedar Mountain Formation. The Stikes Quarry deformed strata encases three dinosaur-bearing
lensoidal masses the largest of which contains a minimum of three baby, four juvenile and one
adult Utahraptor skeletons. The suite of sedimentary structure in the Stikes Quarry is consistent
with the development of a non-steady state artesian spring system that breached a mud layer.
Vigorous eruption rates develop quicksand conditions on the crater floor that trapped Utahraptor
dinosaurs and potentially other organisms.
The initial artesian eruption produced a crater with an attritional accumulation of
disarticulated and fragmented bones. The crater was subsequently reactivated up to three
additional times and trapped the various dinosaurs. Fluctuating pressure through time caused by
recharging the aquifer produced smaller springs that continued to trap the dinosaurs.
The Stikes Quarry death trap provides a stratigraphic and sedimentologic model that can
further be tested during preparation of additional material and provides an important new
mechanism attributed for trapping and preserving vertebrates.
ACKNOWLEDGMENTS
Matt Stikes is thanked for reporting this site to the Utah Geological Survey. Excavations
were conducted under Utah state permits # 2005-346, 2008-368, 2011-402, and 2014-438.
Thanks to all the volunteers, students and scientists that visited the site and aided in the
excavation. Special thanks are due to Utah Friends of Paleontology members D. Gray and P.
Policelli. Students and friends of the Washington University paleontology program contributed
mightily to the early phases of excavation. Numerous scientists have visited and worked with us
on the site over the years providing an invaluable sounding board for some of the ideas presented
here, including K. Poole, T. Birthisel, R. Chapman, R. Gaston, J. Foster, G. Hunt, J. Cavin, R.
Hernandez-Rivera, J. Choiniere, M. Loewen, M. Madsen, C. Suarez, M. Suarez, M. Joeckel, G.
11
Ludgvigson, and A. Moller. J. Cross of Cross Marine Projects, D. Harrison of High Desert
Excavation, H. Firm, and D. Brummel provided critical logistic support in bringing the massive
9-ton fossiliferous plaster jacket down off the cuesta with funding by the Utah Geological
Survey, Utah Friends of Paleontology, Andrew Leitch, and Jim Cross. Kutztown University
Research Committee funded participation of KU students and staff; E. Heness, S. Ireland, K.
Livingston, E. Laub and M. Malenda are thanked for their help in the field. Reviews by E.
Roberts. M. Chan, B. Gates, M. Hayden, D. Loope, M. Lowe, B. Sames, L. Sherrod, and M.
Hylland are appreciated.
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FIGURE CAPTIONS:
FIG. 1.—Quarry. A) Stratigraphic framework at the Stikes Quarry. The ridge is now called
Utahraptor ridge. B) Locality of the Stikes Quarry modified from Kirkland and Madsen (2007).
Lake Madsen section is red dot. C) Measured section in the upper Yellow Cat Member. Fossil
bone is the stratigraphic position of the Stikes Quarry. D) Panorama. Note the lateral continuity
of quarry strata. Circled track hoe sits on haul road. Yellow vertical bar is ~ 14 m thickness. E)
Panel constructed along the haul road. Aquifer and aquicludes are labeled. Stikes Quarry is not
shown in detail (See Fig. 4).
FIG. 2.—Photomosaic of the Stikes Quarry March 2015. Haul road on the right was developed to
remove large plaster jacket. All blocks are removed except for the lowest iguanodon-sauropod
block—sand bags are covering plaster jacket which was buried during reclamation. Figure on
right is 1.75 m tall.
FIG. 3.—Nonmarine Ostracoda from the lower gray shale in the upper Yellow Cat Member
below the Stikes Quarry. A) Mongolianella stirlingensis (Loranger 1951). B) Candona
albertensis (Loranger 1951). C) Cypridea (Pseudocypridina) inornata. D) Cypridea
(Longispinella) longispina (Peck 1941).
FIG. 4.—A) Stikes Quarry in May 2014. Person on the right is 1.8 m tall. B) Same photograph as
in A with stratigraphy, soft-sediment deformation and excavated blocks labeled. C) Stratigraphy
south of the Stikes Quarry. Note the lateral continuity of the strata and the apparent absence of
soft-sediment deformation. People are circled. Uppermost figure is 1.75 m tall.
FIG. 5.—Field photographs. A) Domal form present in lower sandstone in the Stikes Quarry.
Scale is 5 cm. B) Convolute bedding in lower sandstone near turn in haul road. Scale is 5 cm.
FIG. 6.—Field photographs of soft-sediment deformation structures along the haul road, March,
2015. Hammer is 31 cm in length.
FIG. 7.—Soft sediment deformation at contact of the lower rippled sandstone and the heterolithic
mudstone and sandy red and gray mudstone along haul road. A) Base of the heterolithic
mudstone and sandy red and gray mudstone. Note the fining upward sequence from siltstone to
more mudstone dominated facies from right to left. Field book is 18.5 cm in length. B)
Enlargement showing the pebbly mudstone intrusion cross cutting the siltstones and mudstones.
Scale is 5 cm.
FIG. 8.—Cartoons of the relationship of the sill-like sandstone masses. A) Map view
reconstruction of position of clastic pipe and dike, and fossiliferous lensoidal-ovoidal masses. B)
View of clastic pipe connecting to the Utahraptor block.
22
FIG. 9.—Utahraptor growth series. A–C: Utahraptor dentaries growth series in left-lateral view.
Natural History Museum of Utah–Vertebrate Paleontology Collection. A, juvenile,
UMNH.VP.20497 as found in field; B, adult, UMNH.VP.20501; and C, juvenile,
UMNH.VP.20487. D, E) Premaxillary growth series. D, “Baby” Utahraptor left premaxillary,
UMNH.VP.20488; and E, Adult Utahraptor left premaxillary, Utah State University Eastern,
Prehistoric Museum CEUM 184v.300 from the type locality of Utahraptor (Gaston Quarry) 5.7
miles (9.1 km) nearly due east (Kirkland et al., 1993) in left-lateral view. Note the intact teeth
(damage due to post-burial breakage or collecting effects). Size roughly reflects the age of the
Utahraptors.
FIG. 10.—Photographs of the base of the iguanodont block. A) Vertical photograph of the
underside of the iguanodont block. Note the sharp contact between the sandstone and gray shale.
Scale is 15 mm. B) Iguanodont limb bone (brown color). Located in upper part of block in A. C)
Interbedding of sandstone and gray mudstone. Scale is 15 cm. D) Vertical contact between
sandstone and gray mudstone.
FIG. 11.—Field and slab photographs. A) Dike connecting to the underside of main Utahraptor
block. B) Slab of dike stratification. Note the presence of numerous ripped up mudstones from
dike walls. Scale in cm. C) Enlargement of reworked intraclast containing differently oriented
ripped up chips highlighted in yellow. Scale in mm.
FIG. 12.—Field photographs of soft-sediment deformation. A) Rippled-sandstone cut by fault.
Both sides of the fault plane are highlighted in black dash with sense of motion shown in yellow
arrow. Photo taken May 2014. B) Soft sediment normal faults. Figure is 1.65 m tall. C) Near
vertical fault with hanging wall syncline. Hand is for scale.
FIG. 13.—Field photographs taken in March, 2015 of hanging wall strata and associated increase
in deformation proximal to the syndepositional fault. This is the same block as shown in Fig.
12A but reduced in size by construction of the haul road (see Fig. 1D). A) Graded beds of fine-
grained sandstone to green mudstone. Scale is in cm. B) Folded and fluidized graded beds. Scale
is in cm. C) Homogenized fine-grained sandstones with mudstone ripped-up chips. All scales are
in cm.
FIG. 14.—Photomicrographs. A) Lower sandstone facies. B) Clasts in the sill structures (blocks).
C) Mud matrix in the Utahraptor block. D) Upper rippled sandstone.
FIG. 15.—Slab and field photographs of upper rippled sandstone. A) Outcrop photograph 10 m
east of Stikes Quarry. Note the thinning-upward bedding made of rippled sandstones. Scale is in
cm. B) Slab of upper rippled sandstone. Note the mudstone draped ripple bedforms. Scale is in
cm.
FIG. 16.—Photomosaics of fluid-gas escape structures. A) Boiling sand spring, Nebraska. Spring
is flooded by high-water event. Note the geometry of the pit and reduction in the size of the
overpressured zone. Pit is ~ 20 meters across. B) Collapse crater partially filled with mudstone at
Lake Powell Delta, Glen Canyon National Recreation Area, Hite, Utah. Various geomorphic
features are labeled. Figure is 1.8 m tall.
FIG. 17.—Cartoon reconstruction of the Stikes Quarry. Dinosaurs illustrated by Julius Csotonyi.
