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Taphonomy and Rare Earth Element Geochemistry of the Stegosaurus sp. at the Cleveland Lloyd Dinosaur Quarry, Emery County, Utah. by Celina Suarez Trinity University Temple University San Antonio, TX Philadelphia, PA. Geologic Setting. Morrison Formation Brushy Basin Member

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Taphonomy and Rare Earth Element Geochemistry of the Stegosaurus sp. at the Cleveland Lloyd Dinosaur Quarry, Emery County, Utah

by Celina Suarez

Trinity University Temple University

San Antonio, TX Philadelphia, PA


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Geologic Setting

  • Morrison Formation

    • Brushy Basin Member

  • Exposed by the San Rafael monocline

  • Located below variegated beds of the upper most Brushy Basin, in a section dominated by gray siltstones, lacustrine limestones, and small channel sandstones.


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The Cleveland Lloyd Dinosaur Quarry

  • The largest deposit of Allosaurus fragilis in the world – 47 (Gates, 2002)

  • over 10,000 bones

  • Deposited in a calcareous mudstone with small concretions to large concretionary layers of carbonate, capped by a lacustrine limestone

  • Most recent research: ephemeral pond that accumulated bones as the result of multiple drought events (Gates, 2002)


Taphonomy and rare earth element geochemistry the stegosaurus sp in the cldq l.jpg
Taphonomy and Rare Earth Element Geochemistry the Stegosaurus sp. in the CLDQ

  • Is the taphonomic analysis of the Stegosaurs in the research square significantly different than the taphonomic analysis of the Allosaurs?

  • Is the REE geochemistry of the Stegosaurs significantly different from the Allosaurs?

  • Does the REE geochemistry analysis support the findings of Gates (2002)?

  • Population Study

  • Various taphonomic approaches to Cleveland Lloyd…

    • Bone positioning

    • Taphonomic markings or bone alteration and surface features

    • Lithologic Evidence

    • Rare Earth Element Geochemistry


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Review collections material => population number of Stegosaurus

Excavation and Mapping => biostratigraphic positions and orientation of bones

Taphonomic Analysis => abrasion, weathering, fracture, surface traces

Rare Earth Element Geochemistry => concentrations and ratios


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Results: Population Survey

  • Minimum of six individuals of Stegosaurus based on the number of humeri and scapulae


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Stegosaurus

Allosaurus

Other

Mapping and Excavation

Sauropod and Stegosaur

Stegosaur

Allosaur

Stegosaurus

Allosaurus


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Bone Positioning

  • Mostly flat lying

  • Some degree of orientation due to seasonal fluvial activity

  • Bones in the research square are autochthonous based on the presence of large bone material and small sediment size, which is also consistent with findings by Gates (2002).


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Taphonomic Markings

  • Pathologic Deformation-left side


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Taphonomic Markings: Fracture

  • Only one: Allosaurus gastralia

  • 30% of bones in the bones surveyed by Gates (2002) have fractures

  • No significant trampling


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Taphonomic Analysis: Surface Traces

  • Teeth Marks – only Stegosaurus, none on Allosaurus bones

    • Throughout the quarry, bones of herbivorous dinosaurs contain the most teeth marks (Gates, 2002).

  • Allosaurs preferentially prey upon the herbivorous animals, rather than scavenge


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Abrasion

  • Abrasion – mostly low, and slightly more on Stegosaurus bones

  • Gates (2002), notes prevalence of low level of abrasion on centra of vertebrae

  • Bias since majority of Stegosaurus material were vertebrae

  • Supports some fluvial activity when combined with bone orientation data


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Taphonomic Markings

  • At least portions of the bones in the quarry were exposed because of evidence of scavenging/ predation.

    • Weathering stages between 0 and 1 – not significant exposure

  • Stegosaurs were more susceptible to predation due to drought conditions (Gates, 2002).

    • Bias of teeth marks on the Stegosaurus bones versus the Allosaurus bones

    • Allosaurus preferred predation rather than scavenging since there are less teeth marks on Allosaurus bones


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1mm

1 mm

1mm

Results: Lithology – Thin Sections

  • Mostly clays, CaCO3, plagioclase, quartz, some hematite

  • Microfossils – ostracodes and charophytes

  • Microfossils – indicative of shallow, low-energy water


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Rare Earth Element Geochemistry

  • La – Lu

  • During weathering, REE undergo fractionation

  • Aqueous REE signatures vary with pH and redox conditions in different depositional environments


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Fractionation and REE of Fossil Bone

  • REE substitute for Ca in the biogenic apatite crystal structure during early diagenesis

  • Bones record the pore-water REE chemistry of the original depositional/diagenetic environment


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REE Signatures

  • HREE are associated with alkaline waters (high pH)

  • LREE are associated with acidic and neutral waters (low pH)

  • Alkaline environments include: evaporitic lacustrine settings – established lakes with high degree of evaporation, carbonate deposition

  • Acid environments include: water-logged settings such as swampy areas


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REE Geochemistry Bone Sampling

  • Cortical bone was collected from Allosaurus and Stegosaurus bones excavated from the research square

  • Cortical bone has a higher concentration of REE than trabecular bone


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Comparing the Allosaurus and Stegosaurus bones:

All bones have similar signatures (shape)

All bones are fossilized in same environment

Signatures of bones in the quarry are flat with a slight depletion of HREE indicating a neutral pH to slightly acidic environment

Eu anomaly indicates volcaniclastic REE source


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Ternary Diagram

  • The ternary diagram is a way to quantify spider diagram in a more presentable format

  • Ternary shows relative ratios of

    • Light REE – Nd

    • Middle REE – Gd

    • Heavy REE – Yb

  • Points are clustered showing similar REE ratios i.e. the same depositional environment

  • Supports an autochthonous deposit of bones – also seen in taphonomic evidence


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Indicate:

Neutral pH environment

Fluvial activity

* orientation

* abrasion

* rip-up clasts

(Gates, 2002)

REE concentrations of total data set:

Includes bones from quarry: mudstone, contact, and capping limestone; plus limestone ridge to the north


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REE Geochemistry: Depositional Setting

  • Supports the “ephemeral” pond setting described by Gates (2002).

    • Occasionally to seasonally dries out

    • Flooding/ or wet season refreshed the pond with neutral pH giving flat REE signatures, and orienting the bones

    • Neutral pH pond area, not established lake


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Conclusions

  • Six Stegosaurs are currently found at the CLDQ. One Stegosaur is represented in the study area.

  • All the bones in the quarry were fossilized in the same depositional environment, supporting an autochthonous accumulation.

  • The depositional environment of Cleveland Lloyd was a neutral pH environment

    • Ephemeral pond

    • Some fluvial action due to oriented and slight abrasion of bones and enough sediment supply to depress the formation of only limestone, and give flat REE signatures

    • Not enough water to support aquatic fauna or significant plants

    • Microfossils support shallow water environment

  • These occasional to seasonal variations supported by paleoenvironmental interpretations of the Morrison Formation as being highly seasonal by Dodson et al. (1980)


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Acknowledgements

  • Temple University: Dr. David E. Grandstaff and Dr. Dennis O. Terry Jr.

  • Trinity University: Dr. Edward C. Roy Jr.

  • Univ. of Utah: Dr. Scott Sampson, Bucky Gates, Lindsay Zanno

  • Utah Museum of Natural History: Mike Getty, Monica Castro, Joe Gentry, Jerry Golden

  • BLM – Price Field Office: Mike Leschin, Frank Davis, Sam Espinoza, Elsa Langrane

  • Univ. of Pennsylvania: Dr. Peter Dodson and his Evolution of Dinosaurs class

  • Doreena Patrick

  • Dr. Clive Trueman

  • Financial Support: Trinity University, Tinker Family, GSA South-Central Undergraduate Research Grant Program, Bureau of Land Management

  • Marina Suarez, and all friends, family, and reviewers


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References

  • Dodson, P., Behrensmeyer, A.K., Bakker, R.T., and McIntosh, J.S., 1980, Taphonomy

    and Paleoecology of the dinosaur beds of the Jurassic Morrison Formation:

    Paleobiology, v. 6, no. 2, p. 208 – 232.

  • Gates, T.A., 2002, The Cleveland Lloyd Dinosaur Quarry as a

    drought-induced assemblage: late Jurassic Morrison Formation,

    central Utah [Master of Science Thesis]: Salt Lake City, Utah University of Utah, 57p.

  • Trueman, C.N., 1999, Rare earth element geochemistry and taphonomy of vertebrate assemblages: Palaios, v. 14, p. 555-558.

  • Trueman, C.N. and Tuross, N., 2002, Trace elements in recent and fossil bone apatite, in Kohn, M.J., Rakovan, J.F., Hughes J.M., eds., Reviews in mineralogy and geochemistry: Phospates: geochemical, geobiological, and materials: Washington D.C.:The Mineralogical Society of America, v. 48, p. 489-521.


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