Analysis of Freshwater Limestones at the Cleveland-Lloyd Dinosaur Quarry, Emery County, Utah

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Analysis of Freshwater Limestones at the
Cleveland-Lloyd Dinosaur Quarry, Emery County,
Utah

• By Marina Suarez

Trinity University, San Antonio, TX
Temple University, Philadelphia, PA
2
General Information

• Northwestern flank of the San Rafael Swell
• Brushy Basin Member of the Morrison Formation
• Dinosaur bones are in a matrix of gray calcareous
  mudstone, which is overlain by limestone
• Over 10,000 bones
• Greatest concentration of Allosaurus fragilis
• Predator to Prey ratio of 31

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Location
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Limestone outcrops - Cleveland-Lloyd Study Area

• Determine stratigraphic relationships of the
  limestone unit(s) and bones contained within them
• Interpret a possible depositional environment

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Methods

• Field
• Determine Extent of the limestone
• Measure limestone thicknesses (32 measurements)
• Describe stratigraphic sections (14)
• Collect rock and fossil samples (102 collected)

• Lab
• Compiled stratigraphic info
• Identified fossils
• Analyzed thin sections
• Analyzed REE concentrations in vertebrate fossils

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Thin Sections

• A lower unit shows greater amounts of
  siliciclastic material (approx. 5-7)
• An upper unit shows less amounts of
  siliciclastic material (approx. 1-2)
• note figures removed to reduce file size

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Gastropods
3mm
3mm
Lymnaea sp.
Gyralus sp.
3mm
Amplovalvata sp.
Fossaria sp.
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Gastropod Paleoecology

• Fossaria sp.- Small bodies of waterat home on
  sticks, stones, and other debris in the water or
  on its edge.
• Gyralus sp.- Found adhering to sticks in standing
  water.
• Lymnaea sp.- In more or less stagnant parts of
  ponds, lakes or rivers, about vegetation,
  floating among weeds and algae.
• (Baker, 1928)

Gastropods present in the upper limestone unit
and in the limestone northeast of the quarry
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Ostracodes

• Present in all limestone units
• Theriosynoecum sp.
• Paleoecology Freshwater to brackish water
• (Van Morkhoven, 1963)

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Charophytes
Paleoecology Shallow lakes or ponds (less than
15 meters), in muddy substrates (Tucker and
Wright, 1990)

• Present in all limestone outcrops.

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Plant fossils

• Gingko and conifers
• Present only in upper limestone unit

• Identified by
• Dr. William D. Tidwell,
• Dr. Brooks Britt, and
• Kirk Johnson.

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Assemblages of invertebrate fossils in different
units
Lower Units Ostracodes Charophytes
Northeast Unit Ostracodes Charophytes Gastropods
Upper Units Ostracodes Charophytes Gastropods Pla
nt Fragments
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Rare Earth Elements

• Become incorporated into fossil bones quickly
  through adsorption and substitution
• The REE geochemistry in bones records the pore
  water REE chemistry at the time of
  deposition/fossilization
• REE concentration of pore water are a reflection
  of aqueous conditions (pH, redox) of the
  depositional environment
• (Trueman and Tuross, 2002)

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Bones northeast of the quarry
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Dinosaur Bones
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(No Transcript)
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• There is no significant difference between bones
  in the mudstone and bones in the limestone within
  the quarry
• Bones in the quarry are LREE and MREE-enriched
• Therefore bones within the mudstone and
  limestone within the quarry were deposited in
  similar water chemistries (near neutral pH)

GdN
YbN
NdN
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• Bones in limestone northeast of the quarry are
  HREE-enriched
• Therefore, the two sites do not correlate
• Bones in the limestone NE of the quarry were
  deposited in a more alkaline, higher pH
  environment than those of the quarry. This is
  consistent with drier climate.

GdN
YbN
NdN
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Stratigraphy
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Generalized cross section looking south, toward
the quarry and visitor center. Not to scale
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Conclusions

• Limestone units are lacustrine in origin
• There are two to three limestone units in the
  immediate vicinity of the CLDQ.
• One (lower limestone unit) that directly overlies
  the bone-bearing mudstone.
• One (upper limestone unit) that overlies the
  lower limestone unit, separated by mudstone.
• A third unit exists NE of the quarry that is
  distinct from the quarry based on REE
  geochemistry.
• This unit can neither be correlated with or
  distinguished from the upper limestone unit.

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Conclusions (cont.)

• Based on REE, dinosaur bones in the quarry were
  deposited in neutral pH water. Also, the
  deposition of calcareous mudstone suggests
  fluvial influence to the body of water.
• As conditions became drier, reduced recharge,
  coupled with aquatic plant growth, resulted in
  increased alkaline condition and carbonate
  deposition.
• The data are consistent with other studies
  suggesting alternating wet/dry environments for
  the Morrison Formation.

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Acknowledgments

• Numerous persons from the University of Utah,
  College of Eastern Utah, BYU, and Bureau of Land
  Management
• Faculty of the Department of Geosciences at
  Trinity University, especially my thesis advisor,
  Dr. Edward C. Roy
• Geoscience Department Secretaries Linda Hyatt
  and Blanca Kirkman
• Additional advice, guidance, critiques provided
  by Dr. Clive Trueman, Dr. Elizabeth
  Gierlowski-Kordesh, Dr. Perry Roehl, Dr. David
  Grandstaff, Doreena Patrick, Patricia Jannett,
  Kirk Johnson, Celina Suarez
• REE analysis by XRAL Laboratories, Canada
• Thin section preparation by National
  Petrographics, Houston, TX
• Financial support from Trinity University,
  GSA-South Central Region, BLM, parents

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References

• Baker, F.C., 1928, The Freshwater Mollusca of
  Wisconsin. Madison Wisconsin Academy of
  Sciences, Arts, and Letters, part 1, 507p.
• 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.
• Tucker, M.E., and Wright. V.P. 1990, Carbonate
  sedimentology. Boston Blackwell Scientific
  Publications p.164-190
• Trueman, C.N. and Tuross, N. 2002, Trace elements
  in recent and fossil bone apatite, in Kohn, M.J.,
  Rakovan, J.F., Hughes, J.J., eds, Reviews in
  mineralogy and geochemistry Phosphates
  geochemical, geobiological, and materials
  Washington D.C. The Mineralogical Society of
  America, v. 48, p.489-531.
• Van Morkhoven, F.P.C.M., 1963, Post-Paleozoic
  Ostracoda. New York Elsevier Publishing Co. vol.
  2, 478p.