Geochemical Determination of Calcareous Gravel Provenance

1
Geochemical Determination of Calcareous Gravel
Provenance

• Elizabeth A. Bell1
• David L. Barbeau, Jr.2
• Eric Tappa2
• Elizabeth Baresch3

1Earth and Space Sciences Dept., UCLA 2Geological
Sciences Dept., U. of South Carolina 3Pioneer
Natural Resources, Dallas, TX
2
Provenance Studies

• In foreland basins denudational history of the
  associated mountain belt.
• Alluvial fan conglomerates higher-resolution
  information on source evolution.
• Usually, provenance determination by gravel clast
  lithology
• Difficulties source areas with thick carbonate
  successions
• Little diversity in outcrop lithology
• Carbonate clasts subject to chemical alteration.
• Objective develop a higher-confidence,
  higher-resolution carbonate provenance method.
• Mountains of Northern Spain
• Appenines

3
Archeological Analogy Marble

• Geochemistry an accepted method for marble
  provenance
• trace elements, stable isotopes.
• A database has been compiled
• for marbles of the Mediterranean
• region
• Ancient and more recent
• marble quarries
• d13C, d18O, trace element data
• Problem less severe exposure to diagenetic
  agents.
• Is carbonate gravel likely to be similarly
  unaltered?

4
Necessary Conditions

• To successfully determine carbonate gravel
  provenance, one needs
• Compositional data for possible source rocks.
• Gravel that has undergone little to no chemical
  alteration during and after transport.
• A method for determining which gravel has been
  altered beyond recognition.

5
Weathering and Chemical Diagenesis
6
Weathering and Chemical Diagenesis
7
Geologic Setting
8
Geologic Setting

• Right CCR carbonate succession
• Source units we use for discriminant analysis
  shown
• CCR margin of Ebro Basin alluvial fan
  conglomerates
• Paleocurrent indicators sediment source was CCR
• Conglomerate clasts mainly carbonate material

After Domingo et al., 1982
9
Methods

• Source carbonates sampled throughout the CCR
  carbonate succession.
• Clasts were collected from 3 conglomerates
• Lower, middle, and upper basin section
• Geochemical Analyses
• d13C d18O gas-source mass spectrometry
• Major and trace elements ICP-AES
• Discriminant Analysis
• Samples in a multivariate data set are assigned
  to one of several pre-defined categories.
• Categories CCR source units

10
Results

• The vast majority of gravel falls into CCR
  carbonate compositional fields in several
  variables
• d13C, d18O, Ca, Fe, Mg, Mn, Sr

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Results

• The vast majority of gravel falls into CCR
  carbonate compositional fields in several
  variables
• d13C, d18O, Ca, Fe, Mg, Mn, Sr
• Gravel is systematically lower than CCR
  carbonates in two variables
• Al, Ti

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Results

• The vast majority of gravel falls into CCR
  carbonate compositional fields in several
  variables
• d13C, d18O, Ca, Fe, Mg, Mn, Sr
• Gravel is systematically lower than CCR
  carbonates in two variables
• Al, Ti
• Notably NOT our provenance indicators (Mn,
  1000Sr/Ca, Fe)

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Results

• The vast majority of gravel falls into CCR
  carbonate compositional fields in several
  variables
• d13C, d18O, Ca, Fe, Mg, Mn, Sr
• Gravel is systematically lower than CCR
  carbonates in two variables
• Al, Ti
• Notably NOT our provenance indicators (Mn,
  1000Sr/Ca, Fe)
• Also, not in the variables d13C or d18O

17
Results

• Discriminant analysis
• 4 models were constructed which maximized the
  confidence of our clast assignments
• Variables d13C, Ca, Fe, Mg, /-Mn, /-Sr
• Models accurately classify CCR source units
• 85.4 to 78.0
• Only minor disagreement among the models
• We report clast assignments on which 3 to 4 out
  of the 4 models agreed.

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Discussion Ebro Implications

• Variations in gravel compositions can be
  attributed to provenance.
• Chemical diagenesis likely is not severe.
• Yields new provenance information not seen in
  gravel-lithology studies.
• Low sample size for each conglomerate
• Presence vs. absence more significant than the
  exact proportion of clasts from each source unit.
• Absent in the lower conglomerates Triassic
  carbonate material.
• Present throughout the basin fill upper
  Cretaceous carbonate material.

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Conclusions

• Ebro Basin gravel clasts lack evidence of
  systematic alteration from CCR carbonates.
• The majority of gravel can be assigned to a
  subdivision of the CCR stratigraphic column.
• Given similarly low degrees of alteration,
  calcareous gravel in other settings should be
  conducive to the same methods.

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Acknowledgments

• Funding for this study was provided by a Magellan
  Undergraduate Research Grant (USC), a South
  Carolina Honors College Senior Thesis Grant, and
  the USC Dept. of Geological Sciences.
• We would like to thank Bob Thunell for use of USC
  Marine Sediments Laboratory equipment for
  analyses.
• Statue photo on slide three found at
  http//www.davestravelcorner.com/photos/turkey/Ist
  anbul-Marble-Statue.jpg

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References

• Marble provenance
• Attanasio, D., Platania, R., and Rocchi, P.,
  2005, The marble of the David of Michelangelo a
  multi-method analysis of provenance. Journal of
  Archaeological Science, v. 32, p. 1369 1377.
• Attanasio, D., Brilli, M., and Rocchi, P., 2008,
  The marbles of two early Christian churches at
  Latrun (Cyrenaica, Libya). Journal of
  Archaeological Science, v. 35, p. 1040-1048.
• Gorgoni, C., Lazzarini, L., Pallante, P., Turi,
  B., 2002. An updated and detailed
  mineropetrographic and C-O stable isotopic
  reference database for the main Mediterranean
  marbles used in antiquity. In Herrmann Jr.,
  J.J., Herz, N., Newman, R. (Eds.),
  Interdisciplinary Studies on Ancient Stone.
  Archetype Publ., London, pp. 115e131.
• Herz, N., 2006, Greek and Roman white marble
  geology and determination of provenance. In
  Palagia, O., ed., Greek Sculpture Function,
  Materials, and Techniques in the Archaic and
  Classical Periods, Athens, Greece p. 280 306.
• Carbonate diagenesis
• Moore, C. H., 1989, Carbonate diagenesis and
  porosity. Developments in Sedimentology 46.
• Veizer, J., 1983, Chemical diagenesis of
  carbonates theory and application of trace
  element technique, in Stable Isotopes in
  Sedimentary Geology, SEPM Short Coarse No. 10,
  Society of Sedimentary Geology, Tulsa, OK.
• Ebro Basin and CCR geology, including (Baresch,
  2006) earlier gravel provenance results
• Baresch, E.F., 2006, Constraining the effects of
  autocyclicity, tectonics and climate on alluvial
  fan architecture, SE Ebro Basin, Spain, M.S.
  thesis, University of South Carolina, Columbia,
  South Carolina.
• Colodron, I., Nunez, A., and Ruiz, V., Cabanas,
  I., Uralde, M. A., Nodal, T., Bretones, R.,
  1972b, Cornudella Instituto Geologico y
  Minerologia de Espana, Mapa Geologico de Espana
  445, scale 150 000.
• Domingo, A. G., Olmedo, F. L., and Barnolas, A.,
  1982b, Horta de San Juan Instituto de Geologia y
  Minerologia de Espana, Mapa Geologico de Espana
  496, scale 150 000.