Geochemical Determination of Calcareous Gravel Provenance


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Geochemical Determination of Calcareous Gravel Provenance

  • Elizabeth A. Bell1

  • David L. Barbeau, Jr.2

  • Eric Tappa2

  • Elizabeth Baresch3


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


Archeological Analogy: Marble

  • Geochemistry: an accepted method for marble provenance

  • A database has been compiled

  • for marbles of the Mediterranean

  • region:

  • Problem: less severe exposure to diagenetic agents.

    • Is carbonate gravel likely to be similarly unaltered?


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.


Weathering and Chemical Diagenesis



Weathering and Chemical Diagenesis



Geologic Setting



Geologic Setting



Methods

  • Source carbonates sampled throughout the CCR carbonate succession.

  • Clasts were collected from 3 conglomerates:

    • Lower, middle, and upper basin section
  • Geochemical Analyses:

    • δ13C & δ18O : 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


Results





Results





Results





Results



Results

  • Discriminant analysis:

    • 4 models were constructed which maximized the confidence of our clast assignments
    • Variables: δ13C, 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.





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.



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.



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/Istanbul-Marble-Statue.jpg



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: 1:50 000.
    • 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: 1:50 000.



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