Geochemical Determination of Calcareous Gravel Provenance

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

• trace elements, stable isotopes.

• A database has been compiled

• for marbles of the Mediterranean

• region:

• Ancient and more recent
• marble quarries
• δ13C, δ18O, trace element data

• 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.