Geochemical Determination of Calcareous Gravel Provenance

Elizabeth A. Bell1

David L. Barbeau, Jr.2

Eric Tappa2

Elizabeth Baresch3

1Earth and Space Sciences Dept., UCLA2Geological Sciences Dept., U. of South Carolina

3Pioneer Natural Resources, Dallas, TX

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…

1. Compositional data for possible source rocks.

2. Gravel that has undergone little to no chemical alteration during and after transport.

3. A method for determining which gravel has been altered beyond recognition.

Weathering and Chemical Diagenesis

Weathering and Chemical Diagenesis

Geologic Setting

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., 1982After Domingo et al., 1982

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

•The vast majority of gravel falls into CCR carbonate compositional fields in several variables:

•δ13C, δ18O, Ca, Fe, Mg, Mn, Sr

Results

•The vast majority of gravel falls into CCR carbonate compositional fields in several variables:

•δ13C, δ18O, Ca, Fe, Mg, Mn, Sr

•Gravel is systematically lower than CCR carbonates in two variables:

•Al, Ti

Results

•The vast majority of gravel falls into CCR carbonate compositional fields in several variables:

•δ13C, δ18O, Ca, Fe, Mg, Mn, Sr

•Gravel is systematically lower than CCR carbonates in two variables:

•Al, Ti

•Notably: NOT our provenance indicators (Mn, 1000*Sr/Ca, Fe)

Results

•The vast majority of gravel falls into CCR carbonate compositional fields in several variables:

•δ13C, δ18O, Ca, Fe, Mg, Mn, Sr

•Gravel is systematically lower than CCR carbonates in two variables:

•Al, Ti

•Notably: NOT our provenance indicators (Mn, 1000*Sr/Ca, Fe)

•Also, not in the variables δ13C or δ18O

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

ReferencesReferences• 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.