Research Interests

Uranium-series isotope and trace element studies of ocean sediments and their application to the fields of paleoclimatology, low-temperature geochemistry, and tectonics.

Research Interests:

Paleoclimatology

My research specialization is in dating fossil corals using uranium-series methods, which are based on the radioactivity of uranium. Uranium has two isotopes that are parents of long decay chains. 238U decays with a half-life of 4.5 billion years (how long it takes half of a given number of 238U atoms to decay away) through many short-lived isotopes, the intermediate daughter products, to the final stable daughter, 206Pb (lead). 235U decays with a half-life of 713 million years through mostly short-lived daughters to 207Pb. 230Th, an intermediate daughter of 238U, has a half-life of 75,000 years. Rocks on Earth's surface contain both 238U and 230Th. However, during weathering uranium dissolves and is transported to the ocean whereas thorium is insoluble and remains behind in the rocks. This fractionation of thorium from uranium sets up an ideal chronometer in fossil corals. Corals grow their skeleton from elements taken out of seawater, using mostly CaCO3 to form the mineral aragonite. Uranium is also incorporated in concentrations of ~3 parts per million, but there is essentially no thorium due to its insolubility. Thus, the corals incorporate a significant amount of the parent isotope, but no daughter isotope. The ingrowth of 230Th is like a ticking clock, providing a chronometer. Because 230Th is an intermediate daughter, after approximately 6 to 7 half-lives the amount of 230Th stablizes, giving this chronometer a range of ~600,000 years.

Fossil corals provide important records of sea level history during the last several hundred thousand years. Dating of fossil corals has previously resulted in important sea level information that test the Milankovitch theory, the primary theory for the cause of the ice ages. New super high-precision methods for U-Th dating of fossil corals make it possible to generate a higher resolution sea level record than was previously possible and to better identify well-preserved fossil corals. Improving the resolution of the Earth's sea level history will dramatically improve our understanding of how Earth's climate responds to external (orbital) forcing and to internal (feedbacks in the climate system) forcing.

Precambrian Geochronology/Tectonics

The Precambrian rocks of Minnesota have an incredibly intricate story to tell about the building of the North American Craton. Unfortunately, there is insufficient age control to give the story a detailed timeline. I am interested in constraining the history of the Vermillion District in NE Minnesota high-precision uranium-lead dating of zircon crystals.

Publications

Winter, A., Miller, T., Kushnir, Y., Sinha, A., Timmermann, A., Jury, M.R., Gallup, C.D., Cheng, H., Edwards, R.L. (2011). Evidence for 800 years of North Atlantic multi-decadal variability from a Puerto Rican speleothem, Earth and Planetary Science Letters 308 (1-2), 23-28.

Webster J.M., Braga J.C., Clague D.A., Gallup C. D., Hein J.R., Potts D.C., Renema W., Riding R., Riker-Coleman K., Silver E., Wallace L. (2009). Coral reef evolution on rapidly subsiding margins, Global and Planetary Change, v. 66, 1-2, 129-148

Gallup, C. D., D. M. Olson, R. L. Edwards, L. M. Gruhn, A. Winter, and F. W. Taylor (2006), Sr/Ca-Sea surface temperature calibration in the branching Caribbean coral Acropora palmata, Geophysical Research Letters, 33, L03606, doi:10.1029/2005GL024935.

Riker-Coleman, K. E., C. D. Gallup, L. M. Wallace, J. M. Webster, H. Cheng, and R. L. Edwards (2006), Evidence of Holocene uplift in east New Britain, Papua New Guinea, Geophys. Res. Lett., 33, L18612, doi:10.1029/2006GL026596.

Cheng H., Wang Y., Edwards R. L., Kelly M. J., Gallup. C. D., Liu W., Kong X., and Ming Y. (2006) A penultimate glacial monsoon record from Hulu Cave and two-phase glacial terminations. Geology: Vol. 34, No. 3, pp. 217-220, doi: 10.1130/G22289.1.

Edwards, R.L., Gallup, C.D., K.B. Cutler, Cheng, H., (2004). Geochemical Evidence for Quaternary Sea Level, in Treatise on Geochemistry, Eds. H.D. Holland, K.K. Turekian, Elsevier. Volume 6, Oceans and Marine Geochemistry, Ed. H. Elderfield, 343-364.

Webster, J.M., Clague D.A., Riker-Coleman K., Gallup C. D., Braga J.-C., Burr G., Potts D., Moore J.G., Winterer E.L., Paull C.K. (2004) Drowning of the -150 m reef off Hawaii: A casualty of global meltwater pulse 1A? Geology 32, 249-252.

Webster J. M., Wallace L., Silver E., Applegate., B., Potts D., Braga J. C., Riker-Coleman K and Gallup C (2004) Drowned carbonate platforms in the Huon Gulf, Papua New Guinea, Geochemistry, Geophysics, Geosystems - G-Cubed.

Lal D., Gallup C.D., Somayajulu B.L.K., Vacher L., Caffee M.W., Jull A.J.T., Finkel R.C., Speed R.C., and Winter A. (2005) Records of cosmogenic nuclides, 10Be, 26Al and 36Cl in corals: first studies on coral erosion rates and potential of dating very old corals. Geochimica Cosmochimica Acta, 69 (24), 5717-5728.

Webster, J.M., Wallace L., Silver E. Potts D., Braga J.-C., Renema W., Riker-Coleman K, Gallup C.D. (2004). Coralgal composition of drowned carbonate platforms in the Huon Gulf, Papua New Guinea; implications for lowstand reef development and drowning, Marine Geology 204, 59-89.

Edwards, R.L., Gallup, C.D., Cheng, H., (2003). Uranium-series Dating of Marine and Lacustrine Carbonates. Reviews in Mineralogy and Geochemistry, Vol 52, 363-405.

Cutler K.B., Edwards R.L., Taylor F.W., Cheng H., Adkins J., Gallup C.D., Cutler P.M., Burr G.S., Chappell J., and Bloom A.L. (2003). Rapid sea-level fall and deep-ocean temperature change since the last interglacial. Earth and Planetary Science Letters, 206, 253-271.

Gallup, C.D., Cheng, H., Edwards, R.L. (2002). Direct determination of the timing of sea level change during Termination II. Science, 295, 310-313.

Cheng, H., Edwards, R.L., Hoff, J.A., Gallup, C.D., Richards, D.A., Asmerom, Y. (2000). The half-lives of uranium-234 and thorium-230. Chemical Geology, 169, 17-33.

Gallup, C.D. 1997. High-precision uranium-series analyses of fossil corals and Nicaragua Rise sediments: The timing of high sea levels and the marine 234U value during the past 200,000 years. Ph.D. Thesis, University of Minnesota.

Galewsky, J., Silver, E.A., Gallup, C.D., Edwards, R.L., and Potts, D. 1996. Carbonate platform dynamics in the Huon Gulf, Papua New Guinea, Geology, 24, 819-822.

Min, G.R., Edwards, R.L., Taylor, F.W., Gallup, C.D., and Beck, J.W. 1995. Annual cycles of U/Ca in coral skeletons and U/Ca thermometry. Geochim. Cosmochim. Acta. v. 59, no. 10, pp. 2025-2042.

Gallup, C.D., Edwards, R.L., and Johnson, R.G. 1994. The timing of high sea levels over the past 200,000 years. Science 263, 796-800.

Taylor, F.W., Quinn, T., Gallup, C.D., and Edwards, R.L. 1994. Quaternary plate convergence rates at the New Hebrides Arc from the chronostratigraphy of Bougainville Guyot (Site 831). Proceedings of the Ocean Drilling Program, Scientific Results, v. 134, 47-57.

Edwards, R.L. and Gallup, C.D. 1993. Dating of the Devils Hole calcite vein. Science 259, 1626-1627.

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