2005 Salt Lake City Annual Meeting (October 16–19, 2005)

Paper No. 11
Presentation Time: 8:00 AM-12:00 PM


UFNAR, David F., Geology, Univ of Southern Mississippi, Hattiesburg, MS 39406, LUDVIGSON, Greg A., Kansas Geological Survey, University of Kansas, 1930 Constant Ave, Lawrence, KS 66047-3726, GONZÁLEZ, Luis A., Department of Geology, University of Kansas, 1475 Jayhawk Blvd, Lindley Hall Room 120, Lawrence, KS 66045-7613 and DAVIS, Jeremy, Geoscience, Univ of Iowa, 121 Trowbridge Hall, Iowa City, IA 52240, David.Ufnar@usm.edu

Exposure surfaces in the shallow marine carbonates of the Glen Rose Formation, Texas contain pedogenic carbonates that provide a record of meteoric-vadose evaporative enrichment. The isotopic values of the pedogenic calcites yield positive linear covariant trends (PLCTs) in δ18O vs. δ13C values. A 2-meter thick, sequence bounding paleosol developed at the top of the Glen Rose Formation near Kerrville, Texas yields a meteoric calcite line (MCL) with a mean δ18O value of –3.8 permil and δ13C values that range from –3.7 to –4.8 permil VPDB. Pedogenic carbonate nodules and micrite-dominated domains yield a PLCT that extends from the MCL to δ18O values of +1.1 permil and δ13C values of –2.7 permil VPDB. The PLCT results from pedogenic calcite precipitation from vadose fluids that were isotopically enriched through evaporation. The PLCT trends have been used to estimate zonally-averaged evaporation rates at 25°N paleolatitude during the Albian greenhouse warming. Terrestrial greenhouse world paleosol carbonate proxy records and quantitative reconstructions of the mid-Cretaceous hydrologic cycle show that heat transport through the atmosphere by water vapor may have played a greater role in cooling the tropics and warming the poles than it does today. A stable isotope mass-balance model of evaporative enrichment in the Glen Rose Formation suggests that evaporation rates at 25°N paleolatitude were 1.5 to 2 times present levels. The increased amount of heat removed from the tropics was transferred poleward and released through condensation and contributed to greater polar warmth.