Determining terrestrial paleotemperatures using the oxygen isotopic composition of pedogenic carbonate

Quantifying terrestrial paleotemperatures has proven to be a challenging endeavor. This paper explores the use of the oxygen isotopic composition of pedogenic calcite for terrestrial paleotemperature reconstructions. We generate three paleotemperature equations, two of them derived by simultaneous solution of equations that describe the fractionation of oxygen isotopes in the exogenic cycle, while the third equation is derived using a linear regression through modem delta O-18(cc)/MAT (oxygen isotopic composition of pedogenic calcite versus mean annual temperature) data. We use the paleotemperature equations to evaluate climate change across the K-T boundary by analyzing the oxygen isotopic composition of pedogenic carbonates from a series of stacked paleosols in west Texas. The fabrics in the calcite nodules were evaluated in order to identify soil carbonate components that have the best chance of containing isotopic information that represents ancient pedogenic conditions. The average temperature for West Texas during the time period studied is 18+/-0.5 degrees C. Two temperature excursions are recognized prior to the K-T boundary in which terrestrial temperatures increase by about 4 degrees C for relatively short periods of time. These short greenhouse events documented in west Texas correlate with changes in marine temperatures as well as terrestrial temperatures in North Dakota during the same time period. Latitudinal temperature gradients generated using the West Texas and North Dakota data indicate that the spatial simultaneous solution yields the most reliable temperature reconstructions of the three equations considered in this study. (c) 2005 Elsevier B.V. All rights reserved.