Each sample was air-dried at ambient temperature, disaggregated, and sieved to <2 millimeters (mm). The <2-mm material was then crushed to <150 micrometers (µm) prior to chemical analysis. Total carbon (C) was determined by the use of an automated carbon analyzer. The sample was combusted in an oxygen atmosphere at 1,370 °C to oxidize C to carbon dioxide (CO2). The CO2 gas was measured by a solid state infrared detector in a method similar to Brown and Curry (2002).

Brown, Zoe Ann, and Curry, K.J., 2002, Total carbon by combustion, chap. R of Taggart, J.E., Jr., ed., Analytical methods for chemical analysis of geologic and other materials, U.S. Geological Survey: U.S. Geological Survey Open-File Report 02-223, 4 p.