GEOCHEMICAL METHODS Carbon, Nitrogen, and Sulfur Analyses Total carbonate and inorganic carbon in most samples were determined by coulometry (Engleman and others, 1985). Values of organic carbon (OC) were determined by difference between total carbon and carbonate carbon. Percent CaCO3 was calculated by dividing percent carbonate carbon by 0.12, which is the fraction of carbon in CaCO3. Percentages of organic carbon and total nitrogen were measured on some samples using a Carlo Erba CHN analyzer. See Arthur and others (1987) for a comparison of methods of carbon analyses by different methods on samples from DSDP Hole 603B. Concentrations of sulfur were measured with a LECO sulfur analyzer. Rock-Eval Pyrolysis Rock-Eval pyrolysis was used to determine the type of organic matter in samples. The Rock-Eval method provides a rapid determination of the hydrogen and oxygen richness and degree of preservation of sedimentary organic matter (Tissot and Welte, 1984; Peters, 1986). Concentrations of free and adsorbed hydrocarbons (HC) released by programmed heating of the sample in a stream of helium at a relatively low temperature (250°C) for 5 min are recorded as the area under the first peak on a pyrogram (S1) (milligrams of HC per gram of sample). The second peak on a pyrogram is composed of pyrolytic hydrocarbons generated by thermal breakdown of kerogen as the sample is heated from 250° to 550°C (S2) (milligrams of HC per gram of sample). CO2 also is generated by kerogen degradation and is retained during the heating interval from 250° to 390°C, and it was analyzed as the third peak on the pyrogram (S3) (milligrams of CO2 per grams of sample). The Rock-Eval instrument also records the temperature of maximum hydrocarbon yield (Tmax). The S2 and S3 peak areas, when calibrated and normalized to percent total organic carbon (TOC), yield a hydrogen index (HI) and an oxygen index (OI) expressed as milligrams of HC and CO2 , respectively, per gram of TOC. Carbon Isotope Analyses of organic matter Stable carbon-isotope ratios of bulk organic matter were determined by standard techniques on decalcified samples (Pratt and Threlkeld, 1984). A powdered sample was reacted with buffered acetic acid for 24 hours to dissolve carbonate minerals. The residue was then centrifuged, decanted, washed, and dried. The residue was then combusted at 1000° C with copper oxide in a sealed quartz tube. The resulting CO2 was purified in a high-vacuum gas-transfer system, and the isotope ratios determined with an isotope-ratio mass spectrometer. Results are reported in the usual per mil?delta-notation relative to the Vienna Pee Dee belemnite (VPDB) marine-carbonate standard, delta ‰ =[(Rsample/RPDB)-1] x 1000, where R is the ratio (13C:12C) or (18O:16O). Carbon and Oxygen Isotope Analyses of Bulk Carbonate Stable-carbon and -oxygen isotope ratios were determined using standard techniques (Dean et al., 1986). Powdered whole-rock samples for determining carbon and oxygen isotope ratios in carbonate were reacted with 100% phosphoric acid, and the evolved CO2 was dehydrated and purified in a high-vacuum gas-transfer system. All isotope ratios in CO2 were determined using an isotope-ratio mass spectrometer. Results are reported in the standard per mil (‰) delta-notation relative to the Vienna Pee Dee belemnite (VPDB) marine-carbonate standard, delta ‰ =[(Rsample/RPDB)-1] x 1000, where R is the ratio (13C:12C) or (18O:16O). Inorganic Geochemical Analyses For inorganic geochemical analysis, splits of powdered samples used for carbon analyses were analyzed for concentrations of 10 major elements (Si, Al, Fe, Mg, Ca, Na, K, Ti, P, and Mn) by wavelength-dispersive X-ray fluorescence spectrometry (XRF; Taggert and others, 1987). The same samples were analyzed for 40 major, minor, and trace elements by induction-coupled, argon-plasma emission spectrometry (ICP; Lichte and others, 1987). REFERENCES: Arthur, M. A., Hagerty, S., Dean, W. E., Claypool, G. E., Daws, T., McManaman, D., Meyers, P. A., and Dunham, K., 1987, A geochemical note: comparison of techniques for obtaining CaCO3, organic carbon, and total nitrogen in limestones and shales, in van Hinte, J. E., Wise, S. W, Jr., and others, Initial Reports of the Deep Sea Drilling Project: U. S. Government Printing Office, Washington, v. 93, p. 1263-1268. Dean, W. E., M. A. Arthur, G. E. Claypool, 1986. Depletion of 13C in Cretaceous marine organic matter: Source, diagenetic, or environmental signal? Marine Geol., 70: 119-157. Engleman, E. E., Jackson, L. L., Norton, D. R., and Fischer, A. G., 1985, Determinations of carbonate carbon in geological materials by coulometric titration: Chemical Geology, v. 53, p. 125-128. Lichte, F. E., Golightly, D. W., and Lamothe, P. J., 1987, Inductively coupled plasma-atomic emission spectrometry, in Baedecker, P. A. (ed.), Methods for Geochemical Analysis: U. S. Geological Survey Bulletin 1770, p. B1-B10. Peters, K. E., 1986, Guidelines for evaluating petroleum source rock using programmed pyrolysis: American Association of Petroleum Geologists Bulletin, v. 70, p. 318-329. Pratt, L. M., and Threlkeld, C. N., 1984. Stratigraphic significance of 13C/12C ratios in mid-Cretaceous rocks of the Western Interior, U.S.A., in Stott, D. F., and Glass, D. J., (eds.), Mesozoic of Middle North America, Canadian Society of Petroleum Geology, Memoir 9, p. 305-312. Taggert, J. E., Jr., Lindsay ,L R., Scott, B. A., Vivit, D. V., Bartel, A. J., and Stewart, K. C., 1987, Analysis of geologic materials by wavelength-dispersive X-ray fluorescence spectrometry, in Baedecker, P. A. (ed.), Methods for Geochemical Analysis: U. S. Geological Survey Bulletin 1770, p. E1-E19. Tissot, B. P., and Welte, D. H., 1984, Petroleum Formation and Occurrence, 2nd ed.:, New York, Springer-Verlag, 538 p.