A shallow lacustrine delta is forming at the northern end of the Great Salt Plains reservoir in Alfalfa County, north-central Oklahoma. Although sediment is supplied solely by the river, organic matter may be derived from the land surface (and transported by the river) or derived

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from the lake itself. The total amount of organic carbon in the surface sediments increases with distance from the river mouth and is accompanied by a decrease in mineral grain size as expected. However, within a single sediment sample, organic carbon content is not a strong function of grain size over the range from 5 to 11^phgr. Visual examination of the separated insoluble organic matter showed that structured, wood-derived organic matter predominates in the coarser fractions (> 62µ) but the finer fractions (< 62µ) contain mainly microorganisms and amorphous material. Pyrolysis experiments gave a ratio of (total response/organic carbon content) that increased from low values in the coarse fractions to higher values in the fine ones--a trend consistent with the visua kerogen observations because high ratios are usually produced by amorphous organic matter. However, infrared spectra of the organic matter from coarse and fine sediments closely resemble that generally observed for the humic substances associated with soils, suggesting that even the finer grained, amorphous organic matter is derived largely from the terrestrial organic matter. X-ray diffraction indicated the presence of quartz, feldspars, calcite, dolomite, mica, kaolinite, illite, and montmorillonite in the sediments. The composition was rather uniform with no major variations due to clay size or areal distribution.

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