Hydrogen isotope values in lacustrine kerogen

Kerogen derived from plankton and sedge/cattail that accumulated in sediment during two distinct phases of Swan Lakeʹs development was extracted from segments of radiocarbon dated cores. Carbon (C), hydrogen (H), and nitrogen (N) amounts, and the δD values of kerogen extracts were determined. Kerogen extracts younger than 3900 YBP contained higher average H/C and N/C atom ratios than older kerogen (5000 to 3900 YBP). The more recent kerogen extracts were derived primarily from plankton in open water sediment and are characterized by significantly higher lipid and protein fractions than those from the sedge/cattail that formed the marsh layer. Plankton-derived kerogen was more depleted in δD, averaging ∼20 per mil (‰) lighter than that from older extracts (∼5000 to 3900 YBP) which, according to pollen analysis, were dominated by sedge/cattail-derived kerogen. In the sediment profiles, differences in the δD values appear more related to kerogen source than to postdepositional hydrogen loss or temperature.