Total Organic Carbon content and Rock Eval pyrolysis ...

Total Organic Carbon content and Rock Eval pyrolysis on outcrop samples across the Cretaceous/Tertiary boundary, Seymour Island, Antarctica ROSEMARY A. ASKIN Department of Earth Sciences University of California Riverside, California 92521

STEPHEN R. JACOBSON Chevron Oil Field Research Company La Habra, California 90633-0446

Forty outcrop samples from Seymour Island, northeastern Antarctic Peninsula, were run for Total Organic Carbon (TOC) content and Rock Eval pyrolysis. These samples span 23.5 meters of section (figure 1) that includes the Cretaceous/Tertiary boundary as defined by dinoflagellate cysts (section Bi,

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between samples 109 and 110, Askin 1988b). The aim was to evaluate preserved organic matter for quantity, quality, thermal maturity, and environment of deposition, to recognize changes in environmental conditions, if any, across the Cretaceous/Tertiary boundary. These samples contain consistently low amounts of total organic carbon with similar poor quality (virtually no hydrocarbon generative potential) and are thermally immature (table, figure 1). No significant variations in analytic data were found across the Cretaceous/Tertiary boundary. Outcrop samples were collected by F.C. Barbis and J.R. Robinson in December 1983, mostly at 0.5-meter intervals, from about 10-30 centimeters beneath the surface. Outcrop samples are subject to weathering which may have affected the TOC and pyrolysis results. The sediments are unconsolidated, mainly sandy silts and silty sands, with some glauconitic and more clayey beds (figure 1). All samples are rich in fossil pal y nomorphs (Askin 1988a, 1988b). Samples were analyzed by Exlog/ Brown & Ruth Laboratories, Inc., Denver, Colorado. TOC. TOG content of a sample includes the total sedimentary organic matter and is affected by the clastic sedimentation rate and the extent of degradation. Degradation includes oxidation in the depositional basin, diagenesis, and thermal alteration of organic matter due to burial depth or igneous activity, as well as subsequent weathering at the outcrop.

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Figure 1. Location of Seymour Island, lithology in Cretaceous/Tertiary (KIT) boundary section Bi, and TOC trend for 40 samples. (m denotes meter. T.O.C. denotes total organic carbon.)

1988 REVIEW

Results of Total Organic Carbon (TOC) analysis and Rock Eval pyrolysis Sample TOCa number Bi -126 B1-125 Bi -124 Bi -123 Bi -122 B1-121 Bi -120 B1-119 B1-118 B1-117 B1-116 131-115 B1-114 B1-113 B1-112 Bi-ill Bi-ilO Bi -109 B1-108 B1-106 Bi -105 Bi -104 Bi -103 Bi -102 Bi-101 Bi -100 B 1-99 B1-98 B1-97 B1-96 B 1-95 B1-94 B 1-93 B 1-92 B1-91 B1-89 B1-88 B1-87 B1-87B B1-86

0.44 0.33 0.34 0.28 0.28 0.28 0.33 0.34 0.15 0.28 0.37 0.27 0.43 0.33 0.43 0.37 0.45 0.27 0.54 0.40 0.40 0.37 0.35 0.48 0.39 0.39 0.35 0.46 0.39 0.46 0.47 0.50 0.50 0.50 0.44 0.50 0.45 0.41 0.60 0.34

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