Organic Geochemistry and Correlation of Paleozoic Source Rocks and Trenton Crude Oils, Indiana

John Guthrie

Shale samples from four cores of the New Albany and Antrim Shales (Devonian) and from six cores of the Maquoketa Group (Ordovician), representing a broad geographic area of Indiana, have been analyzed for total organic carbon, total sulfur, pyrolysis yield (Rock-Eval), bitumen content, and illite crystallinity data. These data indicate that the New Albany, Antrim, and Maquoketa shales contain a sufficient quantity and quality of organic matter to be good petroleum source rocks. Bitumen ratios, Rock-Eval yields, gas chromatography of saturated hydrocarbons, and illite crystallinity data show that the Maquoketa shales have reached a higher level of thermal maturity than the New Albany and Antrim shales. The level of thermal maturity of the Maquoketa shales suggests a maximu burial depth considerably greater than the present depth.

A geochemical comparison made between the saturated hydrocarbons from possible source rocks and from two crude oils of the Ordovician Trenton Limestone reveals that the Trenton oils resemble more closely the Maquoketa shale extracts than do the New Albany and Antrim shale extracts. In particular, strong odd-carbon predominance at mid-length normal alkanes (C-13, 15, 17, 19) is a conspicuous feature of the Trenton oils and Maquoketa extracts. These preliminary data suggest that the Ordovician Maquoketa shale is the most likely source rock for the Trenton oils. Continuing studies of stable carbon isotopes and molecular biomarkers will further refine the crude oil/source rock correlation. Results of this investigation are directly applicable to future petroleum exploration in lower Paleo oic rocks of Indiana and surrounding areas.

AAPG Search and Discovery Article #91023©1989 AAPG Eastern Section, Sept. 10-13, 1989, Bloomington, Indiana.