Advances in Organic Geochemistry 1985 Org. Geochem. Vol. 10, pp. 35%375, 1986 Printed in Great Britain. All rights reserved 0146-6380/86 $3.00 + 0.00 Copyright © 1986 PergamonJournals Ltd Oil Generation in the Michigan Basin: A biological marker and carbon isotope approach J()RGEN RULLK6TTER', PHILIP A. MEYERS 2, RAINER G. SCHAEFER' and KEITH W. DUNHAM 2 ~Institute of Petroleum and Organic Geochemistry (ICH-5), KFA-Jiilich GmbH, P.O. Box 1913, D-5170 Jiilich l, F.R.G. 2Department of Atmospheric and Oceanic Science, University of Michigan, Ann Arbor, U.S.A. (Received 17 October 1985; accepted 12 March 1986) Abstract--Palaeozoic strata in the Michigan Basin produce crude oils which, despite their rather small volume and economic value, are interesting because of the considerable age of the basin and because of the opportunity to study generation and migration of oils within a relatively simple but ancient geological setting. Based on n-alkane profiles, biological marker distributions and carbon isotope ratios, the oils belong to three main families of different genetic origin and a few less important mixed types. Silurian oils from Salina and Niagara Limestones have broad n-alkane distributions and abundant isoprenoid hydro- carbons. A strong phytane-over-pristane predominance and the lack of diasteranes indicate a carbonate source for these oils. Chemical maturity parameters show that they are more mature than the oils from the other main families from which they are also clearly distinguished by carbon isotope ratios of hydrocarbon fractions and single n-alkanes. Oils found in the calcareous Ordovician Trenton formation contain n-alkane, cyclohexylalkane and alkyl phenanthrene distributions typical of immature oils. Many oils from the Devonian Dundee reservoirs are very similar in overall composition to the Trenton oils. Devonian Traverse oils are considered to be mainly from a Devonian source with some contribution of Ordovician-type oil and are of intermediate maturity. Based on calculations using kinetic parameters of biological marker reactions, considerably deeper subsidence of the Devonian source rock in the past is implied. Key words: carbon isotopes, chemical maturity parameters, cyclohexylalkanes, methylphenanthrenes, Michigan Basin, n-alkanes, oil/oil correlation, Palaeozoic crude oils, sterane isomerization, steroid aromatization INTRODUCTION Petroleum is produced from Palaeozoic strata in the Michigan Basin. Some of the important reservoir formations include the Stray Sandstone (Mississip- pian), the Berea Sandstone, Traverse Limestone, and Dundee Limestone (Devonian), the Salina and Niagara Limestone (Silurian), and the Trenton and Black River Limestones (Ordovician). Michigan Basin oils are interesting despite their rather small volume and economic value, because of the consid- erable age of the basin and because of the oppor- tunity to study generation and migration of oils within a relatively simple but ancient geological setting. The Michigan Basin The geology of the Michigan Basin was described in detail by Dorr and Eschman (1970) and has been recently summarized by Nunn and Sleep (1984), and Nunn et al. (1984). The basin is intracratonic and consists of several kilometers of gently dipping, shallow water sediments. Its shape is nearly circular (Fig. 1). Although some Cambrian and Mesozoic strata exist, nearly all of the sediments in the Michi- Michigan Basin 1 N S Devonian Silurian Ordovician • Well Sites Fig. 1. North-South cross section of the Michigan Basin and location map showing principal production zones from reservoirs of different ages (from Vogler et al., 1981). 359