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A series of 22 sediment samples of Cretaceous and Cenozoic age from DSDP Holes 603, 603B, and 603C at the continental rise off the northeastern American coast near Cape Hatteras was investigated by organic geochemical methods including organic carbon determination, Rock-Eval pyrolysis, gas chromatography and combined gas chromatography/ mass spectrometry of extractable hydrocarbons, and kerogen microscopy. An abundance of terrigenous organic matter, including larger coal particles (almost exclusively consisting of huminite/vitrinite macerals), is the dominant characteristic of the organofacies types at Site 603. Marine organic matter, mostly structurally degraded and in the form of fecal pellets, was preserved in the Valanginian laminated marls and in Cenomanian black claystone turbidites. Long-chain nalkanes reflect the terrigenous imprint in the nonaromatic hydrocarbon fractions, whereas a second maximum at lower carbon numbers in most cases is caused by the presence of more mature recycled organic matter. Abundant isoprenoid and steroid hydrocarbons were found in sediments containing mainly marine organic matter, whereas hopanoids reflect the ubiquitous microbial activity. The organic matter in the Site 603 sediments, in so far as it is not recycled, is thermally immature. INTRODUCTION Drilling at DSDP Site 603 (Fig. 1) was intended to penetrate a nearly complete section dating from shortly after the initial opening of the Atlantic Ocean (Jurassic) to the present. Although this target was not reached, a fairly comprehensive Cretaceous section, about 600 m thick and underlying about 1000 m of Tertiary and Holocene sediments, was recovered (Fig. 2). A number of organic-matter-rich intervals in the Cretaceous have provided valuable material for further investigation of conditions for the accumulation of organic matter in the Mesozoic North Atlantic Ocean. DSDP Site 603 is located on the eastern North American continental margin about 400 km east of Cape Hatteras. Drilling was performed in the first valley of the lower continental rise hills in 4634 m water depth. Sediments from Holes 603, 603B, and 603C in this study are considered to represent a continuous record. This particularly refers to lithologic Unit I (0-960 m, early Pleistocene to middle Miocene) which was recovered in all three holes, whereas the other four lithologic units were only penetrated in Hole 603B. Previous deep-sea drilling on the Hatteras continental rise was performed during DSDP Legs 11 and 44 at Sites 105, 106 (Hollister, Ewing, et al., 1972), and 388 (Benson, Sheridan, et al., 1978). At Site 105 (Fig. 1), drilling penetrated more than 600 m of Holocene to Jurassic sediments into basaltic basement. Organic-matter-rich intervals were recovered in the Aptian to Cenomanian in particular, and organic geochemical results 1 Van Hinte, J. E., Wise, S. W., Jr., et al., Init. Repts. DSDP, 93: Washington (U.S. Govt. Printing Office). 2 Address: Institut für Erdöl and Organische Geochemie, Kernforschungsanlage Jülich GmbH, D-5170 Jülich, Federal Republic of Germany. obtained for them by other investigators will be used for comparison with the Site 603 sediments. Drilling at Sites 106 and 388 (Fig. 1) ended in Tertiary sediments of middle Miocene and Eocene age, respectively. Organic geochemical data for these sites are scarce. In this study, the amount, type, and composition of organic matter in the Site 603 sediments are described, and the results are discussed in terms of their origin, depositional environment, and diagenetic alteration. Comparison with the organic matter content of stratigraphically equivalent sediments will extend the present understanding of organic matter sedimentation and preservation on the eastern North American continental margin. EXPERIMENTAL METHODS Sediments were received frozen and were either large-size (100 cm or more) subsamples of the Organic Geochemistry Panel (OGP) core sections or small-size (a few cm or less) samples of hand-picked material collected on board from apparently organic-matter-rich layers. The frozen samples were dried at 50°C for 12 hr. and ground. Total organic carbon (TOC) was determined with a Leco IR-112 carbon analyzer after treatment of the sediments with 25% HC1 to remove the carbonate carbon. Extraction was performed using a modified flowblending technique (Radke et al., 1978) with dichloromethane as the extraction solvent, the total extracts were separated into nonaromatic (saturated + olefinic) hydrocarbons, aromatic hydrocarbons, and heterocomponents by automated medium-pressure liquid chromatography (Radke et al., 1980). A Siemens L35O gas chromatograph equipped with a 23 m × 0.3 mm internal diameter (ID) glass capillary column coated with SE54 was used for gas chromatographic (GC) analysis of the nonaromatic hydrocarbon fractions. Helium was used as carrier gas. The temperature program was as follows: 80°C for 2 min.; 80 to 254°C at a rate of 3°C/min.; isothermal at 254°C for 25 min. Gas chromatography/mass spectrometry (GC/MS) was carried out on a VG 7070E mass spectrometer linked directly to a Carlo Erba Model 4160 gas chromatograph. Samples were injected in the splitless mode onto a 25 m × 0.3 mm ID fused silica column with a chemically bound Durabond 5 stationary phase; the column was introduced di-

Geochemistry and Petrography of Organic Matter from Deep Sea Drilling Project Site 603, Lower Continental Rise off Cape Hatteras