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The Albian/Cenomanian strata in Hole 53OA are organically richer than are the post-Cenomanian strata. Organic matter is thermally immature and appears to be of dominantly marine origin with either variable levels of oxidation or variable amounts of terrestrial input. Geochemical data alone cannot establish whether the black shales present in Hole 53OA represent deposition within a stagnant basin or within an expanded oxygen-minimum layer. INTRODUCTION A principal objective of Deep Sea Drilling Project (DSDP) Site 530 was to provide information on the paleo-oceanographic evolution of the Angola Basin so that the origin of the middle to Late Cretaceous black shales previously recovered at Site 364 could be further defined. At Site 530 over 250 organic-rich black shale beds of Albian to Coniacian age are interbedded within a red and green claystone sequence of turbidite origin. These organic-rich horizons are time-equivalent to similar beds at Site 364. The remaining Cretaceous strata are dominated by other debris flow deposits, including clastic limestones, and lack the black shale strata. One of the methods used to decipher the evolution of the basin was to study the sedimentary organic matter. This chapter is one of a series which describes the type and quantity of organic matter within Hole 530A. The type and quantity of organic matter preserved in a given area are controlled by such factors as: biologic productivity, mode and distance of transport, sedimentation rate, and biochemical demand (Demaison and Moore, 1980). Based on both physical and chemical properties four principal types of sedimentary organic matter can be recognized (Tissot et al., 1974): type I (lacustrine origin), typical of oil shales and boghead coals; type II (marine origin), deposited under reducing conditions; type III (continental origin), derived from higher plants; and type IV, recycled or residual organic matter (or R.O.M.). Tissot et al. (1979, 1980) have noted that organic matter of types II, III, and IV have been recognized in Cretaceous strata of the Atlantic basins. Type II is characterized, in immature sediment, by high atomic H/C and moderate atomic O/C ratios and by high total extractable and pyrolytic hydrocarbon yields relative to organic carbon content. This material has good potential for the generation of oil upon thermal maturation. Immature type III organic matter is characterized by low to moderate atomic H/C and moderate to high atomic 1 Hay, W. W., Sibuet, J . -C, et al., Init. Repts. DSDP, 75: Washington (U.S. Govt. Printing Office). O/C ratios and by low total extractable and pyrolytic hydrocarbon yields relative to organic carbon content. This material will typically generate gaseous hydrocarbons with minor amounts of liquids upon thermal maturation. Type IV organic matter, derived from previously sedimented deposits, has typically undergone either severe thermal stress or oxidation. Therefore, this material has very low atomic H/C ratios and may exhibit highly variable O/C ratios. It has very low total extractable and pyrolytic hydrocarbon yields relative to organic carbon content. Type IV organic matter is no longer capable of generating hydrocarbons. In this chapter, we have attempted to characterize the organic matter through use of pyrolysis assay and analysis of both soluble (bitumen) and insoluble (kerogen) components. ANALYTICAL METHODOLOGY Thirteen samples of ~ 50 g each were obtained from the frozen organic geochemistry core collection. Their selection was based on organic carbon data supplied by Dr. B. Simoneit (Chairman, Organic Geochemistry Panel). Their stratigraphic positions are summarized in Figure 1. Each of the samples was oven-dried at 60 °C and ground to ~325 mesh. The organic carbon content (Corg) was determined on each sample using a LECO combustion system after decarbonating. Those samples with organic carbon contents 0.5 wt.% were subjected to pyrolysis assay using a Rock-Eval system as described by Espitalié et al. (1977). The kerogen in each of these samples was isolated for elemental analysis (C, H, O, and N). In addition, a portion of each of these samples was extracted using an azeotropic mixture of methanol, acetone, and chloroform, deasphaltened with pentane, and fractionated using liquid chromatography. ANALYTICAL RESULTS Organic Carbon The organic carbon contents of the 13 samples examined ranged from 0.01 wt.% to 2.27 wt.% (Table 1). The organically richest samples were from Albian and Cenomanian strata. Samples from these strata, with the exception of Section 530A-99-5, contain above-average quantities of organic carbon (>0.3 wt.% Corg) relative to the DSDP data base (Mclver, 1975). The post-Cenomanian samples and Section 530A-99-5 contain belowaverage quantities of organic carbon relative to the same data base.

Organic Geochemical Character of Selected Cores, Deep Sea Drilling Project Hole 530A