Abstract: The sedimentary subbasins of Oulad Abdoun and Timahdit (Morocco) were part of a single marine gulf that extended across Morocco for more than 300 km (west to east) from Late Cretaceous through the Eocene. The differential structural development of this basin resulted in the presence of a stable shelf in Oulad Abdoun and a subsident orogenic zone in Timahdit. This structural asymmetry explains the sedimentary asymmetry of the Maastrichtian sequence that consists of a thin, 5-m thick, phosphorite sequence interbedded with dolomitic limestone, marl, and shale near Oulad Abdoun, and an oil shale, 200-m thick, in Timahdit. Widespread reducing conditions that prevailed in the basin resulted in preservation of large amounts of organic matter. Quantitative and qualitative analysis shows an identical phytoplanktonic origin for all of the organic matter in both of the two subbasins, and the organic matter still remains in an immature state. The subsequent history of this organic matter, however, reflects the specific environments of the two related but disparate depositional settings. In each part of the basin, the organic material associated with marls, limestones, and shales contains kerogen, whereas in the phosphate-rich strata the organic matter is in two forms: humic compounds inside the phosphatic grains and kerogen in the matrix. Humic compounds from different lithologies have a similar composition, whereas the kerogen in samples from the phosphate-rich strata shows the effect of oxidation (during synsesimentary reworking), increasing with the amounts of P 2 O 5 of the total rock. These changes in the phosphate-rich strata have allowed the crystallization of apatite and the genesis and preservation of humic compounds trapped inside these phosphatic grains. In the oil shale, large amounts of associated clay resulted in a rapid and total unsolubilization of the organic matter and its evolution toward kerogen. The study of the organic matter, which is associated with a wide variety of facies from both parts of the basin, shows the extreme sensitivity of organic compounds to processes that have affected them from their deposition through all phases of diagenesis. The fate of the organic matter during early diagenesis is related to the presence or absence of clays: the presence of clays led to the formation of black shales and the absence of clays led to the formation of phosphorites.

Abstract A major goal in the application of organic geochemistry to petroleum exploration is to provide the best possible input data for mathematical models that integrate the geological and geochemical information to predict the nature, amount, and time required for oil and gas generation (Tissot and Welte, 1984). During the past decade, pyrolysis has become a common analytical method for the analysis of Kerens and whole rocks because it provides the analyst with information about a number of parameters that can give a measure of the quality, quantity, and petroleum generative potential of prospective source rocks (Peters, 1986; Agnostic and Muller, 1987; Tarawa EC al., 1988). The various pyrolysis techniques that are commonly used in geochemical laboratories are summarized Rock-Eval pyrolysis of whole rock or kerogens provides information on the quantity, quality, type, and thermal maturity of associated organic matter in these materials (Peters, 1986). Pyrolysis methods combined with a high-performance separation technique (capillary gas chromatography) take advantage of the ability of the separation technique to analyze, and identify at the molecular level, the composition of the pyrolysate. The pyrolysate composition provides information that can be used to evaluate, with a high degree of accuracy, the source of the organic material and the maturity level of the samples being analyzed (Larter, 1984). Hydrous pyrolysis of whole rocks is used in the laboratory to simulate the evolution of petroleum-like compounds from the heating of the geological samples, providing a tool to perform oil-source rock correlation studies (Winters et al., 1983; Lewan, 1985).

Abstract A total of 9 oils and 15 rock samples from the National Petroleum Reserve, Alaska (NPRA), have been characterized and analyzed using a variety of organic geochemical techniques by a number of laboratories involved in a multidisciplinary study of these samples. Results presented in this paper will concentrate on two aspects of the study. The first is the determination of biological marker distributions (i.e., steranes and triterpanes) in both the oils and the rock samples using the technique of gas chromatography-mass spectrometry; the second is characterization of the organic matter in rock samples using microscale pyrolysis techniques combined with gas chromatography and gas chromatography-mass spectrometry. Sterane and triterpane fingerprints of the 9 oils permit them to be divided into two main groups. The distributions of steranes and triterpanes in the core samples show that some of these samples can be eliminated as source rocks on a maturity basis. Other cores have distributions of steranes and triterpanes that are sufficiently different from the oils to eliminate them as possible sources for the oils examined in this study. Detailed characterization of organic-rich rocks, or source rocks, by pyrolysis-gas chromatography and pyrolysis-gas chromatography-mass spectrometry allowed distinctions to be made between the rocks on the basis of their source material and, in certain cases, their relative maturities.