As is discussed in Section 3.1.1, great care must be exercised to avoid contamination of extractable hydrocarbon samples by extraneous bitumens, particularly if the TOC (total organic carbon) content is low or if the amount of sample is small. In this study, sediment cores and outcrop samples were pre-rinsed with CH2C12 and dried to remove external contaminants. Where sample size permitted, external surfaces were removed by cutting with a diamond saw. Samples were then hammered to chips which were subsequently crushed to less than 200 mesh in a ring crusher. Rock powders were stored in clean glass containers. Lids were lined with pre-baked aluminium foil. All items used to handle the samples were scrupulously washed with hot water, and then distilled solvent, between each use.

TOC determination and Rock–Eval pyrolysis analysis were found to be particularly informative screening techniques. Samples with less than 0.2% TOC (i.e., <2mgC/g) were generally considered unsuitable for comprehensive hydrocarbon analysis because of the problems of contamination, although elemental and carbon isotopic analyses of their kerogens were parameters which could be reliably established at this low level of organic carbon. Samples with >0.2% TOC were usually assessed using Rock–Eval pyrolysis and the results interpreted using guidelines discussed by Espitalié et al. 1977. The relative proportions of bitumen (the Rock–Eval S1 peak in kg/tonne) and kerogen (S2 peak in kg/tonne), the pyrolysis temperature Tmax (°C), and the overall appearance of the pyrograms all provided useful information.