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Part II: Depositional and Environments |
Department of Geology, Imkperial College, Prince Consort Road, London, S.W.7, U.K.
Study of carbonate ooids from areas of present day ooid production in the Arabian Gulf and the Bahama Banks has shown that they contain significant amounts of light hydrocarbon gases. It is concluded that these gases are generated within the ooids themselves by the bacterial degradation of the contained algal proto-kerogen, in an anaerobic environment. Continuation of the degradation of the contained organic matter by artificial maturation, using enhanced temperature and pressure, in the presence of natural sea-water, has shown that an evolutionary series of kerogen and soluble hydrocarbons exist, which can be related to material isolated from British Jurassic oolitic limestones.
Two principal conclusions arise from these studies. Firstly, that carbonate ooids might provide a model for evaluating the potential of carbonates generally, as source rocks. Secondly, because the reactants and products are frequently isolated by the emplacement of the first phase of calcite cement early during diagenesis, thus trapping and possibly ‘fossilizing’ them, detailed studies of suitable oolitic limestone might lead to better understanding of organic reactions at different stages in diagenesis.
