The presence of hydrocarbon seep is an indirect evidence of the presence of mature source rocks within a geological system. Chemical changes in the environment of surface rocks provided by hydrocarbon seeps form mineralogical alterations. This work focuses on the use of laboratory experiments to recognize chemical and spectral characteristics of hydrocarbon seeps-induced alterations in evaporite and marly limestone formations. To determine the influence of lithology and types of seeps on alterations, rock samples were collected from altered and unaltered Gachsaran (evaporite) and the Mishan (marly limestone) formations in the Dezful embayment, SW Iran (Fig. 1), and subsequently analyzed. Reflectance spectra of samples were measured by ASD spectrometer and chemical characteristics compositions of the samples were acquired by portable XRF analyzer. The concentrations of gypsum and calcite were quantified by the wet chemical analysis. In addition, altered and unaltered samples were analyzed for carbon, oxygen, and sulfur isotope compositions. Comparisons of chemical data and reflectance spectroscopy of altered evaporites and altered marly limestones show that the minerals within alterations facies have distinctive spectral signatures which can be used to map spatial heterogeneities in mineralogy of cap rock (Gachsaran) and its overlaid formation (Mishan) in the Zagros oil fields. The spatial distribution of alteration minerals and the relationships between these types of alteration are important for interpreting hydrocarbon migration pathways.


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