Dolomites in Organic-Rich Muds of the Peru Forearc Basins: Analogue to the Monterey Formation

Abstract

Dolomite from the Peru continental margin is intimately associated with Quaternary organic-rich mudstone deposits and their Neogene counterparts. The present-day upwelling circulation associated with the Peru Current and the regional pattern of organic matter and skeletal calcium carbonate in Holooene sediments suggest that basin tectonics exert a specific control on the distribution of sedimentary facies. This relationship persists throughout diagenetic alteration, after burial and dolomitization of sediments. Similar processes and conditions are believed to have played an analogous role in the development of the Monterey Formation. Organic matter decomposes by bacterial fermentation in the rapidly accumulating carbonate-free mud facies of the subsiding Lima and Progresso basins, whereas in the calcareous mud of the vertically stable Trujillo Basin organic matter undergoes decomposition largely by microbial sulfate reduction. These differences in facies composition and organic matter degradation are recorded in the diagenetic dolomites.