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A New Paradigm for the Formation of Carbonates: Fertilization by Atmospheric Dust


The enigma of the Bahamas is that this highly productive carbonate system has existed for at least 100 million years, building a vast edifice of biogenic and non-biogenic carbonates, 1000s of meters thick, in an essentially nutrient poor environment. Based on measurements of the concentration of insoluble material, the Fe and Al in the carbonate fraction, and the d15N of the sedimentary organic matter, we propose a paradigm shift to explain the formation of the Bahamas and other carbonate platforms. We believe that the Great Bahama Bank is currently and may in the past have been fertilized by atmospheric dust, promoting the fixation of atmospheric N2 by cyanobacteria. These cyanobacteria not only have provided a source of nitrogen to the remainder of the marine communities, imparting a d15N signal characteristic of the atmosphere, but also have been responsible, through the drawdown of CO2, for the initiation of the precipitation of carbonate in the shallow waters leading to the production of large quantities of sediments. This phenomenon might be responsible for the formation of vast amounts of carbonates in the oceans, not only within recent times, but throughout geologic al history, particularly in the early history of the Earth prior to the existence of calcium carbonate secreting organisms.