New carbon determinations of 20 rocks confirm that both the breccias of the Black Member of the Onaping Formation and the mudstones of the Onwatin Formation of the Whitewater Group in the 1.8-Ga Sudbury impact structure contain appreciable amounts of carbonaceous matter. The origin of the carbon has been a long-standing enigma. Carbon-bearing target rocks, either carbonaceous mudstones or carbonate target rocks are not its source, and neither is CO 2 from the atmosphere of the impact area, or carbon from the impacting projectile itself. Fumarolic activity is also ruled out. New isotopic δ13C results of carbon from 17 Black Member breccias, and 1 each from a Gray Member breccia and an Onwatin Formation range from -35.22 to -26.26%. Together with Raman spectra of carbon from 11 of these samples, they lead to the conclusion that the Black Member carbon is biogenic. This unit cannot have formed as an "instant clastic sediment," but must have accumulated over several millions of years while prolific prokaryotic activity (archaea and bacteria) occurred. Isotopic δ13C and Raman results of carbon from an anthraxolite confirm that this carbon is derived from the Onwatin Formation. A search for fullerenes C60 and C70 by high-performance liquid chromatography (HPLC) in 17 rocks from the Black Member of the Onaping Formation, 1 rock from the Gray Member of the Onaping Formation, and by mass spectrometry of 3 breccias from the Black Member failed to find any fullerenes. Elemental sulfur in the breccias from the Gray and Black Members of the Onaping Formation and in one sample of the Onwatin Formation is due to weathering of pyrrhotite. The isotopic composition of the elemental sulfur as well as that of the sulfide-S contains a mass-independent fractionation component whose origin is not understood.
|Number of pages
|Special Paper of the Geological Society of America
|Published - 1999
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