Hydrocarbons of Biological Origin in Sediments about Two Billion Years Old.

Normal paraffins in the C(16) to C(32) range and the saturated isoprenoid hydrocarbons, pristane and phytane, have been found in chert from the Gunflint iron formation (1.9 x 10(9) years old) of the north shore of Lake Superior. The distribution of n-alkanes shows two maxima, one at about C(18) to C(19) and the other at about C(22) with a minimum occurring at C(20) to C(21). No predominance of odd- to even-carbon-number alkanes is observed within the C(16) to C(32) range. The results agree with micropaleontological observations made on the Gunflint chert and provide a chemical characterization of Precambrian life existing about two eons ago.