CLAY MINERALOGY OF LAKE-ONTARIO SEDIMENTS

The presence of discrete vermiculite was not been reported in earlier studies that include the clay mineralogy of Lake Ontario sediments. Th is is conspicuous because terrestrial soil material contributing to th e lake sediment contains appreciable amounts of vermiculite. The objec tives of the present study were to re-examine the mineralogical compon ents of the clay-size fraction of bottom sediments from Lake Ontario a nd quantify the amount of mica and vermiculite in the sediment with de pth. The use of chemical analysis, in addition to seven pretreatments prior to X-ray diffraction analysis, was required for positive identif ication and quantification of vermiculite. Discrete vermiculite is pre sent in Lake Ontario sediments to a depth of 5 m, regardless of the or igin of the sediment. The clay-size fraction of Lake Ontario sediment off Wilson, New York contained, in decreasing order of abundance, dioc tahedral mica, chlorite, vermiculite, kaolinite, and quartz. The mica content showed no trend with depth and averaged 39%. Discrete vermicul ite, not previously identified in these sediments, averaged 12% for al l samples examined within the 5 m core. Chlorite, with lesser amounts of kaolinite, and quartz accounted for the remainder (approximate to 5 0%) of the sample, with the kaolinite content estimated at < 10%. With the exception of quartz, non-phyllosilicates were not detected in the XRD analysis of the clay-sized separates.