MINERALOGY OF VERY FINE-GRAINED GLACIOMARINE SEDIMENTS, COASTAL MAINE

Very fine-grained glaciomarine sediments occur in surface exposures and in the subsurface throughout coastal and interior Maine. These sediments, generally referred to as the Presumpscot Formation, are of variable thickness and are commonly interbedded with sands. Thicker sequences of clay and silt sized sediments are frequently varve-like. Sediments collected from eroding coastal bluffs, gravel pits and vibracores from Mount Desert Island to Wells, Maine are characteristically greater than 90% silt and clay. Clay - silt ratios vary both within and between localities. These glacial-marine deposits all conform to the definition of rock flour. Bulk mineralogy of both silt and clay-sized fractions consist of quartz, albite, microcline, orthoclase, white micas (muscovite, illite and phengite(?)) and chlorite, +/- biotite(?). Kaolinite is locally present in small amounts. Mineral percentages vary with sample location. Mineralogical variation due to grain size tends to include an increased amount of micas in silt-sized portions. Clay-sized portions tend to exhibit increased amounts of quartz and feldspars relative to the micas. Mineralogy also varies between geographic locations. However, this variation does not display an apparent or consistent trend.