MENDENHALL GLACIER LAKE SAND AND GRAVEL APPEARS TO BE ORGANIC MATERIAL REPLACED AND CEMENTED BY SILICATES AND MAGNETITE.

Sand and gravel on the northwest shore of Mendenhall Lake near Juneau, Alaska are presumed to be glacial moraine, single particles of silt, sand and gravel fractured and ground from crystalline tonalite bedrock, and deposited before 1940 as the Mendenhall Glacier retreated and the study site was exposed. However, micro-photos show, sand and gravel at the Mendenhall Lake study site are not a sediment of individual particles but are more likely to be mineralized peat and wood, an interconnected, “petrified,” organic deposit. Photos and radio-carbon dating indicate opal, silicate minerals and magnetite are currently being deposited in fungus and wood, on rocks and in moss and roots along the beach. Organic stems and fibers inside what is supposed to be igneous tonalite reveal a complete continuum from fungus and organic materials to silicates and magnetite. The speckled appearance of the sand is observed to be due to deposition of dark minerals, often magnetite, in pores and in the centers of tubular biological structures that have been replaced by milky colored silicates. Photo processing of micro-photos reveals pinpoints and streaks of “rainbow” colored light on the surfaces of sand, gravel, rocks and organic material, apparently places where pores, fungus, and other organic structures filled with opal are exposed.