Progress Report on Two Unusual Alaskan Sediments--Recent Beach Carbonate From Three Entrance Bay, and Polished Grains From Easter Egg Hill: ABSTRACT

Abstract

Modern southeastern Alaska cold-water skeletal carbonates are composed chiefly of whole and fragmented mollusks, barnacles, echinoderms, and foraminifers mixed with basalt pebbles and sand from the island bedrock. Average CaCO3 content is about 80 percent by weight and increases from 0 percent at -4^phgr (16.0 mm) to 88 percent at 4^phgr (0.0625 mm). Texturally this beach sediment is polymodal, with two dominant modes: a gravel mode about -4^phgr and a sand mode about 2^phgr (0.25 mm). Traces of carbonate mud are present. Fractionating this sediment into carbonate and silicate mineral phases shows that these gravel and sand modes are present in each mineral phase. This suggests that selective size sorting in the beach environment, rather than fragmentation into certain size classes, may be the chief process involved in the formation of modal size classes for this sediment. Highly polished particles occur in (?)Pleistocene pebbly sandy loess on a topographic ridge in interior Alaska. Most polished particles have near-perfect roundness and occur in all sizes between -5.1^phgr (34 mm) and 4^phgr (0.0625 mm). Polished grain surfaces essentially are smooth, with some pits and very few facets. Rounded and polished grains are mixed with totally angular and dull grains. Polished grains seem to have bimodal size distribution, being abundant about -3.6^phgr (12 mm) and 0.5^phgr (0.25 mm). Modes from size analysis of loess do not correspond to modes for abundance of polished grains. Attempts to duplicate polished grains by tumbling unpolished grains from the same locality with wet and dry loess failed. Most polished grains are quartz; some are chert. Origin of the e polished grains is uncertain. The following origins have been rejected: polish by wind-blown silt or ice crystals, solifluction, in situ chemical polish, and inheritance. It is believed that these polished grains are gizzard stones produced by Pleistocene bird(s). Gizzard stones collected from grouse and ptarmigan in late winter are highly polished. Unfortunately, modal classes of gizzard stones from birds now living in interior Alaska do not coincide with modes of polished grains from the loess; average size of grouse gizzard stones is -1.0^phgr (2.00 mm) and of ptarmigan stones is -1.3^phgr (2.5 mm). End_of_Article - Last_Page 532------------