Abstract

In the present note reproducible experiments creating marine (Bahamian) ooids are reported. Laboratory tests involve the crystallization from calcium bicarbonate solutions at a constant temperature of 25 degrees to 30 degrees C while being stirred intermittently. A combination of needle breeding and collision breeding gives rise to the formation of haphazard needle aggregates (with a "snowball" arrangement). Continuous stirring initiated relatively irregular needle aggregates not resembling marine ooids. Intermittent stirring, by introduction of short periods of grinding of the aggregates during bed transport, causes them to become well rounded and polished. Electron microscopy revealed that in the "snowball" aggregates, the fine aragonite needles are held together by normal bonding forces of the CaCO 3 lattice without any cementing agents. Aragonite aggregates closely resembling "grapestones" were formed, along with carbonate aggregates resembling "recrystallized faecal pellets" and the ooid-core aggregates, in laboratory experiments involving crystallization from evaporating bicarbonate solutions and subjected to intermittent stirring. The microfabric developed is identical with that of the cores of Bahamian (marine) ooids, and is distinct from the common spherulitic textures.

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