Microscopic

Aragonite Ooids & Botryoidal Grains - Freshwater Calcite Rims - Pleistocene (0/11/Ple/Bah)

2.5x
5x
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2.5 cross nicols
5x cross nicol
2.5 wave plate
5x wave plate
5x wave plate
5x wave plate
5x wave plate
Outstanding feature Meniscus cements & concentric aragonite ooids with thin coats & micritized nucleae
Folk Classification Oosparite
Dunham Classification Oolitic Grainstone
Common Grains Ooids, & botryoidal grapestones
Sorting Well sorted
Rounding Well rounded
Micritization & envelopes Micritized nucleae, often earlier ooids & botryoidal grains
Cement & diagenetic fabric Meniscus low magnesian calcite rims and equant spar fill
Porosity 30% Interparticle porosity
Depositional Setting Subaerial dunes formed after exposure of an open marine high energy shelf
Diagenetic history Cemented by vadose freshwater calcite leached from the original aragonite grains

The striking meniscus cements are related to evaporation of freshwater charged with dissolved aragonite within these aeolianites. These grains formed on an exposed carbonate shelf and were transported by the wind to their current postion. These aragonite ooids have thin concentric layering of cortex about micritized pelloid nulceae (some after ooids). Botryoidal grains are transported grapestones that form nucleae and are enclosed by aragonite ooid coating. Darkened spots within ooid layers are cyanobacteria colonies that cause local micritization.


Monday, August 27, 2018
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