Microscopic

Radial Calcite Ooids - Spar Filled Micrite Envelopes - Jurassic (O/20/Jur/Eng)

5x
2.5x
5x
5x
5x
2.5 cross nicols
5x cross nicol
5x cross nicol
2.5 wave plate
5x wave plate
5x wave plate
5x wave plate
5x wave plate
Outstanding feature Radial calcite ooids, skeletal grains, spar filled micrite envelopes & equant spar
Folk Classification Oosparite
Dunham Classification Oolitic Grainstone
Common Grains Ooids, & spar filled micrite envelopes
Sorting Good
Rounding Good
Micritization & envelopes Most grains have micrite envelopes
Cement & diagenetic fabric Equant spar
Porosity Dense
Depositional Setting Open marine high energy shoal water
Diagenetic history Cemented by vadose freshwater calcite leached from the original aragonite grains

The equant spar cements are probably freshwater cements dissolved from original aragonite and calcite. The radial calcite ooids accumulated on high energy shoals. Note ooid nulceae of quartz and seletal material. There appear to be a few botryoidal grains enclosed by radial ooid coating. Darkened spots within bioclastic layers are remanents of colonies of cyanobacteria that caused local micritization.


Thursday, November 11, 2021
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