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