Ooid Aragonite Cortex Dissolution - Sparse Calcite Cement - Pleistocene (O/15/Ple/Bah)
5x
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10x
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10x
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2.5x
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2.5x
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5x
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10x wave plate
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5x wave plate
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Outstanding feature |
Meniscus cements & concentric aragonite ooids. Some slight cortex dissolution. Abundant superficial ooids. |
Folk Classification |
Oosparite |
Dunham Classification |
Oograinstone |
Common Grains |
Ooids, pelloids, and bioclasts |
Sorting |
Well sorted |
Rounding |
Well rounded |
Micritization & envelopes |
Micritized nucleae, often earlier ooids, pelloidal grains and bioclasts |
Cement & diagenetic fabric |
Meniscus low magnesian calcite rims & locally equant spar fill. |
Porosity |
30% Interparticle & intraparticle porosity |
Depositional Setting |
Subaerial exposure of dune surface |
Diagenetic history |
Cemented by marine rim with vadose freshwater calcite filling over this, while aragonitecortex of ooids dissolve |
The intial cement appears to be freshwater isopachus rims and meniscus cements related to evaporation of freshwater charged with dissolved aragonite within these aeolian sediments. These grains formed on an exposed carbonate shelf and were transported by waves and wind to their current postion in a now uplifted Pleistocene dune. The aragonite ooids have concentric layering of cortex about bioclasts and micritized pelloid nulceae (some after ooids). Some of the cortex contains evidence of dissolution. Darkened spots within ooid layers are cyanobacteria colonies that cause local micritization.
Thursday, November 11, 2021