Ooid Aragonite Cortex Dissolution - Sparse Calcite Cement - Pleistocene (O/15/Ple/Bah)

10x wave plate
5x wave plate
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
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