Glauconite Grains & Quartz - Trilobite & Echinoid fragments - Cambrian (B/151/Cam/Tex)

2.5 cross nicols
5x cross nicol
Outstanding feature Glauconitic bioclastic debris
Folk Classification Trilobite/echinoderm biosparite with glauconite grains
Dunham Classification Trilobite/echinoderm bioclastic grainstone with glauconite grains
Common Grains None
Sorting None
Rounding Well sorted fine grain carbonate sand with quartz silt
Micritization & envelopes None obvious
Cement & diagenetic fabric Cemented by spar
Porosity None visible
Depositional Setting Adjacent to high energy shoal
Diagenetic history Compacted and cemented grain

Well washed Trilobite/echinoderm biosparite with pelleted glauconite grains and quart from Central Texas. Typical of Cambrian platform (epieric) seas. with grains of glauconite, with trilobite and echinoid fragments. There is a mix of well sorted grains that are both rounded and angular. The matrix is a combination of poorly washed sparite and locally micrite, so portions of this sediment could be considered to be a packstone. Local crinoidial fragments have developed overgrowths.
Glauconite grains are the green pellets, possibly faecal, composed of this iron-rich clay. Glauconite is an indicator of shallow-water, nearshore, marine sedimentation associated with maximum flooding surfaces.

Thursday, November 11, 2021
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