condensed section

glossifungites

maximum flooding surface

transgressive surface

The iron-rich minerals that form glauconites (K,Na)(Fe,Al,Mg)2(Si,Al)4O10(OH)2 are found in sandstones, limestones, and siltstones. These sediments are associated with the widespread condensed sections that are related to maximum flooding surfaces. These often merge landward with transgressive surfaces. glauconites are associated with slow rates of sediment accumulation and occur in conjunction with organic matter, and fecal pellets that fill glossifungites burrows within an oxidizing setting. Examples of glauconite rich sediments include have ages that range from the Precambrian to the present and they are associated with the maximum flooding surfaces of parasequence boundaries that occur just above transgressive surfaces throughout the geologic column.. These glauconite rich sediments are often called "greensands" and are particularly common in the Cretaceous sediments of the United Kingdom and the United States. The minerals of glauconite form in situ on the present day continental shelf.

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The above image is a section photomicrograph of trilobite/echinoderm biosparite with glauconite grains typical of Cambrian platform (epieric) seas that once covered Central Texas. The glauconite grains are the green pellets, possibly faecal, and composed of this iron-rich clay. As explained above glauconite is an indicator of shallow-water, nearshore, marine sedimentation.