Microtextures alveolar

Calcite cements associated with these concretions are dominantly micritic and exhibit circumgranular cracking, alveolar, micrite-spar and meniscus microtextures. Radial spar microtexture is present locally, characterized by bladed radial spar formed around a micritic nucleus (Fig. 1OD). 

Fig. 10. (A) Platy concretion from the middle of the Unnamed Member. Notice the millimetre-sized tube (T) and groove (G) structures. Divisions on the scale are in centimetres. (B) Photomicrograph of alveolar textures (A) from a platy concretion in the Unnamed Member. (C) Rod-shaped concretions from an aeolian sandstone in the Chamisa Mesa Member. Note that several of the rods branch and thin downwards. Divisions on the scale are in centimetres. (D) Radial spar (microcodium) microtexture.

Some outcrops have an irregular wavy laminar (3-10 cm thickness) morphology. Individual laminae vary from 1 to 2 mm in thickness. Units usually have sharp upper and lower contacts. These forms exhibit abundant alveolar and fenestral microtextures (Fig. 1 ID). 

Irregular, unoriented and fenestral millimetresized calcite-filled fractures found in some units are interpreted as brecciation structures. Structures that resemble small folds are probably teepee structures because they are associated with rhizocretions and alveolar microtextures. There is not enough clay in these units to cause expansion, although expansive calcite growth cannot be ruled out. The laminar cemented units in the Zia Formation have abun-... 

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