About This Item
Share This Item
Marine carbonate cementation was the initial stage in the paragenesis of phylloid algal mounds in the Laborcita Formation (Wolfcampian), Sacramento Mountains, New Mexico, and the cements are almost identical to those in Holocene coral reefs of Belize. These cements include relicts of botryoids and crusts of needle crystals, in part defined by inclusion patterns and luminescent "ghosts" in mosaic calcite. Individual needle crystals are pseudohexagonal in cross section and range from less than 1 to 30 µm wide. These nonluminescent early cements line cavity walls, coat phylloid-algal blades and stromatolites, and are interlayered with marine sediment. Early cements also include bladed, fibrous, and rare radiaxial fibrous calcites, which are microdolomite-rich. They have a proximal nonluminescent zone, a central bright-luminescent zone, and a distal blotchy, moderate-luminescent zone. The bright zone may be time equivalent to bright-luminescent micritic coatings on botryoids and grains. Botryoids are encrusted by isopachous bladed cement, some of which has prismatic overgrowths containing an early inclusion-rich zone. This initial cementation was followed closely by: (1) dissolution of algal blades and mollusks, (2) in-situ brecciation, and (3) cementation by blocky calcite.
Botryoidal and acicular cements are interpreted as originally marine aragonite precipitates, based on morphology, occurrence, susceptibility to diagenesis, and similarity to Holocene reef cements. The same criteria, plus the microdolomite inclusions, indicate that the bladed, fibrous, and radiaxial cements had a marine Mg-calcite precursor. This assemblage followed by prismatic overgrowths, dissolution, and blocky-calcite cementation indicates an evolution from marine to freshwater diagenesis.
This early diagenesis was followed by, in order: (1) cementation by multiple stages of blocky calcite (interrupted by episodic fracturing), (2) local dolomitization, (3) stylolitization, (4) dedolomitization and blocky-calcite cementation, and (5) minor chertification.
End_of_Article - Last_Page 315------------