DEVELOPMENT OF SMALL NON-MARINE LIMESTONE LENSES ASSOCIATED WITH THE SULLIVAN BUTTES LATITE, YAVAPAI COUNTY, ARIZONA

Tertiary petromict conglomerates and volcaniclastic sediments near Chino Valley, Arizona contain numerous small thin lenses of fine sandstone overlain by non-marine limestone. These resulted from events associated with the eruptions of the Sullivan Buttes Latite (Oligocene-Miocene) disrupting local drainage pattern forming small topographic depressions or swales. Wind winnowing and surface water overland flow transported fine sand to the floor of the swales. Water entrapment in the swales formed small fresh water ponds no more the a few tens of meters across.

The pond bottoms were first colonized by charophytes. Disintegration of these produced small amounts of calcium carbonate, partially filling the interparticle pore spaces. Pond bottoms were also burrowed by presumably a water-loving insect. These burrows formed traps for charophyte fragments and geochemical pathways between the sediment and water column. A reed producing plant like modern cattails later replaced the charophytes. Within the reed beds flourished an abundant and diverse diatom flora plus ostracods and gastropods. Rising alkalinity of the pond water gave rise to cyanobacteria dominating the pond and reduction of the diatom flora to apparently a single species. Cyanobacteria encrusted the reeds and gastropod shells and coated the pond floor resulting in a micritic lime deposit with encapsulated opaline diatom tests. Eventual desiccation of the ponds resulted in partial dissolution of some sediment and formation of vadose silts and cements.