ABSTRACT

Calcite cements of the Lake Valley Formation (Osagean) consist of clear syntaxial and granular cements in non-biohermal facies; cements in bioherms are dominated by distinctive cloudy cements, but also include clear cements. The clear cements show compositional zoning that comprises an early iron-free zone and a later iron-poor to iron-rich zone. Cathodoluminescence of the non-ferroan calcite cements reveals as many as four zones containing varying amounts of Mn^II. Three of these zones are correlative within single measured sections through about 200 ft of stratigraphic interval; and are correlative laterally for a distance of at least 10 mi. Petrography of the non-ferroan cements from samples inmediately adjacent to post-Lake Valley unconformities dates the oldest of these three zones as pre-Meramecian, and the younger two as post-Meramecian and pre-Atokan. Ferroan calcites largely precipitated during post-early Atokan; a minor amount precipitated in pre-Atokan time.

Cloudy biohermal cements are older than the clear cements, and precipitated contemporaneonsly with sedimentation of the bioherm facies--they are interpreted by this and previous work to be marine cements.

Clear cements are interpreted to have precipitated in the phreatic zone. Evidence includes crystal and zonal geometry, absence of marine hardgrounds, differences from marine cements, and Mn^II and Fe^II content. The stratigraphic and geographic distribution of the non-ferroan clear cement zones is interpreted to reflect ancient phreatic lenses established during pre-Meramec and pre-Atokan subaerial exposures of the Lake Valley Formation.