Chertification in the Mississippian Lake Valley Formation, Sacramento Mountains, New Mexico

Abstract

Chert distribution in the Lake Valley rocks is selective to mud‐supported facies; it is not related to proximity to unconformities. The facies selectivity of the chertification is believed to be a function of the depositional distribution of indigenous silica as sponge spicules, an interpretation that is supported by high positive qualitative correlation of chert with spiculitic rocks. Petrography indicates that the spicules were all originally siliceous, and that they all went through a moldic stage during which many molds were compactively destroyed and distorted. Remaining molds were subsequently cemented by calcite or chalcedony. Chert distribution and spicule petrography argue for an intraformational source for much of the silica. Chert micro‐fabrics are dominated by microquartz, a replacement of grains and lime mud; length‐fast chalcedony, a pore‐filling cement; and megaquartz, a post‐chalcedony pore‐filling cement. Petrography of compaction features within chert masses indicates that chertification occurred after some burial. Based on stratigraphic reconstruction this burial depth was a maximum of about 215 m. and was most likely a few metres to a few tens of metres. Petrography of chert‐calcite cement relationships indicates that chertification occurred before and during first generation, pre‐Pennsylvanian non‐ferroan calcite cementation, and was completed before late‐stage, post‐Mississippian ferroan calcite precipitation. Petrography of chert clasts in basal Rancheria (Meramecian) and basal Pennsylvanian conglomerates proves these clasts derived from the Lake Valley Formation and were chertified before redeposition. Thus, some cherts in the Lake Valley are pre‐Meramecian in age, but all are pre‐Pennsylvanian in age. Furthermore, association of the cherts with the non‐ferroan cements indicates the cherts were probably precipitated in meteoric phreatic lens established beneath the pre‐Meramecian and pre‐Pennsylvanian subaerial unconformities.

Punctuated Sediment Discharge During Early Pliocene Birth of the Colorado River: Evidence from Regional Stratigraphy, Sedimentology, and Paleontology

“…Possible sources of silica include remobilization from volcanic ash, clay minerals, hydrothermal groundwater, and meteoric water. Subaerial exposure may have created intake areas for circulation of silica-rich meteoric waters into the subsurface, a process that is 14 commonly invoked to explain silicification and karst features beneath unconformities in other carbonate successions (Meyers, 1977;Young et al, 2012). The silica casts were later exhumed during erosion that formed the unconformity, and reworked into the upper bioclastic member.…”

Sponge Spicules, Silicification, and Sequence Stratigraphy

“…Although Lees and Miller (1995) stressed that the timing of silicification appears late and unrelated to the considerable amount of sponge-spicule silica, other studies (Meyers 1977;de Brit 1989;Butts and Briggs 2011) found a very similar spatial pattern of silicification that was related to early diagenetic stratigraphic trapping (off-mound chert, silicification of fossils on flanks or along coarse reef-talus deposits). Meyers (1977) andde Brit (1989) demonstrated that this pattern originated during early diagenesis of sediment burial at depths of a few meters to a few tens of meters.…”

What controls porosity in cherty fine-grained carbonate reservoir rocks? Impact of stratigraphy, unconformities, structural setting and hydrothermal fluid flow: Mississippian, SE Kansas

“…Bissell 1959;Cavoroc & Ferm 1968;Meyers 1977;Geeslin & Chafetz 1982;Maliva & Siever 1989;Carlson 1994;Ruppel & Hovorka 1995), including studies of Mississippian rocks in Kansas (Montgomery et al 1998;Watney et al 2001;Franseen 2006). The results presented herein also show an early diagenetic event of dissolution of sponge spicules (thereby leaving molds) and redistribution of silica as evidenced by silicification of original lime-mud material and calcitic fossils.…”