Understanding the origin and extent of pervasive quartz overgrowth cements in an anomalous Eocene sandstone, Wilcox Formation, Mississippi Embayment

Dixie Androes
Department of Geosciences, University of Arkansas

Fayetteville, Arkansas 72701 [email protected]

Tertiary deposits of the Mississippi Embayment are composed primarily of clay, uncemented sand and gravel units.  In marked contrast the Eocene sands of the Wilcox Formation, which crop out on the western flank of Crowley’s Ridge, contain thick (8 meters) quartz arenite lenses with pervasive quartz overgrowth cement occluding all porosity.  These anomalous sandstone units are overlain and underlain by unconsolidated sands and mudstones.  Primary, syntaxial quartz overgrowths account for approximately 20% of the rock. Competing models to explain cementation processes include 1) the horizontal movement of silica saturated meteoric waters at shallow depths and 2) the upward migration of water resulting from compaction and clay mineral dehydration within a deep basin.

The sedimentary sections beneath the Wilcox sandstones are thin and inadequate to supply the volume of water or silica needed through clay mineral dehydration to reduce porosity from 25% to essentially zero. Current models indicate that cementation resulting from horizontal or meteoric circulation of silica saturated fluids requires long time periods (Blatt 1979, Dutta 1986). Apparent time constraints on these Eocene quartz arenites, combined with the shallow burial depths and inadequate vertical flux of silica-saturated fluids, suggest that the current models for quartz cementation may be further refined by understanding this anomalous sandstone.