Diagenesis of the Maxon Sandstone (Early Cretaceous), Marathon region, Texas; a diagenetic quartzarenite

Abstract Environments of deposition, climate, detrital mineral composition, and stratigraphic position within a thick sequence of carbonate rocks were major controls on the diagenesis of Maxon sandstones. Fluvial-deltaic sands, which were subjected to calichification and other pedogenic processes, lost all macroporosity prior to burial. Most sands underwent compaction (average of 14% porosity loss), minor cementation by quartz and kaolinite, possibly during invasion of meteoric water introduced during a low stand of sea level, followed by extensive cementation and grain replacement by calcite. C and O isotopic values of calcite suggest that carbonate was introduced by formation waters derived from adjacent limestones. Mass-balance calculations on the loss and gain of chemical components during diagenesis show there was a major loss of silica (from loss of feldspars) and major gains in CaO and CO 2 (in calcite cement). The overlap of calcite cement on detrital quartz grains gives the impression in thin section that the replacement of quartz by calcite was extensive. However, thin-section and SEM views of samples leached in HC1 show that even partial replacement of quartz is rare and is limited largely to the edges of tiny quartz overgrowths. Ignoring intraformational clasts, most Maxon sandstones now are quartzarenites (Q 86 F 1 R 3 ). However, compensating conservatively for feldspar grains replaced by calcite, sands originally were subarkoses (Q 86 F 10 R 3 ).