ABSTRACT

The Mississippian Newman Limestone in eastern Kentucky contains aquifer-related cements and deeper burial cements. These cements were differentiated by trace elements, cathodoluminescence, staining, and fluid inclusions. Aquifer cements are nonferroan and show a nonluminescent to dull to nonluminescent to bright cathodoluminescent zonation. They fill leached ooid and fossil molds, indicating that pore waters were initially undersaturated with calcium carbonate. Within a regional paleoaquifer, early nonluminescent cement (34 ppm Mn, 33 ppm Fe average) precipitated from oxidizing waters that later became reducing to form dull cement (average 181 ppm Mn, 565 ppm Fe). A second nonluminescent cement was formed following later recharge. Aquifer stagnation, prior to or during burial, was accompanied by bright cementation (2,139 ppm Mn, 252 ppm Fe average). Waters were sourced from post-Newman unconformities. Aquifer cement, which decreases away from recharge areas, was determined by initially staining for late-burial calcite; image analysis was then used to determine the amount of early cement by subtracting late-burial cement from total cement. Later, iron-rich burial cements (778 ppm Mn, 4,295 ppm Fe average) filled the following pore space: (1) remnant intergranular, (2) fractures in compacted skeletal grains, (3) cavities caused by spalling ooid cortices and early cement rims, and (4) tectonic fractures, which are lined with saddle dolomite and pyrite. Secondary fluid inclusions suggest that late-stage fluids were chemically complex brines with temperatures that ranged from 50°C to 160°C and averaged 100°C. These techniques may help to evaluate porosity loss by shallow cementation in paleoaquifers (potential pore plugging prior to hydrocarbon migration) vs. cementation by deeper burial processes.

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