Diagenetic And Sedimentologic Aspects Of Eagle Mills-Werner Conglomerate Sandstones (Triassic-Jurassic), Northeast Texas

Abstract

ABSTRACT The Eagle Mills-Werner sequence occurs in deep wells (12,000 to 18,000 ft.) in northeast Texas and southwest Arkansas. Eagle Mills sandstones unconformably overlie the Paleozoic complex and disconformably underlie the Werner Conglomerate. Werner-Louann evaporites overlie Eagle Mills-Werner siliciclastics. Basaltic sills and dikes transect these sandstones and conglomerates. Eagle Mills-Werner strata consist of greenish-gray conglomerates and green, red, and pink, coarse-grained, lithic-feldspathic arenites which are interbedded with red, gray, and green shales and siltstones. Lithic arenites and conglomerates contain volcanic and sedimentary rock fragments. These strata represent nonmarine paleoenvironments developed within grabens and are the earliest record of Gulf of Mexico rifting. Eagle Mills-Werner sandstones have undergone a complex diagenetic history, including: chlorite cementation, compaction, quartz and feldspar overgrowths, early carbonate cementation, dissolution of framework grains, chloritization and albitization of feldspars, late cementation by ferroan calcite and ferroan dolomite and late replacement by anhydrite and pyrite. Pyrobitumens coat early chlorite cements indicating that most diagenesis post-dated hydrocarbon migration. This suite of authigenic phases records progressive burial of Eagle Mills-Werner strata into a high-temperature diagenetic regime where thermochemical sulfate reduction was the dominant process.