Sedimentology and petrography of a distributary channel complex in the Aguja Formation (Late Campanian), Big Bend National Park, Texas
Schroeder, M. Richard
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The Upper Cretaceous Aguja Formation and the underlying Pen Formation, northwest of the Grapevine Hills in the northcentral part of Big Bend National Park, was deposited in a fluvial-dominated deltaic depositional environment. Shelf mud, prodelta, distal bar, distributary mouth bar, distributary channel, and coastal marsh and swamp facies can be distinguished. A major marine transgression during "middle" Campanian time deposited shales of the McKinney Springs Tongue of the Pen Formation. Marine regression during Late Campanian time resulted in the deposition of the Terlingua Creek sandstone and upper shale members of the Aguja Formation. Paleocurrent analysis indicates that the Late Cretaceous paleo-shoreline was approximately north-south and that the distributary channel complex prograded in an easterly to northeasterly direction. The primary source terrane for the deltaic sediments was volcanic but plutonic igneous, metamorphic, and sedimentary rocks are also observed in samples collected from the study area. The Terlingua Creek sandstone has undergone significant post burial diagenetic alteration. Diagenetic phases observed include: 1.) compaction, 2.) chlorite and iron oxide coatings around detrital grains, 3.) precipitation of quartz overgrowths, 4.) formation of pore filling authigenic clay minerals, 5.) calcite and ferroan cement, 6.) dissolution of feldspar grains and the development of secondary porosity. Based on petrographic analysis it is suggested that the position of facies within the deltaic sandbody strongly influenced the diagenetic history of the Terlingua Creek sandstone.