Browsing by Subject "Aguja Formation (Tex.)"
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Item Paleoenvironmental analysis of coastal marsh deposits in the Aguja Formation, late Cretaceous, Trans-Pecos Texas(Texas Tech University, 1988-12) Record, Richard StoreyUpper Cretaceous carbonaceous shale, lignite, and coal deposits of the Aguja Fomatlon are exposed on the southwest £lank of Rattlesnake Mountain in western Big Bend National Park. These deposits represent accumulation in delta plain marshes and swamps. Variations in depositional environment ranging from prograding delta plain marsh sediments to well-drained swamp deposits are distinguished among the lower, middle, and upper shale members of the Aguja. Llthologic analysis, clay mineralogy, total organic carbon analysis, stable carbon and oxygen isotopic analysis, thin section petrography, and palynology are employed to differentiate facies. On the basis of this facies analysis prograding delta plain marsh environments are interpreted for the lower and middle shale members. The upper shale member is proposed to represent deposition in a well-drained swamp environment. Lithologic variations and a relationship between kaolinite and total organic carbon indicates cyclicity in the lower and middle shale members. The lower shale member overlies the progradational basal sandstone member of the Aguja, and represents deposition in a delta plain marsh with crude cyclicity apparent in the facies found. Lignitic layers cap the marsh cycles, and kaolinite enrichment is found below the lignites. The middle shale member overlies the transgressive Rattlesnake Mountain sandstone member, and is similar in lithology to the lower shale member. The middle shale member consists of carbonaceous shale and lignite, and may represent marsh progradation over the Rattlesnake Mountain sandstone. The upper shale member overlies the Terlingua Creek sandstone member, and represents a departure from marsh deposition. Ijn situ stumps, logs, and sparse organic material in the shale indicate deposition in a well drained swamp, perhaps in a proximal deltaic environment.Item Sedimentology and petrography of a distributary channel complex in the Aguja Formation (Late Campanian), Big Bend National Park, Texas(Texas Tech University, 1988-12) Schroeder, M. RichardThe 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.Item Sedimentology and petrography of deltaic facies in the Aguja Formation, Brewster County, Texas(Texas Tech University, 1987-05) Bohanan, James PaulThe Upper Cretaceous Aguja Formation, northwest of McKinney Hills in the eastern part of Big Bend National Park, Texas, was deposited in a deltaic depositional environment. Prodeltaic, distributary mouth bar, distributary channel, interdistributary bay (including levee, crevasse splay and crevasse channel), and abandonment facies can be distinguished. Two delta progradational episodes are recorded. The basal sandstone member was deposited during the initial progradation (Early Campanian) of a lobate delta complex. The delta system was abandoned and transgressed depositing marine shale of the McKinney Springs tounge of the Pen Formation. Progradation of a slightly elongate delta complex resumed in Late Campanian time depositing the Terlingua Creek Sandstone member and upper shale member. Paleocurrent analysis indicates that the deltas prograded eastward across the Coahuila Platform. The primary source terrane for the deltaic sediments was volcanic but also included plutonic igneous, metamorphic, and sedimentary rocks. It is possible to distinguish the deltaic sub-environmentspetrographically. Distributary channel deposits tend to be richer in rock fragments and abandonment deposits richer in quartz than other deltaic facies. Sandstone porosity has been occluded by quartz overgrowths, authigenic clays, and carbonate cements including calcite, ferroan calcite, and ankerite.