Petrology of the Queen City sandstone (Eocene) Leon County, Texas



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The Queen City Formation in Leon County, Texas is an immature, moderately sorted, silty, very fine sandstone of subarkosic to subchertarenitic composition. Deposition occurred in a continental floodplain marginal to a deltaic plain. Facies that can be distinguished on the basis of texture, grain size, three-dimensional geometry of the beds, sedimentary structures, and the vertical changes in these characteristics are upper point bar, lower point bar, chute, and overbank deposits. Maximum marine regression related to Queen City deposition appears to have been interrupted in the middle third of the section by a marine transgression. An organic-rich overbank to deltaic plain environment of deposition resulted. The upper and lower thirds of the unit record normal continental floodplain deposition. Paleocurrent measurements yield an approximately constant unimodal model, indicating southeasterly flow, throughout the vertical sequence. Likewise, the heavy mineral assemblage, which is dominated by zircon, can be represented statistically as a homogeneous population. This homogeneity is in agreement with the hypothesis that deposition of the Queen City took place very rapidly, in 10,000 years or less. Sediment source area was largely reworked pre-Tertiary sedimentary rocks in Central and North-Central Texas. High-grade metamorphic rocks provided a subordinate sediment source, which was located probably in the Southern Appalachians. Intermediate and acidic igneous rocks are other subordinate sediment sources and were derived from the Southern Rocky Mountains and Ouachita Mountains.



Texas, Eocene, Sandstone