Petrographic Characteristics of Maximum-Transgressive and Regressive Deltaic Sandstones of Upper-Pennsylvanian (Virgilian) Oread Cyclothem, NE Oklahoma
Lu Zhu and Wan Yang
Deltaic sandstones deposited during maximum-transgression and regression are expected to differ in composition and texture, because of different environmental conditions associated with sea-level changes. This hypothesis is tested by petrographic study of 3 sandstones from maximum-transgressive Heebner delta and 4 from regressive Elgin delta in NE Oklahoma. 300 point-counts of each sample document amount of matrix, and composition, grain size, sorting, and skewness of framework grains. The data are compared to display their similarities to interpret paleoenvironments. Heebner and Elgin samples are taken from adjacent locations except W30(30km apart). Heebner has a coarsening upward trend(3-2.2Φ)while Elgin coarsens and then fines upwards(2.5-1.7-3.3Φ). Generally, coarser sandstones are better sorted. However, W32-5(3Φ)has a standard deviation(D)=0.7, while W30, 262-15 7 and 8(3.4, 3.3 and33Φ)have D=1.4, 1.7, and 1.8, respectively. W32-5 has the most feldspar. For samples of similar grain size, the ones with more feldspars are better sorted(comparing 262-13 with 262-11 and W32-6). When the QFL composition is plotted against grain size, the grain size distribution is nearly symmetrical for samples rich in feldspars(W32-5, 262-11, and 262-13, but not W30). The relatively large amount(10%)of lithics causes the strongly fine skewness of W30(similarly 262-15 7 and 262-15 8). The QFL composition also reflects the tectonic setting of provenance(Dickinson, 1983). W32-5, 262-11, and 262-13 probably have similar source lithologies and tectonic settings, whereas W30, 262-15 7 and 8 the other. W30, which was deposited during maximum-transgression, is 30km south to 262-15 7 and 8 which were deposited during regression, but they have similar textures, suggesting the same provenance and deposition environment with a similar shoreline position. The results suggest that the composition and texture of sandstones can be used to aid in interpretation of provenance and paleoenvironments.
AAPG Search and Discovery Article #90176©AAPG Mid-Continent Meeting, Wichita, Kansas, October 12-15, 2013