AAPG ANNUAL CONFERENCE AND EXHIBITION
Making the Next Giant Leap in Geosciences
April 10-13, 2011, Houston, Texas, USA
Petrographic Comparison and Contrast of Fluvial and Deltaic Sandstones, Upper Pennsylvanian Oread Cyclothem, NE Oklahoma
(1) Department of Geology, Wichita State University, Wichita, KS.
(2) Departmetn of Geological Sciences and Engineering, Missouri University of Science and Technology, Rolla, MO.
Upper Pennsylvanian fluvial and deltaic sandstones on Kansas Shelf should be different, because environmental shift due to large sea-level fluctuations and processes in individual environments are different. Our study tests this hypothesis by petrographic characterization of 2 regressive Snyderville fluvial, 2 maximum-transgressive Heebner deltaic, and 2 regressive Elgin deltaic sandstones of the Oread cyclothem. 50 point-counts for each sample document composition and texture of framework grains, porosity, type and amount of cement and matrix. Mean grain size and degrees of sorting and skewness were calculated. Composition and texture were compared among samples of the same and different environmental origins.
All 6 sandstones are quartz arenite and compositionally and texturally supermature. Fluvial sandstones are 2 m apart from 2 point-bar sheets with a composition of Q91F0L9 and Q97F0L3. They are middle-upper fine, very well-well sorted, fine-strongly fine skewed, and well-variably rounded. Their differences are caused by the positions in the point-bar complex. Heebner deltaic sandstones from 2 delta lobes 7 m apart have a composition of Q92F0L8 and Q97F0L3. They are upper fine-lower medium, well sorted, symmetrical-strongly fine skewed, and very well-well rounded. Their differences are caused by varying energy conditions during deltaic progradation. Elgin deltaic sandstones from 2 delta lobes 7 m apart have a composition of Q97F0L3 and Q100F0L0. They are upper-middle fine, well sorted, fine skewed, and very well-well rounded. Heebner and Elgin sandstones are similar, suggesting that sea-level change was not a major control on their characteristics. Fluvial sandstones are coarser, much better sorted, less rounded, and have slightly more mud clasts than deltaic sandstones, reflecting shorter transport, higher flow velocity, less reworking, and a local floodplain source of mud chips of the point-bar sediment and environment. All sandstones as a whole have a composition of Q96F0L4, and are fine, moderately well sorted, strongly fine skewed, and rounded-very well rounded. The high maturity is common in epi-continental areas. The sands were likely recycled from sandstones in Ouachita thrustbelt to the south. The similarities among fluvial and deltaic sandstones suggest that provenance lithology and sediment transport distance are major controls on sandstone properties. Last, the sandstones with an average 14.5% porosity are good potential reservoirs.