Environment of deposition of selected sandstones and conglomerates in southern part of Cahaba basin, Alabama

• Other Authors: Demirpolat, Suleyman.
• Format: Others
• Language: English
• Subjects: Geology
• Online Access: http://purl.flvc.org/fsu/lib/digcoll/etd/3161863

The Pottsville formation in the Cahaba basin, Alabama, contains conglomerates, sandstones, siltstones, mudstones and coals. Primary structures, geophysical well logs, lithology of cores, thin sections and SEM samples were examined, and grain size analyses were done on friable samples to determine the environment of deposition. === Ripple mark crest orientations suggest that the shoreline was oriented northeast-southwest when the sandstone members and conglomerates were deposited. Steep-side modes of asymmetric ripple marks and primary modes of crossbedding indicate sediment transport was toward the northwest, which was probably toward deeper water at the time of deposition. === The presence of possible tidal channels, mica flakes, high angle crossbedding, herringbone crossbedding, organic matter in the troughs of the ripple marks and isolated current type ripple marks suggest that the Pottsville sediments were deposited in an environment influenced by tides. === Fetch calculations reveal that the water body in which the ripple marks formed ranged from 37 km. to 700 km. in width. The ripples induced in the latter might have formed during a storm in an ocean smaller than 700 km. width. Ripple indices suggest that water depth varied from 31 cm. to 100 cm., wave length from 3 m. to 9 m. and wave height from 8 cm. to 28 cm. These are shallow water and modest fetch values which can be met on a broad shallow shelf with well formed waves approaching from offshore. === Scanning electron microscopy (SEM), Energy Dispersive X-Ray Spectrum (EDX) and thin section analysis show that authigenic quartz, illite and kaolinite make up the cement. These analyses also suggest that the Pottsville sandstones have undergone local decementation processes. === Source: Dissertation Abstracts International, Volume: 50-08, Section: B, page: 3359. === Major Professor: William F. Tanner. === Thesis (Ph.D.)--The Florida State University, 1989.