Date of Award


Document Type


Degree Name

Master of Science (MS)



First Advisor

A.F. Jacob


High-sinuosity channel deposits in the Sentinel Butte Formation occur as elongate, tabular beds of sand that fine upward from an erosional base. The sand beds contain epsilon cross-stratification, within which stratification changes upward from large-scale trough crossstratification to horizontal stratification and small-scale crossstratification, indicating upward decrease in flow regime due to accretion of laterally-migrating point bars. Inset in the sand beds are channelplug deposits that are narrow and arcuate in map view and asymmetrically trough shaped in cross-section, and consist of sandy silt and clay. Lowsinuosity channel deposits occur as elongate, trough-shaped sand beds that fine upward from a deeply-channeled base. The abundant high-angle planar eras s-stratification and horizontal stratification probably originated in transverse bars. Epsilon cross-stratification and channel plugs are absent except in one bed that is transitional to a high-sinuosity channel deposit.

Silt beds, containing sandy or clayey lenses, occur in tabular beds overlying high-sinuosity-channel deposits and in wedge-shaped beds adjacent to low-sinuosity channel deposits, and are interpreted to be natural levee deposits. Silt beds become thinner and finer-grained away from channel deposits and interfinger with clay beds. Horizontal stratification, small-scale cross-stratification, distorted lamination, and climbing ripples may be present in the silt beds.

Natural-levee sediment grades vertically and laterally to tabular beds of clay that contain distorted laminations, abundant plant fragments, 3nd lignite lenses, and are overlain by lignite beds. The clay and lignite beds were probably deposited in floodbasins and backswamps.

Lensoidal beds of very fine sand occur in the natural levee and floodbasin deposits and are probably crevasse-splay deposits. Lensoidal sand beds contain horizontal stratification, high-angle planar cross-stratification, and small-scale cross-stratification. Paleocurrent data indicate highly variable current directions.

Vertically stacked low-sinuosity channel deposits that appear to diverge downstream from high-sinuosity channel deposits may be distributaries of highly sinuous streams on a delta. The delta may have prograded into the Paleocene sea in which the marine Cannonball Formation was deposited.

Cherven (200781 kB)

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