Yuejin Liu

Master of Science

March 16, 1990

(B.S., China University of Mining and Technology, 1982)

Directed by Dr. Robert A. Gastaldo

Gravel, ranging from pebble to boulder size, is preserved either inside vitrainized logs or dispersed among them within a coastal-channel sandstone sequence. This sandstone sequence represents a broad channel-fill complex with maximum width of 2 km. The Gravel-bearing layer is found at the top of the sandstone channel sequence, and is interpreted to represent an ancient log-jam deposited during, or resulted in, the abandonment of the sandstone channel transecting the Mary Lee peat swamp. Pebbles have been shown to have been transported inside partially hollowed or hollow logs; cobbles and boulders must have been carried either on or between the log rafts. These unique transport mechanisms for gravels have preserved two clast size of extrabasinal material relevant to the source rocks for the Upper "Pottsville" Formation. The dominance of metamorphic, plutonic igneous, and sedimentary rocks, and the absence of volcanic or volcaniclastic rocks imply a provenance from the deformed and uplift southern Appalachian orogen for this part of the Upper "Pottsville" Formation. This interpretation differs from presently accepted models suggesting provenance from a Ouachita orogen produced by arc-continent collision along the southern margin of the North American continent. The results reported in this study suggest that the role of the Ouachita orogen to the south and southwest of the Black Warrior basin, and its contribution to the basinal deposits in the Upper "Pottsville" were minimal. The possible influence of this system on the Black Warrior basin of Alabama requires further investigation.

The upper Mary Lee coal zone in the study area records a depositional history of transition from coastal terrestrial to nearshore and offshore environments. The coastal non-marine environments were complicated by a westward progradation of a crevasse splay complex, resulting in two depositional areas. The western part of the study area was characterized by a vertical association of the Mary Lee peat swamp, clastic swamps, and overbank lake deposits. The eastern area is represented by a sequence of the Mary Lee peat swamp, a splay complex, the Newcastle peat swamp, and clastic swamp and/or overbank lake deposits. The splay complex sequence consists of three depositional units formed in response to initiation, development, and abandonment stages of the splay complex evolution. The lower mudstone unit is characterized by centimeter-thick graded beds and autochthonous fossil plant horizons with wedge-shaped geometries. The middle sandstone unit is recognized by various associations of channel form and sheet sandstone. The upper siltstone and/or mudstone unit is characterized by rooted horizons. These terrestrial regressive deposits were finally truncated by a transgressive event recorded by a basal ravinement surface and overlying marine deposits. The sedimentary rocks reported in this study, therefore, have depicted two paleogeographical pictures: a coastal regime of non-marine deposition and an area covered by shallow marine sedimentation. A NE-SW oriented shoreline at the time of the initial transgression was probably located in the north of the Carbon Hill.

The ravinement surface identified at the top of the Mary Lee coal zone in the study area separates the underlying regressive sequence from the transgressive one. It marks the stratigraphic position of the transgressive erosional surface. This ravinement surface is recognize by the presence of a thin ravinement bed deposited immediately on the surface. Two variations of ravinement beds are identified in the study area. The first is a mudstone bed with an autochthonous pelecypod and brachiopod assemblage. The second is a sandstone bed with Zoophycos and an allochthonous trilobite-crinoid-brachiopod assemblage. Under subcritical conditions in which the shoreface angle is greater than its climbing angle, gradual rise of sea level causes erosion of the existing shoreface. Landward and upward migration of the shoreface produces two genetic consequences. The first is the formation of a ravinement surface consisting of a series of erosional surfaces. The second is the deposition of ravinement beds whose sediments are controlled by the properties of the eroded shoreline. The current depositional model for the Upper "Pottsville" Formation depicts a single deltaic system consisting of delta plain deposits. The existence of the ravinement surface at the top of the Mary Lee coal zone, and the documentation of additional marine macrofaunal zones between major coal zones, indicates that the Upper "Pottsville" Formation represents a complex of coastal accumulations characterized by at least one transgressive event with subsequent coastal progradation.

See: Bryant, Degges, and Demko for related M.Sc. Theses.