Sediments associated with mid-shelf hardbottoms, Onslow Bay, North Carolina / by Keil A. Schmid.
| Author/creator | Schmid, Keil A. author. |
| Other author | Riggs, Stanley R., degree supervisor. |
| Other author | East Carolina University. Department of Geology. |
| Format | Theses and dissertations |
| Production | 1996. |
| Description | 161 leaves : illustrations, maps ; 28 cm |
| Supplemental Content | Access via ScholarShip |
| Subjects |
| Summary | Hardbottoms, areas of the sea floor with exposed rock surfaces, in Onslow Bay, NC have texturally and compositionally variable Holocene sediments associated with them. The texture, composition and depositional patterns of the Holocene sediment studied at four hardbottom sites appear to be controlled by the morphology and lithology of the surrounding Quaternary and Tertiary hardbottom units. Holocene surface sediments, sampled along transects, almost always consist of two texturally and compositionally unique populations. The fine sand population is composed mainly of quartz with variable amounts of phosphate, depending on the surrounding hardbottom lithology. The fine sands commonly occur on lower hardbottoms as sand aprons at the scarp bases and as a thin pocked and pitted layer over the sandy gravel population. Sandy gravels are composed mainly of carbonate shells and lithoclasts, are megarippled and directly overlie the Miocene strata. They are exposed at the sediment surface as bands paralleling hardbottom scarps adjacent to sand aprons. Above the scarps, on the upper hardbottoms, the Holocene sediments are very thin and represent a mix of the two populations. Sediments associated with low-relief hardbottoms, which consist primarily of Tertiary units, are composed primarily of grains from the eroding units and are selectively sorted into fine sand and sandy gravel deposits. A major storm, dubbed 'the storm of the century', occurred on March 13, 1993. Sediment samples were taken at one site before and after its passage. Fine sands deposited on the lower hardbottom during the waning stages of the storm were partially eroded out within two months, thereby reestablishing pre-storm conditions. Of primary importance is the establishment of the two end-member sediment characteristic, and the role of bioerosion in creating 'new' sediment. The stratigraphic arrangement of the Holocene sand bodies and the sedimentary structures indicate that storm conditions are responsible for creating an maintaining the spatial distribution of the two populations. Production of sediment by subaqueous erosion appears to control the signature of the Holocene sediment, if not the complete composition. |
| General note | Submitted to the faculty of the Department of Geology. |
| General note | Advisor: Stanley R. Riggs |
| Dissertation note | M.S. East Carolina University 1996 |
| Bibliography note | Includes bibliographical references (leaves 118-121). |
| Genre/form | dissertations. |
| Genre/form | Academic theses |
| Genre/form | Academic theses. |
| Genre/form | Thèses et écrits académiques. |