Distribution and petrology of glauconitic sediments in the Miocene Pungo River Formation, Onslow Bay, North Carolina Continental Shelf / by David J. Mallinson.
| Author/creator | Mallinson, David J. author. |
| Other author | Riggs, Stanley R., degree supervisor. |
| Other author | East Carolina University. Department of Geology. |
| Format | Theses and dissertations |
| Production | 1988. |
| Description | vi, 127 leaves : illustrations, maps ; 28 cm |
| Supplemental Content | Access via ScholarShip |
| Subjects |
| Summary | The petrology and distribution of the glaucony facies are determined for the Miocene Pungo River Formation in Onslow Bay, North Carolina. The glauconitic grains comprising the glaucony facies consist of five types which are defined petrographically and chemically. These types represent different stages of evolution from a mixed-layer glauconitic smectite-illite (Type 2) to a glauconitic illite (Type 4) . Type 1 grains may also contain mixed-layer glauconitic smectite-illite, however, data was not sufficient to prove this definitively. Type 5 grains are aggregate glauconitic illite grains that have been reworked. Evolution occurs as ferric and ferrous iron and magnesium substitute for aluminum in the octahedral layer and potassium replaces H2O in the interlayer position. There is a shift of the (001) reflector peak from 10.8-12 angstroms to 10.1 angstroms due to the collapse of the interlayer region. The progressive formation and evolution of the glauconitic minerals, accompanied by the dissolution of the original carbonate substrate grain results in the evolution of grains from Type 1 to Type 4. Regional and stratigraphic distribution indicate that the major sedimentologic controls are sediment grain size and mineralogy. These, in turn, are controlled by paleogeography and water-depths within the depositional basin, the location of sediment point sources and maximum upwelling, and third- and fourth-order sea-level fluctuations. Sedimentary trends indicative of fourth-order sea-level fluctuations were noted in fourth-order depositional sequences. This trend consists of basal carbonate fluorapatite ooids and phosphatized skeletal grains, overlain by glauconitic sediments increasing upwards in abundance and mineralogic maturity, and capped by ferric-hydroxide-stained sediments. This trend is interpreted to represent a portion of a condensed section formed during a fourth-order transgression and highstand and partially eroded and oxidized during a subsequent regression. Analyses of the clay-size fraction revealed the presence of ferric smectites and illites probably of a detrital nature. Also apparent was an upward increase in the iron concentration within the clay-size fraction of several fourth-order seismic sequences. This trend may result from the seaward migration of the nearshore zone of chemical precipitation of iron-hydroxides and oxidation of detrital iron minerals. |
| General note | Submitted to the faculty of the Department of Geology. |
| General note | Advisor: Stanley R. Riggs, |
| Dissertation note | M.S. East Carolina University 1988 |
| Bibliography note | Includes bibliographical references (leaves 98-102). |
| Genre/form | dissertations. |
| Genre/form | Academic theses. |
| Genre/form | Academic theses. |
| Genre/form | Thèses et écrits académiques. |
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