Carbonate petrology and sedimentology of the Miocene Pungo River Formation, Onslow Bay, North Carolina continental shelf / by T. Lori Stewart.
| Author/creator | Stewart, T. Lori author. |
| Other author | Riggs, Stanley R., degree supervisor. |
| Other author | East Carolina University. Department of Geology. |
| Format | Theses and dissertations |
| Production | 1985. |
| Description | 184 leaves : illustrations (some color), maps ; 28 cm |
| Supplemental Content | Access via ScholarShip |
| Subjects |
| Subject | The Pungo River Formation in Onslow Bay, North Carolina is predominantly a siliciclastic sediment sequence with variable amounts of authigenic and diagenetlc minerals including carbonates. Based on examination of 14 of the 16 outcropping Pungo River seismic units, the dominant carbonate component is carbonate mud (low-Mg calclte, dolomite, or a mixture of the two). Calcareous fossils are the next most abundant carbonate component. Calcite cements are a very minor component and are only locally abundant. Four patterns of carbonate sedimentation occur in the Pungo River Formation in Onslow Bay. 1) Cyclic carbonate sediments overlying noncarbonate lithologies and deposited as a couplet during the same fourth-order sea-level cycle are common. Biomicrosparites which grade into phosphorites of seismic unit FPF-1 represent deposition during a fourth-order sea-level maximum when warm Gulf Stream waters flooded the shelf. Calcite-cemented sandstone of BBF-2 grades down section into unindurated quartz sand. Unindurated, muddy, barnacle-rich sands represent fourth-order sea-level regressions. These types of carbonate cap rocks conform to the idealized llthic cycle of the Riggs model of Neogene sedimentation (1984). 2) Sediments of the AF seismic sequence are largely carbonates in northern Onslow Bay and siliciclastlcs in central Onslow Bay. Carbonate content in each fourth-order seismic unit increases up section from AF-1 to AF-4. AF-1 in northern Onslow Bay represents mid to outer shelf sedimentation. AF-2 and AF-3 contain a predominantly reworked fossil assemblage. AF-4 is a barnacle hash, representing formation on shelf edge hardgrounds and deposition off the shelf edge. 3) Sparse fossils and minor carbonate mud occur disseminated in all predominantly noncarbonate lithologies. The major source of calcareous mud is probably from bio-mechanical degradation of larger carbonate grains, primarily shell material. 4) Predominantly carbonate beds interbedded with noncarbonate lithologies include: moldic microsparite which probably represents the carbonate cap on FPF-1 in northern Onslow Bay; moldic microsparite in BBF-1 which may be similar in origin to the carbonate cap of unit C in the Aurora Area; and echinold-foramlniferal blosparltes in FPF-6, which probably formed by winnowing of the fines by marine currents such as Gulf Stream eddies. Dlagenetic carbonates (calcite cements and dolomite) and silicates (opal-CT, microcrystalline quartz, and clinoptllolite) exhibit vertical dlagenetic profiles in some cores. Where carbonate sediments are abundant, effects of fresh water calcite cementation decrease down section. Because syntaxlal cement on echinoids is precipitated faster than rim cements on other fossils, it is a good indicator of the degree of diagenesis undergone by sediments. Dolomite abundance and distribution are sporadic, perhaps reflecting presence or absence of sulfate reducing bacteria in the sediment. Local chert nodule formation is related to abundance of siliceous fossils and to permeability barriers within the sediments. |
| General note | "Presented to the faculty of the Department of Geology ... in partial fulfillment of the requirements for the degree Master of Science in Geology." |
| General note | Advisor: Stanley R. Riggs |
| Dissertation note | M.S. East Carolina University 1985 |
| Bibliography note | Includes bibliographical references (leaves 143-151). |
| Genre/form | Academic theses. |
| Genre/form | Academic theses. |
| Genre/form | Thèses et écrits académiques. |
Availability
| Library | Location | Call Number | Status | Item Actions |
|---|---|---|---|---|
| Joyner | University Archives | ASK AT SPECIAL COLLECTIONS DESK | ✔ Available | Request Material |
| Joyner | NC Microforms | MICROFILM | ✔ Available | |
| Electronic Resources | Access Content Online | ✔ Available |