Petrology and diagenesis of the Pettet interval, Sligo Formation (lower cretaceous) Bossier Parish, Louisiana / by Alan D. Hartsook.
| Author/creator | Hartsook, Alan D. author. |
| Other author | Neal, Donald W., degree supervisor. |
| Other author | East Carolina University. Department of Geology. |
| Format | Theses and dissertations |
| Production | 1983. |
| Description | 83 leaves : illustrations (some color), maps ; 28 cm |
| Supplemental Content | Access via ScholarShip |
| Subjects |
| Summary | The Lower Cretaceous Sligo Formation is the limestone half of a limestone-clastic couplet which was deposited in the Gulf Coast area during a major transgression. The Pettet interval is a porous limestone lentil within the Sligo. It is approximately 90 feet thick and lies approximately 50 feet below the top of the Sligo in the study area, which is located in a portion of northern Bossier Parish, Louisiana. Here, an anticline with an east-west axis and westerly plunge constitutes the local structure. In the study area, five microfacies, named for their dominant lithologies, were recognized in the Pettet interval. They are: 1) oosparite, 2) oomicrite, 3) oobiosparite, 4) poorly washed oobiosparite and 5) biomicrite. These microfacies were deposited on a shallow, warm water shelf approximately 100 miles from the shelf edge. The rate of Pettet deposition exceeded sea level rise and subsidence; therefore, a shoaling sequence evolved. Several individual shoaling upwards oolite cycles within the Pettet possibly formed as a result of several relatively rapid sea level rises, each followed by sedimentary in-filling. Diagenesis began in the marine environment immediately after deposition and continued through deep burial. Porosity and permeability increased with the leaching of aragonitic allochems and dolomite, and decreased with the precipitation of various calcite cements and pressure solution. Meniscus and gravitational cements indicate at least one episode of subaerial exposure. This subaerial exposure may have created a relatively large meteoric-phreatic environment in which syntaxial calcite cement, equant sparry calcite cement and microspar were formed. An adjacent marine-fresh water mixing zone was a site for dolomite formation and possibly for formation of an isopachous calcite cement. There is no statistical correlation between abundance of allochems and porosity and permeability. With the exception of the oomicrite microfacies, the porous and permeable zones occur in all the microfacies, making prediction of trends difficult. Porosity is predominantly secondary moldic, and localized differences in diagenetic alteration seem to control porosity and permeability. Though permeable zones in the Sligo commonly produce oil regardless of structure, production in the study area corresponds with the crest of an anticline. The best potential for expanding production here seems to be along the anticlinal crest in both updip and downdip directions. |
| 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: Donald W. Neal |
| Dissertation note | M.S. East Carolina University 1983 |
| Bibliography note | Includes bibliographical references (leaves 72-78). |
| Genre/form | Academic theses. |
| Genre/form | Academic theses. |
| Genre/form | Thèses et écrits académiques. |