Cores recently drilled along Florida's east coast by the Florida Bureau of Geology have yielded a record of the most complete Florida Hawthorn fossiliferous sediments heretofore available for biostratigraphic analysis. The record of Hawthorn deposition extends from the Early Miocene in sediments near the base of this formation in Nassau County to what appears to be Early Pliocene time in core sediments present in Indian River and St. Lucie counties. / A diversity of microfossil groups including diatoms, silicoflagellates, foraminifera and coccoliths were identified in the Hawthorn sediments. Diatoms, which represented the largest and most definitive number of species, were the primary group used to determine the biochronology and paleoenvironmental interpretations of this important phosphate-bearing formation. Three biostratigraphic zones of Middle Miocene to Late Middle Miocene age can be recognized in the Hawthorn sediments (Coscinodiscus plicatus, Coscinodiscus plicatus/Delphineis penelliptica, Delphineis penelliptica zones). The utilization of the diatom Rhaphoneis lancetulla as a substitution for Coscinodiscus plicatus in these zonal correlations was necessary to make the Florida Hawthorn zonation more adaptable to the observed fauna. / The occurrence of an upwelling diatom assemblage in Hawthorn sediments of four northern cores is believed to be the result of coastal upwelling and/or influx from a postulated offshore cool water current during Middle Miocene time. Alternatively, the absence of an upwelling fauna in the Pliocene sediments was significant and may be related to paleoceanographic changes such as closing of the Isthmus of Panama during the Early Pliocene and/or cessation of upwelling. In general, species diversity was less in the Pliocene sediments as compared to the Middle Miocene sediments. Fluctuations in productivity, as expressed in terms of species diversity and numbers of brackish water species in the Middle Miocene and Pliocene assemblages, are attributed in part to sea level changes on a shallow marine depositional environment. / Source: Dissertation Abstracts International, Volume: 43-06, Section: B, page: 1772. / Thesis (Ph.D.)--The Florida State University, 1982.
| Identifer | oai:union.ndltd.org:fsu.edu/oai:fsu.digital.flvc.org:fsu_74864 |
| Contributors | HOENSTINE, RONALD WOODROW., Florida State University |
| Source Sets | Florida State University |
| Detected Language | English |
| Type | Text |
| Format | 268 p. |
| Rights | On campus use only. |
| Relation | Dissertation Abstracts International |
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