Nannofossil biostratigraphy and magnetostratigraphy of the Taylor and Navarro groups of central and north-central Texas /
Twenty outcrop sections and two cores from the Upper Cretaceous (Campanian Maastrichtian) Taylor and Navarro Groups of central and north-central Texas were examined for calcareous nannofossils. Assemblages are abundant and diverse in most sections and a clear succession of nannofossil biohorizons i...
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| Format: | Thesis Book |
| Language: | English |
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[Place of publication not identified] :
[publisher not identified] ;
1995.
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| Online Access: | http://proxy.library.tamu.edu/login?url=http://proquest.umi.com/pqdweb?did=742535041&sid=1&Fmt=2&clientId=2945&RQT=309&VName=PQD |
| Summary: | Twenty outcrop sections and two cores from the Upper Cretaceous (Campanian Maastrichtian) Taylor and Navarro Groups of central and north-central Texas were examined for calcareous nannofossils. Assemblages are abundant and diverse in most sections and a clear succession of nannofossil biohorizons is present, allowing the sections to be assigned to a standard zonation. The Taylor Group is middle to outer neritic (or deeper) and contains two sets of time transgressive units, which become younger to the north and northeast. The Lower Taylor Marl is assigned to Zones 18b/c near Austin, and is as young as Zone CC 19b near Dallas. The Lower Taylor-Wolfe City contact is also time transgressive and is unconformable in northeast Texas. The Wolfe City Sandstone is assigned to Zones CC 19a/b in central Texas, but is much younger (Zones CC21-22a) in northeast Texas. The Pecan Gap Chalk occurs as two geographically distinct units: both are assigned to Zone CC 19b in the south and west, and become younger (Zones CC21-22a) to the north and east. The Upper Taylor Marl is assigned to Zones CC20- 22a. In the Navarro Group, the Nacatoch Sandstone and Neylandville Marl sections are inner neritic, possibly non- marine, and are barren of nannofossils. The Corsicana Marl is middle(?) neritic and assigned to Zones CC25b/c and CC26a. Nannofossil richness, dominance diversity and equitability are moderate to high and exhibit similar trends up section. In the middle Taylor, these values decrease sharply and then slowly increase upsection; this implies a more stressful environment for a short period, followed by a slow return to more favorable conditions. A preliminary magnetostratigraphy was also developed for the Taylor and Navarro Groups. The Corsicana Clay is predominately normal polarity and may correspond to C30R. The Nacatoch Sandstone is predominantly reversed polarity and correlates to C3 IR. Taylor Group polarities are problematic and tentatively correlated to Chrons 32 to 33 and the top of C34N; this places Chron 32 lower in the section and Chron 34 higher in the section than generally accepted. |
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| Item Description: | Vita. "Major Subject: Oceanography". |
| Physical Description: | xii, 289 leaves : illustrations, maps ; 28 cm. Issued also on microfiche from University Microfilms Inc. |
| Bibliography: | Includes bibliographical references. |