Calcareous nannofossils and size-frequency distribution of reticulofenestrids in the equatorial and western tropical Pacific : implications for neogene paleoceanography /
Middle Miocene to Quaternary calcareous nannofossils
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| Format: | Thesis Book |
| Language: | English |
| Published: |
[Place of publication not identified] :
[publisher not identified] ;
1994.
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| Online Access: | http://proxy.library.tamu.edu/login?url=http://proquest.umi.com/pqdweb?did=741966121&sid=1&Fmt=2&clientId=2945&RQT=309&VName=PQD |
| Summary: | Middle Miocene to Quaternary calcareous nannofossils recovered from six equatorial and tropical Pacific sites were examined. Calcareous nannofossil biostratigraphic data provide a reliable basis for constructing age models for time-series paleoceanographic study. Eleven hiatuses indicated by truncated nannofossil ranges were recognized in the studied sections. Most of these hiatuses occur at both shallow and deep sites and closely correspond to polar cooling events, suggesting that they are the consequences of erosion by intensified circulation. Drastic decrease of Coccolithus pelagicus in the low- latitude Pacific between 4.5 and 3 Ma suggests that this region was warm during most of the early Pliocene. The return of Coccolithus pelagicus at the beginning of the late Pliocene indicates cooling of the low-latitude Pacific and is closely correlated to the emergence of Panama Isthmus and the initiation of northern hemisphere glaciation. Size-frequency distribution of reticulofenestrids at broadly separated equatorial and tropical Pacific sites fluctuate in similar patterns. The most distinct features are short intervals that are characterized by a decrease in large reticulofenestrids and an increase in small morphotypes. Some of these events have been quantitatively documented in the Indian Ocean and Red Sea and can be recognized in the Atlantic from serni-quantitative biostratigraphic data. These reticulofenestrid size distribution events are not the artifact of selective dissolution and are not controlled by evolution. Modern distribution of reticulofenestrids in the Pacific suggested that size distribution patterns may reflect changes in nutrient concentration in the photic water column and, ultimately, it is productivity that controls the proportion of small and large coccoliths. The benthic carbon stable isotope record, organic carbon content, infaunal benthic foraminifer abundance, and phosphorus accumulation rate are, in many cases, well correlated to reticulofenestrid size distribution, suggesting that productivity may be an important controlling factor. On the other hand, the lack of consistent correlation between productivity proxies and size distribution at different sites and different intervals may be partly due to correlation errors but also indicates that they are influenced by complex and yet not well understood processes. |
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| Item Description: | Vita. "Major Subject: Oceanography". Includes 4 charts and 7 figures folded in pocket. |
| Physical Description: | xiii, 188 leaves : illustrations, maps ; 28 cm. Issued also on microfiche from University Microfilms Inc. |
| Bibliography: | Includes bibliographical references. |