Astronomical calibration of late middle Eocene radiolarian bioevents from ODP Site 1260 (equatorial Atlantic, Leg 207) and refinement of the global tropical radiolarian biozonation
<p>The middle Eocene sedimentary sequence drilled at Ocean Drilling Program Site 1260 (Leg 207), Demerara Rise, western equatorial Atlantic, yielded a rich and diverse radiolarian fauna. The exceptionally expanded and complete sedimentary record of this site, as well as the existence of an orb...
| Main Authors: | , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2022-02-01
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| Series: | Journal of Micropalaeontology |
| Online Access: | https://jm.copernicus.org/articles/41/1/2022/jm-41-1-2022.pdf |
| Summary: | <p>The middle Eocene sedimentary sequence drilled at Ocean
Drilling Program Site 1260 (Leg 207), Demerara Rise, western equatorial
Atlantic, yielded a rich and diverse radiolarian fauna. The exceptionally
expanded and complete sedimentary record of this site, as well as the
existence of an orbital chronological framework, allowed us to study a
number of radiolarian bioevents with a very fine temporal resolution. We
compiled a well-resolved succession of 71 radiolarian bioevents (first
occurrences, last occurrences, and evolutionary transitions) and provided
calibrations to the geomagnetic polarity timescale and astronomical timescale. Comparison of the radiolarian successions at ODP Site 1260A with the
northwestern Atlantic IODP Site U1403 and the IODP Sites U1331, U1332, and
1333, situated in eastern equatorial Pacific, allowed the demonstration of the
synchroneity of primary radiolarian bioevents that underpin the middle
Eocene zonal scheme. Several secondary bioevents were also found to be
synchronous between the two oceans and were therefore used to define seven
new subzones for the low-latitudinal middle Eocene sequences: <i>Siphocampe</i> ? <i>amygdala</i> interval
subzone (RP13a), <i>Coccolarnacium</i> <i>periphaenoides</i> interval subzone (RP13b), <i>Artostrobus</i> <i>quadriporus</i> interval subzone (RP14a),
<i>Sethochytris</i> <i>triconiscus</i> interval subzone (RP14b), <i>Podocyrtis</i> (<i>Podocyrtopsis</i>) <i>apeza</i> interval subzone (RP14c), <i>Artobotrys</i> <i>biaurita</i> interval subzone
(RP15a), and <i>Thyrsocyrtis</i> (<i>Pentalocorys</i>) <i>krooni</i> interval subzone (RP15b). This refined radiolarian
biozonation has significantly improved stratigraphic resolution and age
control for the late middle Eocene interval (an average of two subzones per
1.5 million years). A substantial diachronism was also found in 20 secondary
radiolarian bioevents between the two oceans. The majority of radiolarian
species appear to have evolved first in the equatorial Atlantic Ocean and
subsequently in the equatorial Pacific. However, the reasons for this
pattern of diachroneity currently remain uncertain and would require a
greater sampling coverage to be elucidated.</p> |
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| ISSN: | 0262-821X 2041-4978 |