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| Titel |
Biotic change revealed by dinoflagellate cysts and a revised sequence stratigraphy for the Eocene-Oligocene transition at St. Stephens Quarry, Alabama, USA. |
| VerfasserIn |
Willemijn Quaijtaal, Sander Houben, Bridget Wade, Yair Rosenthal, Stefan Schouten, Henk Brinkhuis |
| Konferenz |
EGU General Assembly 2010
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 12 (2010) |
| Datensatznummer |
250037206
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| Zusammenfassung |
| The Eocene-Oligocene transition (EOT, ~34 Myr ago) reflects the final transition from the
early Paleogene Greenhouse into the present Icehouse World and represents the establishment
of a permanent ice sheet on Antarctica. This climatic shift is primarily recorded in benthic
foraminiferal oxygen isotope (δ18O) records as two steps to higher values that are 200 kyrs
apart. Unfortunately, the relative contribution of cooling and cryosphere expansion cannot be
separated in such records. Therefore, independent records of proxy data for temperature and
sea level are required.
The St Stephens Quarry (SSQ) in Alabama, USA, contains a relatively expanded and
presumably complete shelf succession spanning the EOT and is one of the global reference
sections. SSQ sediments bear well preserved foraminifera, suitable for stable isotope- and
Mg/Ca ratios. Moreover, organic matter, notably well-preserved organic walled dinoflagellate
cyst (dinocyst) assemblages and crenarcheotal membrane lipids are present to reconstruct
parameters such as sea level, productivity and paleotemperature.
Dinoflagellates are algae generally dwelling in surface waters and dinocysts have
appeared to sensitively record environmental changes. We infer sea level changes by
distinguishing dinocyst taxa typically associated with respectively lagoonal, high energetic
inner neritic and open oceanic environments. This led us to revise the previously
published sequence stratigraphy and age model for SSQ. Our data reveal a prominent
sequence boundary associated with the second oxygen isotope step. This illustrates the
non-linear relation between temperature and ice-volume, with the first oxygen isotope
step primarily reflecting cooling and the second primarily reflecting increasing
ice-volume.
Our dinocyst record may appear useful for future regional correlation between sites. Two
new dinocyst species have been discovered that may function as biostratigraphic markers for
the American Gulf Region. |
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