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| Titel |
Environmental- and sea-level change revealed by dinoflagellate cysts during the Eocene-Oligocene transition at St. Stephens Quarry, Alabama, USA |
| VerfasserIn |
Willemijn Quaijtaal, Bridget S. Wade, Stefan Schouten, Alexander J. P. Houben, Yair Rosenthal, Kenneth G. Miller, Henk Brinkhuis |
| Konferenz |
EGU General Assembly 2011
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 13 (2011) |
| Datensatznummer |
250051894
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| Zusammenfassung |
| The Eocene-Oligocene transition (EOT, ~34 Myr ago) represents the final transition from
the early Paleogene “Greenhouse” into the present “Icehouse” by the initiation
of Antarctic glaciation. The EOT is recorded in deep-sea benthic foraminiferal
oxygen isotope (δ18O) records as two increasing steps, ~200 kyr apart. However, the
relative contribution of cooling and increasing ice-volume cannot be separated from
such δ18O records. Independent temperature- and sea-level reconstructions are
crucial for understanding the order of events enveloping the onset of Antarctic
glaciation.
The classic reference section for the EOT, St Stephens Quarry (SSQ) in Alabama, USA,
contains a relatively expanded and complete shelf succession. Previous studies at SSQ have
already provided benthic foraminiferal stable isotope- and Mg/Ca based temperature
information. Sea surface temperatures were reconstructed using TEX86 and planktonic
Mg/Ca analyses. Altogether, these data show that the first step of the EOT (precursor or
EOT-1) primarily reflects cooling, whereas the second step (or Oi-1) primarily reflects
increasing ice-volume.
Here, we report on biotic change revealed by evaluating assemblages of fossil remains of
organic walled dinoflagellates (dinocysts). Dinoflagellates are a group of unicellular surface
dwelling algae and are often used to sensitively record environmental changes. We have
inferred sea level change by evaluating dinocyst assemblages in the relatively shallow section
of SSQ. This led us to revise the sequence stratigraphy and age model for SSQ. We document
a minor sea-level fall associated with the EOT-1 and a more substantial sea-level
fall at the Oi-1. At the EOT-1 we furthermore recorded the occurrence of a taxon
typically associated with cold water. This is in accordance with the geochemically
reconstructed temperature drop of 4-6 Ë C. Early Oligocene assemblages above the Oi-1 are
indicative of more productive and shallower lagoonal settings. Our records show that
the EOT was a period of profound environmental change, also in the (sub)tropics. |
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