Roehl, Ursula et al. (2005): The third and final early Eocene thermal maximum; characteristics, timing, and mechanisms of the "X" event

Leg/Site/Hole:
ODP 208
Identifier:
2006-062206
georefid

Creator:
Roehl, Ursula
Bremen University, DFG Research Center for Ocean Margins, Bremen, Federal Republic of Germany
author

Westerhold, Thomas
Universita di Firenze, Italy
author

Monechi, Simonetta
Wesleyan University, United States
author

Thomas, Ellen
University of California at Santa Cruz, United States
author

Zachos, James C.
author

Donner, Barbara
author

Identification:
The third and final early Eocene thermal maximum; characteristics, timing, and mechanisms of the "X" event
2005
In: Anonymous, Geological Society of America, 2005 annual meeting
Geological Society of America (GSA), Boulder, CO, United States
37
7
264
Prominent, widespread dissolution horizons in deep-sea carbonates (e.g., the horizon formed during the Paleocene-Eocene thermal maximum, PETM), may have been caused by significant CH (sub 4) -CO (sub 2) into the ocean-atmosphere system and thus correspond to abrupt climate events. Dissolution horizons signifying repeated, abrupt shoaling of the lysocline and CCD, however, are characteristic features of deep-sea sections and commonly attributed to Milankovitch forcing because of their diagnostic frequencies. The question thus arises whether significant dissolution horizons in upper Paleocene-early Eocene sediments similar to the PETM and the ELMO layer (Lourens et al., 2005; Nature) were also formed as the result of greenhouse gas input, suggesting a similar, Milankovich-modulated cause for all such events, or whether they were related to cumulative effects of periodic changes in ocean chemistry and circulation. We document a 3rd thermal maximum in lower Eocene (about 52 Ma) sediments (ODP Leg 208, SE Atlantic Ocean). The prominent clay layer, named the "X" event, occurs in planktonic foraminifer Zone P7 and calcareous nannofossil Zone CP10 at four Walvis Ridge Transect Sites (water depth range of 2000 m). Benthics foraminifera have low diversity and high dominance, and are dominated by small individuals of Nuttallides truempyi and various abyssaminids, resembling the post PETM extinction assemblages, with more severe effects at deeper sites. Calcareous nannofossil assemblages show similar trends to the PETM, with major changes in the genera Discoaster and Zygrhablithus, but with differences in magnitudes and fluctuations. High-resolution bulk carbonate stable isotope values at relatively shallow Site 1265 show a rapid, 0.6 per mille drop in delta (super 13) C and delta (super 18) O, followed by an exponential recovery to pre-excursion values, a pattern similar to that of the PETM and ELMO. Planktonic foraminiferal delta (super 13) C values (Morozovella subbotina, Acaranina soldadoensis) in the deepest Site 1262 decrease by 0.8 to 0.9 per mille, those of the benthic foraminifera Nuttalides truempyi by 1 per mille. We are evaluating mechanisms for the widespread change in deep-water chemistry, its connection to the surface-water response, and the temporal relation of the event, as well as the PETM and ELMO, with current astronomical solutions.
English
Coverage:Geographic coordinates:
North:-20.0000
West:-10.0000East: 10.0000
South:-40.0000

Stratigraphy; Acaranina soldadoensis; algae; aliphatic hydrocarbons; alkanes; assemblages; Atlantic Ocean; C-13/C-12; carbon; carbon dioxide; Cenozoic; deep-sea environment; Eocene; fluctuations; Foraminifera; geochemistry; high-resolution methods; hydrocarbons; hydrochemistry; Invertebrata; isotope ratios; isotopes; Leg 208; lower Eocene; marine environment; methane; microfossils; Milankovitch theory; Morozovella subbotina; nannofossils; Nutallides truempyi; O-18/O-16; Ocean Drilling Program; organic compounds; oxygen; paleo-oceanography; paleoatmosphere; Paleocene; paleoclimatology; Paleogene; planktonic taxa; Plantae; Protista; solution; South Atlantic; species diversity; stable isotopes; Tertiary; Walvis Ridge;

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