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Paleoclimatic and paleoenvironmental records of the Oligocene-Miocene transition, central Jylland, Denmark
Sliwinska, K.K.; Dybkjær, K.; Schoon, P.L.; Beyer, C.; King, C.; Schouten, S.; Nielsen, O.B. (2014). Paleoclimatic and paleoenvironmental records of the Oligocene-Miocene transition, central Jylland, Denmark. Mar. Geol. 350: 1-15. dx.doi.org/10.1016/j.margeo.2013.12.014
In: Marine Geology. Elsevier: Amsterdam. ISSN 0025-3227, more
Peer reviewed article  

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Keyword
Author keywords
    GDGT proxies; dinocysts; foraminifera; magnetostratigraphy;Oligocene/Miocene boundary; Mi-1 cooling event; delta C-13

Authors  Top 
  • Sliwinska, K.K.
  • Dybkjær, K.
  • Schoon, P.L., more
  • Beyer, C.
  • King, C.
  • Schouten, S., more
  • Nielsen, O.B.

Abstract
    A multidisciplinary study of the Oligocene/Miocene (O/M) transition was carried in two boreholes (Harre-1 and Horn-1) from the Danish land area in order to improve the understanding of the paleodimatological and environmental changes across the Mi-1, the earliest Miocene cooling event. Dinoflagellate cyst (dinocyst) biostratigraphy, supported by re-evaluation of the foraminiferid biostratigraphy, a new set of magnetic data and stable carbon isotope (delta C-13) records were applied to improve the age model for the studied succession; as well as the positioning of the O/M boundary. These data further enabled a correlation of the two investigated profiles with the well-established stratigraphical framework for the Danish area.
    The BIT index (an organic proxy indicating the relative input of soil-derived organic matter), dinocyst assemblages and palynofacies have been applied for establishing the paleoenvironmental changes across the Oligocene/Miocene (O/M) boundary. Our data indicate a shallowing upward trend in the latest Oligocene, resulting in the establishment of a very restricted marine setting in the earliest Miocene. Our study confirms that the O/M boundary is located at a sequence boundary (the local sequence boundary B - SB B) and corresponds to an increase in terrestrial organic matter input.
    A mean air temperature record based on the MBT'/CBT proxy reveals an similar to 2 degrees C drop in temperature at the O/M and the sequence boundary. Our findings confirm previous suggestions that this sequence boundary is a result of the glacio-eustatic sea level fall related with the Mi-1 cooling event The unconformity at the sequence boundary probably correlates with the coldest part of Mi-1, and thus no deposits from this period have been preserved. This suggests that the temperature drop might have been greater than 2 degrees C.

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