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Chronology and eccentricity phasing for the Early Turonian greenhouse (~93-94 Ma): constraints on astronomical control of the carbon cycle
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  • Jiří Laurin,
  • David Uličný,
  • Stanislav Čech,
  • Jakub Trubač,
  • Jiří Zachariáš,
  • Andrea Svobodová
Jiří Laurin
Academy of Sciences of the Czech Republic (ASCR), Academy of Sciences of the Czech Republic (ASCR)

Corresponding Author:[email protected]

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David Uličný
Academy of Sciences of the Czech Republic (ASCR), Academy of Sciences of the Czech Republic (ASCR)
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Stanislav Čech
Czech Geological Survey, Czech Geological Survey
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Jakub Trubač
Charles University, Charles University
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Jiří Zachariáš
Charles University, Charles University
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Andrea Svobodová
Institute of Geology of the Czech Academy of Sciences, Institute of Geology of the Czech Academy of Sciences
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Abstract

The Early Turonian interval represents a unique confluence of climatic and oceanographic conditions including peak surface temperatures, high greenhouse-gas concentrations and maximum Phanerozoic sea level. The susceptibility of this climate mode to astronomical insolation forcing remains poorly understood partly due to a limited time control and unknown phasing of astronomical cycles in this interval. Here we offer a refined astrochronology of the Early Turonian based on laterally consistent precession signals preserved in offshore strata of the Bohemian Cretaceous Basin (central Europe). Pristine amplitude modulation verified through interference patterns in depth-frequency plots provides a robust indication of ~100-kyr and 405-kyr eccentricity phases (maxima and minima) that are pinned to ammonite biozones and new carbon-isotope data from two cores. The Early Turonian is estimated as 885 ±41 (2s) thousand years (kyr) in duration, with the Cenomanian/Turonian boundary predating the first Turonian 405-kyr maximum (no. 232 in the Geological Time Scale 2020) by 82 ±70 (2s) kyr. The results support a possible link of the recovery from Oceanic Anoxic Event II to increasing magnitude of seasonal insolation extremes due to rising eccentricity on 405-kyr and million-year (Myr) time scales. Superimposed upon this trend are small-scale carbon-isotope anomalies the pacing of which passes from ~110 kyr, resembling short eccentricity, to ~170-kyr, possibly related to obliquity modulation. This eccentricity-to-obliquity transition paralleling the rising phase of Myr-scale eccentricity cycle suggests decoupling of the carbon-cycle perturbations from low-latitude seasonal insolation and involvement of mid- to high-latitude carbon reservoirs.
Apr 2021Published in Paleoceanography and Paleoclimatology volume 36 issue 4. 10.1029/2020PA004188