LARGE IGNEOUS PROVINCES (LIPS) AND GLOBAL ENVIRONMENTAL PERTURBATIONS: THE APTIAN ONTONG JAVA-HIKURANGI-MANIHIKI PLATEAU EVENT

The Ontong Java, Hikurangi, and Manihiki Plateaus are dispersed remnants of a once-continuous large igneous province (LIP), the OJHMP, that formed during the early Aptian (lower Cretaceous). This was a magmatic event of mammoth proportions (a volume perhaps 10⁷ km³), with the potential to wreak major global change through volatile outgassing and ocean chemical changes. Although there is no known major biotic extinction event associated with this LIP, the formation of the OJHMP has been linked to an episode of widespread black shale deposition (the so-called “Selli Event” or Oceanic Anoxic Event 1a), a hiatus in marine carbonate sedimentation and a coincident negative carbon isotope excursion, and, possibly, a global warming event. Magnetic, absolute ages and refined biostratigraphy allow detailed assessments of the relative timings of these events, but there remain uncertainties regarding the OJHMP eruption and outgassing history and timing of the response of the carbon cycle. New assessments of orbital chronologies for the early Aptian suggest that the negative carbon isotope excursion occurred over 27 to 41 ka, and the duration of low-carbonate black shale deposition was about 890 ka. A carbon cycle model can produce the pattern, timing and amplitude of carbon isotope variations in organic carbon and carbonate assuming an initial period of rapid volcanic carbon dioxide outgassing followed by a stepwise decrease in rates of outgassing over 2 to 3 Ma. The model also produces a major increase in atmospheric pCO₂ through the Selli Event that could explain observed warming, but the simulated pCO₂ increase (8x) that is produced by the simulation that best fits the carbon isotope record exceeds estimates based on biomarker carbon isotopes and stomatal indices (4x).