Element cycling in the Middle-Late Triassic Shublik Formation: Mineralization vs. recycling of biolimiting nutrients in an unconventional resource play

The Triassic Shublik Formation in northern Alaska is one of the major source rocks in North America, having generated much of the petroleum in Prudhoe Bay and associated fields. The middle Shublik Formation, the focus of this study, is a highly phosphatic, organic-rich carbonate mudstone interval. Apatite cements can occur as phosphatic peloids, steinkerns, elongate or angular nodules, and shells or shell fragments. We propose a model whereby phosphatization is favored in early diagenetic environments that have low concentrations of dissolved iron relative to reactive organic matter in the pore water sulfate reduction zone.