The organic carbon isotopic and paleontological record across the Triassic-Jurassic boundary at the candidate GSSP section at Ferguson Hill, Muller Canyon, Nevada, USA

Abstract

We present new litho-, bio-, and chemostratigraphic data from the Triassic–Jurassic (T–J) boundary section at Ferguson Hill (Muller Canyon), Nevada, USA. This section is a candidate for the base of the Hettangian Stage and thus the T–J boundary. Our measurements yield a 19 m thickness for the Muller Canyon Member of the Gabbs Formation. We recognize the Triassic–Jurassic boundary using the first appearance of Agerchlamys, and place it 9.6 m above the boundary between the Muller Canyon Member and the subjacent Mount Hyatt Member, with the first occurrence of the ammonite Psiloceras tilmanni occurring 0.9 m above this. Our organic carbon isotope record from this section shows two excursions toward lighter values, one at the T–J boundary, and the second in the lower parts of the Jurassic Sunrise Formation. These results are significantly different from a prior report on light stable isotopes from this section.