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Figure 2. Geologic map of New York Canyon,
Nevada, USA. The Involutum Zone coral-collecting
sites labeled A–I are located in the upper layers of
the Js2 unit. Map modified from Ferguson and
Muller, 1949.
comprising central Eurasia and Morocco (Lathuilière and Marchal, Wignall, 2000), the biochronology (Guex, 1995; Taylor et al., GSA TODAY | www.geosociety.org/gsatoday
2009). Jurassic examples from the Americas are rare, while Triassic 2001), and carbon isotopes (Guex et al., 2004; Ward et al., 2007;
corals are relatively common (Stanley, 1997). Porter et al., 2014) have established the Ferguson Hill section as a
relatively complete marine sequence spanning the Upper Triassic
Because Early Jurassic corals from North America are so rare, to Lower Jurassic boundary (Guex et al., 1997; McRoberts et al.,
new occurrences are vital to understanding biotic responses in the 2007; Lucas et al., 2007; Ritterbush et al., 2014).
post–mass extinction interval. Here we make a preliminary report
of the earliest Jurassic corals from the USA and some of the Early Jurassic corals forming the basis of this report were
earliest in North America. These examples occur at New York collected from nine sites in the Ferguson Hill Member of the
Canyon in west-central Nevada’s Sunrise Formation (Fig. 2). The Sunrise Formation (in the vicinity of New York Canyon, Fig. 2)
site has attracted international attention because it is among the including the Involutum Zone Type Section (Taylor et al.,
best documented T/J sections (Lucas et al., 2007). The coral 2001) and the Ferguson Hill section, just above the T/J
occurrences in this section are near the T/J boundary, making the boundary (Fig. 3). All locations are in the Early Sinemurian
Nevada site ideal for understanding the dynamics of coral Involutum Zone, a Cordilleran ammonite zone correlated with
recovery and comparing them with the Tethys. the upper Bucklandi subzone to lower Semicostatum zone of
northwestern Europe (Taylor et al., 2001).
GEOLOGIC SETTING AND BIOCHRONOLOGY OF
NEW YORK CANYON The Involutum Zone at New York Canyon corresponds to the
15-m-thick, thin-to-medium bedded limestone and siltstone
The Gabbs and Sunrise Formations at New York Canyon were superjacent to the more thickly bedded dark gray-to-black chert-
first described by Muller and Ferguson (1936) and have become rich limestone (Taylor et al., 1983). The base of the New York
an international reference section for the T/J boundary. In New Canyon Involutum Zone is well-demarcated by bioclastic lime-
York Canyon, the Lower Jurassic Sunrise Formation and under- stone overlaying more resistant, darker siliciclastic limestone beds
lying Upper Triassic Gabbs Formation represent coherent and (Taylor et al., 2001) and is very pronounced at Ferguson Hill. The
conformable alternating siltstone and limestone marine sequences Involutum Zone occurs in the upper beds of the Js2 unit (Fig. 2).
deposited in the shallow portion of the Luning Embayment.
Investigations on the stratigraphy (Taylor et al., 1983; Hallam and Corals in the New York Canyon area are biostratigraphically
constrained by ammonites in three horizons measured above the
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