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North American coral recovery after the end-Triassic mass
extinction, New York Canyon, Nevada, USA
Montana S. Hodges* and George D. Stanley Jr., University of INTRODUCTION
Montana Paleontology Center, 32 Campus Drive, Missoula,
Montana 59812, USA Mass extinction events punctuate the evolution of marine envi-
ronments, and recovery biotas paved the way for major biotic
ABSTRACT changes. Understanding the responses of marine organisms in the
post-extinction recovery phase is paramount to gaining insight
A Triassic-Jurassic (T/J) mass extinction boundary is well repre- into the dynamics of these changes, many of which brought
sented stratigraphically in west-central Nevada, USA, near New sweeping biotic reorganizations. One of the five biggest mass
York Canyon, where the Gabbs and Sunrise Formations contain a extinctions was that of the end-Triassic, which was quickly
continuous depositional section from the Luning Embayment. followed by phases of recovery in the Early Jurassic. The earliest
The well-exposed marine sediments at the T/J section have been Jurassic witnessed the loss of conodonts, severe reductions in
extensively studied and reveal a sedimentological and paleonto- ammonoids, and reductions in brachiopods, bivalves, gastropods,
logical record of intense environmental change and biotic turn- and foraminifers. Reef ecosystems nearly collapsed with a reduc-
over, which has been compared globally. Unlike the former Tethys tion in deposition of CaCO3. Extensive volcanism in the Central
region, Early Jurassic scleractinian corals surviving the end- Atlantic Magmatic Province and release of gas hydrates and other
Triassic mass extinction are not well-represented in the Americas. greenhouse gases escalated CO2 and led to ocean acidification of
Here we illustrate corals of Early Sinemurian age from Nevada the end-Triassic (Hautmann et al., 2008).
located at three horizons above the T/J boundary. These well-
preserved corals represent one of the earliest Jurassic appearances Reef-building scleractinian corals and spinctozoid sponges experi-
in North America and the earliest in the United States. Their enced severe setbacks after the Late Triassic reef optimum (Stanley,
co-occurrence with bivalves, gastropods, and ammonites adds 2003; Flügel, 2002). Although coral recovery began soon after the
additional faunal elements to the study. The corals are exclusively extinction (Lathuilière and Marchal, 2009), their diversity was low
solitary and occur in profusion packed within beds. They all (Fig. 1). Compared to other calcified biotas, reef-building corals and
belong to the family Stylophyllidae, known to have been extinc- sponges experienced proportionately greater losses (corals, 96.1%;
tion resistant. These post-extinction corals support the Hispanic sponges 91.4%), possibly related to their reduced physiological
Corridor hypothesis and provide new data on biotic recovery control of calcification with respect to aragonite saturation
following the end-Triassic mass extinction. (Hautmann et al., 2008). Most reports of Early Jurassic corals come
from tropical to subtropical regions of the former Tethys, now
Figure 1. Reef diversity through time
plotted by highest to lowest corallite
integration levels. Information derived
from Paleobiology Database; figure from
Shepherd, 2013. Het—Hettangian.
GSA TODAY | OCTOBER 2015
GSA Today, v. 25, no. 10, doi: 10.1130/GSATG249A
*E-mail: montana.hodges@umconnect.umt.edu
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