Page 7 - gt1510
P. 7
Figure 5. In-situ corals from the Ferguson Hill Member displaying reworked Peru (Stanley and Beauvais, 1994). In the Tethys, identical or GSA TODAY | www.geosociety.org/gsatoday
and life positions. Scale bar: 1 cm. Specimen no. UMPC14690. closely related stylophyllids likewise constructed the two known
earliest Jurassic patch reefs (Kiessling et al., 2009; Gretz et al.,
sediment rejection and polyp regeneration. The lack of colonial 2013). Stylophyllopsis, Protostylophyllum, and Haimeicyclus at
corals is unusual and might indicate that these solitary taxa New York Canyon reveal a strong taxonomic connection with
were better adapted at sediment rejection or that they were Tethyan taxa. New York Canyon corals such as Protostylophyllum
ahermatypic and, like many living examples, utilized a simple also reveal close affinities with Upper Triassic Tethyan species of
growth form. the same genus (Roniewicz and Michalík, 2002).
JURASSIC RECOVERY AMONG CORALS Compared to the Tethys, precious little is known about
American corals after the end-Triassic event. In west-central
Many marine faunas underwent an Early Jurassic post- Nevada, Upper Triassic corals are well documented from the
extinction recovery including corals. Earliest Jurassic (Hettangian) Luning and Osobb Formations (Roniewicz and Stanley, 2013).
corals occur in mostly low diversity associations in the former The Triassic corals of Nevada reveal strong North American
Tethys region and appear absent in North America. Sinemurian endemism but strangely lack any representatives of the stylo-
coral deposits are known in reefs of British Columbia, Canada phyllids that are so pervasive in the Triassic Tethys. The cosmo-
(Stanley and Beauvais, 1994), and Sonora, Mexico (González- politan pattern of the Early Jurassic New York Canyon
León, et al., 2005). Sinemurian patch reefs also come from Peru stylophyllid corals compared with those of the Tethys, along
(Wells, 1953). Non–reef building Hettangian to Sinemurian with the endemic pattern of the Late Triassic corals of Nevada,
corals also occur in Peru (Senowbari-Daryan and Stanley, 1994) provide paleobiogeographic support for the Hispanic Corridor
and Chile (Prinz, 1991). The Early Jurassic corals of the (Smith, 1983). The Hispanic Corridor was a narrow, embryonic
Americas are mostly holdover taxa from the Triassic. Atlantic seaway hypothesized to have opened in Pliensbachian
time, creating a shortcut connection between the Tethys and
Tethyan reef recovery started in the Hettangian (Kiessling et eastern Panthalassa (Aberhan, 2001). The New York Canyon
al., 2009; Gretz et al., 2013) but coral diversity was low. From corals indicate the existence of this seaway earlier in the
the standpoint of changes in taxonomic composition, Tethyan Sinemurian, supporting the postulates of Sha (2002).
corals show a recovery within the post-extinction survival
interval (Beauvais, 1989). Their taxonomic composition reveals DISCUSSION AND CONCLUSIONS
dominantly Triassic holdover taxa during the earliest
Hettangian to Sinemurian intervals with increasingly new taxa The collapse of marine ecosystems at the end-Triassic is linked
into the Pliensbachian. By the Toarcian, an entirely new to ocean acidification, and a biocalcification crisis accounts for
Jurassic coral assemblage evolved with few Triassic holdovers the scarcity of corals and reefs in the Early Jurassic (Martindale et
(Beauvais, 1986). From the standpoint of coral and reef diver- al., 2012). The geographic proliferation of Late Triassic reefs
sity, it was not until the Middle Jurassic that the ecosystem was through the Tethys is in stark contrast to their Early Jurassic
fully recovered (Stanley, 1997). By that time most Triassic reduction (Fig. 6). The Early Jurassic reef eclipse is revealed by
holdovers were extinct. only two rare examples, those in southern France (Kiessling et
al., 2009) and Scotland (Gretz et al., 2013). This is the effect
Corals of the family Stylophyllidae (including New York predicted for modern reefs under ocean acidification models
Canyon) survived the end-Triassic extinction in the Tethys and projected 35–60 years from today (Hoegh-Guldberg et al., 2007).
diversified during the Early Jurassic (Melnikova and Roniewicz, In Early Jurassic deposits of the Tethys, stylophyllid corals were
2012). This group is represented by solitary and phaceloid corals, common (Beauvais, 1976), along with cerioid Septastrea and
which flourished briefly in the post-extinction aftermath. The Astrocoenia. Melnikova and Roniewicz (2012) reported Early
branching Phacelostylophyllum rugosum, for example, was the Jurassic corals from the Pamir Mountains (Hettangian-
reef builder in western Canada and Chile, while another Sinemurian) and noted how stylophyllids pass through the
Phacelostylophyllum species dominated the Early Jurassic reef in Triassic briefly proliferating during Early Jurassic time. A late
Sinemurian coral reef reported from an outboard oceanic terrane
in western Canada (Stanley and McRoberts, 1993) was constructed
by large colonies of the stylophyllid Phacelostylophyllum (Stanley
and Beauvais, 1994). A comprehensive database of Triassic and
Jurassic Tethyan corals (Lathuilière and Marchal, 2009;
Roniewicz and Morycowa, 1993) shows the survival pattern.
The New York Canyon corals offer additional information on
recovery in eastern Panthalassa along the craton of North
America. Paleogeographically, the New York Canyon corals show
a strong connection with Tethys but in contrast are exclusively
solitary and exclusively stylophyllid taxa. Hettangian corals are
unknown from North America, so for the present, the New York
Canyon site may be the earliest North American Jurassic
example. Analysis of these corals fills a neglected but important
part of the T/J recovery phase in North America, while lending
support for an earlier opening of the Hispanic Corridor.
7
