Figure 7 - uploaded by Hannah M E Shepherd
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Correlated stratigraphic columns from Yreka-1 and Pulp Mill Hill localities
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... primary purpose of laboratory methods was making suitable casts and identification of the abundant bivalves and scleractinian corals, since large portion of the bivalves, from both The shale section at Yreka-1 and Pulp Mill Hill lie above the black limestone (Fig. 7), and contains abundant trigonid bivalve fossils (Plate 3). All of the trigonid fossils are external molds, and appear to be all of the same species, Myophorigonia paucicostata (Jaworski, ...
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... whether they survived the end-Triassic mass extinction (i.e. existing both in Triassic and Jurassic periods), to form a binomial data set (0=did not survive, 1=survived). I then analyzed this data in the R program (http://www.r-project.org/) using a two sample T-test, and created a boxplot comparing the non-surviving species to those that did not (Fig. 7). ...
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... to the Jurassic and level of integration (2-sided p-value = 0.9345). Only twelve species from this database are found in both the Triassic and Jurassic, so the data set for the t-test was relatively small. Corals with higher levels of integration survived the Triassic-Jurassic extinction about as well as those with lower levels of integration (Fig. 7). This result is counterintuitive, because it is thought that corals with more complex morphology had a closer reliance on stable environmental conditions. Modern highly integrated corals are found mostly at low latitudes and shallow water and require stable temperatures (Oliver and Coates, 1987). Also and perhaps equally important, ...
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... However, the timescale used in Kiessling's compilations is very coarse (it is only divided into Ladinian-Norian-Pliensbachian) and shows a steady decline in diversity throughout this time interval to reach a diversity low in the Middle Jurassic (Bajocian/Bathonian). Nonetheless, this did not deter Kiessling et al. (1999) from identifying a major extinction of reefs at the TJB. Similarly, CCE-influenced analyses show a mass extinction of reefs across the TJB (e.g., Flugel and Kiessling 2002;Shepherd 2013). ...
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The Triassic-Jurassic (T/J) mass extinction boundary is well represented stratigraphically with a continuous depositional section spanning the Gabbs and Sunrise formations at New York Canyon, Nevada. These marine deposits display a sedimentological and paleontological record of intense environmental changes and biotic turnover, particularly for corals. During this period of global climate change approximately 200 million years ago, sea level was dropping and the Central Atlantic Magmatic Province was releasing prodigious amounts of greenhouse gases and volatiles with increasing ocean acidity. Corals reefs collapsed abruptly at the end of the Triassic. While the Jurassic recovery was underway during the first few million years following the extinction, reefs and coral diversity did not fully recover until 25 million years later. Compared to the Tethys, precious little is known about western North America where reefs and diverse corals of the Late Triassic lived around volcanic islands of eastern Panthalassa. Here we report rare early Jurassic corals from New York Canyon. These are mostly solitary and represent a phase of the recovery for the earliest of Jurassic corals of North America. The corals, located approximately 20 meters above the T/J boundary in the Ferguson Hill Member of the lower Sunrise Formation, are in-situ and occur as a meter-thick limestone pavement. They are mostly solitary coral taxa and may be compared with counterparts in the Tethys and elsewhere in North America. Other noteworthy fossils are found at the coral interval including the bivalve Weyla. Ongoing research focuses on these earliest Jurassic corals and others including an exceptional Early Jurassic reef in the Santa Rosa Formation, Sonora, Mexico. In Sonora, the shallow-water patch reefs reach 20-30 meters in thickness and extend laterally for more than a kilometer. The coral faunas of both Nevada and Sonora provide useful data on the paleoecology, paleobiogeography and recovery of corals and reef-faunas following the end-Triassic mass extinction.
During the Late Triassic, roughly 200 million years ago, coral reefs flourished and coral diversity was at a maximum. At the end-Triassic, the supercontinent Pangea began splitting at a massive volcanic rift that released prodigious amounts of volcanic greenhouse gases. Ocean pH increased leading to ocean acidification and sea level dropped. Coral reefs responded by collapsing globally at the end of the Triassic. The transition to the Triassic and Jurassic eras are marked by a major mass extinction at which time more than half of life on Earth and almost 90 percent of marine life died. While the Jurassic recovery was underway during the first few million years following the extinction, corals and reefs did not fully recover until almost 25 million years later. Early Jurassic coral fossils are thus extremely rare worldwide. Only a couple Early Jurassic sites have been reported in North America. Precious little is known about coral recovery in western North America where reefs and diverse corals of the Late Triassic had inhabited volcanic settings (Figure 1). Scleractinian (stony) corals from the Early Jurassic are not well-represented or studied in North America and until now had not been reported in the United States or Mexico. Here we illustrate previously undescribed Early Jurassic corals from New York Canyon in Nevada, USA, and Sierra de Santa Rosa in Sonora, Mexico.
Within the Sierra de Santa Rosa Formation of the El Antimonio Terrane in Sonora, Mexico, are Early Jurassic corals spanning from Sinemurian to Toarcian in age. A global mass extinction occurred at the Triassic-Jurassic boundary and coral reefs experienced considerable stress near the end-Triassic. During this period of global climate change approximately 200 million years ago, sea level was dropping and the Central Atlantic Magmatic Province was releasing prodigious amounts of greenhouse gases and volatiles with increasing ocean acidity. Corals and coral reefs collapsed abruptly during the end of the Triassic. While the Jurassic recovery was underway during the first few million years following the extinction event, reefs were exceedingly rare and coral diversity was further suppressed during the Toarcian Oceanic Anoxic Event associated with the Karoo-Ferrar large igneous province. Corals did not fully recover until the Middle Jurassic. The dynamics of coral collapse and recovery are relevant to understanding marine deposition and the nature of ecological stresses following the mass extinction. Compared to the Tethys, precious little is known about the recovery in western North America where reefs and diverse corals of the Late Triassic had inhabited numerous volcanic settings in eastern Panthalassa. The Sierra de Santa Rosa Formation is divided into lower, middle, and upper members encompassing approximately 1500 meters in thickness and includes fossiliferous, shallow to deeper water marine sequences in strata tectonically overlying Precambrian metamorphic basement rock and conformably underlying the volcanic Cerro San Luis Formation. The Sierra de Santa Rosa Formation has been established as Early Jurassic using bivalves and ammonites along with U-Pb dating of detrital zircons. Early Jurassic corals occur at multiple locations in the middle and upper members of the Sierra de Santa Rosa Formation. These coral locations include Sinemurian solitary corals in impure limestone and Toracian reef-building colonial corals in carbonate rock buildups. Most coral fauna consists of highly recrystallized scleractinian corals which reveal mainly macroscopic details. The analysis of these corals is used to test paleogeographic and tectonic models for northwestern Sonora and adjacent USA. The Sonoran reef-like buildups are perhaps the only Toarcian examples in the USA and Mexico. The coral faunas and other marine fossils of the Sierra de Santa Rosa Formation provide relevant data with which to assess paleoecology, paleobiogeography and biotic recovery during the critical interval following the end-Triassic mass extinction.
A Triassic-Jurassic (T/J) mass extinction boundary is well represented stratigraphically in west-central Nevada, USA, near New York Canyon, where the Gabbs and Sunrise Formations contain a continuou depositional section from the Luning Embayment. The well-exposed marine sediments at the T/J section have been extensively studied and reveal a sedimentological and paleontological record of intense environmental change and biotic turnover, which has been compared globally. Unlike the former Tethys region, Early Jurassic scleractinian corals surviving the end-Triassic mass extinction are not well-represented in the Americas. Here we illustrate corals of Early Sinemurian age from Nevada located at three horizons above the T/J boundary. These well-preserved corals represent one of the earliest Jurassic appearances in North America and the earliest in the United States. Their co-occurrence with bivalves, gastropods, and ammonites adds additional faunal elements to the study. The corals are exclusively solitary and occur in profusion packed within beds. They all belong to the family Stylophyllidae, known to have been extinction resistant. These post-extinction corals support the Hispanic Corridor hypothesis and provide new data on biotic recovery following the end-Triassic mass extinction.
