Volcanism and the Rise of the Dinosaurs

Global paleogeographic setting during the Late Triassic. From X. Fu et al., 2020.

The Carnian Pluvial Episode (CPE), dated to 234–232 Ma, was a time of major turnover in the oceans and on land. It was characterized by global warming, ocean acidification, mega-monsoonal conditions, and a generalised increase in rainfall. In the marine sedimentary basins of the Tethys realm, an abrupt change of carbonate factories and the establishment of anoxic conditions mark the beginning of the climate change. This shift from arid to more humid conditions has been linked to the large-scale volcanism of the Wrangellia large igneous province (LIP). The widespread extinction caused by the CPE was followed by the first substantial diversification of dinosaurs.

Data from Central European Basin, Wessex Basin (United Kingdom), East Greenland (37), Morocco (38), Newark Basin (North America), and the Ischigualasto Basin (Argentina), indicate that increased rainfall resulted in the widespread expansion of the endorheic basins during the CPE. In the Jiyuan Basin, located in the southeast of the Ordos Basin, North China, an expanded Carnian lake succession offers a glimpse into this crucial interval.

 

Some representative palynological genera from the Jiyuan Basin (all scale bars = 20 μm). From Lu, Jing, et al., 2021

During the Early and Middle Triassic, North China was located in eastern Tethys. Later in the Triassic, the North China Plate collided with the South China Plate which resulted in extensive volcanism and the migration of the Ordos Basin depocenter continuously westward. High-resolution chemostratigraphy, palynological and sedimentological data indicate that four pulses of LIP volcanism were likely responsible for the global negative CIEs (carbon isotope excursion) that mark the CPE and drove major environmental changes.

The CPE also marks the first massive appearance of calcareous nannoplankton, while groups, like bryozoans and crinoids, show a sharp decline during this event. On land, palaeobotanical evidence shows a shift of floral associations towards elements more adapted to humid conditions (the palynological record across the CPE suggest at least 3–4 discrete humid pulses). During this interval, several families and orders make their first appearance: bennettitaleans, modern ferns, and conifer families (Pinaceae, Araucariaceae, Cheirolepidaceae), while key herbivorous groups such as dicynodonts and rhynchosaurs, which had represented 50% or more of faunas, disappeared.

Eoraptor lunensis, outcropping from the soil. Valle de la Luna (Moon Valley), Parque Provincial Ischigualasto, Provincia de San Juan, Argentina.

Followed the extinction of rhynchosaurs in most, or all, parts of the world, there was a burst of dinosaurian diversity in the late Carnian, represented by the upper Ischigualasto Formation and coeval units, with mostly carnivorous small- to medium-sized dinosaurs. Then, the long span of the early Norian, from 228.5–218 Ma, during which dicynodonts and sauropodomorph dinosaurs were the major herbivores. Finally, with the disappearance of dicynodonts, sauropodomorph dinosaurs became truly large in the middle and late Norian, from 218 Ma. This was followed by the extinction of basal archosaur groups during the end-Triassic mass extinction, 201 Ma, and the diversification of sauropods, larger theropods, ornithopods, and armoured dinosaurs subsequently, in the Jurassic.

 

References:

Lu, Jing, et al. Volcanically driven lacustrine ecosystem changes during the Carnian Pluvial Episode (Late Triassic), PNAS (2021). doi.org/10.1073/pnas.2109895118

X. Fu et al., A possible link between the Carnian Pluvial Event, global carbon-cycle perturbation, and volcanism: New data from the Qinghai-Tibet Plateau. Global Planet. Change 194, 103300 (2020) doi:10.1016/j.gloplacha.2020.103300

Michael J. Benton et al. The Carnian Pluvial Episode and the origin of dinosaurs, Journal of the Geological Society (2018). DOI: 10.1144/jgs2018-049

The Weissert Event

Paleogeographic map by C.R. Scotese, PALEOMAP project. From Cavalheiro et al., 2021

The continued fragmentation of Pangaea across the Late Jurassic and Early Cretaceous led to large-scale tectonic processes, on both regional and global scale, accompanied by some of the largest volcanic episodes in the history of the Earth, eustatic oscillations of the sea level, potentially heightened levels of anoxia, oceanic stagnation, and sulphur toxicity. The Weissert Event (~133 million years ago), linked with the main magmatic activity of the Parana`-Etendeka large igneous province (LIP), represents one of the most significant paleoceanographic events of the Early Cretaceous. This global perturbation in the C cycle is marked by a positive (+1.5‰) carbon isotope excursion (CIE) observed both in organic and inorganic records.

Global mean surface temperatures (GMSTs) and associated CO2 levels. From Cavalheiro et al., 2021.

A new study analyzed deep sea sediments obtained by the Ocean Drilling Program (ODP) from offshore Antarctica to reconstruct the paleotemperatures. The international team of researchers lead by Liyenne Cavalheiro combinded calcareous nannofossil data and chemostratigraphy, and found that that global temperatures declined by 3.0 °C (±1.7 °C) during the Weissert Event.

Calcareous nannoplankton represent a major component of oceanic phytoplankton. Their calcareous skeletons can be found in fine-grained pelagic sediments in high concentrations and the biomineralization of coccoliths is a globally significant rock-forming process. Additionally, reconstructions of Cretaceous sea-surface temperatures (SSTs) have been revolutionised by the development of the organic palaeothermometer TEX86, based on the distribution of marine archaeal membrane lipids.

 

 

 

References:

Cavalheiro, L., Wagner, T., Steinig, S. et al. Impact of global cooling on Early Cretaceous high pCO₂ world during the Weissert Event. Nat Commun 12, 5411 (2021). https://doi.org/10.1038/s41467-021-25706-0

Erba, E., Bartolini, A., & Larson, R. L. (2004). Valanginian Weissert oceanic anoxic event. Geology, 32(2), 149. doi:10.1130/g20008.1 

Holz, M., Mesozoic paleogeography and paleoclimates – a discussion of the diverse greenhouse and hothouse conditions of an alien world, Journal of South American Earth Sciences (2015), doi: 10.1016/j.jsames.2015.01.001

Forgotten women of Paleontology: Esther Richards Applin

Esther Richards Applin, 1944-1972. From Wikimedia Commons

In the 18th and 19th centuries women’s access to science was limited, and science was usually a ‘hobby’ for intelligent wealthy women. But at the beginning of 20th century, many universities started admitting women, with different motivations, including the lack of men following WWI and the Soviet Revolution. Later, the boom in the oil industry opened opportunities for women.
In 1920, E. T. Dumble, vice-president and general manager of the Rio Bravo Oil Company, put together a consortium agreement in Houston, which included his own company, the Texas Company, and Humble Oil Company. He hired Esther Applin née Richards, Alva Ellisor, and Hedwig Kniker to take charge of the company’s paleontological laboratory in Houston and solve the Gulf Coast stratigraphic problems. Macrofossils were too badly broken to be identifiable as to species, so Esther Applin turned her attention to the microfossils, especially foraminifera. It was the beggining of the micropaleontological revolution.

Esther Richards was born November 24, 1895, in in Newark, Ohio. She attended the University of California, Berkeley, and graduated with honors in paleontology in 1919. A year later, she moved to Houston to work for the Rio Bravo Oil company. In 1923, she married Paul L. Applin, a young geologist. In 1921, Esther presented a paper suggesting that microfossils could be use to stratigraphic correlation. Her study was ridiculed by Professor J.J. Galloway of the University of Texas, who stated: “Gentlemen, here is this chit of a girl, right out of college, telling us that we can use Foraminifera to determine the age of formation. Gentlemen, you know that it can’t be done.”

From left to right: Esther Richards, John Suman, James L. Ballard, Alva Ellisor at Hidalgo Bluff near the Brazos River Botton. (From R.R.Gries. 2018)

In 1924, at a meeting of the American Association of Petroleum Geologists (AAPG), Alva Ellisor, Esther Applin née Richards, and Hedwig Kniker presented their seminal paper: Subsurface stratigraphy o f the Coastal Plain of Texas and Louisiana. Since then, Micropaleontology was quickly embraced by industry, and even Galloway became a defender of this method. However, the role of these women was downplayed over time, and by 1975 the credit for this technology was shifted to four men.

Esther continued her work as a consulting paleontologist and subsurface geologist in Texas. She become a Fellow of The Geological Society of America, a charter member of the Society of Economic Paleontologists and Mineralogists, and a member o f the Mississippi Geological Society. In 1966, in recognition of her contributions to micropaleontology, she was made an honorary member o f the Mississippi Geological Society. She died on July 23, 1972.

References:

Richards Applin, Esther; Ellisor, Alva E.; Kniker, Hedwig T. (1925). “Subsurface Stratigraphy of the Coastal Plain of Texas and Louisiana”. American Association of Petroleum Geologists Bulletin. 9 (1): 79–122.

Gries, Robbie Rice (2018). “How female geologists were written out of history: The micropaleontology breakthrough”. Women and Geology: Who Are We, Where Have We Come from, and Where Are We Going?. doi:10.1130/2018.1214(02).