ABSTRACT

High-precision U-Pb zircon geochronology and intracontinental correlation of terrestrial ecosystems during the 'zenith' of dinosaur diversity in the Late Campanian of North America

Samuel Bowring
EAR-1424892--MIT
ABSTRACT
Non-technical overview:
A major question is whether global environmental change cause changes in biological evolution. The time period between 80 and 70 million years ago has been described as the ?zenith? of dinosaur diversity and western North America contains unparalleled exposures of rocks with abundant dinosaur fossils from this time period. We do not have a good understanding of what triggered this burst of evolutionary diversity but we do know that at the same time were profound, global-scale environmental changes, including an increase in global atmospheric temperatures and an abrupt rise in sea level. However some have argued that the apparent increase in diversity has more to do with preservation than evolution. To test whether global environmental changes or preferential preservation are responsible, we must be able to correlate rocks and fossils from southern Canada to the southwestern United States. This project will focus on high precision dating of volcanic rocks interlayered with fossil bearing rocks so that we determine the rates of evolution across more than 2000 km of latitude in western North America. This will allow us to in turn evaluate whether evidence for environmental change preserved in the rocks can be correlated with dinosaur evolution.

Technical Abstract
This project will focus on developing an unparalleled chronostratigraphy for an approximately ten million year (80-70 Ma) interval across a 2000 km long corridor of Late Campanian (Cretaceous) strata preserved in the Western Interior Basin of western North America (Laramidia). This represents one of the most laterally extensive and fossiliferous continental successions in the world, and includes the famous Two Medicine-Judith River fauna/flora in Montana and Wyoming, the Dinosaur Park fauna/flora in Alberta, the Kaiparowits fauna/flora in Utah, the Kirtland-Fruitland fauna/flora in New Mexico and the Aguja fauna in Texas. The research team will use high-precision U-Pb zircon geochronology on volcanic ash beds to build age models for each area and allow detailed correlations and insight into evolutionary/preservation trends.
The Western Interior Basin has been pivotal in the formation and assessment of many hypotheses relating to Late Cretaceous vertebrates, from physiology and behavior to biogeography and evolution. Recent discoveries from the southern Western Interior (i.e., Utah, New Mexico, Texas, Mexico) and the far north (Alaska) have revealed new Campanian-aged vertebrate faunas, highlighted by an array of previously unknown dinosaurs, other vertebrates and plants. Following more than a century of intense sampling and study, more is known about Campanian terrestrial vertebrates from Laramidia (western North America) than from any other continent-scale region of Mesozoic age. Thus, Campanian Laramidia represents arguably the best time and place to investigate major questions surrounding the tempo and mode of evolution among Mesozoic terrestrial vertebrates and associated ecosystem changes. A major hurdle to addressing questions of these types in ancient ecosystems is the ability to precisely and accurately constrain the depositional age of important fossil localities and to correlate floras and faunas through space. U-Pb zircon geochronology can be used to date ca 90 million year old volcanic ash beds to better than ± 20-30 thousand years. When multiple ash beds are dated in stratigraphic succession, age models can be constructed that allow resolution at millennial to decamillenial levels and thus high-precision correlation.
The proposed project will focus on the following key faunas and floras: 1) the Two Medicine-Judith River formations in Montana and Wyoming; 2) the Dinosaur Park Formation in Alberta; 3) the Kaiparowits Formation in Utah; 4) the Fruitland-Kirtland formations in New Mexico; and the Aguja Formation in Texas. Together, these continental units and their floras and faunas have been interpreted as contemporaneous, and by developing a high precision chronostratigraphy, the research team will create an unparalleled opportunity for investigating the mode and tempo of evolution in a Mesozoic terrestrial ecosystem, with opportunities for investigating and testing concepts of latitudinally arrayed provinciality, turnover rates, diachroneity in evolutionary changes, predictions from molecular studies and the roles of eustasy, tectonics and climate as drivers of such changes. In addition, once completed, it will be possible to compare the record from Laramidia with those from South America and Asia.

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