Guest post by David Middleton
Science News
Fossil site shows impact of early Jurassic’s low oxygen oceans
Date: July 15, 2017
Source: University of Texas at AustinSummary:
Using a combination of fossils and chemical markers, scientists have tracked how a period of globally low ocean-oxygen turned an Early Jurassic marine ecosystem into a stressed community inhabited by only a few species.Using a combination of fossils and chemical markers, scientists have tracked how a period of globally low ocean-oxygen turned an Early Jurassic marine ecosystem into a stressed community inhabited by only a few species.
The research was led by Rowan Martindale, an assistant professor at The University of Texas at Austin Jackson School of Geosciences, and published in print in Palaeogeography, Palaeoclimatology, Palaeoeconology on July 15. The study was co-authored by Martin Aberhan, a curator at the Institute for Evolution and Biodiversity Science at the Natural History Museum in Berlin, Germany.
The study zeroes in on a recently discovered fossil site in Canada located at Ya Ha Tinda Ranch near Banff National Park in southwest Alberta. The site records fossils of organisms that lived about 183 million years ago during the Early Jurassic in a shallow sea that once covered the region.
The fossil site broadens the scientific record of the Toarcian Oceanic Anoxic Event, a period of low oxygen in shallow ocean waters which is hypothesized to be triggered by massive volcanic eruptions. The Oceanic Anoxic Event was identified at this site by the geochemical record preserved in the rocks. These geochemical data were collected in a previous research project led by Benjamin Gill and Theodore Them of Virginia Tech. The oxygen level of the surrounding environment during the Early Jurassic influences the type and amount of carbon preserved in rocks, making the geochemical record an important method for tracking an anoxic event.
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Unsurprisingly…
About 70% of the total world petroleum resources are concentrated in the Tethyan realm, the Mesozoic deposits being the most prolific source rocks of these oil and gas reserves. To understand the depositional controls of these organic-rich facies at the scale of the Tethys is a challenging problem. A recent set of paleoenvironmental maps for the Tethyan realm allows integration of source-rock mapping with other mappable geologic information. This integrated approach is attempted here for three short time intervals of the Mesozoic: Toarcian, Kimmeridgian, and Cenomanian, all of which were periods of good source-rock deposition.
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The Tethys Sea couldn’t have been a better place for petroleum source rock deposition even if it had been designed for such a purpose. The “Tethyan realm” encompassed much of the Jurassic and Cretaceous periods…
Silva et al., 2015. CSEG Recorder. Source Rocks and Petroleum Systems of the Scotian Basin.
It’s hard…
