[Eoas-seminar] MS Defense - Charlie Smith

[eoas-seminar at lists.fsu.edu]

Good morning,

Please join us for Charlie Smith’s Thesis Defense on Tuesday, May 5th at 1:00 PM (EST).

Title: Local Expansion of Reducing Conditions During the Late Ordovician: Implications for the Great Ordovician Biodiversification Event

Name: Charlie Smith
Date: May 5th, 1:00 PM - 3:00 PM
Location: EOA 5067
Major Professor: Dr. Jeremy Owens
Zoom: https://fsu.zoom.us/j/93470688741<https://nam04.safelinks.protection.outlook.com/?url=https%3A%2F%2Ffsu.zoom.us%2Fj%2F93470688741&data=05%7C02%7Ceoas-seminar%40lists.fsu.edu%7Cbfeb4b45396149488c3c08dea9e533b8%7Ca36450ebdb0642a78d1b026719f701e3%7C0%7C0%7C639134999024248157%7CUnknown%7CTWFpbGZsb3d8eyJFbXB0eU1hcGkiOnRydWUsIlYiOiIwLjAuMDAwMCIsIlAiOiJXaW4zMiIsIkFOIjoiTWFpbCIsIldUIjoyfQ%3D%3D%7C0%7C%7C%7C&sdata=THsyk6i17Qk6FhObUkgBTiukYOgumgh%2BiTqLILgDRao%3D&reserved=0>

Abstract: The Great Ordovician Biodiversification Event (GOBE) was a transformative period for marine ecosystems. During this time familial diversity increased more than any other time in Earth’s history coinciding with an expansion and restructuring of marine ecosystems. The cause of this radiative event has been attributed to a multitude of biotic and abiotic factors which include the proliferation of phytoplankton, enhanced nutrient supply and a long-term global cooling event. Additionally, increased marine oxygenation has been proposed as a driver for many dynamic biotic events, with oxygenation improving metabolic conditions that may contribute to the global radiation. A range of redox proxies have been used to investigate shallow marine carbonate shelves; however significantly fewer studies have explored deep water settings.

This study focuses on the Trail Creek Summit section of central Idaho which is a 200-meter-thick sequence of organic-rich mudstones with an interval thinly interbedded siltstone. This section contains the lower to upper Ordovician (Floian to Katian stages encompassing 470 to 449 Ma) using graptolite and conodont biostratigraphy in concert with carbon isotope chemostratigraphy. The Guttenberg Isotopic Carbon Excursion (GICE) is encountered during the bifidus biozone with a +2.6‰ δ13Corg (VPDB) excursion. A multiproxy approach was employed to better constrain the local redox conditions at Trail Creek Summit. Iron speciation supports the presence of persistently ferruginous, anoxic bottom waters with dissolved Fe. Depleted Mn concentrations throughout the section indicate the presence of manganese reduction. The D. caudatus biozone (Katian) shows enrichments up section in V and U alongside a moderate rise in Mo concentrations. Trace metal covariation suggests that the basin is not overly restricted and its general agreement with Fe speciation values lend evidence that enrichments are likely dependent on local redox conditions. Combined with the local Fe speciation suggests a migrating chemocline where porewaters near the sediment water interface transitioned from Fe reduction to sulfate reduction during the Katian. The δ34Spyr record shifts toward more positive values during this inferred rise in sulfate reduction which seems to correspond with published data for the marine sulfate record. Thus, this shift is likely a global record which can be attributed to a global increase in pyrite burial during the GICE which likely decreased the size of the marine sulfate reservoir. In context of the GOBE, locally this basin was consistently anoxic at least near the sediment water interface although there is record of sedimentary bioturbation, but importantly is locally more reducing near the sediment water interface by the Katian and was probably inhospitable for most infaunal and benthic animals. Local redox conditions provide a framework for future work on other global redox proxies that will provide global insight into this highly dynamic period for marine life.



Adea Arrison
Sr. Academic Program Specialist
Department of Earth, Ocean & Atmospheric Science
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