2015 GSA Annual Meeting in Baltimore, Maryland, USA (1-4 November 2015)

Paper No. 41-29
Presentation Time: 9:00 AM-5:30 PM


KELLY, Abigail, Geoscience, Williams College, 2278 Paresky Center, Williamstown, MA 01267 and COHEN, Phoebe, Geosciences, Williams College, 947 Main Street, Williamstown, MA 01267, abigail.a.kelly@williams.edu

The Kellwasser events are two globally expressed black shale beds that are associated with the Late Devonian Extinction Interval and include the Frasnian/Famennian transition. The Kellwasser beds have been interpreted as a signal of widespread marine anoxia correlated with the extinction interval. We sampled the lower Kellwasser event at several localities across Upstate New York, representing deeper marine paleoenvironments to the west and shallower marine paleoenvironments to the east. While larger body fossils are mainly absent within the Kellwasser beds, organic-walled microfossils are abundant and provide a continuous record throughout the event. These fossils are classified as acritarchs and are often inferred to be phycoma, reproductive structures made by members of the green algal group Prasinophycea. However, additional valid interpretations of their taxonomic affinity include the resting stages of metazoan eggs or other algal cysts. In the modern, some algal and metazoan groups are known to produce recalcitrant acritarch-like structures in response to environmental stressors such as anoxia, adding complexity to understanding the environmental and preservational context of the microfossils.

Uncertainties including those discussed above make interpreting the acritarch record across the Late Devonian challenging. To move towards overcoming these challenges, we analyzed microfossil assemblage and abundance variation through the lower Kellwasser event and spatially across the paleo-depth gradient provided by our sampled localities. Here, we present methods for determining relative abundance of microfossils per sample with the use of polyethylene microspheres and total organic carbon (TOC) data in addition to established acid maceration techniques. These methods enable us to quantify abundance changes through the Kellwasser beds and better understand the assemblage and preservational changes throughout the extinction interval. This data will compliment work using trace fossils and geochemical proxies to contribute to our understanding of changing marine environments through the Kellwasser events.