--> Abstract: Carbon and Nutrient Cycling during the Stepwise Frasnian-Famennian Extinction Event, Rocky Mountains, Western Canada, by Joshua H. Payne, Michael T. Whalen, and James E. Day; #90078 (2008)

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Carbon and Nutrient Cycling during the Stepwise Frasnian-Famennian Extinction Event, Rocky Mountains, Western Canada

Joshua H. Payne1, Michael T. Whalen1, and James E. Day2
1Geology and Geophysics Department, University of Alaska Fairbanks, Fairbanks, AK
2Geography-Geology, University of Illinois State, Normal, IL

Well exposed Devonian rocks in the Rocky Mountains of western Alberta record a Late Givetian to early Fammenian 2nd order eustatic sea level cycle and a series of nine 3rd order sea level changes. Two late Frasnian-earliest Famennian transgressive events are associated with a step-wise mass extinction represented by the Lower and Upper Kellwasser events (LKE & UKE). Tropical and subtropical carbonate platform organisms were preferentially affected by these events and a variety of mechanisms have been implicated. C & N stable isotope stratigraphy provides insight into carbon and nutrient cycling and ecologic change associated with these events. Preliminary geochemical analysis of organic matter from a basinal section along the southeast margin of the Ancient Wall platform documents stepwise excursions of both δ13Corg and δ15N during the Late Devonian that correlate biostratigraphically with the LKE and UKE. δ15N and the δ13Corg display positive excursions of ≥4‰ and the δ13Corg lags behind the δ15N during the events. An increase in δ15N may be associated with denitrification mediated by bacteria in sub-oxic to anoxic environments and implies increased primary production. Increased riverine input of nutirents associated with greater terrestrial weatherability due to the rise of rooted land plands and/or deepwater upwelling likely influenced productivity. Increased productivity, rapid burial, eutrophication and development of oxygen-depleted conditions preserved organic matter and resulted in the positive δ13Corg excursion. Similar patterns are found in Upper Devonian sections worldwide confirming the global nature of these events.

 

AAPG Search and Discover Article #90078©2008 AAPG Annual Convention, San Antonio, Texas