Persistent depositional sequences and bioevents in the Eifelian (early Middle Devonian) of eastern Laurentia: North American evidence of the Kačák Events?
Published:January 01, 2007
M. K. DeSantis, C. E. Brett, C. A. Ver Straeten, 2007. "Persistent depositional sequences and bioevents in the Eifelian (early Middle Devonian) of eastern Laurentia: North American evidence of the Kačák Events?", Devonian Events and Correlations, R. T. Becker, W. T. Kirchgasser
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The late Eifelian–earliest Givetian interval (Middle Devonian) represents a time of significant faunal turnover in the eastern Laurentia and globally. A synthesis of biostratigraphic, K-bentonite and sequence stratigraphic data indicates that physical and biotic events in the Appalachian foreland basin sections in New York are coeval with the predominantly carbonate platform sections of southern Ontario and Ohio. The upper Eifelian (australis to ensensis conodont zones) Marcellus Subgroup in New York comprises two large-scale (3rd-order) composite depositional sequences dominated by black shale, which are here assigned to the Union Springs and Oatka Creek Formations. The succession includes portions of three distinctive benthic faunas or ecological–evolutionary sub-units (EESUs): ‘Onondaga’, ‘Stony Hollow’ and ‘Hamilton’. In the northern Appalachian Basin in New York, the boundaries of these bioevents show evidence of abrupt, widespread extinctions, immigration and ecological restructuring. In the Niagara Peninsula of Ontario and from central to northern Ohio, the same sequence stratigraphic pattern and bioevents are recognized in coeval, carbonate-dominated facies.
The correlations underscore a relatively simple pattern of two major sequences and four subsequences that can be recognized throughout much of eastern Laurentia. Moreover, the biotic changes appear to be synchronous across the foreland basin and adjacent cratonic platform. However, the degree of change differs substantially, being less pronounced in carbonatedominated mid-continent sections. Finally, we make the case that the two major faunal changes align with regional sequence stratigraphic patterns as well as with the global Kačák bioevents.
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Devonian Events and Correlations
The Devonian was a peculiar period, characterized by simplified plate tectonic configurations, climatic overheating and widely flooded continents. The bloom of fishes and ammonoids, extensive reef complexes, and the conquest of land indicate major biosphere innovations, punctuated by many global events, including two of the biggest mass extinctions. The Devonian was the first system for which subdivisions were formally defined. This was achieved by significant advances in pelagic biostratigraphy. The chronostratigraphic framework and interdisciplinary techniques allow us to correlate intervals or sudden events across facies boundaries, in order to reconstruct the sedimentary and evolutionary history of the system with highest precision.
This volume honors the lifetime stratigraphic achievements of Michael Robert House (1930-2002). Based on case studies from Europe, North Africa and North America, it shows how the combination of biostratigraphy, chemostratigraphy, magnetostratigraphy, sequence stratigraphy and event stratigraphy can contribute to a much deeper understanding of both regional and global environmental change.