Ecologic changes associated with the Late Devonian mass extinction: Evidence from the Great Basin and Rocky Mountain regions, western United States.

摘要

The Late Devonian Mass Extinction was one of the largest extinctions in the Phanerozoic history of life. Taxonomic estimates of marine faunal diversity within the soft substrate realm show a reduction in generic diversity as high as 65% (Bambach, 2006). Despite this taxonomic diversity loss, analysis of global taxonomic changes indicates that following the extinction the common members of the community rebounded to or exceeded pre-extinction diversity levels. Thus taxonomic data predicts little lasting change in ecosystem structure in the soft substrate realm as a result of this extinction.; The purpose of this research is to test the predictive power of taxonomic and guild data as they pertain to large-scale ecological change during the Late Devonian Mass Extinction and to determine the validity of the assumptions required by studies that use only taxonomic data to investigate large-scale ecological change.; To accomplish this, a relative abundance database was compiled from limestones of the Great Basin and Rocky Mountain regions of the western U.S. that include strata of Upper Devonian and Lower Mississippian ages. Analysis of abundance data contained in this data set allows the reconstruction of large-scale community composition preserved in pre and post-extinction lithologies, which are compared to the taxonomic estimates of community change. Additionally, an encrinite (stalked echinoderm dominated lithology) classification scheme is developed to help describe the nuances of the sediments that dominated Mississippian depositional systems.; The results of this research demonstrate that the Late Devonian Mass Extinction suffered large-scale ecological changes not predicted by taxonomic data. The onset of ecologic change matches more closely with the Frasnian/Famennian (Kellwasser) event than the Famennian/Kinderhookian (Hangenberg) event and the changes are marked by a shift from a brachiopod-gastropod dominated community in the pre-extinction Frasnian to a Pelmatozoan dominated community in the Famennian and Mississippian. The ecologic changes resulting from this extinction produced long lasting effects in the carbonate factory, represented by a shift in dominant sediment producers and the sediments they created. The creation of pelmatozoan sediments in the Mississippian affected community structure, composition and eventually influenced the development of oil and gas reservoirs in Mississippian lithologies.