SUBSIDENCE PATTERNS AND TECTONIC DRIVERS OF DEFORMATION REVEALED FROM CARBONATE-CARBON ISOTOPES: THE CASE OF THE EARLY PENNSYLVANIAN ELY-BIRD SPRING BASIN

Stratigraphic analysis tools, such as carbon isotope stratigraphy and geohistory analysis, are useful in elucidating the history of complexly deformed basins. High-resolution carbon isotope stratigraphy, combined with biostratigraphy, allows for fine-scale correlation across deformed basins to help determine basin filling patterns through time. The shapes of geohistory analysis curves are useful to assess tectonic drivers of basin formation. These methods were applied to the Early Pennsylvanian (Bashkirian/Morrowan-Atokan) Ely-Bird Spring Basin (EBSB); one of a series of stacked, tectonically-generated late Paleozoic basins that formed at the western margin of Laurentia. Elucidating the basin filling history and tectonic driver(s) of the EBSB is made more difficult by subsequent tectonic events that telescoped, deformed, and dismembered these basins.

Carbon isotope and geohistory analyses indicate that the EBSB formed in flexural response to loading to the northwest of the basin. Carbonate-carbon isotope data were obtained from six sections across the basin with well-established stage-scale biostratigraphy. Carbon isotope curves were then correlated using the Match 2.3 algorithm (Lisiecki and Lisiecki, 2002), a program built for stratigraphic signal correlation. Sediment accumulation maps built for 9 time slices from these correlations indicate initial rapid deposition in the eastern EBSB in early Morrowan time, followed by migration of the main depocenter to the northwestern part of the basin during Atokan time. Geohistory analyses of the EBSB sections are most consistent with foreland basin subsidence, in contrast to nearby Ancestral Rocky Mountain (ARM) basins which are more consistent with strike-slip basins. Taken together, these data are consistent with late Paleozoic tectonism in western Laurentia that is distinctly different form synchronous ARM tectonism, but is more consistent with flexural response due to loading from the west and northwest.