HIGH-RESOLUTION CHRONOSTRATIGRAPHIC CORRELATION OF LOWER IBEXIAN SUCCESSIONS IN THE WESTERN U.S

Integrated d¹³C variation, biostratigraphic, and lithostratigraphic correlation of Lower Ibexian sections reveals strong temporal similarity in important lithologic and biostratigraphic horizons between Utah, Wyoming, Colorado, New Mexico, and Texas. At least 4 key levels in the Ibex area, UT succession—all interpreted as 3rd or 4th order sequence boundaries in that area—can be correlated into sparsely fossiliferous successions at better than 0.5 conodont subzonal precision using d¹³C variations: a) the basal Ibexian Lange Ranch eustatic interval, which equates to unconformities in most sections to the east; b) a basal House Limestone horizon, which correlates with the base of well-bedded grainstones in two key western Colorado sections of the Manitou Formation, and to a sharp depositional rate increase in New Mexico and west Texas sections; c) the base of the Burnout Canyon Member of the House Limestone, which correlates very precisely with the youngest strata in the Gallatin Formation in Wyoming and is slightly older than the oldest deposits of well-bedded grainstone at the base of the El Paso Group; and d) the basal Fillmore Formation, which correlates well to a small but distinctive sandstone marker horizon in the middle Hitt Canyon Formation and is more generally correlative to the resumption of deposition following the mid-Rossodus unconformity in the Colorado Front Range.

Correlation of these key horizons, and correlation of d¹³C profiles through the intervening intervals, provide an opportunity to examine the temporal development of 3rd and 4th order sequence architecture across a broad transect from central Texas to western Utah and throughout the US Rocky Mountain region.