Abstract
Tectonostratigraphic assemblages record phases of basin history during which the fundamental controls of tectonic setting, subsidence style, and basin geometry are relatively similar. Because these fundamental controls, in combination with climate and eustasy, influence paleogeography and sediment-dispersal patterns, they should also yield similar patterns or facies of detrital zircon age spectra. Reference curves for these patterns should be documented on the craton in order to make meaningful comparisons to sedimentary rocks from suspect terranes along continental margins. The Rocky Mountains of western North America provide excellent outcrops of sedimentary rocks that record > 500 million years of tectonostratigraphic evolution. One such Phanerozoic section is exposed along the margins of the Bighorn Basin in northwest Wyoming from which we report over 4,000 U/Th/Pb detrital zircon ages from 48 samples that span a stratigraphic interval from the middle Cambrian Flathead Sandstone through the Eocene Willwood Formation. These data provide one of the most complete records of detrital zircon age patterns from this portion of cratonic North America.

The stratigraphic record within the Bighorn Basin can be subdivided into four tectonostratigraphic assemblages. These assemblages record an initial passive margin history, followed by a transitional assemblage to a convergent margin, followed by a marine-dominated retroarc foreland assemblage, followed by a retroarc foreland segmented by local basement uplifts. This tectonostratigraphic architecture is expressed as four, first-order patterns within the detrital zircon age distributions that reflect fundamental changes in paleogeography and sediment dispersal at the 10 - 100 Ma time scale. Detrital zircon ages also provide evidence for linkages between convergent margin process like arc magmatism and sedimentation in the retroarc foreland. During these times of strong arc - retroarc linkage, detrital zircon geochronology provides a potentially useful tool for high resolution chronostratigraphy.