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Joint U-Pb and 40Ar/39Ar geochronology for pyroclastic zircon and biotite crystals from tephra lenses intercalated within eolianite of the Middle Jurassic Page Sandstone on the Colorado Plateau provides the first direct isotopic age for a Jurassic eolianite on the Colorado Plateau and indicates a chronostratigraphic age of 171.5-169.5 Ma for the Page Sandstone. With stated uncertainties in the age boundaries of global stratigraphic stages taken into account, the isotopic age of lower Bajocian is coordinate with the inferred biostratigaphic age of upper Bajocian from lateral correlation of Page Sandstone with equivalent marine strata. Comparative isotopic ages imply that the Page Sandstone was deposited during the same time frame as the Temple Cap Formation, inferred conventionally to be older, and that the J1 and J2 surfaces of the Colorado Plateau are therefore not reliable chronostratigraphic marker horizons. [ABSTRACT FROM AUTHOR]

We report the U-Pb age distribution of detrital zircons collected from central and southern Appalachian foreland basin strata, which record changes of sediment provenance in response to the different phases of the Appalachian orogeny. Taconic clastic wedges have predominantly Ca. 1080-1180 and Ca. 1300-1500 Ma zircons, whereas Acadian clastic wedges contain abundant Paleozoic zircons and minor populations of 550-700 and 1900-2200 Ma zircons consistent with a Gondwanan affinity. Alleghanian elastic wedges contain large populations of Ca. 980-1080 Ma and ca. 2700 Ma and older Archean zircons and fewer Paleozoic zircons than occur in the Acadian clastic wedges. The abundance of Paleozoic detrital zircons in Acadian clastic wedges indicates that the Acadian hinterland consisted of recycled material and Taconic-aged plutons, which provided significant detritus to the Acadian foreland basin. The appearance of Pan-African/Brasiliano- and Eburnean/Trans-Amazonian-aged zircons in Acadian elastic wedges suggests a Devonian accretion of the Carolina terrane. In contrast, the relative decrease in abundance of Paleozoic detrital zircons coupled with an increase of Archean and Grenville zircons in Alleghanian clastic wedges indicates the development of an orogenic hinterland consisting of deformed passive margin strata and Grenville basement. The younging-upward age progression in Grenville province sources revealed in Taconic through Alleghanian successions suggest a reverse unroofing sequence that indicates at least two cycles of Grenville zircon recycling. [ABSTRACT FROM AUTHOR]