Interactions between axial and transverse drainage systems in the Late Cretaceous Cordilleran foreland basin: Evidence from detrital zircons in the Straight Cliffs Formation, southern Utah, USA

摘要

New detrital zircon geochronologic data from the Straight Cliffs Formation of southern Utah provide insight into the controls on stratigraphic architecture of the Western Interior Basin during Turonian-early Campanian time. Detrital zircon ages (N = 40, n = 3650) derived from linked fluvial and shallow-marine depositional systems of the Kaiparowits Plateau indicate the majority of zircons in fluvial strata were derived from the Mogollon Highlands (1.25-1.90 Ga, 67% of fluvial zircons), with subordinate contributions delivered from the Sevier fold-andthrust belt (265-1250 Ma, 17%) and Cordilleran magmatic sources (81-265 Ma, 16%). Integration of these data with fluvial facies distributions, petrography, clast counts, and evidence of magmatic arc sources from the Mohave region of California implies the presence of a northeast-flowing, axial fluvial system. This system was fed by rivers draining the Mogollon Highlands to the south and by transverse drainages from the Sevier fold-and-thrust belt to the west. Compared to the fluvial deposits, shallow-marine sand-stones have a greater proportion of Sevier fold-and-thrust belt-derived zircons (42%), which were delivered via longshore currents from the north. Shallow-marine samples also contain less Mogollon input (44%) compared to contemporaneous fluvial systems, and similar input from the magmatic arc (14%). Although Proterozoic zircons associated with the Mogollon Highlands are also present in the Sevier fold-and-thrust belt, several lines of evidence argue for a distinct southerly source for the Straight Cliffs Formation. These include (1) moderate proportions of feldspar and angular quartz grains in fluvial sandstones, which favor a felsic intrusive source, and (2) prominent 1.4 and 1.7 Ga zircon populations. The 1.4 and 1.7 Ga peaks are the only dominant Proterozoic peaks in samples from the Straight Cliffs Formation, whereas samples derived more directly from the Sevier fold-and-thrust belt tend to have a broader distribution of Proterozoic age peaks.