SEVEN CORDILLERAN PALEORIVERS THAT CONNECTED DEFORMING HIGHLANDS IN IDAHO TO DEPOCENTERS IN CALIFORNIA, OREGON, WASHINGTON, WYOMING, AND, INDIRECTLY, ALASKA

Detrital zircon U-Pb ages and other data provide evidence for two voluminous, short-lived, anomalous pulses of sediment delivery from eroding highlands in Idaho to marine depocenters on the Pacific coast, one in Campanian time (ca. 85-80 Ma) and one in Early-Middle Eocene time (ca. 53-47 Ma). This poster will present updated paleogeographic maps of the western U.S. for these two time slices [doi: 10.1130/G33746.1 and 10.1130/G37286.1].

In the Campanian, strata of the Proterozoic Belt Supergroup in Idaho were strongly folded and uplifted during shortening in the Sevier retroarc [e.g., 10.1130/2016.2522(06)]. Erosion of Belt strata fed four paleoriver systems. The Lemhi Pass–Hawley Creek river system flowed E and sourced a major nonmarine megafan in the Cordilleran foreland basin. The Kione River flowed SW to northern California, where it sourced a very large delta and submarine fan complex within the northern Great Valley forearc basin. Considerable Kione detritus also transited the forearc basin to reach the Franciscan trench, sourcing a pulse of deposition and subduction accretion in central California and even part of southern California. The Swakane River flowed NW out of Idaho into Washington, sourcing the protolith for the high-grade Swakane gneiss. More speculatively, a Yakutat River may have flowed NW and deposited ca. 71-65 Ma Yakutat strata in a trench off Washington or British Columbia, before those strata were translated north to southeastern Alaska.

In the Eocene, central Idaho was re-deformed by major extension in the Bitterroot, Anaconda, Clearwater, and Priest River metamorphic core complexes (53–40 Ma) and by major volcanism in the Challis volcanic field (51–43 Ma). The Princeton River–Princeton submarine canyon system delivered Idaho detritus to the Great Valley forearc basin and the Franciscan trench, the Tyee River to the Tyee forearc basin in western Oregon, and the Idaho River to the Green River basin in Wyoming.

From the perspective of the episodic accretion and growth of the metasedimentary Franciscan subduction complex along the plate margin, these data illustrate the important influences of episodic deformation and erosion in the distant continental interior, changing river pathway locations, and long-distance margin-parallel transport of sediment.