Cosmogenic ۱۰Be-۲۶Al isochron burial ages of Lower Colorado River Gravel Deposits

Evolution of Colorado River has been a hot potato over the last decades among the multiple disciplines of Geo-society, in particular relation to the timing and mode of initiation of Grand Canyon and the uplift of Colorado Plateau. One of the key resources for the debate is a series of alluviums including Bullhead, Santa Fe Railroad, Bat Cave, Topock, and Chemehuevi which were assumed to be initiated from the Colorado Plateau and were deposited along the Lower Colorado River. Despite their importance, however, the depositional timing of each alluvium was poorly constrained because of a lack in reliable numerical dating tools which can be applied to the time frame for the deposits. Most of the previous chronologic scholarships were based on fossils of plants and animals, broadly suggesting their Pliocene to Pleistocene origin. Here we document the cosmogenic ۱۰Be-۲۶Al isochron burial ages of the four alluviums (Topock, Bat Cave, Santa Fe Railroad, and Palo Verde) resting on the Lower Colorado River near Topock, which constitute the key beds of Pliocene to Pleistocene stratigraphy in the region. Age of each alluvium yields ۲.۰۲ ± ۰.۲۴ Ma for Topock, ۲.۰۸ ± ۰.۳۱ Ma for Bat Cave, ۴.۲۵ ± ۰.۶۹ Ma for Santa Fe Railroad, and ۳.۰۳ ± ۰.۲۶ Ma for Palo Verde, respectively. It is noteworthy all ages are well bracketed between the two key stratigraphic units of Pliocene Bouse Formation (~۵.۳ Ma) and Late Quaternary alluviums (<۱۰۰ ka), implying that the ages are reliable and consistent well with published local stratigraphy. Furthermore, the chrono-stratigraphy the present study set up well supports the theory of overflow origin (or aggradational piracy) of time transgressive integration of the Tertiary extensional basins developed along the Lower Colorado River.

کلیدواژه ها:

Colorado River ، Cosmogenic dating ، Basin integration ، Gravel deposit