Late pleistocene sedimentation history of the Shirshov Ridge, Bering Sea

The analysis of the lithology, grain-size distribution, clay minerals, and geochemistry of Upper Pleistocene sediments from the submarine Shirshov Ridge (Bering Sea) showed that the main source area was the Yukon–Tanana terrane of Central Alaska. The sedimentary materials were transported by the Yukon River through Beringia up to the shelf break, where they were entrained by a strong northwestward-flowing sea current. The lithological data revealed several pulses of ice-rafted debris deposition, roughly synchronous with Heinrich events, and periods of weaker bottom-current intensity. Based on the geochemical results, we distinguished intervals of an increase in paleoproductivity and extension of the oxygen minimum zone. The results suggest that there were three stages of deposition driven by glacioeustatic sea-level fluctuations and glacial cycles in Alaska

Detrital Zircon Record of a Mesozoic Collisional Forearc Basin in South Central Alaska: The Tectonic Transition From an Oceanic to Continental Arc

The collision of oceanic arcs with continental margins is an important mechanism for the growth of continents. Ancient forearc basin strata in collisional orogens provide a record of the upper crustal response to this tectonic process. In south central Alaska, Mesozoic forearc basin strata are exposed in a complete crustal section. U-Pb detrital zircon geochronology from the forearc basin strata was analyzed within a similar to 107Ma stratigraphic framework. The Jurassic strata contain unimodal detrital zircon populations that become progressively younger upsection and range from 175 to 151Ma. These strata are derived from the active oceanic Talkeetna arc. The Cretaceous strata were deposited above multiple unconformities that collectively represent as much as similar to 30Ma of nondeposition and/or erosion in the forearc basin. Erosion in the forearc basin and a general absence of detrital zircon ages between 140 and 120Ma are interpreted as a hiatus of magmatism triggered by collision of the oceanic arc with the former continental margin. The Cretaceous strata have two main detrital zircon populations: a Cretaceous population ranging from 90 to 68Ma that becomes progressively younger upsection and a Jurassic population with a broad range of peak ages from 194 to 144Ma. The Cretaceous population marks the establishment of an active Cretaceous continental arc following the collisional event, and the older population reflects continued erosion of the remnant Jurassic oceanic arc plutons. Our results show that detrital zircon geochronology provides a powerful approach for delineating stages of forearc basin collision and the erosion of multiple magmatic arcs.National Science Foundation [EAR-0910945, EAR-0910545]; NSF graduate research fellowship6 month embargo; published online: 06 January 2018This item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at [email protected]