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Macdonald, F.A., 2009

Neoproterozoic stratigraphy of Alaska and Mongolia

Bibliographic Reference

Macdonald, F.A., 2009, Neoproterozoic stratigraphy of Alaska and Mongolia: Cambridge, Massachusetts, Harvard University, Ph.D. dissertation, xvi, 163 p., illust., maps.


The Katakturuk Dolomite is a 2,080-m-thick Neoproterozoic carbonate succession exposed in the NE Brooks Range of Arctic Alaska, and has previously been correlated with the pre-723 Ma Shaler Supergroup of the Amundson basin. Herein I report new composite 13C profiles and detrital zircon ages, and use stratigraphic markers and a compilation of 13C chemostratigraphy from around the world, tied to U-Pb ages, to derive an age model for deposition of the Katakturuk Dolomite. These data suggest that deposition of the Katakturuk Dolomite spanned two Cryogenian glacial events and much of the Ediacaran, that the Neoproterozoic-early Paleozoic Arctic Alaska-Chukotka Microplate was exotic to Laurentia, and that the rotation model for the opening of the Arctic Ocean must be reconsidered. Unique scale microfossils have been recovered from sections in the Yukon Territory that were previously correlated with Ediacaran (635-540 Ma) strata of the upper Tindir Group in Alaska. During mapping, I distinguished two Cryogenian glacial diamictites and determined that the fossiliferous sections are part of the lower Tindir Group, which was deposited before ca. 714 Ma early Cryogenian glacial deposits. This new correlation indicates that the microfossils in the lower Tindir Group are 100-200 Myr older than previous estimates and lays the groundwork for future studies on the biological affinity and evolutionary significance of these peculiar specimens. Last, I report the discovery of new end-Cryogenian glacial diamictites and overlying basal Ediacaran cap carbonates within the Dzabkhan and Khubsugul basins of Mongolia. The identification of the Cryogenian-Ediacaran boundary, coupled with new 13C profiles and sedimentary evidence of a major depositional break, indicates that a ~40 Myr hiatus is present below the phosphorite-bearing Zunne Arts member of the Tsagaan Oloom member in the Dzabkhan basin and in correlative strata in the Khubsugul basin. I propose that the Zunne Arts member and the overlying ~1,600 m of early Cambrian strata were deposited in a foreland basin that formed as the southern margin of the Dzabkhan terrane was subducted beneath the Khantayshir-Dariv arc.

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