Triassic river systems and the paleo-Pacific margin of northwestern Pangea

Abstract

Detrital zircon U–Pb ages from Triassic strata exposed in the circum-Arctic, analyzed by LA-ICP-MS and SHRIMP-RG, are compared at the regional scale to better understand the paleogeography of northern Pangea and help restore rift opening of the Arctic. Data sets are compared based on their zircon age distributions, cumulative age probability plots, and the K–S test. Three major source regions are characterized. These fed clastic material to transcontinental river systems that transported material from the highlands of northwestern Pangea to its once continuous paleo-Pacific continental margin. The paleo-Lena River System was fed from sources in the Baikalian and Altay-Sayan mountainous regions of Siberia. Zircon populations are characterized by a limited number of Precambrian zircons (~1.8–2.0Ga with fewer ~2.5–3.0Ga), lack of 0.9–1.8Ga zircons, and a dominant 480–500Ma and 290–300Ma age population. The paleo-Taimyr River System was sourced from the Uralian orogenic belt region and deposited along a rifted portion of the Siberia–Baltica margin beginning in the Permo–Triassic. Precambrian zircon populations are similar to those of the paleo-Lena system, and samples closest to Siberia have similar populations in the 480–500Ma and 290–300Ma age ranges. Chukotka, Wrangel Island and Lisburne Hills, Alaska, have sparse ages between 900 and 1800Ma, Ordovician ages are younger (~440–450Ma), and, along with abundant ~300Ma ages, they contain ~250–260Ma and lesser ~215–235Ma zircons, interpreted as derived from silicic volcanic centers associated with Permo–Triassic to Triassic continental flood basalt provinces in Siberia, Taimyr and Kara Sea region. The trans-Laurentian River System was likely fed by rift-related uplift along the proto North Atlantic/Arctic margin and delivered sediment to the Cordilleran margin of Pangea. These samples have no significant upper Paleozoic zircons and have a much broader age range of Precambrian zircons.