Lithostratigraphic, conodont, and other faunal links between lower Paleozoic strata in northern and central Alaska and northeastern Russia

Abstract

Lower Paleozoic platform carbonate strata in northern Alaska (parts of the Arctic Alaska, York, and Seward terranes; herein called the North Alaska carbonate platform) and central Alaska (Farewell terrane) share distinctive lithologic and faunal features, and may have formed on a single continental fragment situated between Siberia and Laurentia. Sedimentary successions in northern and central Alaska overlie Late Proterozoic metamorphosed basement; contain Late Proterozoic ooid-rich dolostones, Middle Cambrian outer shelf deposits, and Ordovician, Silurian, and Devonian shallow-water platform facies, and include fossils of both Siberian and Laurentian biotic provinces. The presence in the Alaskan terranes of Siberian forms not seen in wellstudied cratonal margin sequences of western Laurentia implies that the Alaskan rocks were not attached to Laurentia during the early Paleozoic.The Siberian cratonal succession includes Archean basement, Ordovician shallow-water siliciclastic rocks, and Upper Silurian-Devonian evaporites, none of which have counterparts in the Alaskan successions, and contains only a few of the Laurentian conodonts that occur in Alaska. Thus we conclude that the lower Paleozoic platform successions of northern and central Alaska were not part of the Siberian craton during their deposition, but may have formed on a crustal fragment rifted away from Siberia during the Late Proterozoic. The Alaskan strata have more similarities to coeval rocks in some peri-Siberian terranes of northeastern Russia (Kotelny, Chukotka, and Omulevka). Lithologic ties between northern Alaska, the Farewell terrane, and the peri-Siberian terranes diminish after the Middle Devonian, but Siberian afµnities in northern and central Alaskan biotas persist into the late Paleozoic. *

Neoproterozoic–early Paleozoic provenance evolution of sedimentary rocks in and adjacent to the Farewell terrane (interior Alaska)

“…Links between the Alexander terrane and the Farewell terrane may have been initiated during this time. Robust paleontologic data support proximity of the Farewell terrane and Arctic Alaska during the Ordovician; a distinctive biota that includes Siberian, Laurentian, and lesser Baltic endemics occurs in both regions (Dumoulin et al, 2002(Dumoulin et al, , 2014aBlodgett, et al, 2002;Rasmussen et al, 2012). However, few paleogeographically distinctive Ordovician fossils have been reported from the Alexander terrane.…”

“…Deposition of the Terra Cotta Mountains Sandstone coincided with prolonged Silurian drowning of the Nixon Fork carbonate platform (Dumoulin et al, 2002), leading Bradley (2008, p. 2 of the supplementary data) to interpret these turbidites as orogenically derived flysch that accumulated in the foredeep of an arc-passive-margin collision zone; continent-continent collision is another plausible tectonic scenario . Possible sediment sources for the Terra Cotta Mountains Sandstone are discussed further in the following.…”

“…Details of the initiation and demise of this margin, however, remain problematic. Bradley (2008) suggested start and end dates of 545 Ma (early Cambrian) and 435 Ma (early Silurian), but deep-water strata as old as Late Ordovician interfinger with shallow-water strata in the northern Nixon Fork subterrane (Dumoulin et al, 2002(Dumoulin et al, , 2014a, suggesting incipient drowning of the platform by this time. Cumulative distribution function (CDF) plots for our detrital zircon data from the Farewell terrane (Fig.…”

“…Lower Paleozoic rocks in the Farewell terrane have well-documented faunal and lithologic similarities with coeval strata in the central part of the Arctic Alaska-Chukotka composite terrane (Seward Peninsula, western and central Brooks Range; Figs. 1 and 2)-in particular, a highly distinctive early Paleozoic biota that includes Laurentian, Siberian, and some Baltic endemic forms (Dumoulin et al, 2002(Dumoulin et al, , 2014aBlodgett et al, 2002;Rasmussen et al, 2012). Paleontologic and lithologic ties between the Farewell and Alexander terranes (Figs.…”

Ordovician sponges from west-central and east-central Alaska and western Yukon Territory, Canada

“…Their Alaskan occurrences are primarily in the accreted terranes (i.e., Farewell, Livengood, White Mountains, and Alexander terranes), which make up the bulk of the state, but they are also found in Ashgillian (late Late Ordovician) strata of the uppermost Jones Ridge Limestone, situated along the Alaska-Yukon border in autochthonous rocks belonging to Laurentia. Recent paleobiogeographic studies of Early Paleozoic rocks of Alaska's accreted terranes indicate that many of them appear to have a Siberian origin (Blodgett & Boucot 1999, Blodgett et al 2002, Dumoulin et al 2002.…”