Abstract Beneath the Arctic coastal plain (commonly referred to as "the 1002 area") in the Arctic National Wildlife Refuge, northeastern Alaska, United States, seismic reflection data show that the northernmost and youngest part of the Brookian orogen is preserved as a Paleogene to Neogene system of blind and buried thrust-related structures. These structures involve Proterozoic to Miocene (and younger?) rocks that contain several potential petroleum reservoir facies. Thermal maturity data indicate that the deformed rocks are mature to overmature with respect to hydrocarbon generation. Oil seeps and stains in outcrops and shows in nearby wells indicate that oil has migrated through the region; geochemical studies have identified three potential petroleum systems. Hydrocarbons that were generated from Mesozoic source rocks in the deformed belt were apparently expelled and migrated northward in the Paleogene, before much of the deformation in this part of the orogen. It is also possible that Neogene petroleum, which was generated in Tertiary rocks offshore in the Arctic Ocean, migrated southward into Neogene structural traps at the thrust front. However, the hydrocarbon resource potential of this largely unexplored region of Alaska’s North Slope remains poorly known. In the western part of the 1002 area, the dominant style of thin-skinned thrusting is that of a passive-roof duplex, bounded below by a detachment (floor thrust) near the base of Lower Cretaceous and younger foreland basin deposits and bounded above by a north-dipping roof thrust near the base of the Eocene. East-west-trending, basement-involved thrusts produced the Sadlerochit Mountains to the south, and buried, basement-involved thrusts are also present north of the Sadlerochit Mountains, where they appear to feed displacement into the thin-skinned system. Locally, late basement-involved thrusts postdate the thin-skinned thrusting. Both the basement-involved thrusts and the thin-skinned passive-roof duplex were principally active in the Miocene. In the eastern part of the 1002 area, a northward-younging pattern of thin-skinned deformation is apparent. Converging patterns of Paleocene reflectors on the north flank of the Sabbath syncline indicate that the Aichilik high and the Sabbath syncline formed as a passive-roof duplex and piggyback basin, respectively, just behind the Paleocene deformation front. During the Eocene and possibly the Oligocene, thin-skinned thrusting advanced northward over the present location of the Niguanak high. A passive-roof duplex occupied the frontal part of this system. The Kingak and Hue shales exposed above the Niguanak high were transported into their present structural position during the Eocene to Oligocene motion on the long thrust ramps above the present south flank of the Niguanak high. Broad, basement-cored subsurface domes (Niguanak high and Aurora dome) formed near the deformation front in the Oligocene, deforming the overlying thin-skinned structures and feeding a new increment of displacement into thin-skinned structures directly to the north. Deformation continued through the Miocene above a detachment in the basement. Offshore seismicity and Holocene shortening documented by previous workers may indicate that contractional deformation continues to the present day.

ABSTRACT The Neoproterozoic–Early Devonian(?) northeast Brooks Range basinal succession of northern Alaska and Yukon represents a peri-Laurentian deep-marine carbonate and siliciclastic succession within the composite Arctic Alaska–Chukotka microplate. The basal Firth River Group consists of a mixed siliciclastic and carbonate succession that is divided into the informal Redwacke Creek, Malcolm River, and Fish Creek formations. New U-Pb detrital zircon geochronology and δ 13 C carb and 87 Sr/ 86 Sr isotopic data from these strata, in combination with previously reported and new trace fossil discoveries, suggest the Firth River Group is Cryogenian(?)–middle(?) Cambrian in age. These strata interfinger with or are depositionally overlain by the siliciclastic-dominated lower Cambrian–Middle Ordovician(?) Neruokpuk and Leffingwell (new name) formations, which potentially record a distal expression of Cambrian extension and condensed passive margin sedimentation along the northern margin of Laurentia. All of these units are unconformably overlain by the synorogenic Clarence River Group, which is divided into the informal Aichilik and Buckland Hills formations. New U-Pb detrital zircon geochronology and previous macrofossil collections suggest the Clarence River Group is Late Ordovician-Early Devonian(?) in age. Here, we present new sedimentological observations, stratigraphic subdivisions, detrital zircon U-Pb geochronology and Lu-Hf isotope geochemistry, detrital muscovite 40 Ar/ 39 Ar geochronology, and carbonate δ 13 C carb and 87 Sr/ 86 Sr isotope geochemistry from the basinal succession that revise previous tectono-stratigraphic models for this part of Arctic Alaska and support correlations with age-equivalent strata in the Franklinian basin of the Canadian Arctic Islands and Greenland.

ABSTRACT The Whale Mountain allochthon is a structural complex composed of lower Paleozoic mafic volcanic and marine sedimentary rocks that are exposed within three fault-bounded, east–west-trending belts in the northeastern Brooks Range of Alaska and Yukon. Each belt is characterized by a unique structural and stratigraphic architecture. Trace-element systematics from the volcanic rocks define distinctive suites that are geographically restricted to each belt. The volcanic rocks of the southern belt (the Marsh Fork volcanic rocks) have a tholeiitic character and rare earth element trends that resemble modern mid-ocean-ridge basalt. The volcanic rocks of the central belt (the Whale Mountain volcanic rocks) and northern belt (Ekaluakat formation; new name) both have an alkaline character, but the northern belt rocks are significantly more enriched in the incompatible trace elements. New zircon U-Pb data from two volcaniclastic rock units, one from the southern belt and another from central belt, yield unimodal age populations that range from ca. 567 to 474 Ma, with weighted averages of 504 ± 11 and 512 ± 1.4 Ma for each sample. In the central and southern belts of the allochthon, basalt flows are interbedded with discontinuous limestone and dolostone units that contain trilobites and agnostoid arthropods. Three distinct trilobite faunas of late Cambrian (Furongian) age were recovered from widely separated localities. The scarcity of uniquely Laurentian genera, coupled with an abundance of distinctive species that could not be assigned to any established Furongian genus, argues against models that invoke extrusion of these volcanic rocks onto the autochthonous Laurentian shelf or slope. It is thus proposed that the Whale Mountain allochthon formed in a peri-Laurentian setting, possibly as disparate fragments of the northern Iapetus Ocean that were assembled in an ancient accretionary wedge and subsequently accreted to the northern margin of Laurentia during the early Paleozoic.

ABSTRACT The North Slope subterrane of Arctic Alaska extends from the northeastern Brooks Range of Alaska into adjacent Yukon, Canada, and includes a pre-Mississippian deep-water sedimentary succession that has been historically correlated with units exposed in the Selwyn basin of northwestern Laurentia. Sedimentary provenance data, including Sm-Nd isotopes and major and trace element geochemistry, provide detailed geochemical characterization of the regional pre-Mississippian strata of the North Slope subterrane. Combined with paleontological and geochronological age constraints, these new data record a marked shift in provenance in the Ordovician–Devonian(?) Clarence River Group, evidently linked to an influx of juvenile, arc-derived material. The timing and nature of this provenance change are consistent with early Paleozoic tectonic reconstructions of the Arctic margin that restore the North Slope subterrane to northeastern Laurentia (present coordinates), proximal to the Appalachian-Caledonian orogenic belt. Such a restoration requires significant post-Early Devonian sinistral strike-slip displacement to later incorporate the North Slope subterrane into the composite Arctic Alaska terrane.

ABSTRACT The Neoproterozoic–Early Devonian platformal succession of the North Slope subterrane, northeastern Brooks Range, Alaska, represents a carbonate-dominated peri-Laurentian continental fragment within the composite Arctic Alaska–Chukotka microplate. The basal ca. 760–720 Ma Mount Weller Group consists of an ~400 m thick mixed siliciclastic and carbonate succession that records the onset of regional extensional tectonism associated with the separation of southeastern Siberia from northern Laurentia during the break-up of Rodinia. These strata are overlain by ca. 720 Ma continental flood basalts of the Kikiktat volcanic rocks, which provide a link between the northeast Brooks Range platformal succession and the ca. 723–717 Ma Franklin large igneous province (LIP) of northern Laurentia. The overlying Sturtian Hula Hula diamictite and Cryogenian–Ediacaran Katakturuk Dolomite record abbreviated thermal subsidence of the northeast Brooks Range platformal succession prior to renewed Ediacaran–early Cambrian extensional tectonism and deposition of the overlying lower Paleozoic Nanook Group (new name). Equivalent strata of the deep-water Cryogenian–lower Cambrian(?) Ikiakpuk Group (new name) are identified herein with new δ 13 C carb and 87 Sr/ 86 Sr isotopic data from the Fourth Range of the northeastern Brooks Range. The Nanook Group is formally divided herein into the Black Dog and Sunset Pass formations, which record isolated peri-Laurentian platformal carbonate sedimentation along the northern margin of Laurentia, in an analogous tectonic position to the modern Bahama Banks. A profound Late Ordovician(?)-Early Devonian unconformity within the platformal succession is marked by subaerial exposure, paleokarst development, and tilting of the northeast Brooks Range peri-Laurentian platformal fragment prior to deposition of the overlying Lower Devonian Mount Copleston Limestone.