Geology of the western Romanzof Mountains, Brooks Range, northeastern Alaska

Abstract

The western Romanzof Mountains cover a remote 700-square-mile area in the Brooks Range, northeastern Alaska. The area is topographically rugged and geologically diverse; it contains a gramtlc pluton, low-grade metamorphic rocks, sedimentary rocks and mafic igneous rocks, as well as glacial features.Rocks of sedimentary origin, from o1dest to youngest are: l. Neruokpuk Formation (Precambrian, Cambrian, and pre-Mississippian), more than 4,000 feet thick, consists of units of the greenschist facies, including quartziticand schistose-feldspathic to quartzose graywacke; phyllite, argillite, slate; minor chert; and limestone. The succession of units in parts of the area is uncertain. Correlations of these units with each other and with other units in the eastern Brooks Range are provisional. 2. Katakturuk Dolomite (Devonian or older), silicified carbonate rocks, mostly dolomite, with minor dark shale, carbonate conglomerate and breccia beds, pisolite and oolite beds. Probably more than 1,000 feet thick. 3. Kekiktuk Conglomerate and Kayak(?) Shale (Mississippian), a single map unit, 0(?)-420 feet thick, contains quartzite, interbedded dark shale, and some pebbleto boulder-conglomerate in the locally absent lower part (Kekiktuk), and, in its uppermost part, dark shale (Kayak(?)). The unit overlies the Neruokpuk and Katakturuk with angular unconformity, which may reflect either a pre-Kayak(?) or pre-Kekiktuk hiatus or both. 4. Lisburne Group, almost entirely carbonate rocks, is 600-800 feet thick in the northern part of the area and probably 1,200 feet thick in the southern part. Alapah Limestone (Upper Mississippian) of this group, as much as 560 feet thick, includes gray sandy, crystalline, and cherty limestones; minor dark shale; and, in the upper part, dark cherty carbonate rocks. Dark shaly and cherty carbonate rocks abo constitute the lower part of the group in the southern part of the area. The lower contact is gradational with the Kayak(?) Shale. The Wahoo Limestone (Pennsylvanian) conformably overlies the Alapah, is 0-200+ feet thick, and is characterized by light-gray crinoidal limestones in its upper pan. 5. Sadlerochit Formation, consisting of two members: the Echooka Member (Upper Permian) of iron-stained orthoquartzite and dark slate, 175-240 feet thick, which unconformably overlies the Wahoo and Alapah Limestones; and the Ivishak Member (Lower Triassic), consisting of a shale unit of dark shale, slate, and minor quartzite averaging 400 feet in thickness, and a quartzite unit, 700 feet thick, mostly orthoquartzite with minor shale and conglomerate. The basal clastics were probably shed from the north. 6. Shublik Formation (Middle and Upper Triassic), 60Q-700 feet thick, the thin phosphatic sandstone member is overlain by dark phosphatic limestones and limy shales of the limestone member.

Short notes on Alaska geology 1997

“…U-Pb zircon dating has yielded an initial crystallization age of 380 ± 10 Ma (Dillon and others, 1987) for the batholith. Both the batholith and the Franklinian sequence are unconformably overlain by Mississippian to Lower Cretaceous carbonate and clastic rocks of the Ellesmerian sequence (Sable, 1977;. Geochronologic and depositional relationships clearly indicate that the batholith predates the unconformity.…”

“…1) and has been described in detail elsewhere (Sable, 1977;Hanks and Wallace, 1990). It intrudes weakly metamorphosed Proterozoic and Paleozoic sedimentary and volcanic rocks of the Franklinian sequence, which are the oldest rocks exposed in the northeastern Brooks Range (Reiser and others, 1980).…”

Changes in stratigraphic nomenclature by the U. S. Geological Survey, 1977

“…Subsequent mapping by geologists of the U.S. Geological Survey in and east of its type area expanded the Neruokpuk to include additional rock types (Brosg/and others, 1962;Reed, 1968;Reiser, 1970;Sable, 1977), and its name was revised to Neruokpuk Formation. In 1972, its age was revised to Precambrian, Cambrian, and post-Cambrian preMississippian on the basis of marine fauna from some parts (Dutro and others, 1972).…”

Significant metalliferous and selected non-metalliferous lode deposits and placer districts for the Russian Far East, Alaska, and the Canadian Cordillera

“…Barker, 1978Barker, ,1981 (1) zones of disseminated galena, sphalerite, chalcopyrite and pyrite, locally with Au and Ag, in granite; (2) skam in marble with disseminated magnetite, pyrite, pyrrhotite, sphalerite, and galena in gangue of carbonate, clinopyroxene, epidote, amphibole, beryl, tourmaline, and fluorite; (3) disseminated galena, sphalerite, chalcopyrite, and (or) molybdenite in quartz veins along sheared contact in granite; and (4) fluorite greisen in granite. Brosge and Reiser, 1968;Grybeck, 1977;Sable, 1977;W.P. Brosge, oral commun., 1984;Newberry and others, 1986 Disseminated galena, sphalerite, malachite, and barite in quartz veinlets and replacement bodies in phyllite, siltstone, and greenstone of Neruokpuk(?)…”