Preliminary report on sedimentary and metamorphic rocks in part of the Romanzof Mountains, Brooks Range, northeastern Alaska

Abstract

The Romanzof Mountains comprise a high, rugged mountain group in the northeastern Brooks Range. A granite b o w of small batholith size, the "akpilaka granite, occupies the 1 central part of the Romanzofe, and is flanked by sedlmentarp D and metasedimentary rocks which range from pre-~ssisslpplan 1 t to Jurassic in age. Pllaflc dikes and extrusive(?) rocks are of minor occurrence. cretaceous(?) rocks are exposed north of the area. The Neruokpuk formation of pre-Mlssissipplan age l a here mapped to lnclude several sedhentary and low grademetasedlmentary rock units. These lnclude a loner black limestone unit overlain by Interbedded limestones, phyllite, argillite, alate, chert, and quartzite, In turn overlain by a thick section of quartzite and schlstoee quartzite. The total thickness of the Nemokpuk sequence I s believed to be more than 4400 feet, A major angular unconformlty separates these rocks from the overlying Mississippian rocks.. Mlssiaelppian rocks lnclude the Kayak "shalea, a unit of light to dark gray.quartzite, carbonaceous shale, and conglomerate which Is 0 to about 400 feet thick. The Llsburne group, of late ~Mssissippian age, consists of gr& limestone and dolomite, with minor amounts o f chert, black shale, and sandstone, and is as much as 780 feet thick. The .group la overlain at least disconformably by Permian rocks. The Sadlerochlt formation, of ~ermlan-Triassic(?) age Includes a lower Ferruginous sandstone member, about 200 only known granitic body on the northern side of the Brooks Range. In addition, a variety of sedimentary and metamorphic rocks are present, and Pleletocene to Recent valley glaciation features are abundant. Qeologic field Investigatlons were undertaken during the summers of 1957 and 1958 to study the granite and its relationsNpa to addoinlng rocks and to compare the sedimentary and metamorphic rock sequence wlth those in bebter known areas of the Brooke Fbnge. Location,-Size, and Accessibility-of Area The Romanzof Mountains lie within the Mount ?'Kchclson and Demarcation Point Quadrangles, Alaaka, and cover about 600 square miles. They are approximately bounded on the east and west by the Jago and Hulahula Rivera, respectively, and lie between latitudes 6 9 ' 0 5 ' and 6g02j" N (~i g u r e 1). Airline distances to the nearest Alaskan settlements of Barter Island, Bettles, and Barrow are 60, 130, and 320 miles reapectively. No roads or established tralls are present Into or within the area, and access ts most easily accomplished by use of small float-or ski-equipped aircraft. Within the area, travel can beat be accomplished on foot. Although tracked vehlcle travel 1s possible along the Jago, Ckpllak, and Ifulahula Rivera nearly to their headwaters, such travel would be dlificult within the mountains. Shall&

Geology of the Lake Peters area, northeastern Brooks Range, Alaska

“…West of Lake Peters in the Shaviovik-Sagavanirktok Rivers region, the Shublik Formation disconformably overlies the Sadlerochit Formation (Keller and others, 1961, p. 178;Brosge andothers, 1962, p. 2178). East of Lake Peters, in the Romanzof Mountains, the Shublik Formation possibly disconformably overlies the Sadlerochit Formation (Sable, 1965). The contact between the upper part of the Shublik Formation and the overlying Kingak Shale in the Lake Peters area is apparently in structural concordance east of Lake Peters on Karen Creek ( fig.…”

“…Where exposed along the Kongakut and Firth Rivers about 100 miles east of Lake Peters, the older metasedimentary rocks were referred to as the Neruokpuk Schist by Mangus (1953, p. 12). Sable (1959Sable ( , 1965, in the Mount Michelson area, mapped a varied sequence of pre-Mississippian quartzites, slates, and limestones which he designated the N eruokpuk Formation. Norris, Price, and Mountjoy ( 1963) mapped the continuation of these rocks east of the International Boundary as N eruokpuk Formation and tentatively assigned them a Precambrian or Cambrian ( ~) age.…”

“…In the Lake Peters area, the Ignek Formation is not present, and the Kingak Shale is overlain by surficial deposits. Keller, Morris, and Detterman (1961, p. 191) mapped the Kingak Shale to the west of the type ·area, and Whittington and Sable (1948) and Sable ( 1959) mapped it east of the type area. Sable also ( 1965, p. 78) mapped a 75-to 100-foot resistant siltstone unit at the base of the Kingak Shale.…”

“…ECHOOKA RIVER LAKE PETERS AREA HULAHULA RIVER JAGO RIVER KONGAKUT RIVER (Brosge and others, 1962) (This report and Brosge (Sable, 1965) (Sable, 1965) (Brosge and others, 1962) …”

“…The upper Ivishak Member contains a lower shale and minor siltstone unit and an upper siltstone, shale, and sandstone unit. Sable (1965) divided the Sadlerochit Formation in the Romanzof Mountains area, 15 miles east of Lake Peters, into a lower ferruginous sandstone member, a middle shale member, and an upper quartzite member.…”