Lower Paleozoic Rocks of Alaska [Abstract]

ABSTRACT Cambrian rocks are presently known only from east-central Alaska where a succession of shelly fossils, ranging in age from Early through Late Cambrian, occurs in a thin (300 feet) carbonate section that grades downward into the Tindir Group, a thick (10,000+ feet) sedimentary series of Precambrian age. Ordovician rocks occur in a few separated areas and are widely different in facies. Thousands of feet of graywacke, shale, chert, and volcanic rocks in southeast Alaska contrast with thinner, predominantly carbonate sections in the Alaska Range, Seward Peninsula, and Porcupine River. The Road River Formation, a graptolitic shale less than 900 feet thick, seems to represent an intermediate facies in east-central Alaska that spans most of Ordovician and Silurian time. Silurian and Devonian rocks are generally similar in facies to the Ordovician rocks. In the Brooks Range, however, there is a thick (5,000 feet) succession of predominantly argillaceous rocks of Devonian age, and in southeast Alaska there are Silurian and Devonian limestones thousands of feet thick in an otherwise volcanic and detrital sequence. Coarse clastic rocks of Late Devonian age in the Brooks Range (Kanayut Conglomerate) and east-central Alaska (Nation River Formation) indicate uplift of the earlier geosynclinal deposits. 1 Reprinted, with permission, from Oilweek, v. 17, no. 14, p. 23-24. End_of_Record - Last_Page 603-------