Kemik Sandstones, Arctic National Wildlife Refuge (ANWR), Alaska: ABSTRACT

Abstract

In the Sadlerochit Mountains area of ANWR, the Kemik Sandstone of Hauterivian-Barremian age ranges to at least 35 m (120 ft) of very well sorted, fine-grained quartzose sandstone with minor pebble conglomerate. It is an elongate body traceable for over 160 km (100 mi) from the eastern Sadlerochit Mountains into the subsurface near the Sagavanirktok River to the west. In the northeast, it crops out in a belt about 16 km (10 mi) wide; to the southwest in the subsurface, it expands to about 65 km (40 mi) wide. It is a potential petroleum reservoir in the subsurface of ANWR, but its distribution north and east of the Sadlerochit Mountains is unknown. The Kemik overlies a regional angular unconformity with increasing depth of truncation northward; it is overlain by and intertongues with an unnamed pebble-shale unit. Data suggest that the Kemik was derived from erosion of Lisburne Group carbonate rocks and a terrain of mature sedimentary rocks north and east of the outcrop belt. Conglomerate clasts consist dominantly of white leached spicular and foraminiferal chert, silicified carbonate, and quartzite. Although the sand has a nearly uniform grain size from east to west, conglomerate clasts are most abundant to the northeast and become smaller and less abundant westward; few are noted west of the Canning River. This distribution is suggestive of longshore drift from the northeast. A shoreface depositional environment, possibly a barrier island along a coast with low tidal flux, seems to be represented in the Kemik. Beds up to 2 m (6 ft) thick with sweeping low-angle cross stratification are interbedded with parallel laminated units and scattered, thin, maroon siltstone-mudstone beds. Vertical burrows up to 0.5 m (20 in.) long and truncated by overlying beds are conspicuous in some areas. A sparse pelecypod fauna is present, usually in the maroon silty horizons. The Kemik and other coeval sandstone and conglomerate horizons in the subsurface, such as the Put River sands and the Point Thomson sands, are probably separate bodies of sediment derived from uplifted blocks along the rifted Arctic Alaska plate margin. End_of_Article - Last_Page 672------------