A Skeleton in Triassic Rocks in the Brooks Range Foothills

Abstract

Fragments of vertebrate fossils are found in beds of the Shublik Formation, which blanketed most of northern Alaska during Triassic time. Although articulated remains are uncommon, one partial skeleton was discovered in 1950 during exploration of Naval Petroleum Reserve No. 4. ... This note calls attention to the existence of the skeleton and reports on what has been observed of the vertebrate remains. Figs. 1 and 2 locate the site (68°37'15" N, 157°35' W) on Cutaway Creek (Howard Pass 1:250,000-scale quadrangle) in the geologically disturbed zone of the Brooks Range foothills. It is about 200 miles south of Point Barrow and 35 miles northwest of Howard Pass. Fig. 3 is a photograph of the actual bedding-plane exposure. Most of one side of the rib case is exposed, and some limb structures seem preserved. The exposed parts indicate a skeleton more than 5 feet long. Bone fragments are common in the fine talus weathering off the outcrop. Although no invertebrate fossils were seen on the surfaces of beds containing the skeleton, they are abundant in correlative beds; detailed examination of this or nearby exposures should yield pelecypods that will fix the biostratigraphic level of the vertebrate remains. Some features of the Late Triassic environment can be assessed. A sea of remarkably persistent character extended beyond the length of the present Brooks Range and probably more than twice the width of the present Arctic Slope. A shoreline existed near the present northeast coast of Alaska, but coarse detritus was not carried far southward. The bottom elsewhere was below wave base, and the sediment that settled onto it formed thin deposits, first of anaerobic chert, shale and limestone, then aerobic lithographic limestone. Pectens ... are abundant .... The thin chert beds surrounding the skeleton are correlative with beds elsewhere that contain Halabia of Karnian or early Norian age .... The skeleton is older than 200 million years as shown by K/Ar age determinations on minerals in diabase sills that intrude the Shublik Formation about 20 miles to the east .... Vertebrate fragments previously collected from the Shublik have been identified as follows: from this locality and from limestone near Hardway Creek (68°38'5" N, 156°51' W) about 20 miles to the east - vertebra of a possible ichthyosaur and teeth of a probable Mixasaurus ...; in limestone, chert, and shale on Kiligwa River (68°43'45" N, 158 °26' W) about 25 miles to the northwest - probable caudal vertebra of an ichthyosaur ...; and in limestone at the west end of the Sadlerochit Mountains (69°35'15" N, 145°55'5" W), northeastern Brooks Ranges - vertebral, costal, and jaw fragments of either the Shastasauridae or Ichthyosauridae ichthyosaur family .... Helicopters offer the only practical access to the site, for the nearest lake on which a float plane can land is more than 10 miles away. Transportation for preliminary inspection could probably be arranged with any geologic field party working within a hundred miles of the locality. Collection of the skeleton would require that an outfit be landed near the outcrop by ski plane in the spring and retrieved during the fall or winter. We cannot judge the quality or significance of the skeleton but feel that it should be examined by a vertebrate paleontologist as it could yield valuable information on life in the seas during Triassic time at a present arctic latitude.