Shelikof Strait trends northeast between the Kodiak islands and Alaska Peninsula. The seafloor within the strait forms a gently sloping platform gradually deepening from about 170 m in the northeast to over 200 m at the south west boundary of the sale area. Narro, w channels border the platform, adjacent to the islands and the mainland. Sediment of presumed Pleistocene and Holocene age covers folded and glacially eroded sedimentary bedrock. SUrficialsediment grades texturally from muddy sand in the northeast to slightly sandy mud in the south west and represents a Holocene progradational marine deposit from currents enterin;J the northeast end of the strait. The strait is presently a depositional regime, with no evidence of erosion or large-scale bedform movement as in nearby lower Cook Inlet or on Kodiak Shelf. Accumulation rates, judged from sediment thickness overlying a volcanic ash layer from the 1912 Katmai event, are on the order of 10- 40 cm/100 yr. Levels of light hydrocarbon gases in core samples are very low (methane = 30 microliters/liter) except in one core (methane = 1600 microlitersVliter) suggesting a general lack of nearsurface gas-charged sediment. However, seafloor craters and acoustic anomalies deeper in the section might indicate gas saturation in sediment at some localities.
Sediment physical properties other than grain size also show consistent change parallel to the northeasterly trend of the area: water content, plasticity index, and liquidity index increase toward the southwest, whereas vane shear strength and sensitivity decrease.
Shallo, W faults occur near the edges of the strait and near the axis in the northeast and central areas. Some faults offset the seafloor up to 100 m, but are only a fe, w kilometers long, and appear to have experienced recent movement. Earthquake epicenters show no significant concentrations of seismic activity near the high-offset faults. Slope instability is rare in the strait; only one small slide has been identified.
Shelikof Strait, situated between the Kodiak island group and the Alaska Peninsula (Fig. 1), is included in oes oil and gas lease area 60. Environmental geologic studies are being conducted by the u.S. Geological Survey prior to the scheduled September 1981 sale date. Seismic-reflection records, collected with 40- to 95-cm3 airgun, 8OO-joule ' minisparker, 800-joule boomer, and 3.5- and 12kilohertz systems and covering over 6,400 kID of trackline have been examined to identify geologic conditions at or below the seafloor that might affectpetroleum operations. Of the total trackline distance, 865 km were collected in June 1980 aboard the Geological Survey's ship R/V S.P. LEE. The remainder were collected by Nekton Inc. in 1979, under contract to the USGS Conservation Division (Fig. 2). Sediment samples were collected at 42 stations on the June 1980 cruise for geological and geotechnical analysis (Fig. 2).
