CLASTS FROM WELL CORES AND PALYNOLOGY SUGGEST A MID TO LATE TURONIAN AGE FOR THE AVAK IMPACT FEATURE NEAR BARROW, ALASKA

The oldest exploration wells on the Alaska North Slope are near the village of Barrow and on the Simpson peninsula. These wells were drilled between about 1944 and 1955. Exploration wells, gravity and seismic data delineate a subsurface circular feature near Barrow, Alaska. The Avak well tested the central uplift and found pervasively fractured rocks, shatter cones, shocked quartz and both out of sequence and repeated stratigraphic units. This is the Avak impact feature. It is approximately 10 km. in diameter and is currently buried by about 1 km of sedimentary cover. The East and South Barrow gas fields flank the Avak feature.

Examinations of the comparatively shallow Simpson core tests, drilled approximately 50 to 70 km. southeast of the Avak impact site, show there is an assemblage of exotic rock fragments, a breccia, within a section of marine mud and sand. These rock fragments are rounded to angular in shape. They include limestone, black platy shale, red to brown siltstone, chert and quartzite pebbles in sizes up to about 5 cm. These exotic rock fragments occur within the marine mudstone of the Seabee Formation and within poorly sorted, disorganized sands which lack sedimentary structures. Palynology shows the gray mudstone is Turonian to Coniacian. Matrix surrounding the exotic clasts is middle to late Turonian. The sands may represent chaotic surge or tsunami deposition, which is coincidental with a nearby marine impact. The breccia clasts and matrix overlie late Albian litharenties of the Nanushuk Formation.