Chert Outcrop, Shelikof Strait

Red chert is an erosion-resistant rock forming part of the Uyak Formation that extends for approximately 600 km along the Alaska coast from the Shumagin Islands, through the Kodiak Archipelago, and into the Chugach Mountains near Anchorage. Chert is a hard silica-based rock formed from lithified radiolarian ooze. Radiolarian zooplankton are found throughout the ocean and the intricate silica skeletons they produce cover larger portions of the ocean bottom. In areas of high biological productivity, such as nutrient-rich upwelling zones, radiolarian ooze accumulates on the ocean floor and is rapidly buried. After burial, some radiolarian oozes are lithified into chert and incorporated into orogens, or bands of highly deformed rock. Orogenic belts, such as the Uyak Formation, generally consist of long parallel strips of rock exhibiting similar characteristics along the length of the formation and are associated with subduction zones. The Uyak Formation was accreted to the Alaska margin in the late Cretaceous period or about 100 million years ago. Click here to download the CoastView app and explore the chert outcrop and more of Shelikof Strait.