New Siberia Island consists of clastic sediments ranging from Late Cretaceous to Pleistocene in age. The Late Cretaceous sediments consist of extensively folded layers of gray and greenish gray tuffaceous sand, tuffaceous silt, pebbly sand, and layers of brown coal exposed in sea cliffs along it southwest coast. The sand and silt often contain either volcanic glass, fossil plants, rhyolite pebbles, or some combination of them. Eocene sand, silt, clay, and brown coal overlies an erosional unconformity cut into the Late Cretaceous sediments. Within the northwest part of New Siberia Island, these sediments grade into clays that contain fragments of marine bivalves. Directly overlying the Eocene sediments and another erosional unconformity are sands of Oligocene and Early Miocene age. They contain thin beds of silt, mud, clay, and pebbles. These sands contain fossil plants and lagoonal, swamp, and lacustrine diatoms. These sands are overlain by Pliocene sediments consisting of layers of sand, silt, mud, peat, and pebbles.