The Morawan Formation is a Chattian age siliceous marine

geological formation A geological formation, or simply formation, is a body of rock having a consistent set of physical characteristics ( lithology) that distinguishes it from adjacent bodies of rock, and which occupies a particular position in the layers of rock exp ...

of the Oligo-

Miocene The Miocene ( ) is the first epoch (geology), geological epoch of the Neogene Period and extends from about (Ma). The Miocene was named by Scottish geologist Charles Lyell; the name comes from the Greek words (', "less") and (', "new") and mea ...

Japanese Kawakami Group of eastern

Hokkaido prefecture is Japan's second largest island and comprises the largest and northernmost prefecture, making up its own region. The Tsugaru Strait separates Hokkaidō from Honshu; the two islands are connected by the undersea railway Seikan Tunnel. The ...

. The formation is fossil rich and contains source units where toothed baleen whales (

Aetiocetidae Aetiocetidae is an extinct family of toothed baleen whales known from the Oligocene. The whales are from the North Pacific Ocean and ranged in size from long. Many of the described specimens were discovered from the Upper Oligocene of the Japa ...

) and

Desmostylia The Desmostylia (from Greek δεσμά ''desma'', "bundle", and στῦλος ''stylos'', "pillar") are an extinct order of aquatic mammals that existed from the early Oligocene (Rupelian) to the late Miocene ( Tortonian) (). Desmostylians are t ...

ns have been discovered. The Morawan Formation is a very siliceous unit containing hard platy shales interbedded with

tuff Tuff is a type of rock made of volcanic ash ejected from a vent during a volcanic eruption. Following ejection and deposition, the ash is lithified into a solid rock. Rock that contains greater than 75% ash is considered tuff, while rock ...

aceous mudstones and

sandstone Sandstone is a clastic sedimentary rock composed mainly of sand-sized (0.0625 to 2 mm) silicate grains. Sandstones comprise about 20–25% of all sedimentary rocks. Most sandstone is composed of quartz or feldspar (both silicates ...

s, and some

pumice Pumice (), called pumicite in its powdered or dust form, is a volcanic rock that consists of highly vesicular rough-textured volcanic glass, which may or may not contain crystals. It is typically light-colored. Scoria is another vesicular v ...

. The unnamed lower member is a hard platy shale alternating with beds of tuffaceous mudstones and sandstones, the Kamirawan member is a tuffaceous sandstone with pumice, the Lower Hard Shale is a very siliceous hard shale with tuffaceous sandstones and mudstones, and the Middle Hard Shales and the Upper tuffaceous siltstone are similar. Fossil species from the Morawan Formation include: * '' Ashorocetus eguchii'' * '' Morawanocetus yabukii'' * '' Aetiocetus tomitai'' * ''A. polydentatus''

References

{{coord missing, Hokkaidō Prefecture Geologic formations of Japan Paleogene System of Asia Paleogene Japan Chattian Stage Shale formations Mudstone formations Sandstone formations Oligocene paleontological sites Paleontology in Japan Hokkaido