Introduction to the Landforms and Geology of Japan


Tei Mélange and Muroto
  -- Shimanto accretionary complex

Kuromi (submarine sliding and mélange)

Kuromi is in Muroto City, about 45 km from Nishibun on the way to Cape Muroto. Mélange is seen in the Kuromi beach, formed by submarine sliding (debris flow). Submarine sliding is a phenomenon that sediments on the seafloor gravitationally flow down the slope, triggered by earthquakes, an influx of deposits, and so on. The Kuromi deposits belong to the Muroto formation of the Paleogene system. The mélange consists of various-sized blocks of sandstone and matrix of poor sorted black mudstone. The appearance of the mélange is more chaotic than that of the Tei mélange which has a direction of block arrangement in places. Sand dikes intruded the deposits, which are the remains of sand intrusion caused by liquefaction at an earthquake. The Muroto formation is known for many sand dikes.

View Tei melange and Muroto in a larger map

Kuromi melange
Photo 7 Mélange in Kuromi [Another window]
A white line shows the length of about 50 cm.

Sand dike
Photo 8 Sand dike [Another window]

Ripple marks and trace fossils
Photo 9 Ripple marks and trace fossils [Another window]
Ripple marks are often seen on the upper surfaces of sand beds, which are produced by flowing water or wave action. The rock in the photo is a float that probably came from near alternating beds of sand and mud. The trace fossils may be imprints of creeps of animals such as crabs. The scale is 20 cm long.

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