Four carbonate strata of Miocene are exposed in Akita area of northern Honshu, Japan.
Investigations with the electron-microscope revealed that these carbonate rocks are composed mainly of skeletal debris such as diatoms, forminifera, radiolaria and nannoplankton.
The paleo-environments were bathyal to innerneritic. During syn-diagenesis, calcium and magnesium derived from the sea water as well as from volcanic detritus within the basin altered the originally siliceous sediments to dolostone (in deep, cold waters) and limestone (in shallow, warm waters).
After the consolidation, the primary texture of carbonate rocks was destroyed gradually by dehydration and recrystallization during ana-diagenesis.