Hirugaya Alternation

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Hirugaya Alternation Mizuno et al., 1987

Type locality: Hirugaya - Nakanishi, Makinohara city, Shizuoka prefecture
Coherent formation
middle Miocene - Pliocene
Correlation: Susuki Mudstone

Sedimentary facies: Marine
Sedimentary facies: Forearc basin (Sagara-Kakegawa Basin) deposit
Lithofacies: Mudstone-dominant interbedded sandstone and mudstone

Thickness: ca. 150 - 200 m
Upper limit: Conformity (Oyori Mudstone, Yokobuna Mudstone)
Lower limit: Conformity (Sugegaya Alternation)

Sagara Group (Western part)
[ Upper ]
--------------
Hagima Conglomerate
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Oyori Mudstone
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Hirugaya Alternation
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Sugegaya Alternation
~~~~~~~~~~~~~~
[ Lower ]

Sagara Group (Central part)
[ Upper ]
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Hiki Alternation
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Ogane Mudstone
--------------
Sagara Alternation
--------------
Yokobuna Mudstone
~~~~~~~~~~~~~~
[ Lower ]

Sagara Group (Eastern part)
[ Upper ]
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Omaezaki Alternation
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Sagara Alternation
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Susuki Mudstone
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Jitogata Alternation
~~~~~~~~~~~~~~
[ Lower ]

------ Conformity, ~~~~~~ Unconformity, ~~~--- Local unconformity, '''/,, Interfingered, :::::: Fault, /--/-- Thrust, +__+__ Ground surface, ?--?-- Unknown

Distribution: Hirugaya - Nakanishi - Shinden, Makinohara city, Shizuoka pref.; Iwachi - Yokobuna, Omaezaki city, Shizuoka pref.
Fossils: Sponges (Sagarites chitanii), Calcareous nannofossils
Fossls (Foraminifera): Globorotalia tumida plesiotumida, Neogloboquadrina acostaensis

Sugiyama et al. (1988) Geology of the Omaezaki District, Quadrangle Series, Scale 1:50,000, Geological Survey of Japan, 153p. (in Japanese with English abstract 6p.)