1:45 PM - 3:15 PM
[O07-P10] Research into Moriya Formation Formed in Northen Fossa Magna
Keywords:Moriya Formation, Fossa Magna
1.Research motive
There is Moriya Formation around Mt.Moriya in Suwa. It didn’t investigate its details such as geological age or connection with other areas. So I thought I wanted to investigate them.
2.Research wayI did research in 13 places across Moriya Formation and I recorded fossil, lithofacies, and strike and dip. Based on the results of my research, I drew a geological map or make a conjecture about Moriya Formation’s geological age. And I compared with Shimonita Formation.
3.Research results
Research results and Geological map
Based on the results of my research, I drew a geological map. However, Shell fossils were produced from two outcrops, and these were called outcrops A and B. Outcrop A deposits volcanic ash gravel layer, gravel layer, and silt layer from the bottom, and outcrop B deposits volcanic ash gravel layer, coarse-grained sand layer, fine-grained sand layer, coarse-grained sand layer, and silt layer from the bottom.
Fossils of Moriya Formation
The fossils produced from outcrops A and B and the age of development of the major fossil species produced are shown in the figure. The fossils produced are divided into four types: those that inhabited the gradual Miocene, those that inhabited the Early Miocene and Middle Miocene, and those that inhabited after the Miocene.
Shimonita Formation’s Research
Since the Shimonita Formation is certified as a Japanese Geopark, I compared mainly the materials and literature surveys of previous studies. From Kurihara(2005), the Shimonita Formation has developed early Miocene species as a whole. And Sr isotope analysis using Mytilus tichanovitchi showed 20.4 ± 0.2 Ma, and the upper limit was around 16.8 Ma from the production of planktonic foraminifera.
4.Considration
Based on the research results, I drew columnar maps of the Moriya outcrops A and B and the Shimonita Formation. Comparing them, it is considered that there is no big difference in the geological ages of the two layers because they have something in common, such as the production of Macoma and Mytilus tichanovitchi, which were developed from the Oligocene. In addition, the Moriya Formation has many mid-Miocene development species, but it is not found in the Shimonita Formation, and the Shimonita Town Formation shows 16.8 Ma, so the geological age of the Moriya Formation is 16 Ma, which is a little newer than the Shimonita Formation. Presumed. Matsumaru (1962) reported the production of large higher foraminifera in warm waters from the Moriya Formation, and it is believed that the Moriya Formation was formed in warm waters. We collected Kimura scallops and Anadara genus, which are characteristic of the Miocene Kadonosawa fauna, which developed from the Moriya Formation in the warm sea. However, Mytilus tichanovitchi from the Moriya class is considered to be evidence of the early Miocene cooling event. In that case, the Moriya Formation is considered to have been deposited in the cold sea, which is inconsistent with the results of previous studies. However, Anadara and others are not effective phase-indicating fossils, and it is possible that they could adapt to the cold sea. However, no other strata, such as the Moriya Formation, where fossils of the Early Miocene cooling event period and the Middle Miocene Kadonosawa Animal Group coexist have been confirmed at this time. From the above, it is considered that the Moriya Formation was deposited during the transition period from the cold Miocene to the warm Miocene around the Early Miocene and the Middle Miocene.
There is Moriya Formation around Mt.Moriya in Suwa. It didn’t investigate its details such as geological age or connection with other areas. So I thought I wanted to investigate them.
2.Research wayI did research in 13 places across Moriya Formation and I recorded fossil, lithofacies, and strike and dip. Based on the results of my research, I drew a geological map or make a conjecture about Moriya Formation’s geological age. And I compared with Shimonita Formation.
3.Research results
Research results and Geological map
Based on the results of my research, I drew a geological map. However, Shell fossils were produced from two outcrops, and these were called outcrops A and B. Outcrop A deposits volcanic ash gravel layer, gravel layer, and silt layer from the bottom, and outcrop B deposits volcanic ash gravel layer, coarse-grained sand layer, fine-grained sand layer, coarse-grained sand layer, and silt layer from the bottom.
Fossils of Moriya Formation
The fossils produced from outcrops A and B and the age of development of the major fossil species produced are shown in the figure. The fossils produced are divided into four types: those that inhabited the gradual Miocene, those that inhabited the Early Miocene and Middle Miocene, and those that inhabited after the Miocene.
Shimonita Formation’s Research
Since the Shimonita Formation is certified as a Japanese Geopark, I compared mainly the materials and literature surveys of previous studies. From Kurihara(2005), the Shimonita Formation has developed early Miocene species as a whole. And Sr isotope analysis using Mytilus tichanovitchi showed 20.4 ± 0.2 Ma, and the upper limit was around 16.8 Ma from the production of planktonic foraminifera.
4.Considration
Based on the research results, I drew columnar maps of the Moriya outcrops A and B and the Shimonita Formation. Comparing them, it is considered that there is no big difference in the geological ages of the two layers because they have something in common, such as the production of Macoma and Mytilus tichanovitchi, which were developed from the Oligocene. In addition, the Moriya Formation has many mid-Miocene development species, but it is not found in the Shimonita Formation, and the Shimonita Town Formation shows 16.8 Ma, so the geological age of the Moriya Formation is 16 Ma, which is a little newer than the Shimonita Formation. Presumed. Matsumaru (1962) reported the production of large higher foraminifera in warm waters from the Moriya Formation, and it is believed that the Moriya Formation was formed in warm waters. We collected Kimura scallops and Anadara genus, which are characteristic of the Miocene Kadonosawa fauna, which developed from the Moriya Formation in the warm sea. However, Mytilus tichanovitchi from the Moriya class is considered to be evidence of the early Miocene cooling event. In that case, the Moriya Formation is considered to have been deposited in the cold sea, which is inconsistent with the results of previous studies. However, Anadara and others are not effective phase-indicating fossils, and it is possible that they could adapt to the cold sea. However, no other strata, such as the Moriya Formation, where fossils of the Early Miocene cooling event period and the Middle Miocene Kadonosawa Animal Group coexist have been confirmed at this time. From the above, it is considered that the Moriya Formation was deposited during the transition period from the cold Miocene to the warm Miocene around the Early Miocene and the Middle Miocene.