1:45 PM - 3:15 PM
[O08-P07] Various rocks from Tojoko Lake
Contrast Sirakawa aria and Sandatiki in Kobe group
This study is a continuation of last year's research. The Kobe Formation is a group of rocks that extends from present-day Nishi and Suma wards of Kobe City to Awakawa-cho, Yoshikawa-cho, and Sanda City in the Kitagami area. Although the Kobe Formation has been familiar with the region since ancient times, outcrops have been disappearing year by year due to coastal protection and land development to prevent flood damage in recent years. The Kobe Group is home to a wide variety of plant fossils, which are very important for understanding the environment of the city of Hyogo Prefecture. Therefore, various studies have been conducted mainly in Shirakawa, but due to the decrease in the number of outcrops, not enough research has been conducted. Therefore, we thought that we could preserve the outcrops of the Kobe Group by conducting research on the Kobe Group before the outcrops disappear and by drawing the attention of the local community. We decided to conduct our research in the Tojo Lake area in Kurotani, Kato-shi, Hyogo Prefecture, because we learned from our research that the Kobe Group exists in the Tojo Lake area. The map of the Kobe Formation in Lake Tojo was found to be overlying the Arima Formation. In addition, while the Shirakawa area in Kobe City is completely covered, the columnar map of the Sanda area shows some blank areas. The authors conducted their research with the goal of filling in these blank areas.
In the year before last, the authors compared the ashlar layers found in Lake Tojo with the tuff layers in the Shirakawa area and found similarities. In addition, they prepared tuff flake specimens and made observations to see if there were any similarities in the mineralogy of the rocks. Middle
In addition, fossil wood chips were discovered during an outcrop survey at Lake Tojo last year (Figure 4). This fossil was quite brittle and looked and felt like decayed wood, so we were interested in how it differed from silicified wood and wood, and made a comparison.
During the outcrop survey at Lake Tojo this time, we were able to collect 17 plant fossils at two sites (Figure 5) (Figure 6). We then identified the plant fossils. The method of identification was to look for the external characteristics of the plant fossils collected, and then to search for similar species in botanical illustrated books. Because the Kobe Formation has been studied for a long time and various fossils have been collected, we mainly used Jisaburo Hori's collection of plant fossils from the Kobe Formation as our plant identification guidebook (Fig. 7).
In parallel with the fossil study, we also investigated the strata of Lake Tojo. The upper strata of Lake Tojo were known to be tuff strata based on the research of Sennen's group, but the map of the water-soaked part of the lake had not been clarified. However, because the water level of Lake Tojo was drier than usual during the outcrop survey this time, we were able to examine the map of the submerged area. As a result, it was found that the tuff layer was underlain by mudstone garden and stockstone tuff layer, and then tuff layer. (Fig. 8) The rocky pseudolimestone layer was found to be the second largest after the upper M graystone layer.
The location and amount of plant fossils collected at sites 1 and 2 differed, and more plant fossils were collected at site 2 than at site 1. The areas that could not be sampled at each site were in the ashlar layer, suggesting that the site had experienced repeated large eruptions and that the vegetation had recovered afterwards.
The most likely reason for this is that the site is located in the middle of a large area. In addition, the identification of plant fossils suggests that Lake Tojo was not a flat terrain but a mountainous area at that time, since most of the plants are distributed in the temperate zone and grow naturally in mountainous areas.
The outcrop survey revealed that the strata of Lake Tojo consisted of tuff, mudstone, rocky pseudolimestone, and limestone layers from the top.
A total of 17 fossils were collected from two sites around Lake Tojo. The plant fossils were classified into nine types. However, no relationship could be found between these fossils and the Shirakawa area, as there are no strata in which these plant fossils were produced. The identification of plant fossils suggests that Lake Tojo was a mountainous area at that time, but the small amount of plant fossils collected makes it difficult to determine that it was still a mountainous area.
The water level of Lake Tojo was lower than in previous years, which revealed the layers in the submerged areas. As a result, the strata of Lake Tojo may be located between 56 and 57 of the Shirakawa Formation.
6,References
.
In the year before last, the authors compared the ashlar layers found in Lake Tojo with the tuff layers in the Shirakawa area and found similarities. In addition, they prepared tuff flake specimens and made observations to see if there were any similarities in the mineralogy of the rocks. Middle
In addition, fossil wood chips were discovered during an outcrop survey at Lake Tojo last year (Figure 4). This fossil was quite brittle and looked and felt like decayed wood, so we were interested in how it differed from silicified wood and wood, and made a comparison.
During the outcrop survey at Lake Tojo this time, we were able to collect 17 plant fossils at two sites (Figure 5) (Figure 6). We then identified the plant fossils. The method of identification was to look for the external characteristics of the plant fossils collected, and then to search for similar species in botanical illustrated books. Because the Kobe Formation has been studied for a long time and various fossils have been collected, we mainly used Jisaburo Hori's collection of plant fossils from the Kobe Formation as our plant identification guidebook (Fig. 7).
In parallel with the fossil study, we also investigated the strata of Lake Tojo. The upper strata of Lake Tojo were known to be tuff strata based on the research of Sennen's group, but the map of the water-soaked part of the lake had not been clarified. However, because the water level of Lake Tojo was drier than usual during the outcrop survey this time, we were able to examine the map of the submerged area. As a result, it was found that the tuff layer was underlain by mudstone garden and stockstone tuff layer, and then tuff layer. (Fig. 8) The rocky pseudolimestone layer was found to be the second largest after the upper M graystone layer.
The location and amount of plant fossils collected at sites 1 and 2 differed, and more plant fossils were collected at site 2 than at site 1. The areas that could not be sampled at each site were in the ashlar layer, suggesting that the site had experienced repeated large eruptions and that the vegetation had recovered afterwards.
The most likely reason for this is that the site is located in the middle of a large area. In addition, the identification of plant fossils suggests that Lake Tojo was not a flat terrain but a mountainous area at that time, since most of the plants are distributed in the temperate zone and grow naturally in mountainous areas.
The outcrop survey revealed that the strata of Lake Tojo consisted of tuff, mudstone, rocky pseudolimestone, and limestone layers from the top.
A total of 17 fossils were collected from two sites around Lake Tojo. The plant fossils were classified into nine types. However, no relationship could be found between these fossils and the Shirakawa area, as there are no strata in which these plant fossils were produced. The identification of plant fossils suggests that Lake Tojo was a mountainous area at that time, but the small amount of plant fossils collected makes it difficult to determine that it was still a mountainous area.
The water level of Lake Tojo was lower than in previous years, which revealed the layers in the submerged areas. As a result, the strata of Lake Tojo may be located between 56 and 57 of the Shirakawa Formation.
6,References
.