Holocene sedimentary history of some coastal plains in Hokkaido, Japan V. Sedimentary history of Kushu Lake and Akkeshi

Abstract

Diatom assemblages of sediments obtained from Kushu Lake and Akkeshi were analyzed in order to clarify the local Holocene sedimentary history. The results revealed the following: 1) Sometime before about 9000 yr B.P., Kushu Lake was originally a freshwater environment. 2) The first marine diatom zone (MD1 Zone) was deposited on the bottom of the paleo-Kushu Bay between 8500 and 6000 yr B.P. 3) This site changed to become the bottom of the paleo-Kushu Lagoon around 6000 yr B.P. owing to the formation of a bay-mouth bar across the paleo-Kushu Bay and the first Holocene regression resulted in a freshwater lake at about 4500 yr B.P. 4) At this time, the Akkeshi site changed from a sublittoral shore in a drowned valley to a peat moor. 5) The second Holocene transgression at about 3000 yr B.P. was detected at the Akkeshi site. 6) At Kushu Lake site the occurrence of Mastogloia elliptica between 7000 and 5000 yr B.P.suggested the influx of the Tsushima warm current into the Japan Sea.

Diatoms from Lake Kushu: A pilot study to test the potential of a Late Quaternary palaeoenvironmental archive from Rebun Island (Hokkaido Region, Japan)

“…Whether this time difference is due to the extracting location of the peat moor core at the southern margin of the basin (Kumano et al, 1990a) or to an imprecise or incorrect age model (Sato et al, 1998) remains open. Both scenarios seem to be plausible since the marine diatoms documented by Kumano et al (1990a) are benthic diatoms suggesting that the area in the south was less influenced by marine tides compared to the RK12 core location and the age model published by Kumano et al (1990a) is based only on four radiocarbon dates representing the ca. 16 m sediment core.…”

“…In Hokkaido, several water bodies have been analysed including Lake Akan (Tuji et al, 2003), Hii River (Ohtsuka, 2002), and Lake Tokotan (Sawai, 2002). Diatom-inferred environmental reconstructions for the Holocene were obtained from coastal plains including the Tokoro Region (Hamano et al, 1985), Akkeshi Estuary (Kumano et al, 1990a), Kushiro Moor (Ihira et al, 1985;Kumano et al, 1990b), and Kutcharo Lake (Kumano et al, 1984).…”

“…On Rebun Island, Kumano et al (1990a) and Sato et al (1998) analysed a 16.25 m sediment core spanning the last ca. 9000 years as suggested by the four 14 C dates given in their studies.…”

Environmental change and cultural dynamics of Holocene hunter–gatherers in Northeast Asia: Comparative analyses and research potentials in Cis-Baikal (Siberia, Russia) and Hokkaido (Japan)

“…Since the main climatic parameters of modern Hokkaido and northern Honshu are highly correlated, it is thus possible to use the data from these two lakes to build for Hokkaido the same kind of biome and tree cover distribution models as for the Baikal region but with much better temporal resolution and accuracy. Of further assistance will be the partial varve sequences available from Lake Abashiri in Northern Hokkaido and Lake Kushu on Rebun Island (Figure 3; Kumano et al, 1990), the latter recently cored by scholars associated with the BHAP (Dr. H. Yonenobu, personal communication, February 2012). Despite the Hokkaido"s much better potential for high resolution modeling of Holocene climates and environments, many of the challenges described above, particularly the theoretical ones, will need to be reckoned with too.…”

Reconstructed Holocene sea level curve from the Akkeshi barrier system in eastern Hokkaido, Japan

“…1, 2 1971Figs. 1, 2 , 1974 0 2 m Kumano et al 1990 Fig Furukawa, et al, 2006) in the study area; ellipsoids indicate the rupture areas of interplate earthquakes in 1843, 1856, 1894, 1952, 1968, 1973, and 2003, and the probable rupture area of multi-segment mega-earthquakes (M8.6; Nanayama et al, 2003). (c) Map showing the location of the study area between the Akkeshi lowlands and the Kiritappu marsh, and the location of radiocarbon age data reference sites shown in Table 2 and Fig.…”