Pollen stratigraphy, tephrochronology, and correlation to oxygen isotopic records were examined on bottom cores from GS400 (400m long) and 63B (200m long) sites in Lake Suwa, Nagano Prefecture, Japan. The tephras of Pm-I', Pm-I, Pm-II, Aso-4, Pm-III, and AT are intercalated in the middle to upper horizons. From the results of pollen analysis, the sediments are divided into ten pollen zones, SUWA-I to SUWA-X in ascending order. In SUWA-I, IV, VI, VIII-IXa, and IXc-X pollen zones, sub-arctic conifers such as
Picea,
Tsuga,
Abier, and
Haploxylon are dominant. In SUWA-II-III, V, VII and IXb zones, which occur between the subarctic zones, however, temperate conifers such as
Cryptomeria,
Sciadopitys, Taxaceae-Cephalotaxaceae- Cupressaceae and deciduous broad-leaved trees of
Fagus,
Carpinus-
Ostrya,
Lepidobalanus, and
Ulmus-
Zelkova prevail.
These cyclic changes of pollen flora show a repetition of five cool and four warm periods during middle to late Pleistocene times, 185ka to >25ka, as deduced by tephrochronology. Each period corresponds to stages 6 to 2 by δ
18O (Martinson
et al., 1987), as follows: SUWA-I--stage 6, II-III--5e, IV--5d, V--5c, VI--5b, VII--5a, VIII--4, IX--3 and X--2.
The SUWA pollen zones are correlated to those of the coeval sediments in Lakes Nojiri and Biwa as follows (Suwa, Nojiri and Biwa are abbreviated as S, N, B): S-V-VII--N-
Cryptomeria zone, S-VIII--N-Pinaceae zone, S-IX--N-
Larix-
Betula zone to
Quercus-
Fagus zone and S-X--N-
Picea-
Abies-
Tsuga zone; S-I--B-X, S-II-III--B-XI, S-IV--B-XII, S-V--B-XIII, S-VI--transitional part of the B-XIII and B-XIV, S-VII-VII--B-XIV, S-IX--B-XV and S-X--B-XVI.
The Suwa palynostratigraphy shows correlation to the oxygen isotopic records and can be used as a standard for palynologycal correlation of the middle to late Pleistocene in Central Japan.
View full abstract