Fossil Pollen Assemblages of Core Samples from Lake Suwa, Nagano Prefecture, and Their Correlation to Other Pollen Assemblages in Central Japan

Abstract

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 δ¹⁸O (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.