珪藻遺骸群集からみた北海道厚岸地方における完新世後半の相対的海水準変動と古環境の復元

概要

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Paleoenvironmental surveys, using diatom assemblage analysis, have been carried out in Akkeshi Moor and its surroundings to obtain records of Holocene sea-level changes. Surface sediments from various modern environments were taken, and water salinity at each locality was measured to assess geographical distribution, environmental optima and tolerance of living diatom species. The living diatoms were classified into eight species-groups that characterize the following environments : (I) fresh water, (II) fresh water (adhered to plants), (III) moor, (IV) brackish water, (V) brackish water (gregarious on aquatic plants), (VI) mud marsh in brackish water, (VII) saline water (gregarious on aquatic plants), and (VIII) outer and inner bays. Fossil diatom assemblages and radiocarbon ages of drilled core samples from three sites in the moor were then examined, demonstrating relative sea-level fluctuations during the last five thousand years, with the following sequence of events : (1) a shallow bay spread over most of Akkeshi Moor, with gregarious oysters around the moor (ca. 4700 yr B. P.), (2) the sea-level became about 1 meter below the present level (ca. 2700yr B. P.) and (3) the sea-level increased to become about 1 meter above the present level (ca. 1000 yr B. P.), then moor vegetation formed after this transgression.
日本古生物学会の論文
1996-12-15