西オーストラリア州ハメリンプールの完新世二枚貝Fragum erugatumの形態から復元した塩分濃度変化とストロマトライトの形成条件についての意義

抄録

 Hamelin Pool is well known as one of the best and most extensive localities of modern stromatolites. The distribution of stromatolites at this locality can be explained by the existence of a high-salinity environment. Salinity variations reflect sea-level fluctuations combined with changes in landform during the post-glacial period. Stromatolite formation apparently began at 1250 BP in Hamelin Pool. It has been assumed that this event was also related to salinity changes. Focusing on Fragum erugatum (Bivalvia: Cardiidae), which is known to change the height/length ratio of shells with salinity, the author attempted to reconstruct paleosalinity over a period of 4000 years at Hamelin Pool. Shells were sampled at 13 points along a 500-m transect perpendicular to the coastline on a ridge northeast of Flagpole Landing. The height/length ratio was measured and the ¹⁴C age was determined. Furthermore, the height/length ratio was converted into a salinity scale based on several previous studies showing the relationship between ratio and salinity. Results showed that salinity rose rapidly to 58‰ when stromatolites first developed at Hamelin Pool.