Research into the origin and geological history of the Lake Hamana

为了阐明分布在滨名湖及其周边地区的全新世沉积物的沉积过程，我们已经开始了一个多学科的研究项目。作为该项目的一部分，从湖中的四个地点收集了四个钻孔岩心样品。85 H-1（-12米深）、85 H-2（-5米深）、85 H-3（-5米深）和86 H-4（-3米深）的岩心长度分别为16.45米、41.46米、50.45米和23.96米。取芯沉积物均为全新世沉积，4个孔底均达到全新世与更新世的界线，并对钻孔岩心的岩相进行了详细描述。用火山灰年代学和14 C方法测定了样品的地质年龄，发现了厚30毫米的冲木火山灰（约9,300年前），厚44.58米（H-3）。啊火山灰在8.98m（H-2）、14.25m（H-1）和15.75m（H-4）的地层中也发现了一对火山岩，厚度为10 ~ 15 mm（约2，800年BP）和Kg浮石在6.52 - 6.57m（H-1）和4.86 - 4.95m（H-4）观测到约3，000年前的古生物量（加速器质谱）技术，许多放射性碳年代测定从非常小的贝壳碎片和木屑样品的核心沉积物。H-1孔底28.15m处的~（14）C值为7140 ~ 140 yr BP，H-2孔底46.4m处的~（14）C值为10, 000 yr BP。最高海平面之后的海退发生在4000 ~ 3500年BP。

In order to elucidate the depositional process of the Holocene sediments distributed in and around Hamana Lake, we have started a multidisciplinary research project. As a part of this project, four boring core samples were collected from four sites in the lake. Cores of 85H-1(-12m in depth), 85H-2(-5m in depth), 85H-3(-5m in depth), and 86H-4(-3m in depth) are 16.45m, 41.46m, 50.45m and 23.96m long, respectively. The coredd sediments are all Holocene age, and the bottoms of all four holes reached the boundary between Holocene and Pleistocene.The lithofacies of the boring core samples were described in detail. The geological age of the samples were determined by tephrochronological and 14C methods.Oki volcanic ash (ca.9,300 yr BP) was found with thickness of 30mm in 44.58m(H-3). Ah volcanic ash (ca.6,300 yr BP) was also found in 8.98m(H-2), 14.25m(H-1) and 15.75m(H-4) with 10 to 15mm in thickness.A pair of tephras, Os scoria (ca.2,800 yr BP) and Kg pumice (ca.3,000 yr BP) was observed in 6.52 - 6.57m(H-1) and 4.86 - 4.95m(H-4).By using the AMS (Accelerator Mass Spectrometry) technique, many radiocarbon dates were obtained from very small shell fragments and wood chip samples in the core sediments. The 14C data for the bottom of the H-1 core is 7140 140 yr BP at a depth of 28.15m, and for the H-2 core is about 10,000 yr BP at a depth of 46.4m.These data suggest that during the early Holocene there was not just one but two discrete marine transgressions, first before about 8,500 to 8,000 yr BP and the second after 8,000 to 7,000 yr BP, and the marine regression after the highest sealevel occurred rapidly from 4,000 to 3,500 yr BP.