A study on growth history of reef terraces deduced from the U-series method of dating

以u系列珊瑚日期为时间尺度，阐明了琉球群岛的Kikai岛、巴布亚新几内亚的Huon半岛、菲律宾群岛和斐济群岛的珊瑚礁梯田在过去几万年间形成的历史。本文的主要研究结果如下：1。u系列测年和地层研究表明，在Kikai岛海拔约10 ~约65 m处，零星分布着低于同位素阶段5a的珊瑚灰岩。这种灰岩覆盖在礁前沉积物上，属于第3至第5阶段。这些事实表明，从同位素阶段5e到3的回归，珊瑚礁是在海底逐渐变浅的过程中形成的。α -光谱^<230>Th/^<234>U方法也可用于解释全新世珊瑚礁阶地的生长历史。该岛全新世珊瑚灰岩在约10 ka时开始沉积在水深5 ~ 10 m处。海侵体系域和高地体系域在海平面上升时期沉积，并在7.5 ka前达到最高高度（约12 m）。随着海平面的下降，陆源物质逐渐短缺，7 ka左右开始生长出边缘礁。2 .在宫古群岛外大陆架的外缘下发现了埋藏的珊瑚礁，表明末次冰期高峰时海平面深度为126米。3 .根据Huon半岛晚更新世珊瑚的u系列测年和氧同位素分析表明，约140 ka时海平面的快速上升在约135 ~ 130 ka时中断，并在一度下降后重新开始。在Panglao、Bohol和Mactan群岛确认了5e期形成的珊瑚礁阶地的分布。在巴拉望岛的西侧也出现了5e级的潮汐缺口。古海岸线的这些指标的高度表明，菲律宾群岛的一些地区没有上升，尽管它们位于西太平洋地区的活动边缘。少

The growth history of coral reef terraces at Kikai Island (Ryukyu Islands), Huon Peninsula (Papua New Guinea), Philippine Islands, and Fiji Islands, which were formed during the last several tens of thousands years, has been elucidated by using U-series dates of corals as a time scale. The main results obtained in this study are outlined as follows :1. As the result of U-series dating and stratigraphic study, coral limestone younger than the isotope stage 5a was sporadically distributed at an altitude of ca. 10 to ca. 65 m in the Kikai Island. Such limestone overlies the fore-reef sediments assigned to stage 3 to 5e. These facts suggest that coral reefs have been formed on the sea floor being successively shallowed with the regression from isotope stage 5e to 3. In contrast, alpha-spectrometric ^<230>Th/^<234>U method was also useful for interpreting the growth history of Holocene coral reef terraces. The Holocene coral limestone at the island began to deposit at ca. 10 ka in water dep … More th of 5 to 10 m. Then the transgressive and highstand systems tracts were deposited during the times when sea level raised and attained to the maximum height (ca. 12 m) up to ca. 7.5 ka. As lowering of the sea level, the terriginous materials became gradually in short supply and a fringing reef started to grow around 7 ka.2. A buried coral reef implying that the sea level at the last glacial maximum was 126 m in water depth, was found beneath the outer edge of insular shelf off the Miyako Islands.3. It was explicated, from U-series dating and oxygen isotopic analysis of late Pleistocene corals at Huon Peninsula, that the rapid rise of sea level at ca. 140 ka has been interrupted at ca. 135-130 ka and restarted after it has been once lowered.4. The distribution of coral reef terrace formed during the stage 5e was confirmed at Panglao, Bohol, and Mactan Islands. A tidal notch of the stage 5e also occurred at the west side of Palawan Islands. The altitude of those indicators for paleo-shoreline denotes that some areas in the Philippine Islands have not uplifted, even though they are situated in the active margin in the western Pacific region. Less