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Shimajiri Group equivalent sedimentary rocks dredged from sea knolls off Kume Island, central Ryukyus: Implications for timing and mode of rifting of the middle Okinawa Trough back-arc basin
Island Arc ( IF 1.5 ) Pub Date : 2021-09-10 , DOI: 10.1111/iar.12425
Ritoko Kikunaga 1 , Ke‐han Song 2 , Shun Chiyonobu 3 , Kazuhiko Fujita 1, 2 , Ryuichi Shinjo 1, 2, 4 , Kyoko Okino 5
Affiliation  

The late Cenozoic geohistory of the Ryukyu arc is closely related to the rifting history of the Okinawa Trough. The submarine geology and stratigraphy of areas around Kume Island, which is situated near the eastern rifted margin of the middle Okinawa Trough, provide key constraints to understand the timing and mode of Okinawa Trough rifting. Here we report the lithology of sedimentary rocks dredged along slopes of ~1000-m-deep sea knolls located north and northwest off Kume Island, and their depositional ages determined by calcareous nannofossils and strontium (Sr) isotope analyses. Various types of sedimentary rocks, such as siltstone, very fine-grained sandstone, medium-grained sandstone, fossiliferous coarse-grained sandstone, and tuffaceous sandstone, were recovered at two dredge sites. These sedimentary rocks are lithologically similar to those in the Aka Formation and a part of the Maja Formation of the Shimajiri Group in nearby Kume Island. Calcareous nannofossils and Sr isotope analyses indicate their depositional ages from the early Pliocene to the early Pleistocene, which are generally consistent with those of the Aka Formation. The finding of the dredged rocks similar in lithology and ages to the Aka Formation indicates that marine deltaic area continued toward north and northwest from Kume Island during these periods. The presence of the Shimajiri Group equivalent sedimentary rocks at the dredge sites are likely related to the main rifting of the Okinawa Trough after ca. 2 Ma in the central Ryukyus.

中文翻译:

从琉球中部久米岛海丘中挖出的岛尻群等效沉积岩:对冲绳海槽中部弧后盆地的时间和裂谷方式的启示

琉球弧的晚新生代地史与冲绳海槽的裂谷史密切相关。位于冲绳海槽中部裂谷东缘附近的久米岛周围地区的海底地质和地层为了解冲绳海槽裂谷的时间和模式提供了关键约束。在这里,我们报告了沿着位于久米岛北部和西北部的约 1000 米深海丘陵斜坡挖掘的沉积岩的岩性,以及通过钙质纳米化石和锶 (Sr) 同位素分析确定的沉积年龄。在两个疏浚地点回收了各种类型的沉积岩,如粉砂岩、极细粒砂岩、中粒砂岩、含化石粗粒砂岩和凝灰质砂岩。这些沉积岩在岩性上与久米岛附近的 Aka 组和岛尻群 Maja 组的一部分相似。钙质纳米化石和 Sr 同位素分析表明它们的沉积年龄从上新世早期到更新世早期,与 Aka 组的沉积时代基本一致。在岩性和年代与阿卡组相似的疏浚岩石的发现表明,海相三角洲地区在这些时期从久米岛继续向北和西北部延伸。在疏浚地点存在岛尻群等效沉积岩可能与冲绳海槽的主要裂谷有关。2 马在琉球中部。钙质纳米化石和 Sr 同位素分析表明它们的沉积年龄从上新世早期到更新世早期,与 Aka 组的沉积时代基本一致。在岩性和年代与阿卡组相似的疏浚岩石的发现表明,海相三角洲地区在这些时期从久米岛继续向北和西北部延伸。在疏浚地点存在岛尻群等效沉积岩可能与冲绳海槽的主要裂谷有关。2 马在琉球中部。钙质纳米化石和 Sr 同位素分析表明它们的沉积年龄从上新世早期到更新世早期,与 Aka 组的沉积时代基本一致。在岩性和年代与阿卡组相似的疏浚岩石的发现表明,海相三角洲地区在这些时期从久米岛继续向北和西北部延伸。在疏浚地点存在岛尻群等效沉积岩可能与冲绳海槽的主要裂谷有关。2 马在琉球中部。在岩性和年代与阿卡组相似的疏浚岩石的发现表明,海相三角洲地区在这些时期从久米岛继续向北和西北部延伸。在疏浚地点存在岛尻群等效沉积岩可能与冲绳海槽的主要裂谷有关。2 马在琉球中部。在岩性和年代与阿卡组相似的疏浚岩石的发现表明,海相三角洲地区在这些时期从久米岛继续向北和西北部延伸。在疏浚地点存在岛尻群等效沉积岩可能与冲绳海槽的主要裂谷有关。2 马在琉球中部。
更新日期:2021-09-29
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