Studies on the Paliogine tephron in Northwest Kyushu and West Chugol

早渐新世非海相Tsuyazaki组的Koinoura凝灰岩段由三个非焊接的流纹质和英安质火山碎屑流床（KP-A，-C和-D），可能的火山碎屑涌和潜水火山灰瀑布床（KP-B），两个河流夹层和顶部的火山碎屑流床组成。KP-A和-D的浮石流层和KP-C的灰流层含有烧焦和硅化的化石树干，显示出典型的丝质体结构。KP-D的上部有排气管，底部有接地层。该火山碎屑流层可与拉哈尔相比拟，沉积在KP-D中的河道中，含有大量反射率变化很大的树干化石，KP-B下部为薄层细粒凝灰岩，上部为整合的1.6m厚的增生火山砾凝灰岩。前者含有丰富的桉树树干，往往涂上灰喷雾。后者包括： ...更多信息 致密堆积的粗加积火山砾，在整个厚度上没有显示出岩性差异。这些特征表明KP-B的下部可形成涌浪沉积物，上部由潜水期的灰流形成。KP-A和-D的浮石和灰流层中的烧焦树木的反射率表明，沉积时的温度约为550 ℃，以及金伯利进程的激增B为330 ℃左右，根据所含古树干的优选方位得到的火山碎屑流和涌浪的流向为W → E和NW → SE，与河流的流向一致夹层这些数据表明，火山碎屑流的来源位于Tsushima-Goto群岛的西部，在晚始新世和早渐新世时代的九州和Tsushima群岛的古地理调整的结果。那里的火山构成了一个火山链，与San 'in地区相连。在始新世晚期和渐新世早期，全球海平面的下降很可能导致了一次重大的海退，称为翁加海退。由于海退期间对马群岛和九州大陆之间的河流陆地面积扩大，海洋变窄，火山碎屑流可能冲过这些陆地和海洋地区，到达北九州。火山碎屑流和共熔凝灰福尔斯遍布九州北部和中国西部的整个古近纪煤田盆地，形成了一套厚层凝灰岩。少

The Koinoura Tuff Member of the Early Oligocene non-marine Tsuyazaki Formation consists of three non-welded rhyolitic and dacitic pyroclastic flow beds (KP-A, -C and -D), and possible pyroclastic surge and phreatoplinian ash fall beds (KP-B), two fluvial interbeds, and a volcanic debris flow bed at the top. The pumice flow beds of KP-A and -D and the ash flow beds of KP-C contain charred and silicified fossil tree trunks which show a typical fusinite exture. The KP-D has degassing pipes in the upper part and a ground layr in the basal part. The volcanic debris flow bed, referable to a lahar, is deposited in a channel dccply croded in the KP-D and contains a great number of fossil tree trunks whose reflectances are very mauch varied.The KP-B comprises thin-bedded fine-grained tuff in the lower part and conformably succeeding 1.6m thick accretionary lapilli tuff in the upper part. The former contains abundant carbonized wood-trunks which are often coated with ash-spray. The latter compri … More ses densely packed coarse accretionary lapilli, and show no lithologic differences throughout the thickness. These features indicate that the lower part of the KP-B is referable to surge deposits and that the upper part formed by phreatoplinian ash-fall.Reflectance of the charred trees in the pumice and ash flow beds of the KP-A and -D indicate that the temperature of the beds at the time of deposition was about 550ﾟC, and that of the surge of the KP-B was about 330ﾟC.Flow directions of pyroclastic flow and surge obtained from the preferred orientation of the contained fossil tree trunks are W to E and NW to SE.They are concordant with flow directions of the fluvial interbeds. These data suggest that the source of the pyroclastic flows was situated to the west of the Tsushima-Goto Islands, in consequence of the paleogeographic adjustment of Kyushu and the Tsushima Islands in Late Eocene and Early Oligocene times. The volcanoes there constituted a volcanic chain that is connected to the San'in district. It is very likely that global lowering of sea level during Late Eocene and Early Oligocene time caused a major regression, called the Onga regression. As a result of expansion of fluvial land area and narrowing of the sea between the Tsushima Islands and mainland Kyushu during the regression, torrential pyroclastic flows could have rushed over these land and sea areas, and reached to North Kyushu. The pyroclastic flows and co-ignimbrite ash falls were spread over the whole Paleogene coalfield basin in North Kyushu and West Chugoku, and formed a thick sequence of tuff beds. Less