Studies on the Paliogine tephron in Northwest Kyushu and West Chugol

渐新世早期陆相Tsuyazaki组Koinoura Tuff段由3个未焊接的流纹岩和英安质火山碎屑流层(Kp-A、-C和-D)、可能的火山碎屑涌流和深成灰层(Kp-B)、两个河流夹层和顶部的火山泥石流组成。KP-A和KP-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，显示出典型的丝质结构。KP-D型除气器上部有除气管，底部有地面铺设。火山泥石流地层为火山岩，沉积在KP-D中的一条河道中，含有大量反射率变化很大的古树干，KP-B下部为薄层细粒凝灰岩，上部为1.6m厚的增生凝灰岩。前者含有大量碳化的树干，经常被喷灰覆盖。后者比…更复杂粗大的吸积玄武岩更加密集，整个厚度的岩性差异不明显。Kp-A和Kp-D浮石和灰流层中烧焦的树木反射率表明，沉积时床层的温度约为550ﾟC，KP-B的涌流温度约为330ﾟC。从所含化石树干的优先方向获得的火山碎屑流和涌流的流动方向为W-E和NW-SE，与河流夹层的流动方向一致。这些资料表明，火山碎屑流的源头位于对马-后藤岛以西，这是九州和对马岛在始新世晚期和渐新世早期进行古地理调整的结果。那里的火山构成了与萨宁地区相连的火山链。很可能是始新世晚期和渐新世早期全球海平面下降导致了一次重大的回归，称为Onga回归。回归过程中，由于对马群岛与九州大陆之间的河流面积扩大，海域缩小，可能会有大量的火山碎屑流冲过这些陆地和海域，到达九州北部。火山碎屑流和共生褐煤灰降遍布九州北部和中部西部的整个古近系煤田盆地，形成了一套较厚的凝灰岩层系。较少

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