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The Upper Neogene Miyazaki Group is distributed in the low hills along the Pacific coast in the southeastern part of Miyazaki Prefecture. The group overlies the Cretaceous to Lower Miocene Shimanto Supergroup, the Lower Eocene to Lower Miocene Nichinan Group and the Middle Miocene Osuzuyama silicic igneous rocks unconformably and is in fault contact with the Upper Miocene Uchiumigawa Group. The Nichinan and Uchiumigawa Groups are distributed in the inland and coastal parts, respectively, of the Minaminaka Mountains to the southwest and the others are in the Kyushu Mountains to the west-northwest of the hills. In the Miyazaki Group in the sense of Shuto (1952, 1961), the Aoshima facies is older than the Tsuma and Miyazaki facies in geologic age, so only the Miyazaki and Tsuma facies are redefined as the components of the Miyazaki Group. The Aoshima facies is distinguished from the Miyazaki Group and included in the Uchiumigawa Group proposed by Takehi (1978MS). The Miyazaki Group forms a gentle syncline plunging east apparently. The strata on the north flank of the syncline strike NNE-SSW to NE--SW and dip 10° eastwards homoclinally. On the other hand, there are many faults on the south flank of the syncline. The strata strike NW-SE to NS and dip 10 to 20 eastwards between the axis of the syncline and the Niinazume-Uchinohae fault. On the south of the fault the strike changes NE-SW to NS and dip increases to 20 to 30° eastwards. Lithologically the Miyazaki Group is divided into the Higashimorogata, Kiyotake, Tonokori, Saito and Koyu Formations. The Kiyotake Formation overlies the Higashimorogata Formation and is overlain by the Tonokori Formation conformably. The Saito Formation interfingers with the above three formations. The Koyu Formation, the uppermost formation in the group, overlies the Tonokori and Saito Formations with conformity. The Higashimorogata Formation comprises the Tano and Aya Members in ascending order. The former is composed of conglomerate, fine sandstone and muddy sandstone, and the latter of sandy mudstone. The Kiyotake Formation comprises four members which are the Kamurano, Kurokita and Oyodo Members in ascending order and the Kuraoka Member interfingering with the above three members. The Kamurano Member consists of an alternation of sandstone and mudstone with interbedded conglomerate, the Kurokita Member of the alternation dominated by sandstone, the Oyodo Member of the alternation dominated by mudstone, and the Kuraoka Member of an alternation of thick sandstone and mudstone in equal amounts. The Tonokori Formation is subdivided into the Uryuno and Niinazume Members in ascending order. The former is composed of laminated fine sandstone and an alternation of sandstone and mudstone, and the latter of sandy mudstone. The Saito Formation comprises the Kawabaru and Tsuma Members in ascending order. The former is composed of conglomerate, fine sandstone and muddy sandstone, and the latter of sandy mudstone. The Koyu Formation is subdivided into the Sadowara and Takanabe Members in ascending order. The former is composed of an alternation of sandstone and mudstone, and the latter of sandy mudstone. The benthic foraminifers and molluscs from the Higashimorogata Formation indicate that the Tano Member was deposited in an inner sublittoral zone and the Aya Member in an outer sublittoral zone. The sedimentary environments of the Kiyotake Formation, excepting the lower part of the Kamurano Member, and the Tonokori Formation are an outer sublittoral zone to an upper bathyal zone. The sedimentary environment of the Koyu Formation is an upper bathyal zone. On the basis of planktonic microfossils, the boundary between foraminiferal zones N 17 and N 18 (Blow, 1969) is situated in the lower part of the Kurokita Member of the Kiyotake Formation and the strata below this boundary is the upper Upper Miocene. The boundaries between calcareous nannoplanktonic zones CN10b and CN10c and CN11 and CN12 (Okada and Bukry, 1980) are probably in the upper part of the Kiyotake Formation and in the lower part of the Takanabe Member of the Koyu Formation, respectively. Furthermore the boundary between foraminiferal zones N20 and N21 is within the upper part of the Takanabe Member of the Koyu Formation. No microfossils of Pleistocene age were found from the Miyazaki Group. The group ranges in age from the latest Miocene to the latest Pliocene. Most of faults in the Miyazaki Group are normal ones and trend NE-SW. Fault planes are clean-cut in the lower part, but obscure in the upper part of the group. The principal stresses estimated from an analysis of the minor faults are horizontally NW-SE trending σ_3, vertical σ_1 and 45 mean shear angles (2θ). This analysis indicates that the Miyazaki Group was cut by many faults under extentional stress in a southeast direction soon after deposition.

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