Diatomaceous rocks are widely distributed around the circum-Pacific region as Miocene to Lower Pleistocene deposits, including the Monterey Formation, California, USA (Ingle, 1981; Isaacs, 1987). The Middle to Upper Miocene Onnagawa Formation is a typical diatomaceous rock in northern Japan. The alternation of hard and soft layers is a characteristic feature, as shown in this picture. The hard layers consist of thick (< several tens of centimeters) porcelanite, while the soft layers consist of thin (< 10 cm) siliceous mudstone. The Onnagawa Formation is known as an excellent petroleum source rock in Japan. The total organic carbon (TOC) contents of porcelanite and siliceous mudstone are generally 0.1 to 3wt% and 2 to 6wt%, respectively. The Yurihara–Ayukawa oil field is located about 5 km west of this outcrop. The Onnagawa Formation is also a reservoir rock, in which oil and gas are reservoired in pores expanded by the diagenetic phase transformation of silica minerals. Moreover, the Onnagawa Formation draws attention as a shale oil resource.
(Photograph: Yuichi SAITO, Explanation: Takashi TSUJI, Amane WASEDA and Satoru YOKOI; Photographed on May 22, 1988)
Journal of Geography (Chigaku Zasshi), 2013, 122(1), 1.
DOI: 10.5026/jgeography.122.1
Journal of Geography (Chigaku Zasshi), 2013, 122(1), 8.
DOI: 10.5026/jgeography.122.8
Unexpected Form of Oil Accumulation under Abnormally High Pressure Condition (Original Article)
Journal of Geography (Chigaku Zasshi), 2013, 122(1), 16.
DOI: 10.5026/jgeography.122.16
Journal of Geography (Chigaku Zasshi), 2013, 122(1), 34.
DOI: 10.5026/jgeography.122.34
Journal of Geography (Chigaku Zasshi), 2013, 122(1), 69.
DOI: 10.5026/jgeography.122.69
Journal of Geography (Chigaku Zasshi), 2013, 122(1), 90.
DOI: 10.5026/jgeography.122.90
Journal of Geography (Chigaku Zasshi), 2013, 122(1), 116.
DOI: 10.5026/jgeography.2012ap01
Journal of Geography (Chigaku Zasshi), 2013, 122(1), 139.
DOI: 10.5026/jgeography.2012ap02
Coseismic and Postseismic Groundwater Pressure Changes (Review Article)
Journal of Geography (Chigaku Zasshi), 2013, 122(1), 159.
DOI: 10.5026/jgeography.2012ap03
Journal of Geography (Chigaku Zasshi), 2013, 122(1), 170.
DOI: 10.5026/jgeography.122.170
Effects of Chemical Osmosis on Groundwater Flow in Sedimentary Formations (Original Article)
Journal of Geography (Chigaku Zasshi), 2013, 122(1), 192.
DOI: 10.5026/jgeography.122.192
Journal of Geography (Chigaku Zasshi), 2013, 122(1), 214.
DOI: 10.5026/jgeography.122.214
Pictorial 1: Range of Concepts Related to Trap and Seal Mechanisms
Journal of Geography (Chigaku Zasshi), 2013, 122(1), i.
DOI: 10.5026/jgeography.122.i
Pictorial 2: Spatial and Temporal Scales of Slow Subsurface Fluid Flow Processes
Journal of Geography (Chigaku Zasshi), 2013, 122(1), ii.
DOI: 10.5026/jgeography.122.ii