Paleoecological and paleoenvironmental information decorded from hard substrates ichnofacies

钻岩遗迹化石以双壳类、腹足类、腕足类、藤壶类、多毛类环节动物、海绵类、苔藓虫类等钻岩生物为特征。这些遗迹化石通常被用作古岩岸的指示物，并可用于古环境的重建。富含钻岩双壳类的北海道浅海相沉积于中新世。我在北方北海道的两个地方研究了钻岩双壳类和它们的棍棒状钻孔。在Akebono地区，Sankebetsu组的基底部分不整合地覆盖在基底上，由细粒砂岩组成。钻岩的双壳类，如Penitella kotakae和Platyodon nipponica被确认，Penitella，Gastrochaenchaenburbinatus的棍棒状钻孔，主要在地下室。该产状代表原地产状，推测为古岩质海岸的浪蚀阶地。在Yamato地区，Yamato组的底部不整合地覆盖在基底上，由基底砾岩组成。砾岩碎屑中以双壳类为主，基底中未见双壳类。钻岩双壳类，P sp.，和它们的棒状钻孔，G. turbinatus，在碎屑中占主导地位。该产状为半原地产状，推测为古岩质海岸的漂石海滩。岩岸是在中新世海侵事件中形成的。海洋岩石表面上的生物侵蚀被证明是揭示地质事件的一个非常好的工具，例如海平面的相对振荡、侵蚀/沉积速率和物理扰动的强度。

Rock-boring trace fossils are characterized by boring organisms such as bivalves, gastropods, brachiopods, barnacles, polychaete annelids, sponges, bryozoans, etc. In general, these trace fossils are used as indicators of ancient rocky shores, and are useful for reconstruction of pal eoenvironments.The shallow-marine facies of Hokkaido rich in rock-boring bivalves was deposited during the Miocene. I studied rock-boring bivalves and their clavate borings at two localities in northern Hokkaido. In locality Akebono, basal part of the Sankebetsu Formation unconformably overlies the basement and is composed of fine-grained sandstone. Rock-boring bivalves such as Penitella kotakae and Platyodon nipponica are recognized, and the clavate boring of Penitella, Gastrochaenolites turbinatus, dominated in the basements. This occurrence represent autochthonous, and is presumed to wave-cut bench of ancient rocky shore. In locality Yamato, basal part of the Yamato Formation unconformably overlies the basement and is composed of basal conglomerate. Boring bivalves dominated in clasts of conglomerates, and no occurrence on the basements. Rock-boring bivalves, P sp., and their clavate borings, G. turbinatus, dominated in the clasts. This occurrence represent semi-autochthonous, and is presumed to boulder beach of ancient rocky shore.The paleoecological characteristics of the molluscan and ichnofossil assembleges in these localities reflect changes in the sedimentary environment during a sea-level transgression. The rocky shores were formed during the transgression events in the Miocene time. Bioerosion on marine rocky surfaces demonstrates to be a very good tool to reveal geological episodes such as relative oscillations of the sea-level, erosion/sedimentation rates and intensity of physical disturbance.