概要 |
Distinctive Triassic deposits are discovered in the Motobu Peninsula of Okinawa-jima. Though the older rocks of this area have been generally regarded as Paleozoic, the strata are at least in part Car...nian in age, as evidenced by the occurrence of numerous characteristic ammonoids and Halobia. The deposits named here the Nakijin Formation are 450-500m thick, composed mainly of limestone and basaltic lava with a subordinate amount of calcareous siltstone, and tuffaceous and calcareous mudstone. This formation is divided into two members in accordance with the stratigraphic and lithologic features. The limestones of the Lower Member are massive semi-crystalline, bearing calcareous algae, sponge (?), bryozoans (?), while those of the Upper one are of pelagic facies, containing numerous cephalopods, halobiids and microfossils. The Upper Triassic ammonoids collected from the Upper Member not only provide reliable evidence for the interregional correlation of the Nakijin Formation but also present an interesting clue to the facies analysis of the pelagic carbonate rocks in which the ammonoids occur.続きを見る
|