Discovery of mangrove (Kandelia sp.) pollen from the Miocene Kadonosawa Formation, Ninohe district, Iwate Prefecture, Northeast Japan

Abstract

Molluscan and plant fossils from ancient mangrove swamps are known from upper Lower to lower Middle Miocene sediments in Southwest Japan. Given that the mangrove-swamp-dwelling bivalve Geloina was recently found in the Tate Sandstone Member of the Kadonosawa Formation in the Ninohe district, northeastern Japan, it was expected that mangrove pollen would also be found at this site. To investigate this possibility, 26 samples were collected from the Tate Sandstone Member at two sites (Tate and Kitadate). The pollen composition at both sites is characteristic of the NP-2 zone of Neogene pollen zones (Yamanoi 1992a). Mangrove pollen (Kandelia sp.) fossils were first found in the uppermost part of the Tate Sandstone Member at the Kitadate site, representing the northernmost record of Miocene fossil mangrove in Japan. Based on present-day mangrove assemblages and distribution, the average wintertime temperature in the Ninohe area at the time represented by the pollen fossils is estimated to have been about 11°C higher than that of today.