Responses of Japanese Cenozoic molluscs

• Main Author: Kenshiro Ogasawara
• Other Authors: The Pennsylvania State University CiteSeerX Archives
• Format: Text
• Language: English
• Subjects: Key words; Cenozoic; Pacific; gateway; Bering Strait
• Online Access: http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.531.4780; http://satori.geociencias.unam.mx/19-3/(7)Ogasawara.pdf

The Cenozoic history of Pacific Ocean gateways can be divided into seven stages, extending from the Eocene onset of the Tasmanian seaway to the Pliocene closure of the Central American seaway. The first stage was the interval before 43 Ma, tentatively named the proto-Tasmanian stage. Development of the Tasmanian seaway (43-29 Ma) occupied the second stage. The third stage (29-23.5 Ma) was the oceanographically and paleoceanographically most open system, because the Pacific was not isolated from other oceans. The 4th stage consists of the closing of the Bering Strait prior to closure of the Indonesian seaway (23.5-17 Ma). The 5th stage was the time during which the Indonesian and Bering Seaways were both closed (17-5 Ma). The 6th stage consisted of a closed Indonesian seaway, and an open Bering Strait and Central American seaway (5-2 Ma). The 7th and final stage is the modern situation, with a closed Central American seaway. The responses of Japanese Cenozoic molluscan faunas to these Pacific gateway events reflect Pacific-wide patterns. The remarkable faunal changes from the late Eocene to the early Oligocene record the transition from warm-water environments to temperate or cool-water environments. The Oligocene Ashiya and Asagai molluscan faunas evidently developed as a response to oceanic cool-