Marine climatic responses to Neogene tectonics of the Pacific Ocean seaways

Abstract

Based upon surface marine climatic evolution on both sides of the Pacific Ocean recently revealed by biochronostratigraphy in Japan and South America, the tectonics of Pacific Ocean seaways and associated responses of adjacent seas and ocean currents are discussed. The rapid opening of the Sea of Japan at about 15 Ma in early Middle Miocene time, mainly by the rotation of the Southwest Japan arc, can be correlated with the abrupt appearance of a cold-water fauna on the Pacific coast of Northeast Japan beginning ca. 15 Ma and an extensive hiatus along the Pacific coast of southwestern Japan spanning 15 Ma to 12 Ma. The abrupt and extensive development of biosiliceous lithofacies along the Pacific coast of Peru beginning about 14 Ma might also represent a response to the tectonic anticlockwise rotation of the Peruvian Block of the Andean Mountain Range, estimated to have occurred sometime during the Miocene. As the tectonic closing of the Indonesian seaway would have strongly intensified the warm Kuroshio current in the Northwest Pacific, it is most probable that this seaway was effectively closed just prior to 15.5 Ma in the earliest Middle Miocene, when tropical marine faunas were developed in most of the Japanese Islands. The closing of the Central American seaway is estimated to have been completed at 3.5-3 Ma in Pliocene time. The closure of this seaway would likely have intensified the warm Kuroshio current, affecting the marine fauna along the Pacific coast of southwestern Japan. It is also possible that a decrease in surface temperatures at about 3 Ma along the Pacific coast of Ecuador was due to this Pliocene tectonic event.