Miocene Magnetostratigraphy and Relative Paleointensity of Deep-Sea Sediments at IODP Site U1490 in the Western Equatorial Pacific

Abstract

We present palaeomagnetic results from the Miocene section of the International Ocean Discovery Program (IODP) Site U1490. Detailed paleomagnetic investigations are crucial for providing a long-term record of Miocene relative paleointensity (RPI) variations, as well as the palaeoclimatic and paleoceanographic history of the Cenozoic Equatorial Pacific. These investigations also aim to enhance the database of Pacific magnetostratigraphy. Magnetic measurements were conducted at a 1 cm resolution on u-channel samples from the spliced section, with the goal of extracting a high-resolution magnetostratigraphic and RPI records. Stepwise demagnetization of the natural remanent magnetization yielded well-defined magnetostratigraphy over a time interval of approximately 9 million years, between the bottom boundaries of the Chron C5Dr.2r (18.066 Ma) and the Chron C4An (9.105 Ma), partially assisted by astronomically tuned isotope stratigraphy. The main magnetic carriers are both single-domain magnetofossils with equant octahedral morphology and pseudo-single-domain detrital magnetite. Our RPI data from the western equatorial Pacific are of the highest quality from 18 to 12 million years ago, comparable to the long-term RPI record from IODP Site U1336 in the eastern equatorial Pacific during the late Early to Middle Miocene with common fluctuations of 10⁴–10⁵ years timescale. The comparison also indicates that the method for Quaternary RPI-assisted chronostratigraphy can also be applied to older sediments to enhance the resolution of stratigraphic correlation.