Possible Paleomagnetic Secular Variation Patterns in Taiwan for the last 6 kyrs Teh-Quei Lee (1), Kuo-Yen Wei (2) and Chih-An Huh (1) 1. Institute of Earth Sciences, Academia Sinica, Taiwan 2. Department of Geosciences, National Taiwan University, Taiwan

Why do we study the paleomagnetic secular variation in Taiwan? Secular variation is one of the main characteristics of the earth magnetic field. It is an important key to probe the physical properties of the earth deep interior and to investigate the origin of the geomagnetic field.

Fluid motion at CMB Bloxham and Jackson, 1991

Why do we study the paleomagnetic secular variation in Taiwan? Secular variation is one of the main characteristics of the earth magnetic field. It is an important key to probe the physical properties of the earth deep interior and to investigate the origin of the geomagnetic field. Paleomagnetic secular variation pattern could be a very powerful tool for core correlation and for establishing well controlled age model.

Why do we study the paleomagnetic secular variation in Taiwan? Secular variation is one of the main characteristics of the earth magnetic field. It is an important key to probe the physical properties of the earth deep interior and to investigate the origin of the geomagnetic field. Paleomagnetic secular variation pattern could be a very powerful tool for core correlation and for establishing well controlled age model. However, secular variation of the earth magnetic field is generally regional dependent.

Why do we study the paleomagnetic secular variation in Taiwan? Secular variation is one of the main characteristics of the earth magnetic field. It is an important key to probe the physical properties of the earth deep interior and to investigate the origin of the geomagnetic field. Paleomagnetic secular variation pattern could be a very powerful tool for core correlation and for establishing well controlled age model. However, secular variation of the earth magnetic field is generally regional dependent. High resolution paleomagnetic secular variation records for the Holocene in East Asia are very rare in the past.

To Establish a Standard Paleomagnetic Secular Variation Pattern in Taiwan, we need: High resolution continuous records from marine or lake sediment cores which has well and reliable age dating to set up its chronology. The paleomagnetic directions of the samples should be well determined. Usually, this depends on the major magnetic mineral contained in the samples. To obtain a well referred paleo-intensity records, the magnetic minerals should be fine grained and homogenous distributed. A marine sediment core taken from the eastern offshore of Taiwan was analyzed!

Water Depth of the site: 760 m Site Locality: 121.5°E, 22.7°N Water Depth of the site: 760 m Core Recovered Length: 1.87 m OR1-715-21

spp. and Dating Material: Planktonic foraminiferal shells (>250 μm, >6 mg, Globigerinoides spp. and Orbulina universa) Depth (cm) AMS 14C age (yrB.P.) error (years) 5 407 40 70.5 3491 35 144 5694 152 5752 164 6229 174 6454

Typical IRM acquisition curves of the samples from Core OR1-715-21

S-ratio>.95 Major magnetic mineral: magnetite

(King et al., 1983)

Typical Orthogonal Component Plots and Normalized Intensity Curves of NRM during AF Demagnetizations

Paleomagnetic Secular Variation Pattern of Core OR1-715-21

Hyoto et al. (1993)

Paleomagnetic Secular Variation Pattern of Core OR1-715-21

Summaries: The obtained paleomagnetic secular variation patterns including both the direction and intensity variations from the core OR1-715-21 could be very “possible” been used as a standard reference records for the last 6 kyrs in Taiwan and its neighboring area, which shows most dipole-like variation.