Eocene Krabi basin (southern Thailand): Paleontology and magnetostratigraphy

Abstract

We present the magnetostratigraphy of the late Eocene Krabi section from the Krabi basin, Thailand. The investigated section is about 105 m thick and consists of red and yellow siltstones, sandstones, gray claystones, lignites, and limestones. We collected 86 samples at 43 different stratigraphic levels from the 105-m-thick section. The samples yielded a paleomagnetic direction, and paleomagnetic analyses give favorable demagnetization behaviors; two magnetic components can be isolated. Rock magnetic experiments show that the natural remanent magnetization generally results from the presence of titanomagnetite. The first component has roughly the direction of the present-day field. The second component displays only reversed polarity, with a mean direction: declination = 192.34, inclination = −15.5, N = 71, α 95 = 4.7, k = 14 (after bedding correction). Mammalian biostratigraphy indicates a late Eocene age. Correlation to the Geomagnetic Polarity Time Scale relies on biostratigraphic data previously proposed for the fauna found in the same section. These correlations have been achieved by comparing variations in the sedimentation rate derived from the alternative correlation. The proposed correlation puts the Krabi section in chron C12r or chron C13r. This suggests sedimentation rates of 4.9 and 9.4 cm/k.y., respectively. This correlation suggests that the Krabi section is older than 31 Ma and younger than 34 Ma.