Paleontology and magnetostratigraphy of the Eocene Krabi basin (Southern Thailand)

Author : Mouloud Benammi, Yaowalak Chaimanee, Jean-Jacques Jaeger, Varavudh Suteethorn & St├ęphane DucrocqPublication : Bulletin of the Geological Society of MalaysiaVolume : 43Page : 545-553Year : 1999


Bulletin of the Geological Society of Malaysia, Volume 43, Dec. 1999, pp. 545 - 553


Paleontology and magnetostratigraphy of the Eocene Krabi basin (Southern Thailand)


1 Laboratoire de Paleontologie, ISEM, Cc 064, Universite Montpellier II, Place Eugene Bataillon, F-34095 Montpellier cedex 5, France

2Labo de Geophysique et Tectonique, Case 60, Universite de Montpellier II, PI Eugene Bataillon, F-34095 Montpellier cedex 5, France

3Geological Survey Division, Department of Mineral Resources, Rama VI Road, Bangkok 10400, Thailand


Abstract: Excavations undertaken since several years in the Eocene sites of the Krabi basin (southern Thailand) has yielded six genera of reptiles and 31 different species of mammals, among which are several forms new to Southeast Asia. Nearly all vertebrate remains have been collected from lignite levels, and their study indicates a rather closed area submitted to a tropical climate. In addition to considerably increase our knowledge of the early Tertiary terrestrial vertebrate faunas of southern Asia, these Thai remains allow to propose an accurate age for this mammal fauna. They also can be related to known late Eocene and/or early Oligocene forms from Europe, North Africa, Asia, or even North America. The study of the evolutionary stages of the different taxa of the Krabi fauna, and comparisons with other well dated mammalian faunas from Eurasia and North Africa, led us to propose a late Eocene age for the mammal fauna (about ±37 to ±34 Ma).

A magnetostratigraphic study has been carried out on the late Eocene fluviatile/lacustrine Krabi deposit (southern Thailand). 87 samples in 43 different stratigraphic levels were collected from a thickness of 105 m of the section. These paleomagnetic samples were analysed, and they yielded a paleomagnetic direction. Rock magnetic experiments show that the NRM generally results from the presence of magnetite. The Krabi section that has been sampled displays only reverse polarity. The mean direction for reversed polarity samples was D = 192.34, I = -15.5 (N = 71, α95 = 4.7, k = 14). The correlation to the Geomagnetic Polarity Time Scale (GPTS) relies on the biostratigraphic data previously proposed for the fauna found in the same section. These correlations have been achieved by comparing variations in the sedimentary rate derived from the alternative correlation. The proposed correlation puts Krabi section in the chron C13r (34.1 Ma) or C15r (35.14 Ma). This suggests sedimentation rates of 9.4 and 26 cm/ky respectively, but the second sedimentation rate is too high for this type of sediments (lignite). Hence, the most probable correlation for the Krabi section is with chron C13r (33.54-34.65 Ma).